History of CERN, III (History of Cern, Vol 3)

VOLUME i n

edited by JOHN KRIGE Centre de Recherche en Histoire des Sciences et des Techniques Cite des Sciences et de Vlndustrie Paris, France

1996

ELSEVIER Amsterdam • Lausanne • New York Oxford • Shannon • Tokyo

North-Holland ELSEVIER SCIENCE B.V. Sara Burgerhartstraat 25 P.O. Box 211, 1000 AE Amsterdam, The Netherlands

ISBN: 0-444-89655-4 © 1996 Elsevier Science B.V. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science B.V., Copyright & Permissions Department, P.O. Box 521, 1000 AM Amsterdam, The Netherlands. Special regulations for readers in the U.S.A.- This publication has been registered with the Copyright Clearance Center Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the U.S.A. All other copyright questions, including photocopying outside of the U.S.A., should be referred to the copyright owner, Elsevier Science B.V., unless otherwise specified. No responsibility is assumed by the pubHsher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. This book is printed on acid-free paper. Printed in The Netherlands.

Preface This third volume of the History of CERN takes the story from the mid-1960s, after the second generation of accelerators had been chosen, and carries it through to the late 1970s. With Volume I, published in 1987, and dealing with the launching of the European Organization for Nuclear Research, and Volume II, published in 1990, and covering the first decade after CERN was officially established in 1954, we now have a pretty comprehensive picture of the first three decades of this laboratory's Ufe. In addition a short history of CERN, written by myself and Dominique Pestre, and which reflects our specific interests and competence in deaUng with an organism as multifacetted as this, is in preparation. CERN, one might say, has been well served by historians. The structure of this book differs in two important and related ways from that of its predecessors. Firstly, whereas the first two volumes were the product of a team of historians working together in offices on the laboratory site in Geneva, this book is, rather, a collection of studies by authors with very different professional backgrounds and institutional locations. This structure was imposed by the dispersion of the former team members, Krige excepted, to their home countries on the completion of Volume II to pursue other lines of research. To replace them the present editor solicited the support of two or three other historians (including Pestre from the earlier project) and - a major innovation with respect to the previous volumes - physicists and engineers with an interest in history but not trained as historians. A special attempt was made to find scientists who were not CERN staff* members in the hope that, as people not totally imbued with the CERN ethos, they would be able to raise critical questions which might elude the gaze of one who had been enclosed in the laboratory's walls for much of his professional Ufe. The second point we want to make about this volume, and which differentiates it from the first in particular, is that it consists of distinct case studies dealing with a number of issues which we deemed important, but having no tight connection with each other. This is partly related to the geographical dispersion and intellectual diversity of the authors. More fundamentally, though, it reflects the polymorphic character of a laboratory like CERN from the 1960s onwards, a place in which many very different things happened, things with their own relatively autonomous histories. The first introductory chapter of the book draws the content of the various chapters together around a generic theme but, this overview apart, the reader will not find a continuous narrative flowing through the text. The book is organized in three main parts. The first, containing contributions by historians of science, perceives the laboratory as being at the node of a complex of interconnected relationships between scientists and science managers on the staff, the users in the member states, and the governments which were called upon tofinancethe laboratory.

vi

Preface

Four of them deal with the negotiations surrounding the acquisition of big equipment: accelerators (including the proton-antiproton collider), bubble chambers and the An electronic detector with which Carlo Rubbia and his team did their Nobel prizewinning work in the early 1980s. To complete the picture this section also includes one chapter on the construction and operation of the ISR, decided in 1965, and, fundamental to the entire period, another chapter describing the new relationships between the laboratory and its outside users precipitated by the concentration of the European high-energy physics effort in Geneva, and the increasing importance of electronic detection techniques. Parts II and III contain chapters by physicists and an engineer (with the exception of the chapter on the development of position electronic detectors written by Ivana Gambaro, she too being an historian). Their approach is typical of that followed by authors with this professional background, in that they are at once comprehensive and seek to pick out, from the viewpoint of the present state of scientific knowledge, the significant contributions to the field made at the Geneva laboratory, and by individuals who worked there, duly allocating priority and credit. Part II surveys the physics results obtained at CERN. It comprises three chapters, one dealing with the scientific role of the Theory Division up to the late 1970s, another dealing with the laboratory's weak interaction physics programme, and a third exploring the science and the science policy debates surrounding the programme with the on-line isotope separator (ISOLDE) installed at the 600 MeV synchrocyclotron in the late 1960s. Part III contains two chapters on engineering and technology, the first dealing with the evolution and sophistication of the CERN accelerator complex (including of course the work done by Simon van der Meer on stochastic cooling, and for which he was awarded the Nobel prize along with Carlo Rubbia in 1984). The other describes the research and development of position electronic detectors, notably the Nobel prizewinning work (1992) of Georges Charpak and his team on the multiwire proportional chamber. There are two omissions in this list. The first is a chapter on the construction of the Super Proton Synchrotron, similar to that on the ISR. This omission was deUberate, for we judged that a perfectly adequate account of this existed already,^ and that there was no need to do another study here. The second more regrettable gap is a chapter on strong interaction physics at CERN to complement that on weak interactions. This chapter was planned and commissioned, but the first author was forced to abandon it due to pressure of work, and his replacement, Giuseppe Fidecaro struggled valiantly to complete the study by the end of 1995, without success. With the book already long delayed, and with other authors who had met their deadlines two years earlier understandably becoming impatient, it was regretfully decided to omit this chapter too. Volumes I and II are often regarded by the community of science historians as 'official' histories of CERN; volume III will do nothing to disperse that image - on the contrary, it

^M. Goldsmith and E. Shaw, Europe's Giant Accelerator. The Story of the CERN 400 GeV Proton Synchrotron (London: Taylor and Francis, 1977).

Preface

vii

can only reinforce it. After all, the collection aims to be reasonably comprehensive in its coverage, and it deals with all or most of CERN's major 'successes' (as seen from today's viewpoint). Certainly many chapters are not uncritical of CERN. But given the timespan covered, and the abiUty of scientists and science administrators to learn from their mistakes, even the setbacks and 'failures' redound to the positive image of the laboratory in the long run as long as they are not repeated. We cannot then deny the claim (or accusation?) that what we have presented in these volumes is an official history of sorts. That granted an important quaUfication is immediately called for. If this history is 'official' it is so in the sense that certain topics have not been left out, have had to be treated. They 'have' to be treated because, whether the historian likes it or not, CERN 'is', at least partly, what the physics community and the governments which fund it perceive it to be - and both of them prize scientific and technological achievement and success. A history of CERN which did not reflect that image would therefore miss an essential aspect of the laboratory. This is not to say, of course, that we need only discuss those features of CERN which impress themselves on the key actors as being of significance for understanding its evolution and development. But time and money are not infinite resources, and the enormous demands on them made by producing an in-depth, 'classical' successoriented history of CERN have made it impossible to develop seriously alternative viewpoints and approaches. If our history is 'official' in its coverage of topics, it is not, nor is it intended to be, in its approach to those topics. As historians we have always striven to retain our critical spirit, never to accept unquestioningly the views of our actors (or indeed of our professional colleagues). And even though that was well known, no member of the laboratory staff" or management, no fundgiver or government official has ever tried to censor or to suppress our results, or to deny us access to key individuals or archival material. We have always been free to say what we think and to write what we like, even when our findings have been harshly critical of the conventional wisdom about the laboratory and the role of certain groups or individuals within it. We have tried to write history and to avoid hagiography, and if and when we have failed to do so it is due only to personal limitations not external pressures. The initial support for this third volume was provided by Edoardo Amaldi^ who, at the launch of Volume II at CERN, pubUcly suggested that there should be a sequel covering the period up to the late 1970s but not entering into the choice of the Large Electron Positron CoUider (LEP) as CERN's next big machine. Josef Rembser, a senior member of the German delegation to the CERN Council, and then at the Bundesministerium fur Forschung und Technologic, generously offered to provide core funding for the project provided that other member states were wiUing to contribute the balance. In the event research bodies in seven countries contributed to the overall budget. (A complete Ust follows this Preface). CERN offered infrastructural faciUties and unrestricted access to its archives (the most important primary sources used in this study), but did not provide direct financial support - a further guarantee, it was said, of the historian's freedom of expression.

viii

Preface

Individual authors have acknowledged the help and support of specific persons who provided them with material or who commented on their texts. Several other people deserve a generic words of thanks. First and foremost, Alfred Gunther, who has stood by the CERN history project from its inception over 15 years ago, and who has continued to provide invaluable administrative support for it well into his retirement. Paul Levaux, the chairman of the CERN History Advisory Committee, and a longstanding representative of his government at CERN, has watched over the rather slow progress of this third volume with concern and understanding. Roswitha Rahmy, the CERN archivist, has provided her usual gracious assistance for those wishing to consult an archive which has become extremely rich with the passage of time. Katherine Anderson built much of the thematic subject index; the name index was 'automatically' produced. Corinne Rambaldi, who transformed the original texts into camera-ready copy for the publisher deserves special mention for her efficiency, professionalism and good will. Finally, I must thank all the contributors to this volume whose labours, often undertaken in the pores of an already overcrowded research programme of a very different nature, have made this product possible. John Krige

This project has been supported financially by the following institutions: Bundesministerium fur Forschung und Technologic, Bonn, Germany Departement federal des affaires etrangeres, Bern, Switzerland Economic and Social Research Council, Swindon, UK IN2P3, Centre Nationale de la Recherche Scientifique, Paris, France Istituto Nazionale di Fisica Nucleare, Rome, Italy Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), The Hague, The Netherlands Swedish National Science Research Council, Stockholm, Sweden

IX

Notes on Contributors

Michael C. Crowley-Milling worked as a research engineer in industry from 1938 to 1963. He spent the next eight years as a member of the Directorate at the Nuclear Physics Laboratory in Daresbury (UK). In 1971 he was invited to CERN as SPS group leader responsible for computer control systems, and he was an SPS Division leader from 1976 to 1978. From 1978 to 1980 he was Director for the accelerator programme. He subsequently served as a consultant to various high-energy physics laboratories throughout the world. He is the author of John Bertrand Adams, Engineer Extraordinary, and many scientific publications. Ivana Gambaro was a research associate in the Office for the History of Science and Technology, University of California, Berkeley in 1985 and in 1987-88. In 1990 she joined the History of CERN Project. Her research interests include the history of XVIIth century astronomy and the history of XXth century physics. She is currently working on the Joliot-Curies and French physics in the inter-war period, and was a CNRS research associate in the Centre de Recherche en Histoire des Sciences et des Techniques at the Cite des Sciences et de ITndustrie, Paris during 1996. P. Gregers Hansen has been the John A. Hannah Professor of Physics at Michigan State University since 1995. During his lengthy earlier association with Aarhus University, Denmark, he was active at CERN as Senior Physicist and Group Leader responsible for the ISOLDE experimental programme (1969-1979), as Chairman of the CERN Proton Synchrotron and Synchrocyclotron Committee (1981-1985) and as member of the CERN Scientific PoHcy Committee (1986-1993). His research interests include atomic, nuclear and particle physics. John Iliopoulos completed his doctorate in theoretical physics at the University of Paris at Orsay in 1965. He held a post-doctoral position in the CERN Theory Division from 1966 to 1968, and spent the next three years at Harvard. Iliopoulos returned to Europe in 1971, when he entered the French CNRS. He is presently in the Theoretical Physics Department at the Ecole Normale Superieure in Paris. He has made important contributions to the Standard Model. John Krige has worked extensively on the history of CERN. He is currently leading a project to write a history of the European Space Agency, where he deals predominantly with questions of science and technology policy and the politics of European integration. He is the Executive Editor of the international journal History and Technology and series editor for Harwood Academic Publishers of Studies in the History of Science, Technology

Notes on Contributors

xi

and Medecine, He is a Directeur de Recherche Associe in the CNRS and the Director of the Centre de Recherche en Histoire des Sciences et des Techniques at the Cite des Sciences et de rindustrie, Paris. Dominique Pestre has mainly worked on French physics in the 20th century and on the history of CERN. He is currently studying the scientific and technological practices in university, military and industrial contexts between the 1930s and the 1960s. He is Directeur de Recherche in the CNRS and works at the Centre de Recherche en Historire des Sciences et des Techniques at the Cite des Sciences et de ITndustrie, Paris. Arturo Russo is Professor of History of Physics at the University of Palermo, Italy. During the last few years he has been involved in the project for the history of the European Space Agency (ESA), studying in particular the development of ESA's science programme and telecommunications programme. Klaus Winter studied physics at the University of Hamburg and finished his graduate studies at the College de France (Paris) with a PhD degree at the Sorbonne. He then joined CERN (Geneva) and has led several experiments in particle physics, including a measurement of the 71° Ufetime, the first experimental confirmation of the discovery of CP violation in K° decay, and a precise test of the AS/AQ rule. Since 1975 he has performed a series of neutrino experiments at CERN, with special emphasis on the study of neutral current phenomena. He is Professor of Physics at the University of Hamburg; currently he is guest professor at the Humboldt University, BerUn and has been Regent's Professor at the University of California. He was awarded the Stern-Gerlach gold medal of the German Physical Society in 1993.

This Page Intentionally Left Blank

Contents Preface v List of supporting institutions Notes on Contributors x Contents xiii

PARTI. 1

INTERACTIONS

CERN from the iiiid-1960s to the late 1970s John KRIGE

1.1 Some preliminaries 7 1.2 The growth in the user population 13 1.3 Machines and beams 18 1.4 Detectors 26 1.5 The member states 29 Notes 35

2

Gargamelle and BEBC. How Europe's last two giant bubble chambers were chosen Dominique PESTRE

39

2.1 2.2

Towards a first choice for a heavy Uquid chamber, Gargamelle 40 The emergence of hydrogen bubble chamber projects and Gregory's proposal for a tripartite solution, September 1964 - May 1965 43 2.3 The decision and construction of Gargamelle 49 2.4 The decision to construct BEBC and the CERN-Franco-German convention. Summer 1965 - July 1967 52 2.5 Some remarks about the construction of BEBC, 1967 - 1972 58 2.6 Some words by way of conclusion 60 Notes 61

3 The difficult decision, taken in the 1960s, to construct a 3-400 GeV proton synchrotron in Europe 65 Dominique PESTRE 3.1 3.2

The situation in 1965, when the decision on the ISR was taken 67 Revival of the project, shppages caused by the American decision, and sudden halt, 1966 - 1967 70

xiii

xiv

Contents

3.3 1968, the year of paradoxes 76 3.4 Adams' first attempt to revive the project and the setback in January 1970 82 3.5 Adams' second scheme for reviving the project: towards a Genevan solution 87 3.6 Conclusions 92 Notes 93 4 The Intersecting Storage Rings. The construction and operation of CERN's second large machine and a survey of its experimental programme 97 Arturo RUSSO 4.1 A few technical essentials about the ISR 100 4.2 Getting started 107 4.3 Building the machine 112 4.4 Setting up the physics progranmie 127 4.5 Keyhole physics 134 4.6 Particle physics in the 1970s 137 4.7 ISR physics 145 4.8 Epilogue 154 Notes 156 References 164 5

The relationship between CERN and its visitors' in the 1970s John KRIGE

171

5.1 The underlying causes of outside users' discontent in the early 1970s 173 5.2 The setting up of ECFA Working Group 3. A brief chronology 176 5.3 First point of friction: the construction of big equipment 178 5.4 Second point of friction: CERN's indefinite contract pohcy 182 5.5 Third point of friction: visitors' participation in decision-making 185 5.6 Fourth point of friction: the working conditions of visitors at CERN 190 5.7 Fifth point of friction: salary differentials between CERN staff and outside users 193 5.8 The visitors question: a quick survey of later developments 196 5.9 Concluding remarks 199 Notes 200 6 6.1 6.2

The ppbar project. I. The collider John KRIGE

207

Introduction 208 The first steps towards defining CERN's next big machine in the mid-1970s and the management's need for an intermediate' project 209 6.3 Proposals for the quick discovery of the W and the Z - at CERN and at Fermilab 213 6.4 1977: ICE cools its first beams and the competition hots up 224 6.5 CERN launches a ppbar collider at the SPS and Fermilab drops definitively out of the race to search for the W 232 Notes 243

xv

Contents 7

The ppbar project. II. The organization of experimental work John KRIGE

7.1 Introduction 252 7.2 How are collaborations formed and how international are they? 255 7.3 How are collaborations organized internally? 260 7.4 How is credit allocated in large teams? 265 7.5 Is teamwork antithetical to individual autonomy and creativity? 267 Notes 272

PART II. 8

P H Y S I C S RESULTS

Physics in the CERN Theory division John ILIOPOULOS

277

8.1 Introduction 278 8.2 Birth of the group 279 8.3 The Copenhagen years 279 8.4 Moving to Geneva 289 8.5 CERN, the Center of Europe 295 8.6 The rise of the Standard Model 307 8.7 Beyond the Standard Model 312 8.8 Conclusions 323 References 324

9

The SC: Isolde and Nuclear Structure Gregers HANSEN

327

9.1 Introduction 329 9.2 The early interest in nuclear physics at CERN 330 9.3 Experiments with muons and pions 340 9.4 The early ISOLDE 351 9.5 The SC improvement programme (SCIP) 370 9.6 The evolution of the scientific programme at ISOLDE 380 9.7 Another discussion about the future of the SC: 1979 - 1981 393 9.8 Concluding remarks 401 Notes 403 References 405 10

Experimental studies of weak interactions Klaus WINTER

415

10.1 Introduction 416 10.2 Neutrino physics 420 10.3 Discovery of the bosons of the weak interactions W and Z 445 10.4 CP violation 450 10.5 The weak hadronic current 459 References 469

251

xvi

Contents

PART III. 11

TECHNOLOGIES

The development of accelerator art and expertise at CERN: 1960 - 1980. Twenty fruitful years 477 Michael CROWLEY-MILLING

11.1 Introduction 479 11.2 Accelerator designs and major improvements 481 11.3 The proton-antiproton collider (p-pbar) 499 11.4 Beam instrimientation and its use 512 11.5 Accelerator components 521 11.6 Relations with industry 547 11.7 Concluding remark 552 Notes 552 References 553 12

The development of electronic position detectors at CERN (1964 - late 1970s) Ivana GAMBARO

12.1 Introduction 561 12.2 Early spark chambers 563 12.3 Film-less spark chamber techniques 566 12.4 The multiwire proportional chamber 569 12.5 The multiwire drift chamber or drift chamber 589 12.6 The multistep avalanche chamber (MSC) 600 12.7 Concluding remark 604 Notes 606 References 613 Name index 623 Thematic Subject Index 644

559

PARTI

Interactions

This Page Intentionally Left Blank

CHAPTER 1

CERN from the mid-1960s to the late 1970s John KRIGE

Contents 1.1 Some preliminaries 1.2 The growth in the user population 1.3 Machines and beams 1.3.1 The Proton Synchrotron 1.3.2 The Synchro-Cyclotron 1.3.3 The Intersecting Storage Rings 1.4 Detectors 1.5 The member states Notes

7 13 18 19 22 23 26 29 35

(CRHST, CNRS and Cite des Sciences et de I'lndustrie, 75930 Paris, France) 3

Before surveying the years in the Ufe of CERN covered by this book, let us pause for a moment to consider the periodization itself. How should one dissect this organizationdedicated-to-science? What moments is the historian to elevate to the status of 'turning points', so giving shape to the narrative but also inevitably imposing a particular rhythm and logic on it? There is no one answer to these questions, no one criterion for making one's cuts, no one way to transform a story into a history. The choice that we made - if one can call it a choice, for it was initially made only half-consciously - was to organize the history of CERN around the decisions to equip it with its major accelerators. Thus volume I took us up to 1954, when the organization was officially established with its 600 MeV synchro-cyclotron and its 28 GeV proton synchrotron ^ Volume II took us up to 1965 when it was decided that CERN should be equipped with a proton-proton collider, the Intersecting Storage Rings to be followed as soon as possible by a major fixed-target machine, formally adopted in fact only six years later (the 300 GeV Super Proton Synchrotron)^. This volume covers the period up to the late 1970s, precisely so as to include the decision to build a proton-antiproton collider at the SPS and to avoid entering the debate surrounding the decision to build CERN's next major accelerator, a large electronpositron collider. Studies on a LEP machine began in 1976, and the first major design report for an accelerator of circumference 22 km which was cost-optimized on 70 GeV per beam was pubHshed in 1978. In that same year the European high-energy physics community formally adopted a LEP as its next big machine. The debates over its design, ultimate target energy and funding were complex and controversial, and would have drawn us into the 1980s, a period deemed too recent to permit a sober historical analysis when the work on this volume got under way about five years ago. This mode of periodization bears reflection, all the more so since our use of it has never been explicitly questioned by the high-energy physics community itself. Its significance is twofold. Firstly, the kind of physics one can do depends on the kind of machine that one has at one's disposal: its energy, its intensity, and itsflexibilityare crucial variables in the definition of a research programme. Secondly, machines are expressions of power and prestige: power to shape and to dominate the research frontier, power to compete effectively at the world level, power to raise money from governments. At heart then the periodization adopted in these three volumes of CERN's history is one which reflects and reinforces the ambition of the European high-energy physics community, and the science administrators and governments who supported them so reliably, to have the equipment needed to place them among the world leaders in their field of research. If the dates that have structured our narrative are necessarily to be taken as 'turning points' it is in the sense that at that moment another step was taken up the spiral of ever-increasing energy, a

decision was taken to build an even more powerful machine. It is this that our history celebrates and legitimates. This choice of timespans is not without interest, far from it, but as we have said it is not the only one possible. We could, for example, have delimited our research using Nobel prizes missed and won (the two neutrinos, the J/psi, the W and the Z...). Or the reigns of the laboratory's successive Directors General (the Weisskopf era, the Gregory era...). Or the national science policies and foreign policies of CERN's member states, most notably Britain, France and Germany (which would have forced us to situate the laboratory in the context of European economic, political and miUtary reconstruction)^. Each of these options imposes its own rhythm and chronology as well as its own set of pertinent questions. No one is all-encompassing, no one of them can give us a 'complete picture' of CERN's history. Indeed no such picture exists; it is rather up to the historian to fabricate a picture out of the materials available - documents, interviews, first hand experience. This picture will necessarily be framed by a variety of implicit and explicit assumptions and questions, assumptions and questions which are specific to the conjuncture in which the work is produced. The characteristics of the period which we have chosen to cover here, bounded as it is by decisions about accelerators, are not easily captured in a few lines. For volume I our task was simple: we described the launch of CERN, how and why a handful of European scientists and science administrators imposed a costly laboratory equipped with machines far bigger than anything ever constructed in Europe on a physics community and on governments which were often sceptical, not to say hostile to the feasibihty and indeed desirabihty of the project. Similarly, for volume II, we quickly settled on a catch-all phrase. The book described the building and the early running of the laboratory: the construction of the machines, the negotiations over the laboratory's internal structure and experiments committee system, the difficulties raised for scientists and governments alike in moving from a period of machine construction to one of exploitation, the sometimes bruising debates with the outside users community over access to the laboratory's facilities, the first physics programmes, and the choice of CERN's next generation of accelerators. Now as we move into the next period, many of these earlier difficulties have been resolved. There were of course moments of great drama: the titanic struggle to have the SPS accepted by governments as CERN's major fixed-target machine for the 1970s, the visitors revolt in the early 1970s, the announcement of weak neutral currents and the disbehef and depression that 'the ISR [had] missed the J/psi and later missed the upsilon'"*, the testing and implementation of the beam-shrinking technique of stochastic cooling. But these moments of drama apart, CERN seems to have 'ticked along' quite smoothly in these years, its global budgets, its equipment, its experimental programmes, and its staff (as well as their experience in managing a major laboratory), expanding steadily. A little story will make the point. In volume II we made much of CERN's unpreparedness for doing physics at 28 GeV, as evidenced typically by its lack of suitable beam transport equipment, a criterion which encapsulated many features of the young CERN: inexperience on the experimental floor, in the directorate and in the Council, the Notes: p. 35

6

CERNfrom the mid-1960s to the late 1970s

relations between physicists and engineers and about what it meant to do physics, the emergence of a number of mandarins each determined to control a part of the physics programme for himself. Indeed when the PS experimental programme got under way early in 1960, CERN had only three beam transport elements of its own. The first beams were made without lenses and with magnets begged or borrowed from various sources. Welding generators were put into service as power supplies and the ordinary town water was used for cooling. Something like a third of the South [experimental] Hall was still a workshop and the North Hall was still being used as an assembly area by the PS Division'. Ten years later there were about 250 beam transport elements at hand for the PS experimental programme, and floorspace had almost quadrupled from 2500m^ to 9000m^. The laboratory staff had learnt what it meant to do physics around big machines^. John Adams, who had directed the construction of the PS, surely had the traumas of the early 1960s in mind when he wrote, in 1977, that 'One of the triumphs of the SPS Programme planning [for which he was partly responsible of course] [...] was that the accelerator and the massive detectors were ready at the same time so that experimental research could begin this year without delay'^. In short, in the period covered by this book, CERN had overcome many of its early difficulties and was functioning efficiently as a European organization-dedicated-to-science. Seen in this light, there seems to be another kind of logic linking our three volumes of CERN's history. It is the pervasive and pernicious logic of birth, adolescence and adulthood (what a happy coincidence that we have just three tomes!), each one following on the other and consolidating the 'lessons' learnt before. This spurious continuity, this superficial metaphor must be resisted at all costs. For it masks the specificity of different periods in the laboratory's development, the displacements and ruptures which differentiate contexts and practices from one another over time. For example, the political and economic world in which CERN hved in the late 1960s was totally different from that in the early 1950s when it was established. Experimental practice in high-energy physics in the early 1970s was quite other in complexity and in kind to that just a decade before. To speak of CERN as growing into maturity over the 30 years covered by our histories is to impose a priori an abstract homogeneity on the rich, differentiated texture of the past. Wherein lies the specificity of the period covered by this book? It is, we would suggest, in the way in which CERN was situated, and situated itself, vis-a-vis its outside users and member states' governments. In the late 1950s and early 1960s CERN was thought of as being a leading research laboratory deliberately isolated from the world around it, an ivory tower for a select few whose dominant task was to do high-energy physics. This conception began to change in the late 1960s and early 1970s. Now the outside users and the governments alike increasingly demanded that CERN take their interests into account, respect their needs. The laboratory was allowed to expand, to concentrate (almost) the entire European high-energy physics effort on its site - but on condition that it responded to the demands made by national physics communities and science administrations. For the first decade of its life CERN had traded on the myth of the nuclear and of European reconstruction to create a space in which it was more or less immune to the usual financial

Some preliminaries

1

and political constraints of a research laboratory, and was easily able to fend off criticisms from its users about the sometimes arrogant and patronising behaviour of its Senior Staff. This was no longer possible. A new generation of physicists, many of them trained on big equipment in the US during the sixties, moved to positions of prominence in the field and were simply not prepared to be regarded as less able than the inhouse CERN staff. The member states, squeezed by economic recession, by fears regarding a supposed 'technological gap' which had opened between the two sides of the Atlantic, and by the demands for funding from other areas of science and technology, notably space, were simply not prepared to pour money into CERN without seeing some direct benefits for their national research efforts and their industry'^. From being a privileged laboratory having a high degree of autonomy CERN was predominantly seen, in the late 1960s and 1970s, as a research faciUty jointly owned by the European high-energy physics community and its governments, and accountable to them. This leitmotif, rather than a summary of the contents of each chapter, has informed the selection of material for this introduction. It is based almost exclusively on the chapters in this book and on CERN Annual Reports (or documents of similar status) so as to maintain a uniform level of analysis. In adopting this approach, which is obviously selective, we hope to capture something of the transformation in the character of the laboratory during this time. That character is sometimes elusive and difficult to pin down behind the superficial continuities, the efficient organization, the onward and upward expansion and growth. But it is surely there, its presence revealed by a number of events which, collectively, attest to a new conception of this phenomenon that was the CERN of the late 1960s and the seventies^.

1.1 Some preliminaries Before getting under way we need to provide some basic information about CERN in our period which will be useful, not only for the argument developed here, but throughout the entire volume. The period covered includes the reigns of four Directors General, Bernard Gregory (1966-1970), Williband Jentschke and John Adams (1971-1975), when CERN was momentarily spUt into two laboratories (cf. below), and John Adams and Leon Van Hove (1976-1980), the former baptized the Executive Director General, the latter the Research Director General. These nominations merit two quick comments. Firstly, in the first decade of CERN's life a major effort had been made to attract a physicist of high prestige, who had spent a good deal of time in the United States, to head the laboratory, both to ensure the international reputation of the new research centre and to reverse the 'brain drain'. Hence the choice, first of FeUx Bloch, and then of Victor Weisskopf (with CorneUs Bakker and John Adams sandwiched between them). This criterion was no longer dominant. Of course the CERN member states still wanted people of renown and influence in their own countries to fill this highly important post. But it Notes: p. 36

8

CERNfrom the mid-1960s to the late 1970s

sufficed that they were respected nationally and internationally and, above all, that they had the skills appropriate to the phase the laboratory was passing through. This phase was characterized essentially in terms of major heavy equipment programmes. Thus Bernard Gregory, senior Polytechnicien with an extensive experience with bubble chambers, the first chairman of CERN's Track Chamber Committee in 1960, and director of research under Weisskopf, was chosen to take over from the latter for the second half of the sixties precisely when the bubble chamber technique was blossoming at CERN and when ongoing contact was essential with the scientists, engineers, officials and industries in France and in Germany who were constructing the next two big bubble chambers to be installed at CERN, the 'French' heavy liquid chamber Gargamelle and the CERN-Franco-German hydrogen chamber BEBC (Big European Bubble Chamber). Gregory was followed by Jentschke and by Adams. The former was a founder of the Deutsches Elektronen-Synchrotron (DESY) laboratory in Hamburg estabUshed in 1959, and chairman of its first board of directors, member of the German CERN delegation from 1964 to 1967, then first chairman of the ISR experiments committee in 1968, and the man chosen to take over the laboratory in the year that the Intersecting Storage Rings were first available for physics. John Adams, the constructor of the PS, called back to CERN to save the Super Proton Synchrotron project, was temporarily granted his own division, but when the member states finally agreed to build the SPS they kept their promise and established a second laboratory parallel to the first with Adams as DG. This system of two DGs was maintained once the machine was completed. The two laboratories were fused into one in 1976, the year the SPS reached its design energy, John Adams was kept on as Executive Director General of CERN, and he was now twinned with Leon Van Hove, theoretical physicist of high repute who had had a loftgstanding relationship with the TH division at CERN, and who was to be responsible for the laboratory's research programme. When CERN's first DG was appointed early in the 1950s there was a turgid debate over the need to have a laboratory head who was knowledgeable about accelerators but someone, too, who was able to lead the scientific programme and create a 'scientific atmosphere' on a laboratory site dominated by bulldozers and big equipment^. This kind of argument probably played a role again in 1975 when the Council accepted to appoint two DGs. But the heart of the matter was surely Adams' ambition, and his determination to maintain control over the life of the laboratory, and 'his' SPS machine in particular. Kjell Johnsen, who had led the construction of the ISR, had benefitted enormously from the institutional and financial autonomy allowed him as head of a 'supplementary programme' having its own distinct budget. But he had always remained a senior member of management within the existing CERN structure. John Adams demanded and got more. The Council recalled him in December 1968, 'the intention being to appoint him DirectorGeneral of the new European High-Energy Laboratory once its construction has been officially approved'^^. At the time it was thought that the SPS would be built elsewhere than in Geneva. When Adams showed that it would be technologically and financially interesting to use the PS as an injector for the SPS - so breaking a deadlock between governments over where to put the new accelerator - the Council had no choice but to give

Some preliminaries

9

him a second laboratory at CERN (Laboratory II) during the construction phase of the big machine^ ^ His competence, authority, prestige and charisma ensured that he retained this office even after the machine was built, and the two laboratories were fused again into one. The decision to set up two parallel laboratories was the only really significant change to the internal structure of CERN in the Gregory and Jentschke-Adams eras. Gregory's main innovation was to group the existing divisions at CERN into a number of departments, so inserting another layer of hierarchy between the DG and the division leaders and opening up another set of top-level posts to the CERN Senior Staff (although sometimes the department head and the division leader were the same person). This structure was also used to create new divisions for relatively short-lived well-defined projects. Typically the construction of an 800 MeV booster for the PS was asssigned to the SI (Synchrotron Injector) division inside the Proton Synchrotron Department. This division existed from 1968 to 1972, it was headed by Giorgio Brianti and its total staff complement never exceeded 100 persons. The Adams-Van Hove regime made a number of important changes to the CERN organigramme. They abolished the departmental structure, and established a directorate of half-a-dozen members who reported directly to them. They also set up a research board (chaired by Van Hove) and an executive board (chaired by Adams) in which the directorate, the appropriate division leaders and (in the case of the research board) the chairs of the experiments committees could consult regularly. The divisions concerned with experimental equipment were also totally reorganized. The long-standing spUt based on kind of technique (bubble chambers or electronic) was done away with^^. In its place two new divisions were created. Experimental Physics Facilities and Experimental Physics. EPF was responsible for all heavy equipment required for experimentation on the CERN site and, in the view of the Executive DG, was similar to the accelerator divisions at CERN in terms of the Icind of work carried out and the responsibiUties involved'^^. EP grouped together the experimental physics community, including the outside users, and was the biggest division by far at CERN: 1780 people at the end of 1976, over 1200 of them nonCERN staff. During the first decade covered in this volume the experiments committee system, like the organigramme, was barely changed. In the early 1960s the structure was organized by experimental technique, and there were three main committees dealing respectively with experimental proposals using emulsions (EmC), track chambers (TCC) and electronics detectors (EEC)^"^. Towards the end of 1964 it was proposed to add a nuclear structure committees to deal with the growing interest in studies of that kind at the SC. This committee met only seven times before it was merged, in 1966, with the EmC (reflecting the decreasing importance of emulsions) and renamed the Physics III Committee. These three committees remained in place until 1975. However, they remained limited to work done at the PS and the SC. The experimental programmes on the two new accelerators that were commissioned in our period were not channelled through them but through two new machine-dedicated committees. The first, the ISR experiments committee, was set up Notes: p. 36

10

CERNfrom the mid-1960s to the late 1970s

in 1968 with Jentschke as its chairman as we said a moment ago^^. The second, the SPS experiments committee, was set up in 1973 with Pierre Lehmann as its chairman. In 1976 Adams and Van Hove 'rationalized' the system by abolishing completely a committee system based on experimental technique, and using the machine as the defining criterion: henceforward we have the SCC, the PSC (fused into the PSCC in 1978 to advise on research at both machines), the ISRC and the SPSC. Two other points about the decisionmaking procedures on the experimental programme should be noted. Firstly, in our period the CERN practice was put in place of having a two-tiered system of open meetings with free access for all those interested, followed by a closed meeting where a small group defined their recommendations for the experimental programme^^. Another innovation was that those users with a special interest in a particular piece of heavy equipment, like Gargamelle or the ISOLDE, set up their own 'user's committees'. These committees existed independently of the experiments committees that had been officially sanctioned by the Council and were less formal in constitution. They defined the priorities of those who wanted to experiment with the corresponding facility and funnelled a joint request for beam time and infrastructural support to the appropriate higher-level body (e.g. the Physics III committee for ISOLDE)^'^. Turning now to the Council and its committees, we note (as in Volume II) the internal cohesion of the 'legislative arm' of CERN and the relatively small turnover of a core of senior delegates who had had a long and close association with the laboratory. Indeed many of the CERN 'pioneers' were still engaged with it well into the seventies. Let us limit ourselves to the period up to 1978. Bannier had only left the year before - indeed both Dutch Council representatives, Bannier and Wouthuysen remained unchanged through to 1977! Willems remained in the Council representing Belgium until his death in 1971, when his place was taken by Levaux, who was immediately nominated chairman of the Finance Committee. Amaldi represented Italy until 1972, serving as Council president in 1970 and 1971, years crucial for the resolution of the SPS site problem and when governments gave the green light for the construction of the machine in Geneva. France was represented by Perrin until 1972, when his place was taken by Gregory, recently released from his responsibilities as CERN DG. For Sweden Funke stayed on until 1971, serving as Council president from 1967 to 1969. Chavanne continued to represent Switzerland. Gentner, who had built the SC in the late 1950s and had chaired the Scientific Policy Committee from 1968 to 1971, repesented Germany in the Council from 1971 onwards, and served as Council president from 1972 to 1974, when he handed the responsibiUty over to Leveaux. We shall stop there: the point has surely been made. Throughout our period CERN continued to enjoy the support of a nucleus of senior scientific statesmen and science administrators many of whom had been associated with the laboratory from its very inception, who identified with it and with its success, and who could be counted on to do all that was possible to further its interests in their national state apparatuses^^. Figure 1.1 shows the functional distribution of CERN's expenditure since the start of the organization, at 1974 prices, the last year for which such illuminating diagrams were presented. Some of the categories (all of which include the associated personnel costs)

It: "5

OlDllil

Some preliminaries

aaaaaaaaaaaaa^ v

••••••••••••••a ••••••••••••••• • ••••••••••••••I "•••••••••••••• ••••••••••••••a • ••••••••••!•••• •••••••••••••a • ••••••••al •••••••••••••a ••••••••••••••ri • •••••••••••••_, ••••••••••• ••••••••••• •••••••••••a aaaaaaaaaaaaaari aaaaaaaaaaaaaa^aaaaaaaaaaaaa aaaaaaaaaaaaail aaaaaaaaaaaaa aaaaaaaaaaaaail aaaaaiaaaaaaail aaaaaaaaaaaaail aaaaaaaaaaaaail aaaaaaaaaaaaail a a a a a a a a a a a a a il a a a a a a a a a a a a a al aaaaaaaaaaa ~ " a a a a a a a a a a a a 11 aaaaaaaaaaaaH__ r aaaaaaaaaaaa aaaaaaaaaaarf

aaaaaaaaaaari

11

:3

<

u

C3

I Notes: p. 36

12

CERNfrom the mid-1960s to the late 1970s

require clarification. The lower two curves refer respectively to the more or less routine expenditure on accelerators, beams, detectors and computers required for the research programme and, secondly, the design, construction or major modifications to such equipment for research purposes that did not require special Council agreement. The category of improvements is dominated by the costs of construction of the ISR up to 1968, while by 1971 the band is shared equally between the machine and items like the construction of a booster for the PS (which needed Council approval). The curve marked 'Laboratory IF obviously refers to the SPS construction programme, while the little segment marked '2/3 BEBC is the contribution by the French and German governments to the construction of the big bubble chamber. Thisfigurecalls for three comments. First, we see a roughly Unear increase in the overall budget during the first decade of CERN's life, with a sharp change in slope when the ISR and a variety of improvement programmes were approved in the mid-1960s. This new rate of growth was sustained until the peak of the SPS construction programme, touching some 625 MSF, from where it declined gradually. Second notable point: the construction of the SPS was, at the Council's behest, undertaken against a background of gradually falling budgets for the rest of the laboratory's activities (a reduction of 210MSF overall between 1971 and 1978 was called for). Meeting this demand caused endless debates at CERN about possible cuts in the existing experimental programme, but also encouraged the promotion of new projects which were scientifically justifiable and which could help sustain the level of the CERN budget until the end of the decade (notably the protonantiproton coUider)^^. Finally, and related to this point, we note that despite the 'rigorous' regime imposed on CERN, there was a sharp increase in expenditure on major items of experimental equipment in 1971, the investments here remaining constant at a new, significant level for the rest of the period covered by this graph. In short, the CERN research programme may have been squeezed a little financially in our period, but by and large what strikes one is the ongoing generosity of its fundgivers. The growth in staff numbers confirms the point. In 1966 the CERN staff totalled 2115 persons. This had increased to 2639 by 1968 and to 3092 by 1972: a 50% increase in just four years! The rate of change then decreased, but still the staff numbers climbed to a peak of 3618 persons in summer 1975, a peak from which they then began to decline, albeit gradually. Much of this increase in the early 1970s was of course connected with the construction of the SPS. That said it must also be noted that the staff complement of Laboratory I also increased steadily, if less rapidly than that of Laboratory II, in the early 1970s, reaching 3181 when the global figure touched its highest level in mid-1975.^^ The willingness of governments to support CERN was symptomatic of a number of factors. Thefieldstill carried considerable prestige, and competition with the United States was still intense. The big accelerators and detectors promised to contribute to the development of new technologies and skills in areas like superconductivity which were deemed to be of immense economic importance. High-energy physics also retained a political importance at a global level. In the context of detente in the early 1970s, as exemplified by the ratification of the Salt II nuclear disarmament agreement in 1973, high-energy physics

13

The growth in the user population

was specifically identified as the kind of activity that could strengthen international 'security and cooperation', and the physics community once again began discussing the possibiUty of building a world machine^ ^ Couple this with a huge expansion in the size of the European high-energy physics community during the 1960s - it had roughly trebled to about 2000 people by 1972^^-, and one can appreciate that the pressure on governments to continue pouring resources into thefieldwas intense. CERN benefitted from this. But the support given was no longer unconditional. Returns were sought, not simply by the production of world-class physics results, but also in provision for the needs of outside users and in spin-offs to national industry. The Geneva laboratory became the centre of the European high-energy physics effort in our period but at a certain cost to the autonomy of its staff* and of its Council. As we mentioned earlier in this chapter, it is this new role that will structure the remainder of this introductory survey of CERN from the mid1960s to the late 1970s.

1.2 The growth in the user population The community of physicists served by CERN expanded sharply in size, and changed notably in its character during the period we are considering here. The most significant development affecting these reorientations was the increase in the importance of electronic modes of detection, which gradually replaced the bubble chamber as the preferred technique for high-energy physics. This had a direct impact on Ufe at the laboratory for whereas the majority of the 'bubbles' community analyzed their data in their home institutes, physicists using electronic techniques had to spend protracted periods of time on the experimental floor at CERN taking and analyzing data. The number of 'visitors' doing high-energy physics on site in Geneva thus grew rapidly between the mid-1960s and the late 1970s, their numbers further swelled by parallel programmes, hke nuclear studies with the on-Une isotope separator (ISOLDE) at the SC. The effects of this change in experimental practice were ampUfied by the decision to build the ISR in 1965, and to build the SPS at CERN in 1971 - a choice of site which was not foreseen originally - , decisions which meant that European high-energy physics became progressively concentrated in one laboratory. National programmes were effectively phased out in Italy, then in France and finally in Great Britain as governments decided that they could not also maintain meaningful research programmes at home in a field of research which was far from the market (to use current jargon). Only Germany, with its electron synchrotron laboratory in Hamburg (DESY) could aff*ord to sustain an internationally competitive high-energy physics activity of its own. The CERN staff" and matiagement could do nothing to stop this tide. If in the early 1960s they had tended to regard the laboratory as 'theirs', as a laboratory of which they were the masters, rather hke a national laboratory, by the 1970s it was made clear to them that the visitors deeply resented such attitudes. As the Chairman of ECFA and spokesman for the entire European high-energy physics community was to put it in 1975, the users Notes: p. 36

14

CERNfrom the mid-1960s to the late 1970s

regarded CERN as 'their laboratory' too, as 'the laboratory of us alF; it was not to be 'an ivory tower for a select body of physicists on site'^^. And if these protests carried weight it was because the trend towards increasingly large and complex detectors, both bubble chambers and electronic, demanded financial and human resources beyond those which CERN could muster on its own. Most member states no longer invested heavily in national accelerators, but they did supplement their contributions to CERN by financial and other means (e.g. with computing time) to ensure that their physics communities could play an active role in exploiting the machines available in Geneva. CERN needed the material, financial, and political support of European physicists, science administrators and governments, and had increasingly to bend to their demands. It could no longer perceive itself as a 'host' laboratory opening its doors to 'visitors', with the imbalance of power and privilege that that implied. It was a multinational laboratory with a small permanent research staff serving an ever-growing and influential community of users. It is difficult to track these movements with quantitative precision; considerable data was assembled by CERN and by ECFA on these issues but it was used to answer different questions or to serve different purposes depending on the context in which it was generated. Even if incomplete and not always comparable, it is nevertheless highly indicative of the trends we are discussing, and is presented here in that spirit. Figure 1.2 shows the evolution in the number of scientists on the CERN site between 1966 and 1975. It distinguishes fellows (generally young researchers paid by CERN to spend some time at the Geneva laboratory) from paid and unpaid 'associates', the term which replaced the word 'visitors' in CERN management parlance after the user 'revolt' in the early 1970s^'^. It also charts the number of experimental research staff on the CERN payroll in this period. It has two outstanding features. Firstly, it shows clearly the very slow change in the number of staff on the payroll: it remains roughly steady at between 75 and 90 physicists (of which about half were permanent staff with indefinite contracts, while the remainder stayed at CERN for three to six years). Secondly, it shows the exponential increase in the number of outside users up to about 1973, whereupon the rate of growth slows down. We see then that, if in 1966 there were a little over 350 outside users at CERN at the end of the year, by 1970 this has doubled to about 700, and by 1975 it has more than tripled to about 1150. To put this figure in perspective it is useful to compare it with the situation prevailing at around the same time at CERN's major US rival, the Fermi National Accelerator Laboratory, whose machine reached its design energy of 400 GeV in December 1972. Of course we expect the number of outside users here to be far smaller precisely because in the US, unlike Europe, there were several leading high-energy physics laboratories scattered around the country. What is more Fermilab had one machine whereas CERN had three. All the same the difference is striking: in September 1974 the American laboratory estimated that there were about 250 users on site taking part in experiments at any time. This number was expected to increase as all of the beam lines were brought into action, but it was doubted that it would go much beyond 350 people, if only for financial reasons^^. In other words, there were about as many outside users at Fermilab in 1975 as there were at

The growth in the user population t/5 CC

15

•

m 1300

>• <

z

1200 h

^ ^ TOTAL

h /

/

ACTUAL/*^

/

/

h

h

UNPAID ASSOCIATES

^ ^

/^^^°n\

^ ^

ESTIMATE

1971 ESTIMATE ^

FELLOWS AND ASSOCIATES PAID BY CERN

ACTUAL CERN STAFF (EXPERIMENTAL PHYSICISTS)

1

1

1

1

\

1

[

1

\

^

Fig. 1.2 The number of scientists at CERN on the 31 December of each year, for the years 1966 to 1975. (Source: CERN Annual Report, 1975, p.30^^).

CERN in 1965 - a concrete manifestation, if ever one was needed, of how European highenergy physics became concentrated in the Geneva laboratory. The data in Fig. 1.2 do not distinguish between the scientific activities in which the fellows and associates were involved. In fact far and away the bulk of them were attached to the so-called NP division where they were doing physics with electronic detectors: there were never more than 100, and generally around 50 to 70 non-CERN scientists on site in the Track Chamber division, while the Theory division usually had about 30 to 40 fellows and associates annually in its ranks. Figure 1.3, which charts the number of associates from the CERN member states and non-member states in the NP division makes the point clearly. Its overall shape mirrors that in Fig. 1.2. It shows that there was a more or less linear increase in the number of outside 'electronics' users from 1965 to 1970, when the number from the CERN member states reached almost 400, a sharp rise to a new plateau of about 650 scientists when the ISR was commissioned, and another sharp upturn once the preparations for the SPS experimental programme got under way. The other interNotes: p. 36

CERNfrom the mid-1960s to the late 1970s

DMS •NonMS

1966

1966

1967

1970

1971

1972

1973

1974

197S

Fig. 1.3 The number of associates at CERN on the 31 December of each year in the NP division, i.e. mostly engaged in electronics experiments. A distinction is made between those from the member and those from the nonmember states. As we do not have data drawing the same distinction for fellows, we have omitted this category of outside user. There were about 20 a year in NP in the first five years covered by the graph, and about 30 in the second. (Source: CERN Annual Reports, for the years in question.)

esting point about Fig. 1.3 is the jump in the number of associates from non-member states in 1971. It reflects the interest which US scientists, in particular, had in exploring the new energy range and the new mode of practice opened up by the ISR. There is one last point we would like to illustrate about the presence of outside users on the CERN site: their national distribution. This is shown for the 1970s in Fig. 1.4. Here we see that about 70% of the fellows and associates were from the 'Big Four' European countries, as one would expect. Within those the two that had no major national facility left in the 1970s, France and Italy, were the two best represented, while Germany and Britain were both considerably lower - although we notice the UK's figure beginning to climb at the end of the period as the high-energy machine at the Rutherford Laboratory was closed down and attention was focused on exploiting the SPS. The smaller countries are noticeable for the similarity in the size of their national scientific communities at CERN, which generally vary from 30 to 50, Switzerland being a little higher due, no doubt, to the proximity of its major universities and research centres to Geneva. The most important non-member state scientific community on the CERN site was, of course, that from the US, and it is interesting to note that its size in 1978 was comparable to that from Britain or Germany. The information we have given so far does not tell the whole story about the increasing role which CERN played as a service centre for the European physics community. In addition to the people on the site, one must also bear in mind the huge number of

The growth in the user population

17

0 1971

Fig. 1.4 The evolution in the number of fellows and associates (paid by CERN or not) on 31 December of each year, broken down by nationaUty. (Source: CERN Annual Report, 1978, p. 157).

physicists who remained at their home institutes to measure and analyze bubble chamber film^^. Only a few track chamber scientists - 50 to 70 for most of the decade from 1966 to 1975, as we said moment ago - are included in our global data in Figs. 1.2 and 1.4. The vast majority stayed in their universities or national research institutes. While we have very imprecise data on the numbers involved here, we can get some idea of the role which CERN had in this regard from data on the numbers of track chamber pictures taken in Geneva. This is shown in Fig. 1.5, which charts the number of pictures (in 1000s) taken at CERN (i.e. at the PS) and breaks that down into those which were distributed among groups which did not include a CERN component, and those that did. It should be said that the data usually only include pictures taken with hydrogen or deuterium either in the 1.5 m British chamber (for 1965 only), the 80 cm Saclay chamber (which was taken out of service in 1971 having taken 16 million pictures at CERN) and the CERN 2 m hydrogen chamber. We note that about 3-4 milUon pictures were taken between 1965 and 1968 (apart from a drop in 1966 caused by a major failure in the PS magnet supply), followed by a sharp rise to a new plateau of 6-7 million pictures. This was possible because the new PS magnet permitted double-pulsing of the CERN 2 m chamber. The drop in 1975 arose Notes: p. 36

CERNfrom the mid-1960s to the late 1970s

Q Total • nonCERN only • CERN+nonCERN

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

1975

Fig. 1.5 The number of bubble chamber pictures taken at CERN (in 1000s) mostly with the CERN 2 m and Saclay 80cm hydrogen bubble chambers (until 1971), but also including some pictures with Gargamelle, (1971-75), BEBC (1973-5) and HYBUC, a hyperon bubble chamber (1972-3). (Source: CERN Annual Reports for the years in question.)

because the CERN chamber underwent a major overhaul that year. Whereas it took 5.1 million pictures in 1974, it took about one-third as many during the three months it was in operation the year after. As we said a moment ago, we have no way of translating these data into a number of researchers. We do know that about 90% of the film taken at CERN was analyzed offsi te^^, while in 1972 CERN DG Jentschke indicated that the numbers of electronics and bubble chamber physicists were then about the same in Europe, a figure roughly confirmed by ECFA data^^. To a first approximation then, it seems that in the early 1970s there were about 1500-1750 European high-energy physicists wholly or partly dependent on CERN for their experimental data, their number equally spHt between the two then-standard experimental techniques, and about half of them regularly on the CERN site.

1.3 Machines and beams The increasing demands of experimentation, and the need to satisfy an expanding user community whose physiognomy was traced in the previous section, posed ongoing technical challenges to the engineers and applied physicists at CERN. The performance of the accelerators, the nature and the number of the beams, the power of the detectors all affected the kind and the quality of the physics that could be done: the direct correlation between the intensity of the PS and the fluctuations in the number of pictures taken with

Machines and beams

19

the bubble chambers, as presented in Fig. 1.5, is just one indicator of the essential role they played in the experimental programme. In what follows we shall describe in some detail this dimension of the laboratory's life. 1.3.1 THE PROTON SYNCHROTRON As we explained in the previous volume, when the PS was commissioned in November 1959 neither the physics community nor the laboratory were ready to launch an experimental programme around the machine^^. On the one hand there was a dearth of proposals for experiments in the new energy range opened up by the accelerator. On the other, there was a serious lack of beam transport equipment - bending and focussing magnets, separators and power suppUes. The first run with CERN's 30 cm hydrogen bubble chamber took place in March 1960 in an experimental hall cluttered with ancillary equipment. This situation was gradually rectified over the next two years. By the end of 1961 two batches of beam transport equipment had arrived and an order had been placed for 55 additional elements. Two short separators on loan from Padua University, which had been essential for the construction of relatively pure beams, were supplemented by the first of CERN's giant 10 m electrostatic tanks. The 2500 m^ of space in the North and South experimental halls had been liberated and four bubble chambers were on hand: the CERN 30cm hydrogen and Im heavy liquid chambers, an almost identical heavy liquid chamber on loan from the Ecole Polytechnique and an 80 cm hydrogen chamber built at Saclay. These were joined in 1964 first by the 1.5 m British hydrogen bubble chamber and then by CERN's 2 m hydrogen chamber, which had its first cool down in December and started doing useful physics soon thereafter. To accommodate all this equipment and a programme of electronics experiments using mostly spark chambers and Cerenkov counters an additional experimental area, the East Hall, had been commissioned in 1963. To get this equipment to function routinely and reliably required a major learning process. Contrary to what the engineers who built the machine originally thought - they expected to go home in 1959 once the PS reached its design energy - they soon 'realized that a machine of this kind will never be 'ready' - ready in the sense of a machine that is switched on and off* and runs without a change'. It had constantly to be modified and new systems had to be added 'to increase its capabilities as a source of high energy particles, to ease its operation, to improve control of the many parameters [affecting its performance], and to reduce damage due to irradiation of the synchrotron components' as the intensity of the circulating beam was increased^ ^ During the first six or seven years of PS operation the average intensity of the PS beam was increased by about a factor of ten to 10^^ protons/pulse. This was largely due to a better understanding of the beam dynamics in the Linac (50 MeV linear injector) and the installation, in 1966, of a new ion source which produced beams of up to 140mA at 50 MeV. The next major step forward was the installation, in 1968 of a new power supply for the main magnet. This enabled the machine either to be run regularly at higher beam Notes: pp. 36 ff.

20

CERNfrom the mid-1960s to the late 1970s

energies (27GeV) or at higher intensities (by providing a long flat top for counter experiments and double pulsing for the hydrogen bubble chambers - cf. Fig. 1.5). By this means the PS reached a peak intensity of 2 x 10^^ protons/pulse in time for its tenth birthday in November 1969. In addition to developing the PS's capabiUties as a supplier of proton beams for experiments, it had to be adapted for use as an injector for the ISR. This required a further increase in the beam intensity of an order of magnitude. To achieve this higher intensity with a minimum beam blow-up due to space charge effects it was necessary to increase the injection energy further. Various ways of doing so were considered and finally it was decided that a four-ring booster synchrotron operating between 50 and 800 MeV would be the most suitable alternative. A special division (SI: Synchrotron Injector) was created to build it, and the new complex was used for physics for the first time in November 1973. The PS intensity was now about 5 x 10^^ p/p, and it was able to increase immediately the neutrino flux to the Gargamelle bubble chamber by a factor of three (at the time when pathbreaking studies on the weak neutral currents were being made - see below). A year later the PS reached an intensity of 10^^ protons/pulse for the first time, and was being prepared as an injector for the SPS. It only remains to add that as its intensity increased so too did its reliability. In 1967 the scheduled running time for physics experiments on the PS was around 6000 hours per year, and the unscheduled down-time on the machine due to unexpected faults was about 10% of that. From the mid-1970s onwards it retained the same scheduled running time (while also serving as an injector for the ISR) and the unscheduled down time had been reduced to about 400 hours a year^^. The second major research and development initiative undertaken to improve the power and versatility of the PS as an experimental tool was the production of extracted beams. These were virtually neglected when the machine was designed but rapidly assumed importance as the advantages of Using external rather than internal targets were appreciated by the PS engineers (reduction of proton losses in the machine) and the experimenters aUke (more freedom in the lay-out of the secondary beams around the target). Two different systems were developed. Fast ejection (the removal of the whole beam or part of the beam within two microseconds, the time it took to travel one turn in the accelerator) was required for bubble chamber work. It became a high priority in the early 1960s when DG Weisskopf decided to launch a major neutrino programme, and the first fast ejected beam came into operation in summer 1963. Slow ejection (peeling off a small portion of the beam every revolution for as long as 100 ms) was needed for electronics experiments. It was also first tried that year, but did not raise much interest among the physicists, who were happy with internal targets and could not easily assess the advantages of the new procedure. In the event the technique proved rather difficult to implement. It called on the operators systematically to increase the ampHtude of the oscillations of protons in the ring until the particles jumped into a septum magnet, which then ejected them. It was only towards the end of the decade that slow extraction systems which worked to the satisfaction of operators and customers alike was put in place^^.

21

Machines and beams

Fig. 1.6 gives one some idea of the complexity of the beam layout around the PS and its variety at the end of 1974, its peak year of use before attention was switched to the SPS (see Fig. 1.7 below). We note that only two internal targets were in use, one providing five and the other two beams for the South Hall. A fast ejected beam from straight section 58 coupled with three possible target positions gave a choice of three beams for use with the CERN 2m hydrogen bubble chamber: U5 with three RF separation cavities, and two electrostatically separated beams labeled m6 and kg. The East area was also served by a slow ejected beam from straight section 62, this beam being divided into three branches each with its own external target, from which a variety of secondary beams were derived. Straight section 74 was used to provide a fast ejected primary beam for neutrino experiments in the South-East Hall with the heavy liquid chamber Gargamelle along with a spark chamber assembly. A beam could also be peeled off the target for the g-2 (magnetic moment of the muon) experiment. The West Hall (not shown in Fig. 1.6), was equipped with the Big European (hydrogen) Bubble Chamber (BEBC) and the Omega Spectrometer (an electronics facility we shall describe later). It was served by a beam extracted from straight section 16, which traveled in tunnels to the experimental area where it was divided into branches. One used fast ejection onto a target from which a secondary beam purified with three RF separation cavities was directed into BEBC. The other used slow ejection

GARGAMELLE

o

SPARK CHAMBERS

Fig. 1.6 Schematic diagram of PS external beams and experimental complexes in 1974. The West experimental area is not shown (Source: CERN Annual Report, 1974, 75). Notes: p. 37

22

CERNfrom the mid-1960s to the late 1970s

and an external target to produce a test beam and a secondary beam for the Omega. The main beam was also used to inject protons into the ISR rings in opposite directions. Embedded in this intricate web of equipment the PS, its intensity amplified by the booster in its first full year of operation, supported 27 counter experiments at the machine itself and produced tracks for 6.5 milUon bubble chamber photographs in 1974, as well as serving as an injector for the ISR. 1.3.2 THE SYNCHRO-CYCLOTRON In contrast to the PS, the remaining two machines that we shall discuss, the SC and the ISR, had a rather more turgid life in our period. Originally conceived as an intermediate device to fill time until the PS was commissioned and to train European physicists on big accelerators, the synchro-cyclotron rapidly established itself as a research tool in its own right with an important particle physics and nuclear structure programme using muons and pions^"^. In parallel the SC supported ISOLDE, a nuclear structure facility which came onstream in 1967, and in which an isotope separator for studying radio-active elements was placed on-line with the extracted proton beam of the machine^^. During the mid-1960s the demand for the SC increased steadily, and the requirements of the users could only be met by increasing the number of available beams (from 5 to 9) and by extensive beam sharing and time sharing arrangements. By 1969 there were twenty user groups, totaling almost 150 physicists, 90% of them from outside laboratories, working at the machine. Over 6500 hours of time was available for physics for 'prime users' while 'parallel users' benefited from over 7200 hours, for an overall total of almost 14000 hours of machine time. Unscheduled downtime had been reduced to a mere 3 % of operating time. That same year the SCIP (SC Improvement Programme), which had been under discussion for some time, got under way. Its aims were twofold. Firstly, to improve the extraction efficiency of the primary beam (which was only about 7%), so reaching at least 1/xA. Secondly, and more fundamentally, to increase the internal beam intensity by a factor of ten to about lO/iA by replacing the ion source and, above all, by increasing the repetition rate of the frequency modulator. To this end an order was placed with an external firm for a rotating condenser system to replace the tuning fork system which had been installed with the SC in 1957^^. The positive attitude expressed by the CERN management towards the SC, as evidenced by the decision to proceed with the SCIP, quickly began to wane. On the one hand, there was the danger of obsolescence as a physics tool for nuclear structure studies. A new generation of proton accelerators, called meson factories because their main aim was to deliver very intense secondary beams of muons and pions, was on the horizon not only across the Atlantic (at Los Alamos and in Vancouver) but in Switzerland itself (the SIN, or Swiss Institute for Nuclear Research, in VilHgen). This danger was ampHfied by unprecedented delays in the delivery of the rotary condenser. These factors, along with the constraints on the CERN budget imposed by the construction of the SPS, and the absence of a strong internal lobby of CERN physicists - the SC was largely used by non-CERN

Machines and beams

23

scientists - meant that the possibiUty of shutting down the SC and transferring its nuclear physics programme to SIN was actively discussed in the early 1970s. By the end of 1972, and despite the doubts and hesitations, the future of the SCIP seemed assured by the convergence of a number of otherwise conflicting interests. As summarized by Hansen, the arguments for keeping the programme going were that (i) It was in CERN's interest to hold on to its role as Europe's most prominent physics laboratory by having a broad scientific programme, and (ii) this also broadened the science-political support base in the member countries, of which especially the smaller ones (iii) were interested in institutionalized access to a big-science laboratory with its intellectual climate and technical know-how. Finally (iv) some of those initially opposed to SCIP had come to fear that a transfer of activities to SIN would imply direct or indirect transfer of funds to SIN in an amount that would exceed the cost of continued SC operation^^.

In short CERN's wish to retain the support of all its users and their governments, including in the smaller member states, at a time when the laboratory was embarking on its most ambitious and expensive project ever, and was under attack for tending to see itself as 'a rather exclusive laboratory for privileged particle physicists' were crucial to the 'salvation' of the SC at this time^^. In June 1973 the SC machine was shut down to make the modifications foreseen in the SCIP; it was restarted for physics with a new name, SC2, in January 1975. But its troubles were not over. Certainly after some 18 months its extraction efficiency had been improved from about 7% to 70% and its internal beam intensity from l/zA to a mean value of about 2)uA and a peak value of about 4/iA. But the rotating condenser system was unreUable to the extent that between November 1975 and April 1976 the operating time for physics use was reduced to 1800 hours, with 1400 hours of unscheduled down time^^. And with money being tight the question arose again as to whether or not the SC programme should be maintained. Indeed around 1978 Directors General John Adams and Leon van Hove suggested that both the ISR and the SC should be closed to finance the LEP construction, and proposed again that the entire research programme could be shifted to SIN. Strong opposition from the ISOLDE users, in particular, once more prevailed. The SC was given a further lease of life on condition that it be used preferentially with the on-line separator. The machine wasfinallyclosed down in December 1990, and the ISOLDE programme was transferred to a new installation at the IGeV PS booster"^^. 1.3.3 THE INTERSECTING STORAGE RINGS If the interest of the research programme and the pressure from the outside users and, indirectly, their national administrations, were able to protect the SC from the increasingly cost-conscious CERN management and Council delegates, the same cannot be said for the ISR. From the very beginning a major and ongoing effort was required to increase its luminosity to useful levels. Experimentation was further complicated by a number of Notes: p. 37

24

CERNfrom the mid-1960s to the late 1970s

unfortunate misconceptions about the kinds of detectors needed at its intersecting regions (see below) and by the sheer practical difficulties of using it as an experimental tool. The nadir was reached when first the J/psi (1974) and then the upsilon (1977) particles were discovered in the United States, even though the ISR could, in principle, have found them'^^ Although the construction of the ISR 'proceeded fairly uneventfully', to quote Kjell Johnsen who was the man responsible for it,"*^ it was in fact a tribute to careful planning and budgeting: officially the machine began operating four months ahead of schedule and it was built within the original cost estimate of 332 miUion Swiss francs in 1965 prices. Yet if it was a masterpiece of technology, its use as a physics tool was immediately compromised by one of the considerations which had always made the physicists wary of building it at all: its luminosity."^^ When the machine first worked this was about 10^^ cm"^ sec~\ to be compared with a design luminosity of 4 x 10^^ cm~^ sec~^ There were a number of reasons for this including transversal and longitudinal instabilities in the beams and the dispersive effects of beam-beam interactions. But the most important limitation to beam currents which quickly emerged was the beam-induced pressure rises. Protons in the circulating beams ionized part of the residual gas in the beam pipe. These ions were driven into the wall of the vacuum chamber by the beam potential of 1 kV and penetrated considerably deeper into the wall material than did the normal cleaning methods. This ion bombardment led to desorption from the wall, releasing more gas which could be ionized, with an avalanche effect which caused dramatic local vacuum variations followed by beam loss. The source of the difficulty being identified a major and long-drawn out programme was undertaken to remedy it. It involved the addition of about 500 titanium sublimation pumps, an increase in the vacuum bake-out time and temperature from 5 hours at 200 °C to 24 hours at 300 °C, and glow-discharge cleaning of all the critical vacuum components. The first two measures improved the vacuum in the rings from an average pressure of 3 X 10"^^ torr in 1973 to about 8 x 10"^^ torr in 1976. With the addition of glow discharge cleaning this could be improved by another factor of two or three by the end of the decade"*^. As the vacuum increased so did the luminosity. One needs to be careful here, however. For whereas CERN texts and graphs repeatedly referred to the maximum luminosity achieved at any one time, the regular performance of the ISR was generally far lower and depended strongly on beam energy"^^. Indeed we would go so far as to say that the ISR only reached its design luminosity of 4 x 10^^ cm~^ sec~^ during 'average' running in 1974, three years after it was officially commissioned (see Table 1.1). In addition to improving the vacuum, the other main way in which luminosity was increased at a specific intersection was by adding a system of quadrupoles which focused the beams to smaller vertical dimensions at the crossing point (the so-called low-beta insertion). A trial system of this kind was first installed at intersection 7 in 1974 using magnets borrowed from the Daresbury laboratory in the UK and from DESY in Hamburg, along with spares from the ISR and PS Departments. The local luminosity was

25

Machines and beams Table 1.1 Operating conditions of the ISR as reported in the CERN Annual Report, 1974, p. 102. Momentum, Gev/c

Running time. per cent

11.8 15.4 22.5 26.5 31.4 Different in each ring

13.4 16.4 22.5 37.2 5.4 5.1

Beam current range, amps

Luminosity, Maxima x 10^^

Luminosity, averages x 10^^

Ar-6

0.5 2 7 12.7 2.4 various

0.2 0.6 3 5 0.5 various

6-10 7-18 8-22 Ar-9

various

increased by a factor of 2.3, this however being the Hmit obtainable with conventional quadrupoles. The next step was to develop superconducting quadrupoles, and when a system of this kind was eventually introduced in 1981 it increased the local luminosity in intersection 8 by a factor of 6.5"*^. The difficulties of experimental practice at the ISR added to its limitations as a routine physics tool. Complex scheduUng was required to harmonize the very different requirements of the experiments. In one example cited later in this volume there were about 100 hours scheduled for physics in one week in May 1975, mostly at night, and most of the sessions called for different intersecting beam energies and/or beam currents'*^. The bulk of the experimental equipment was in the tunnel, and so could only be accessed for changes or repairs when the beam was switched off. The experiments themselves could influence the performance of the machine through the perturbing effects of their analyzing magnets and other equipment, and special operating conditions were required to prevent undue influence on the circulating beam. There can be no doubt that many of these practical difficulties had been mastered by the early 1980s. A highly powerful axial-field magnetic detector was available, luminosity was at record levels in intersection 8, and a rich experimental programme was on the agenda. But against the background of past difficulties - in a community that prizes Nobels, missed opportunities are hard to forget - , with a steady migration of users in the mid1970s to the SPS (see Figs. 1.7 and 1.8) - which had orders of magnitude higher luminosity and greater experimental flexibility even if its centre-of-mass energy was lower - , with high energy proton-antiproton coUisions available in the SPS, and with the financial constraints imposed by the construction of LEP, the ISR enthusiasts could not muster the support they needed to keep the machine alive. The first proton-proton collisions took place in the ISR on 27 January 1971. The last colliding beam run was terminated on 23 December 1983.

Notes: p. 37

CERNfrom the mid-1960s to the late 1970s

26

(PS + ISR + SPS) experiments

I

45

PS experiments

ISR experiments

1970

1971

1972

1973

1974

1975

Fig. 1.7 The number of experiments on the floor and in preparation during the years 1970 to 1975. The effects of the SC shutdown are apparent as is the attraction of the SPS as a research tool. The 300 GeV machine wascommissioned in June 1976 and its experimental programme began in earnest early in 1977 (Source: CERN Annual Report, 1975, p. 30)

1.4 Detectors In commenting on Fig. 1.1 earlier in this chapter - which showed the overall evolution of CERN's expenditure and the functional distribution of resources within it - we noted the steady increase over the years in the cost of new experimental equipment, with a particularly sharp rise in the early 1970s. A considerable part of this money was spent on the acquisition and operation of new, state-of-the-art bubble chambers and electronic detectors which were demanded by an experimental practice which, if it was to remain internationally competitive, called for increasingly heavy, complex and costly equipment. The aim of this brief section is simply to explore a little further the circumstances which precipitated the change in shape of the curves for experimental equipment which we noted in Fig. 1.1. In the late 1950s much of the experimental apparatus used around an accelerator could be built by the physicists themselves with the help of a few technicians. With the emergence

27

Fig. 1.8 Number of physicists working on approved experiments at the ISR each year, as surveyed in August of that year. The lure of the SPS in the mid-1970s is confirmed. (Source: M. Jacob in CERN Yellow Report 84-13, 1984, p. 36).

of bubble chambers at the end of that period, and of hydrogen bubble chambers in particular, expert groups of designers and constructors were required to build devices that were technically complex and potentially dangerous. Electronic detectors followed suit with a delay of about ten years. Initially custom built for a particular experiment, as accelerator energies increased they grew in size and complexity, and some of them became, Uke bubble chambers, general purpose faciUties serving a dedicated user community which carried out a wide range of experiments with them over a considerable period of time. In short by the end of the 1960s detectors had become 'technological achievements in their own right', to use John Adams' happy phrase"^^, and there was a visible, if sometimes blurred, dividing Une between those who designed, built and operated big detectors, and those who used them for research. As we explained earlier this spUt was formalized at CERN when Adams and van Hove took over as Directors General in 1976 and established the Experimental Physics Facilities and the Experimental Physics divisions. Two big bubble chambers, Gargamelle (heavy liquid) and BEBC (hydrogen) were commissioned at CERN in this period. The construction cost of the former was essentially paid by the French Commissariat a I'Energie Atomique, while the costs of building BEBC were shared equally between CERN, France and Germany (cf. Fig. 1.1)"^^. Table 1.2 Usts their overall cost and the size and structure of the teams required to build them, illusNotes: p. 37

CERNfrom the mid-1960s to the late 1970s

28

Table 1.2. The major hydrogen and heavy liquid chambers used at CERN in the late 1960s and the 1970s (Source: J. Adams in CERN Annual Report, 1977, 13-18). Bubble Chamber-^

CERN 2m

GargameUe

BEBC

Construction approved/ commenced First pictures taken Magnetic field (Tesla) Cost of construction

1959

1965

1967

1964 1.7 45MSF (1964 prices)^

1970 2 30MSF (1969 prices) + personnel and infrastructure ~50, + 8 engineers and physicists*^ 7MSF/year 44

1973 3.5 (sc)^ lOOMSF (1966 prices) + 24MSF for liquids etc.

Size of construction team Costs of operation Size of operating, maintenance and dpmt. team

60 ~ 8MSF/yr 39 + 7 engineers

90 (maximum)** -lOMSF/year 60

^BEBC used a superconducting magnet ^Of which 30MSF were material costs *^Rousset names about 80 people who were involved in the construction, development and operation of GargameUe. This does not include people employed by industry^^. **Thisfigureis cited by Dominique Pestre in section 2.5, chapter 2, this volume.

trating the reasoning behind Adams and Van Hove's internal reorganization. Figs. 1.9 and 1.10 give one an idea of their physical dimensions. As for electronic detectors, two major devices should be mentioned. The split-field magnet spectrometer facility combined a huge magnet which sat astride an intersection at the ISR with an array of proportional wire chambers around it. Decided on in 1969, the SFM took five years and about 23 MSF to build and commission. The Omega spectrometer combined a superconducting magnet with a variety of electronic detectors (spark chambers, proportional wire chambers, Cerenkov counters, etc) to study processes peaked in the forward direction. Initially intended for work at the PS, this device was decided on in 1968 and produced its first results in 1972. Its material cost alone amounted to some 20MSF. The SFM and the magnet of the Omega are illustrated in Figs. 1.11 and 1.12^^ As the energy of the machines increased at CERN in the 1970s, with the commissioning first of the SPS and then its conversion into a 270 GeV on 270 GeV proton - antiproton collider, so did of the size of the electronic detectors as well as of the experimental teams using them. By 1977 the average number of physicists in a team at the SPS was 28, of whom only three were CERN staff, and three teams had more than 50 scientists in them^^. One of these was the embryonic UAl collaboration, which was to build a huge, 2000-ton An electronic detector to search for the W and the Z at the coUider. This detector cost about 100 MSF to construct (though that figure is very approximate given the many collaborating institutions which put time and money into it) and in the early 1980s the team building and using it numbered over 100 scientists. CERN may have opened its

The member states

29

Fig. 1.9 A general view of Gargamelle (Source: CERN Annual Report, 1977, 18) (Photo CERN-117-1-77).

doors increasingly to outside users in the late 1960s and the 1970^^—t^ut it has to be said that the human and material resources now needed to run a high-energy physics programme left the laboratory no choice but to be welcoming^^.

1.5 The member states For the first decade or so of its existence the member states' governments had barely 'interfered' in the hfe of CERN. They had watched with satisfaction its machines being commissioned in the late 1950s. They had paled at the additional resources required to exploit the PS in the early 1960s but, Great Britain apart, they had not protested. For most of them CERN was a high-energy physics laboratory par excellence, a shining example of successful European scientific and technological cooperation, a 'model' which inspired similar initiatives (e.g. in space). They were not going to allow narrow national self-interest to impede the laboratory's growth. Of course they were aware that, unfettered, the laboratory could spiral out of their control. But they placed their faith in their Council delegates, scientific statesmen and science administrators who stoutly defended their autonomy vis-a-vis their national state apparatuses, who knew CERN intimately (many of them had been involved from the very start of the project), and who insisted that they Notes: p. 37

30

CERNfrom

the mid-1960s to the late 1970s

Fig. 1.10 BEBC chamber body (Source: CERN Annual Report, 1977, 19) (Photo CERN-216-12-71).

could be counted on to put in place the necessary formal and informal mechanisms for controlling its expansion without damaging its health^"^. The relative autonomy of the Council to shape CERN's trajectory in consultation with the management, its role as a buffer between the laboratory and the national state bureaucracies, began to be chipped away, even seriously challenged in the late 1960s. This was not because there was a major turnover in the Council delegates, because a new generation with different values to the 'founding fathers' moved into positions of authority - far from it, as we saw in section 1.1. It was rather a consequence, as we mentioned earlier, of the new economic and political context in which CERN was situated: a slowdown in economic growth, fears over the 'technological gap', Gaullist-inspired tensions in the European (and Atlantic) alliance. Add to this a crisis in the 'parallel' European space effort, where governments became increasingly convinced that scientific and technological projects had to be situated in the broader framework of industrial poHcy, and we have the seeds for a re-assessment of what the aims of the Genevan laboratory should be^^.

Fig. 1.11 The Split-Field Magnet at the ISR surrounded by Cerenkov counters (Source: CERN Annual Report, 1977, 77) (Photo CERN-173.7.77).

Fig. 1.12 A general view of the magnet of the Omega spectrometer (Source: CERN Annual Report 1977, 22) (Photo CERN-33-8-72). Notes: pp. 37 ff.

32

CERNfrom the mid'1960s to the late 1970s

The Federal Republic of Germany's position over the construction of the 300 GeV Super Proton Synchrotron provides the most dramatic example of this new attitude^^. Two different issues were at stake here: the design of the machine itself and its location. In 1967 the scientists, administrators and industrialists on the German Atomic Energy Advisory Committee criticised the design then being discussed at CERN as technologically obsolescent and unnecessarily costly. They wondered in particular whether the use of new technologies Uke superconducting magnets and computer controlled beam handling had been seriously considered, and suggested that a more 'advanced' design could cut costs. Their point of reference was the proposal for the 400 GeV machine being promoted by Robert Wilson across the Atlantic for what was to become the Fermi National Accelerator Laboratory in Batavia, Illinois, a proposal which combined radical technological innovation with sharp cost reductions. CERN managed to deflect these criticisms rather rapidly; the fact remains that, for the first time in the laboratory's history, one of its technical proposals had been criticised openly by influential personalities, including scientists and engineers, in a key member state. This served at once to undermine the claim, repeatedly made by the CERN staff", that they were the technological leaders in their field in Europe and, by showing that 'the experts' were divided, to undermine the authority of their Council delegates in the eyes of national state bureaucracies. The second issue over which Germany dug in its heels was that of the site for the SPS. The first tentative discussions on this question got under way in 1964. At the time it was assumed that the location would be somewhere other than Geneva. This was both to avoid concentrating all Europe's front-line high-energy physics capacity at CERN, and to allow member states other than France and Switzerland to capitalize on the prestige and the industrial benefits of having a site on their soil. The delicacy of the issue quickly emerged: nine of CERN's member states put in (sometimes multiple) bids for the laboratory. Fearful of losing control over the siting decision, the Council hoped to depoliticise the issue by basing the choice on 'objective criteria'. 'Three Wise Men' from among its number were selected and asked to assess the merits of the offers received. Their impartiality was 'assured' by choosing them from countries which had not offered sites, by their eminence and by the shared understanding that the Council wanted above all to make a 'rational' choice which could not be contested by the national poUtical systems. The Site Evaluation Panel duly assessed the merits of the proposals along three axes pertaining respectively to the suitablity of the site in terms of construction, operation and conviviality, giving scores for each. No site got top marks in all three categories, though locations in France and in Italy came out best in two of them. The panel laid its report before the Council towards the end of 1967. The document was warmly praised - and promptly buried, its sought-for objectivity predictably impugned by the disagreements between the member states over the appropriateness of the evaluation criteria used. More to the point Germany demanded that the machine be located at its site in Drensteinfurt no matter what the position of this location was on the panel's league table (it received a j8 for suitability of construction, an a for operation, and a y for conviviality)^^. The German delegation was so recalcitrant on this point that even after

The member states

33

they had agreed to join the project they forced the cancellation, at the last minute, of an interministerial meeting called by the Swiss to settle the site question in January 1970, fearing that the decision would not be in their favour. The problem was only resolved by a fundamental revision of the terms of the debate. In February 1970 Adams suggested that the accelerator be built in two distinct phases on the existing CERN site, so reducing sharply the costs of construction of the machine and spreading them over a longer time span. Germany could not but yield. Germany's attempt to impose its will on the Council and on its fellow member states in CERN was not only indicative of its determination to do all it could to build up its hightech industry. More profoundly it was consonant with its growing self-confidence in the European political arena. For the first decade after the war Germany had to ease its way back gradually into political legitimacy. European collaborative ventures, particularly in sensitive areas like the nuclear and space, were an ideal avenue whereby the Federal Republic could at once shake off* the historical burden of her past, show herself to be dedicated to Europe and to the Western aUiance, and reinvigorate her national programmes in key sectors of science and technology. Prudent at first, she gradually became more selfassertive. She demanded equal rights for the German language in official CERN documents. She participated in the construction of BEBC specifically so as to build up the technical knowledge of her scientists and engineers in this field, and even insisted that her share of the expenditure be channelled back into her industry, a demand for a 'fair return' which was totally at variance with CERN's usual contract policy^^. She insisted that the SPS, if built, contain the most advanced technologies available. And she was prepared to stop the entire project, to jeopardise the competitivity of the European high-energy physics eff'ort, if the new machine was not built on her soil. Of course it was normal for member states to demand that their interests be protected at CERN. But whereas previously they had left their delegates to the Council considerable scope to interpret what that entailed, now a different set of national interests, economic, industrial and poUtical, had come into play, interests which the Council delegates could not be reUed on to defend. The broader poUtico-economic fabric into which CERN had always been woven was changing its texture and the laboratory was obliged to change with it if it wanted to survive. It was not only Germany who saw in CERN a tool for furthering some of its broader national objectives. France did too, using the laboratory as an element in the new geopoUtical orientations of de Gaulle's foreign policy in the late 1960s. In July 1967 CERN signed an official agreement with the appropriate Soviet authorities in which it undertook to design, build, test and instal a fast ejection system and radio-frequency particle separators for use at the 76 GeV proton synchrotron at Serpukhov, brought into operation a few months later. In return the CERN scientists could collaborate with their Soviet colleagues in electronics and bubble chamber experiments at what was, for a while, the most powerful machine in the world. This initiative was surely inspired by the possibiUty of exploring the new research frontier opened up by the Soviet machine, but not by that alone. The CERN ejection system and separators were to feed a large hydrogen bubble chamber called Mirabelle, which had been built at Saclay and was to be installed on the Notes: p. 38

34

CERNfrom the mid'1960s to the late 1970s

floor in Serpukhov^^. And the decisions to collaborate with the Soviets were signed shortly after de Gaulle had withdrawn French forces from NATO command and in the midst of ongoing and increasingly more frequent interministerial meetings between the French and Soviet governments. The fast ejection system and the RF separators were technological objects at the service of European science and French foreign policy. CERN was not only an instrument of bilateral foreign policy. It was also a resource to be mobilised to express and to consolidate European scientific and political collaboration in other fields. In 1970 the European Southern Observatory signed an agreement with CERN whereby ESO's stafi* would construct a 3.6 m telescope to be installed in Chile using the administrative, technical and professional experience available on the laboratory site, including CERN offices and personnel.^^ Three years later, in May 1973, the Agreement setting up the new European Molecular Biology Laboratory (to be established in Heidelberg, Germany) was signed at CERN^^ Certainly such initiatives were not entirely novel in the 1960s: a key meeting establishing a preliminary organization to plan a European space effort had been held at Meyrin in 1960. What differed though was the nature of the agreements now signed, which were far more formal and politically significant than before. For the governments involved what was important was not just the physics done at CERN, but the fact that it was a source of technical innovation and accumulated know-how, an example of European scientific collaboration, the oldest member of a family of organizations held together by a core of senior science administrators who circulated between them^^. As one engineer remarked who was present at the debate on collaboration with ESO in the CERN Committee of Council, 'It was remarkable that practically everyone [...] entirely lost sight of the original aim, the construction of the telescope, and rather emphasized the scientific importance of the collaboration between astronomy and high-energy physics [and] common technical developments such as data handling, and the political aspect: the formation of a 'Communaute scientifique europeenne' in which there would be room also for other organizations for fundamental science'^"^. CERN was not to be an 'ivory tower' surrounded by the protective moat of a cooperative Council. It was increasingly part of European scientific, technological, industrial and political integration. The laboratory had no choice but to respond. In 1974 it organized a conference attended by 300 industrialists, directors of appHed research, senior staff* from technical universities and science journalists where it displayed some of its technological achievements in the hope that those present could find ways of applying the techniques and abiUties that had been developed at the laboratory^"^. In 1975 it published a report by an outside consultant on the economic returns from the member states' investments, in which it was claimed that 'for each Swiss franc spent by CERN in European industry, 5.5 Swiss francs of economic utility were generated'^^. That same year one number of the CERN Courier, the laboratory's inhouse magazine, was devoted almost entirely to describing the medical and other applications of accelerated nuclear particles^^. CERN's primary justification still lay in its doing world-class high-energy physics research. It could not be its only one.

Notes

35

When this history project got under way late in 1981 there was an air of anxiety at CERN. The member states, who had just agreed to fund a stripped-down version of LEP within tight budgetary constraints, were not only concerned about the 'practical' value of the laboratory, but also about the quality of the physics being done there. After three decades of activity CERN's performance, as measured by Nobel prizes, was uninspiring. The 1970s, in particular, were a period of frustration and disillusionment. One of the key findings of the early 1970s - weak neutral currents - , announced at CERN in 1973, was made by a team at Gargamelle but many of those involved felt that they were never given due credit for it. The difficulty of the experiment, the scepticism of senior physicists and management, the confirming and then conflicting results obtained with a parallel electronics experiment at Fermilab - and the dread that CERN would publish a result disconfirmed by a team in the US - , all served to create a corrosive climate of doubt and uncertainty which severely diluted the impact of the results obtained with the heavy-liquid chamber^^. This disappointment was amplified by the failure to observe the J/psi at the ISR in 1974, and the upsilon in 1977, due essentially to the low luminosity of the machine and the construction of detectors which were optimized in the forward direction when, it was realized later, there were particularly interesting events at wide solid-angles^^. It was against this background of missed opportunities that DGs Leon Van Hove and John Adams decided that CERN had to take the risk of launching a ppbar colUder project if it was to retain its credibility as a world-class high-energy physics laboratory. The first 'candidate events' for the long sought-for W boson were obtained in November 1982 using antiprotons cooled stochastically by a technique developed by Simon van der Meer, and a huge detector built by a collaboration led by Carlo Rubbia. A parallel experiment, led by Pierre Darriulat, confirmed the result.^^ The Nobel prize for physics followed in 1984 and with it the 'proof that CERN and European physics could compete, at last, on an equal footing with the best in the world.

Notes 1. A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN. Volume I. Launching the European Organization for Nuclear Research (Amsterdam: North Holland, 1987). 2. A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN. Volume H. Building and Running the Laboratory (Amsterdam: North Holland, 1990). 3. An approach along these lines is taken in J. Krige, 'The politics of European scientific cooperation', in J. Krige and D. Pestre (eds) Science in the Twentieth Century (Harwood Academic PubUshers, 1997). See also D. Pestre, 'Vers un modele de relations scientifiques radicalement nouveau: le cas des physiciens allemands et fran9ais apres 1945', in Y. Cohen and K. Manfrass (eds), Frankreich und Deutschland. Forschung, Technologic und industrielle Entwicklung im 19. und 20. Jahrhundert (Miinchen: Beck, 1990), 130-41. 4. The formulation starts Maurice Jacob's survey of the ISR experimental programme in an invited talk he gave at the last meeting of the ISR experiments committee, just after the machine had been shut down; see M. Jacob and K. Johnsen, A Review of Accelerator and Particle Physics at the CERN Intersecting Storage Rings (CERN Yellow Report 84^13, 1984). Notes: p. 38

36

CERNfrom the mid-1960s to the late 1970s

5. The quotations in this paragraph are from the article * 1959-1969. Ten Years in the Life of a Machine,' CERN Courier, 9(10), 1969, 337-347. It was compiled by the editor with the help of senior PS engineers. 6. This is from his introduction to the CERN Annual Report, 1977, 13. 7. For the way the technological gap in the space sector was then perceived on both sides of the Atlantic see, for example, Lorenza Sebesta, T h e Politics of Technological Cooperation in Space: US-European Negotiations on the Post-Apollo Programme', History and Technology, 11 (1994), 317-41. We should add that the need to *seir CERN to governments became even more pressing in the 1980s, see J. Krige, 'L'Image publique du CERN', AUiage N** 16-17 (Ete Automne 1993), 290-7. An EngHsh translation, 'The Public Image of CERN', appeared in J. Durant and J. Gregory (eds). Science and Culture in Europe (London: The Science Museum, 1993), 153-7. 8. This conception is clearly present in the German delegation's attitude on the SPS (see chapter 3) and in the arguments mobilized by the outside users in the early 1970s (see chapter 5). 9. I described these debates in more detail in volume I, chapter 8.4 (cf. note 1). 10. CERN Annual Report, 1978, 24. 11. Pestre describes the debate over the choice of the site for the SPS in chapter 3 (this voliune). 12. Pestre discussed the origins of the fissure along these lines in volume II, chapter 8 (cf. note 2). 13. This paragraph and the quotations therein owe much to Adams' extremely valuable introduction to the CERN Annual Report , 1977, pp. 13-24, wherein he reviews the major particle detectors at CERN. The quotations are on pp. 13 and 14 respectively. 14. Pestre describes the setting up of this structure in volume II, chapter 8 (cf. note 2). 15. For the debate surrounding the establishment of this committee see Russo, chapter 4, section 4.4 (this volume). 16. This procedure is briefly described by Hansen in chapter 9, section 9.2.2 (this volimie). Also chapter 5.5. 17. For some information on these substructures see Hansen, chapter 9, section 9.4.2 (this volume), and Pestre, chapter 2, section 2.3.2 (this volume). 18. For the importance of what we have called the CERN *lobby' see Pestre, volume II, chapter 7.1 (see note 2), and Dominique Pestre and John Krige, 'Some Thoughts on the Early History of CERN', in P. Galison and B. Hevly (eds) Big Science: The Growth of Large Scale Research (Stanford University Press, 1992), 7899. 19. This debate is discussed in my chapter 6, section 6.2 (this volume). 20. The data for the 1960s and 1970 is from the Annual Reports of the years in question. CERN Annual Report, 1976, 140, shows the change in the staff complement over the previous five years. 21. For more information on this see footnote 11 in my chapter 6 (this volume) on the ppbar collider. 22. This figure is given by Hermann in volume II, chapter 3.2.1, 49 (cf. note 2). 23. Document on ECFA notepaper entitled 'Farewell address to professor W. Jentschke pronounced at the CERN Council Session on December 17 1975 by the Chairman of ECFA'. Undated, unsigned (DGR21311). 24. This is described in detail in my chapter 5 in this volume. 25. The graph in the mentioned source is captioned 'the number of scientists reckoned in "man-years" drawing their research material from CERN during the years 1966-1975.' This suggests that it may also include those in their home institutes using bubble chamber film produced at CERN. A comparison of the data given in the graph with the tables regularly given in each Annual Report for the number of persons on the site at the end of the year reveals, however, that it is these figures that have been used. 26. 'Fermi National Accelerator Laboratory,' CERN Courier, 14 (9), 1974, 283-92. 27. For the role of CERN in building a European bubble chamber physics community in the early 1960s, see J. Krige, 'The Contribution of Bubble Chambers to European Scientific Collaboration,' Nuclear Physics B (Proc. Suppl.) 36 (1994), 419-26. 28. The figure, given by DG Gregory in 1970 (see CERN Annual Report, 1970, p. 13), is coherent with the trend established earlier in the decade (see Krige, ibid.. Table 1.3).

Notes

37

29. For Jentschke, see CERN Annual Report, 1972, 23. The ECFA data is presented in Fig. 7 of my chapter 5 in this volume. 30. This is described in detail, and its causes analyzed, in my chapter 9 of volume II (cf. note 2). 31. See the account of the PS quoted in note 5 for the quotations in this paragraph. 32. These paragraphs are based primarily on the article cited in the previous note, on section 11.2.3.2 of chapter 11 by Crowley-Milling, in this volume, and on John Adams' paper on The CERN Accelerators,' CERN Annual Report, 1976, 12-3. 33. Crowley-Milling (sections 11.5.5.1, 11.5.5.2) of chapter 11 in this volume gives technical information on fast and slow extraction. See also the article in the CERN Courier cited in note 5. 34. This programme is described by Ulrike Mersits in volume II, chapter 3 (cf. note 2), and by Gregers Hansen in chapter 9, section 9.3, this volume. 35. ISOLDE is the subject of a separate chapter by Gregers Hansen in this volume. 36. The operating parameters of the SC cited here are taken from the CERN Annual Report, 1969,14-5,43. For details on the SCIP see Hansen, chapter 9, section 9.5, this volume. 37. From Hansen, chapter 9, section 9.5.4, this volume. 38. ibid., for the quotation, which resonates with the remarks made by the ECFA Chairman (cf. note 23 ) and the general dissatisfaction of the user community described in my chapter 5. 39. This data is from Adams' introduction to the CERN Annual Report, 1976, p. 11-12, where his lack of enthusiasm for maintaining the SC is manifest. 40. The renewed debate over the future of the SC between 1979 and 1981 is described by Hansen, chapter 9, section 9.7, this volume. 41. The construction and operation of the ISR is the subject of a detailed study by Arturo Russo in chapter 4 in this volume. See also the report by Jacob and Johnsen cited in note 4. 42. See the Yellow Report cited in note 4, at p. 4. 43. Dominique Pestre in chapter 12 of volume II of the CERN history (see note 2) has described the strong opposition by physicists to the ISR in the years leading up to the decision to build it, which was taken in 1965. 44. Russo, Fig. 4.7, chapter 4, this volume, depicts the improvement in the vacuum over time. 45. See for example the usual graph provided by Johnsen (Fig. 9 in the Yellow Report cited in note 4) which is reproduced as Fig. 4.7 in chapter 4 by Russo, this volume. This graph gives the maximum luminosity and states that the design luminosity was reached at the end of 1972. The (maximum) luminosity given for 1974 is about 2 X 10^^ cm~^ sec~\ which is to be compared with the figures from the Annual Report for that year reproduced in Table 1. 46. For this paragraph see the CERN Annual Reports, 1974, 100 and 1975, 113, as well as Johnsen's account in the CERN Yellow Report 84-13, 1984, section 3.1.9 (cf note 4). 47. See Fig. 4.3 in Russo, chapter 4, this volume. 48. See his introduction to CERN Annual Report, 1977, 13. 49. The decisions to build the two big bubble chambers are descibed in detail by Dominique Pestre in the next chapter of this book. An account of the construction and operation of the former has also been provided by Andre Rousset, one of the physicists intimately involved with the project from the start - see A. Rousset, Gargamelle et les courants neutres (Paris: Ecole des Mines, 1996). 50. Op. cit. note 49, Annex 1-2. 51. Arturo Russo, in chapter 4 (this volume) devotes considerable attention to the decision to equip the ISR with a Split-Field Magnet detector, and Ivana Gambaro has dedicated an entire chapter (chapter 12) to electronic position detectors in general, including the SFM. 52. This data is provided by Van Hove in the CERN Annual Report, 1977, 25. 53. This detector, and the structure and functioning of the collaboration which built it, are explored in detail in my chapter 7, this volume. 54. On the role of the CERN Council, see note 18.

38

CERNfrom the mid-1960s to the late 1970s

55. This is descibed at length in J. Krige and A. Russo, Europe in Space, 1960-1973, Report-ESA SP1172 (Noordwijk: ESTEC, 1994). 56. These paragraphs are based on Dominique Pestre's chapter 3, this volume. 57. See the Report of the Site Evaluation Panel on the Site Offers by the Member States for the 300 GeV Accelerator Laboratory, CERN/761, 4/12/67, 12. 58. See Pestre chapter 2, section 2.4 (this volume). 59. For one of many descriptions of the CERN/Serpukhov collaboration which, of course, makes no reference to the political dimension of the arrangement, see the report in the CERN Courier, 10 ( 2 ) , 1970. 60. This is described extensively in A. Blaauw, ESO's Early History. The European Southern Observatory from Concept to Reality (Garching bei Miinchen: ESO, 1991), chapter 9. 61. There is a report in CERN Courier, 13(5), 1973, 139. 62. Just two examples: Bannier was the ESO Council President at the time the ESO-CERN agreement was signed, having taken over from Funke in 1969. At that time too Zelle was the chairman of the ESO Finance Committee, and also Vice-President of the European Molecular Biology Conference. 63. Letter Zilverschoon to Blaauw, 27/11/69, quoted in Blaauw, op. cit., 171. 64. There is a report on the meeting, whose proceedings were also published as a Yellow Report, in the CERN Courier, 14(4), 1974, 111. 65. 'Paying our Way? An Analysis of the 'Economic Utility' of CERN', CERN Courier, 15(9), 262-4. The findings were published as a Yellow Report, author H. Schmied. It was followed by another study some years later. 66. This was Volume 15, N° 11. 67. See Winter's chapter 10.2 (this volume) for an account of the weak neutral currents story. Historians of science have also worked extensively on it, e.g. P. Galison, 'How the First Neutral-Current Experiment Ended,' Rev. Mod. Phys. 55 (1983), 477-508, and How Experiments End (Umwersity of Chicago Press, 1987), and A. Pickering, 'Against Putting the Phenomena First: The Discovery of the Weak Neutral Current', Stud. Hist. Phil, of Science 15 (1984), 85-117. A participant in the experiment has also just published another account, cf. Rousset, note 49, where a more extended reference list can be found. 68. These points are made in Jacob (cf. note 4) and in Russo, chapter 4.4 and Gambaro, chapter 12.4.4.2, this volume. 69. The basis for this programme is described extensively in my chapters 6 and 7, this volume. See also Winter, chapter 10.3 and Crowley-MilHng, chapter 11.3.

CHAPTER 2

Gargamelle and BEBC. How Europe's Last Two Giant Bubble Chambers were Chosen Dominique PESTRE

Contents 2.1 Towards the decision for a heavy liquid chamber, Gargamelle 2.1.1 A snap-shot of events, January-June 1964 2.1.2 How are we to understand such a rapid decision? 2.2 The emergence of hydrogen bubble chamber projects and Gregory's proposal for a tripartite solution, September 1964-May 1995 2.2.1 Converging on a single CERN-Franco-German project, Autumn 1964 2.2.2 Having the project endorsed by the European physics community, January-February 1965 2.2.3 Formalising the relations between the three partners. The agreement of 4 May 1965 between Jentschke, Perrin and Weisskopf 2.3 The decision and the construction of Gargamelle 2.3.1 The complications surrounding Gargamelle and the final solution, February-December 1965 2.3.2 The principle dates in the construction of Gargamelle 2.4 The decision to construct BEBC and the CERN-Franco-German convention, Summer 1965-July 1967 2.4.1 Technical discussions around the various possibiUties, June 1965-February 1966 2.4.2 The budget again and the drafting of the report on the big hydrogen chamber, February-October 1966 2.4.3 Financing the chamber and its cost increase, drafting the convention, and setting up the group to construct it, October 1966-July 1967 2.5 Some remarks about the construction of BEBC, 1967-1972 2.6 Some words by way of conclusion Notes

39

40 40 42 43 43 45 48 49 49 51 52 53 54 56 58 60 61

In the closing months of 1963, the debate in the United States was well under way on the large bubble chambers necessary for the 1970s and 1980s. At this time hydrogen chambers of about 2 metres were already being used at Berkeley and, for less than a year, at Brookhaven. The importance of neutrino physics, a domain in rapid expansion since 1961 and 1962, was the reason most often given by those supporting projects for new chambers. This was a physics which required the presence of very large volumes if one was to obtain an interaction rate which was not totally negligible. As a corollary those who used this argument insisted that the bubble chamber was still the detector par excellence, the detector which recorded all charged particles without a priori selection. It still was the 'universal detector', to use an expression coined by Alvarez in 1957 when he tried to convince the physics community that his device would dominate electronic detectors in the future. It was against this background that, in January 1964, R.P. Shutt, who was responsible for the 80-inch hydrogen chamber commissioned the previous year at Brookhaven, produced a report for the laboratory management. Surveying the studies made at Stanford and elsewhere on the East Coast during the preceding months, Shutt concluded that a 'good compromise' would be to build a heavy Uquid chamber of 10,000 litres or a hydrogen chamber of 40 m^ ^

2.1 Towards the decision for a heavy liquid chamber, Gargamelle 2.1.1 A SNAP-SHOT OF EVENTS, JANUARY-JUNE 1964 The open debate in Europe got under way in January/February 1964. As in the United States however, the question of the next generation of bubble chambers had been on the agenda for some months. The first report to be published in Europe was written by Andre Lagarrigue, one of the three most important people at the Ecole Polytechnique in Paris and one of the leaders of heavy liquid chamber physics at CERN. According to Andre Rousset, then a close collaborator of Lagarrigue, the matter of a new large heavy liquid chamber was first raised in 1963 during the international particle physics colloquium held in Siena, Italy. Lagarrigue's report, dated 10 February 1964, proposed the construction of a common European heavy Hquid chamber 8 metres long and 1.65 metres in diameter (i.e. of some 17,000 Htres), a chamber to be built under the supervision of CERN^. Such a pro-European attitude on the part of someone who, we can be sure, envisaged playing the crucial role in the realisation and use of this new detector shows that the lessons of the years 1958-1961 had been 40

Towards the decision for a heavy liquid chamber, Gargamelle

41

learned. Since there was little room for too many heavy and relatively immobile detectors like bubble chambers around the giant accelerators at CERN or at BNL, it was indispensable to negotiate the number and the kind of such devices in advance. As far as heavy liquid chambers were concerned, this certainly meant that it was impossible to build and to instal at Geneva more than one single chamber. This explains why Lagarrigue first mentioned a joint project with Franzinetti and the Italian groups (and possibly also with British groups), and that he proposed a 'neutral' zone like CERN as the official centre for the project. In March, with the American physicists apparently advancing rapidly, Lagarrigue and Franzinetti gathered together at Geneva the European heavy liquid specialists. Their aim was to ensure that they would not be forgotten at a moment when 'the most serious competition to the heavy liquid chamber for neutrino physics', what looked 'very much like the ultimate weapon for physics in the 10 GeV region' seemed to be 'the very large (e.g. 40 m^) hydrogen chamber such as proposed by Shutt'. This fear of being marginalised had two consequences. Firstly - and this was the purpose of the meeting - the heavy liquid speciaHsts felt that they had to react quickly. Secondly, they thought it best to capitaUse on what were their strengths - i.e., that heavy liquid chambers were relatively cheap and simple to build and that it would be possible to have one operational well in advance of any (American or European) hydrogen chamber. They felt it was therefore essential not to lose a moment, to start immediately on studies, and if necessary to reduce the size of the chamber. This is what Lagarrigue proposed early in April, suggesting that its volume be reduced from 17 to 10 m^ ^. Two different attitudes emerged at the meeting held at CERN on 9 April 1964. The first one was that of the French and Italian physicists who wanted a very big heavy liquid chamber constructed rapidly. They disagreed, however, on the length of the chamber. While everyone understood Lagarrigue's reasons for reducing the chamber length from 8 to 4-5 metres, opinions were divided as to the effect that this would have in the long term (the chamber risked becoming obsolete rather rapidly). It was thus suggested that the size question be reconsidered later. The second attitude was that of the CERN management. As expressed by Hine, it was that 'since the budget for 1966 and the forecasts for 1967 and 1968 would not be fixed until December 1964, CERN could not make any commitment before then [...]'. There was some truth in the argument, obviously, but one can also see in it a wish to be cautious on the part of an organisation which had always tried to have the best equipment possible. Clearly, CERN wanted to compare the respective advantages of a heavy liquid chamber and a hydrogen chamber before committing itself to anything put forward by outsiders'^. Mine's proposal to wait could easily have slowed down the entire process - particularly since the Italian physicists apparently were not able to gather the money needed for their participation. In the event this did not happen. This was because the French physicists in these years were rather rich, so that an agreement was rapidly reached between Francis Perrin, High Commissioner of the CEA, Bernard Gregory, the director of research at CERN, and Louis Leprince-Ringuet, the most senior physicist at the Ecole Polytechnique, to have France take overall responsibility for the chamber. An agreement was then Notes: p. 61

42

Gargamelle and BEBC

reached at the end of June. It stated that two-thirds of the construction costs would be borne by the CEA, that the remaining costs of the construction would be paid by the Ecole Polytechnique with a contribution from the Geneva laboratory, and that the costs of installation would be charged to CERN. Certainly no formal decision could be taken by CERN, for the reasons given by Mervyn Hine. However, it seems difficult to imagine that the other European physicists would refuse the French 'gift' and that they would not succeed, in due course, in having the necessary sums included in the organisation's budget. As for the construction, it was planned to do this at the CEA's laboratory at Saclay under the direction of R. Florent^. In brief then a project crystalised in less than six months - Lagarrigue's final proposals regarding a chamber reduced in size being temporarily accepted. This first extremely rapid phase of the decision-making process calls for certain comments. 2.1.2 HOW ARE WE TO UNDERSTAND SUCH A RAPID DECISION? Firstly, by mentioning the American situation. One trigger for the quick acceptance of Lagarrigue's proposal was the rapid progress in America during the last months of 1963. The American threat was the first reason put forward by the partisans of bubble chambers in 1964, and it was accepted as a strong and legitimate argument by their colleagues. The second factor accounting for the quick acceptance of Lagarrigue's proposal was the importance which neutrino physics had in Europe. During the two previous years this research had been strongly supported by Victor Weisskopf and had become of central importance at CERN. Heavy liquid bubble chambers were detectors well adapted to it. Perhaps they were not the only kind of chamber suitable for this work, but neutrino physics was one of the areas in which they were known to perform extremely well. The third reason why this 'choice' was so quick was that only one group of protagonists was involved in this debate, that there was no competing project: in fact there was no choice in the usual sense of the word since only Lagarrigue's project was on the table. Presenting the American studies led by Shutt as a menace for Europe, the French and Italian heavy liquid specialists formulated a response centred around their competence and know-hows which looked sensible. And since they rather quickly found an independent source of finance, nearly nothing could be opposed to their choice. The final element is related to the strong French bubble chamber network. On one side was Francis Perrin who was able quickly to commit money and who preferred to see an investment made in large equipment for use at CERN rather than in a national accelerator, as advocated by some, and which would necessarily be 'small'. On the other side were Leprince Ringuet's former students at the Ecole polytechnique, Charles Peyrou, Bernard Gregory and Andre Lagarrigue. All were involved in bubble chamber physics and, having the material infrastructure of the French CEA at their disposal - via Perrin -, they agreed to continue with the new large heavy liquid chamber advocated by Lagarrigue. In this way, they could be among the international leaders in the field - and could not only preserve French excellence but also play a key role in Europe^.

43

The emergence of hydrogen bubble chamber projects 2.2 The emergence of hydrogen bubble chamber projects and Gregory's proposal for a tripartite solution, September 1964-May 1965

As we have already mentioned, a hydrogen chamber is more complex a detector than a heavy liquid chamber, if only because one has to manipulate liquid hydrogen at a very low temperature. It is also a device whose construction costs are several times those of an equivalent propane or benzine chamber. Scientifically speaking, on the other hand, there are distinct advantages when it comes to interpreting the photographs taken with the device. Since the incident particles only interact with protons (the nuclei of hydrogen) and not with the nuclei of complex molecules the events produced are 'cleaner' and their interpretation is faciUtated^. 2.2.1 CONVERGING ON A SINGLE CERN-FRANCO-GERMAN PROJECT, AUTUMN 1964 In contrast to Lagarrigue's project, no dominant centre appeared for the construction of a hydrogen chamber. On the contrary we find, in the space of a few months, three 'groups' declaring their wish to construct or to participate in the construction of such a chamber. These projects, because they were more spectacular and ambitious, rapidly created a widespread interest in the entire community - and ultimately threatened to reduce seriously the need and the use of Lagarrigue's chamber! A first proposal originated in the group of Andre Berthelot, Director of LPCHE, the CEA's high-energy physics laboratory at Saclay. Berthelot was less integrated than other French groups in the management at CERN and he wanted to retain a certain autonomy in the building of big chambers. In September 1964, he proposed that a large European hydrogen chamber be built from separate, independent modules. In his proposition he suggested two types of basic modules. One was 4 m^ in volume (diameter 1.3 metres, length 3 metres), the other 8 m^ (diameter 1.6 metres, length 4 metres). With the first, chambers of six or nine metres in length, and of L3 metres in diameter, could be installed. With the second, the chambers would be eight or twelve metres long and 1.6 metres in diameter. Berthelot thought that he could rapidly construct one module and use it as an independent chamber at the CEA's accelerator 'Saturne' at Saclay, or at Serpukhov where he had contacts. At a later stage this chamber module could be assembled with other identical modules which would together comprise a big chamber for CERN. In this way, Berthelot argued, Europe could decentralize decision-making and distribute the work among various builders, without hindering the construction of the big equipment necessary to compete with the United States^. The reaction of the CERN physicists (or of those who used Geneva as their central base) was very unfavourable. They pointed out that the technical structure proposed by Berthelot added an unnecessary degree of complexity, that the process of assembling the device would not be simple, that a number of undesirable effects would probably arise in the thermodynamic equilibrium of the whole, and that the total cost would probably Notes: p. 62

44

Gargamelle and BEBC

increase considerably. Berthelot's idea was thus rapidly dismissed, the bubble chamber leaders (who controlled the Track Chamber Committee at CERN) preferring one single hydrogen chamber based on Shutt's new ideas^. Although this proposition by the director of LPCHE was rejected, it had consequences since it urged everybody at CERN to act immediately. CERN could not afford to leave the terrain free to Berthelot who could obtain support from the CEA and in this way hinder the Geneva laboratory. Since there is never an infinite amount of money available, and since France was one of the key players in the European bubble chamber lobby, Berthelot's initiative could not be overlooked and allowed to gather momentum. Anyway, following the publication of Shutt's brand new design in the spring, CERN physicists had already considered the question of a large European hydrogen chamber. In the fall of 1964, CERN management started to act. On the one hand, the need 'to give serious consideration to the construction of a [very big] liquid hydrogen bubble chamber' was included in the medium-term projects, notably in the four-year PS improvement programme. In the document which he drafted for the SPC in mid-October, Hine wrote that this chamber 'would be circular with a diameter of four to five metres and the useful volume would be about 25 m^ of liquid hydrogen'. He added that 'metal plates would be mounted in the chamber' - which in fact was word for word Shutt's project. The first step taken by the CERN management was thus to confirm the need for a big hydrogen chamber and to encourage everyone to think along American Unes^^. The second step was to convene a meeting of the Track Chamber Committee with the aim of 'surveying the problem of the new generation of bubble chambers' and to officially answer Berthelot's proposals. The committee met on 18 November, and Hstened to three presentations. One was by Berthelot, another was by Lagarrigue on Gargamelle (this being the name that the French had given to their heavy liquid chamber). The third presentation was by Charles Peyrou, the director of the hydrogen chamber division at CERN, who explained Shutt's ideas. On this occasion, the German physicists officially announced their intention of also constructing a large hydrogen chamber. A bubble chamber policy working group comprising the most senior Europeans in this domain was then set up. It held its first meeting in Geneva on 2 December 1964^^ The third initiative, decisive for the speeding up of the decision process, was effectively taken in Germany. Towards the beginning of November six directors of physics institutes (Fuchs and Faissner from Aachen, Paul from Bonn, Jentschke from Hamburg, Filthuth from Heidelberg and Heisenberg from Munich) wrote a long letter to the Minister of Research. They asked him to include in the agenda of the Ministerial Working Group on High-Energy Physics, which was to meet on 30 November 1964, a project for financing a very big hydrogen chamber. Their point of departure, the model on which they proposed to base their discussion, was also Shutt's project. Stating that such a chamber was indispensable for Germany - the field was dominated by the French and the British, according to the report - the signatories asked for the resources to study it in detail. The cost of construction was estimated to be 40 million Deutschmark (Shutt's estimate), and CERN was expected to provide 15-20 millions for installing the chamber in Geneva. Just

45

The emergence of hydrogen bubble chamber projects

as Lagarrigue had done, the authors of the letter suggested that the chamber should be paid for and built by Germany (and notably German industry), and that it should then be transported to Geneva and used collectively by all Europeans. What the German physicists wanted was for their country to acquire a new expertise in the technology of hydrogen chambers, feehng that they were behind France and the CERN staff in this area^^. The meeting of the bubble chamber policy working group on 2 December 1964 reached agreement on two main points. Firstly, 'the majority' - meaning everybody except Berthelot - recommended the construction of 'a large HBC, similar in size to Shutt's proposal'. The group added that 'it is felt that it might not be justified to first construct an intermediate size chamber'. Then, since Lagarrigue had not been forgotten, the text added that 'supplementary projects like Gargamelle should be considered'. This reference to the heavy liquid chamber was made with the quaUfication that the project should in no way impede the hydrogen chamber, which was the priority project^^. From this date onwards Weisskopf on the one hand, Gregory, Perrin and the senior members of the German physics community on the other^^, seem to have focussed their minds on the idea of having a very big hydrogen chamber which would be built tripartitely by CERN, France and Germany. Unfortunately our documents are not particularly precise on this point^^. What is certain is that 'certain official French and German quarters' agreed, by the end of December, to have a feasibility study prepared as soon as possible. Indeed, in the last days of December Gregory asked Florent to draft a working document which would summarise the discussions held until then. Florent submitted his report, entitled 'Draft agreement for a feasibility study for a large European bubble chamber' on 5 January 1965. It stated that CERN, the French CEA, and a German organisation not yet decided (probably the Minister of Atomic Energy) 'envisaged the joint construction' of a large bubble chamber estimated to cost 60 MSF, and that the project would be financed in 'equal parts by the three participants'. In the following days, Gregory tried to set up the political and technical infrastructure needed for this feasibility study ^^ 2.2.2 HAVING THE PROJECT ENDORSED BY THE EUROPEAN PHYSICS COMMUNITY, JANUARY-FEBRUARY 1965 Two major problems now had to be solved by Gregory, then Director of Research at CERN. It was first important to associate the organised community of high-energy physicists with the project. This meant to have them approve it and declare that it was indispensable for European physics in the 1970s. It was also necessary to set up a tripartite (CERN, France, Germany) technical group which would be under the supervision of those who were paying. Its task would be to conceive a detailed and, if possible, innovative design of a viable chamber. The first problem required discussing carefully the 'scientific value of the project - this to be judged by a fairly large number of people', to cite the formula used by Gregory in a letter of 15 January to his future French and German colleagues. Classically, this entailed Notes: p. 62

46

Gargamelle and BEBC

passing through three successive phases. To begin with a report (a plea one could say) would have to be drafted by the partisans of bubble chambers. For this, Gregory approached the CERN Track Chamber Committee which was the 'official representative' of this part of the community. Then it was necessary to have 'the value of the instrument' recognised by 'the physicists who are not involved in the technique'. In other words, one had to neutralise that part of the community which worked with electronic means of detection, and which was separately organised. This was to be done by the Scientific Policy Committee, the usual body responsible for vaHdating CERN's scientific projects. Finally, and strengthened by its unanimous recommendation - the proposals of the SPC were made in the name of all European physicists -, political representatives would be contacted. That meant the Council, as far as CERN was concerned, and administrators in the relevant agencies for France and Germany. There were three aspects to the second problem which Gregory had to solve: have the money committed, appoint the men who would have to design and build the chamber, and draft the convention, i.e., the text which would regulate the relations between the three partners. Here Gregory proposed to be pragmatic and prudent, and not to look beyond the short term. To set the ball rolling, there was to be a meeting between Weisskopf, Perrin and Jentschke who 'should agree on setting up for 1965 a study group [who would make a technical study of the chamber] with the oral agreement that if a proper convention can be found [...] the share of money from each country would be of the order of one-third each'. Thereafter the money for the technical feasibility study was to be committed for a year or 18 months, and those who would manage the project were to be nominated. Finally, and in parallel, one should begin to think about the drafting of the convention. The actual construction ought to start, Gregory suggested, towards the end of 1965 or during 1966^^. The first months of 1965 were dedicated to finding a solution to the first problem: to associate the organised community of physicists with the project. On 10 February the Track Chamber Committee submitted its report entitled 'Future of Bubble Chambers at CERN and in Europe'*^ The TCC reaffirmed, firstly, that 'physicists need an unbiased and universal instrument for the systematic study of high-energy collisions', insisting that bubble chambers were still the best detector for this purpose. In Europe bubble chambers had the additional function of 'keeping the social peace' since they enabled universities to be directly associated with the advanced research done at CERN. The preparation of the runs with bubble chambers only required a limited investment in time and the analysis of photographs could be done at home - in contrast to electronic experiments which were more individualistic and idiosyncratic and which could really only be carried out by full-time researchers who were able to spend long periods based in Geneva. The ideal chamber which the report described was of very large volume and simply took up the ideas developed by Shutt's group. It was cylindrical in shape (useful volume of 25 m^) but mounted vertically (4 to 5 metres in diameter and 2 to 3 metres high). The dimensions of its windows would be reduced thanks to the use of new optical and photographic techniques and of scotch-lite, a reflecting material which would line the inside

The emergence of hydrogen bubble chamber projects

47

surface of the chamber. Metal plates would also be added inside the chamber so as to enable a good detection of gamma rays and the determination of their energy. The Track Chamber Committee's report (drafted by Peyrou) also remarked that France had proposed building a heavy liquid chamber for use at CERN. Stressing that such a chamber would in no way serve as a replacement for a hydrogen chamber, the report insisted all the same that it would be extremely interested to have this device at CERN. The heavy liquid chamber would be ready two years before the hydrogen chamber, and it would therefore allow 'immediately an impressive progress in neutrino physics'. Once the hydrogen chamber came on line the heavy Uquid chamber would allow for a more balanced programme, and would help supply universities with photographs. Director-General Victor Weisskopf introduced two important nuances when commenting on this report to the meeting of the SPC. Firstly he insisted that the design of the hydrogen chamber was not yet to be regarded as settled. Important sums of money were involved, and the chamber would have a central place in CERN's future programme. It was then important to be sure that there were not other scientifically interesting alternatives. Taking up a theme that was common at the time, Weisskopf suggested for example the study 'of a faster cychng bubble chamber with spark chamber arrangements', i.e., a combination of the electronic and bubble chamber techniques. The second nuance introduced by Weisskopf- and perhaps this was really more than simply a nuance - was that he gave clearer support to Gargamelle than the TCC report. He not only stressed the interest of having a chamber which could do neutrino physics two or three years before anyone else in the world. He also stressed 'the very good arguments why national groups should remain active in building bubble chambers', the advantage in terms of experimental flexibiUty which the presence of two chambers would have for CERN in the 1970s, and the fact that it was an excellent deal since the costs for CERN would be negUgible! From this Weisskopf concluded that if no decision could yet be taken on the hydrogen chamber - the design was not yet ready and CERN's budgets had not yet been fixed for the years to come - the same was not the case for Gargamelle. 'Since time scale plays a major role in the arguments supporting that project', and since 'our share in the Gargamelle project is [...] small', it was not inconceivable for CERN to arrive rapidly 'at a decision in principle even if the budgets are not exactly known'^^. Two days later, on 16 February, the SPC adopted the conclusions of these two reports and recommended to the Council 'that a working party be set up to study in detail all the questions concerning the specifications of [the giant hydrogen chamber]'. As for Gargamelle, it proposed that 'a decision be taken at one of the next Council sessions, since its design is already well advanced and it could be built quickly'^^.

Notes: p. 62

48

Gargamelle and BEBC

2.2.3 FORMALISING THE RELATIONS BETWEEN THE THREE PARTNERS. THE AGREEMENT OF 4 MAY 1965 BETWEEN JENTSCHKE, PERRIN AND WEISSKOPF Towards the end of February 1965 steps were taken to find a solution to the second problem, namely to set up a technical group who had to design the chamber under the supervision of the three fundgivers. Here the most delicate question was that of who should be in charge of the group doing the technical study. This was because, from the outset, Charles Peyrou and his division demanded to be responsible for almost the entire project. Their main argument was that they and they alone had the necessary expertise, that most of the skills 'were to be found already at CERN in terms of number of people, of experience with big chambers and industrial installation, and even of the spirit of invention'. On the French (and German) sides feelings were obviously very different and, to the extent that the costs were shared, it seemed obvious that they ought to be associated in all aspects of the construction - if only in this way to acquire the know-how which was needed for this kind of task^M Gregory was asked to find a solution informally. With the agreement of Jentschke, Perrin and Weisskopf he opened negotiations with the principal protagonists, i.e., Florent for the French, Teucher for the Germans and Peyrou for the hydrogen chamber division at CERN. Without going into the details of the successive proposals which were put forward let us simply note that, from April onwards, people were thinking in terms of a double structure^^. At the head of the project a study committee would be set up. It would be comprised of six persons whose task it would be to make the important technological choices, to guide and to examine the proposals coming from the working groups, to establish the financial framework and to plan the overall realisation of the project. It would be formed of two representatives from CERN, namely Peyrou and Schmeissner, have two people from France, Gregory and Florent, and two German representatives, Filthuth and Teucher. In short, this study group would have five physicists and one builder (Florent) distributed equally between two nationalities. Although his existence was never clearly recognised in the documents, Peyrou's deputy at the head of the TC division. Burger, also participated at all the meetings of the committee in 1965^^. Below the study committee a working group was envisaged. It was to be comprised of physicists, engineers and technicians from CERN and from the two countries involved and its task was to carry out the studies as such. Several ways of managing it were discussed. Initially there was the idea of having a single director, namely Peyrou for the design phase and Florent for the construction phase. Then the idea was floated of having a two-headed management structure, Florent-Schmeissner, to be followed by Florent-Filthuth. This proved to be acceptable only in the short term and to the Franco-German group. Finally, the principle of a 'non-integrated management' was adopted, i.e., a non-choice was made, and 'those responsible for representing the three partners (Filthuth, Florent, Schmeissner) would each have authority over their staff' whom, as a matter of fact, were always paid in this early stage by the laboratories from which they came^"^.

49

The decision and the construction of Gargamelle This agreement, which was not easily reached, was confirmed at a meeting held on 4 May between Jentschke, Perrin and Weisskopf. The study committee met for the first time on 8 June in line with the rather informal practice initiated three months earlier^^. The working group, for its part, was officially set up at the end of May, and it developed very rapidly. To anticipate a little, let us simply note that in December it comprised 21 people, 4 Germans (3 physicists, 1 engineer), 7 French (1 physicist, 4 engineers, 2 draftsmen) and 10 members of CERN (6 engineers and 4 draftsmen)^^. What we find then is a tripartite arrangement sought for and supported by the members of the establishment but which encountered some difficulties when it came to setting it up in practice. As is so often the case it was rivalry between people and institutions which was at the base of the conflicts. In this particular case, the difficulties encountered were rigidified by national interests. Even if these were not at the root of the skirmishes, they were a supplementary 'resource' to which actors could appeal to break or to reverse a decision which they did not like. It was for example possible to block the arrangement in which there was a single strong manager by appealing to national interest, an argument that was all the more weighty in this case since from the start it had been understood that there would be an equal distribution between the three participants. Weisskopf, Perrin and Jentschke were all aware of this limit, but they felt that it would be difficult to reverse it in the short term. All the same, they hoped to overcome it during the construction phase^^. 2.3 The decision and the construction of Gargamelle As we have seen after the SPC meeting in February 1965 the trajectory of the decision for Gargamelle differed noticeably from that for the hydrogen chamber. Two of the main protagonists, Weisskopf and Gregory, effectively considered Gargamelle to be a simple case (the business was said to be technically uncontroversial) and more or less arranged from the political point of view (since the chamber was 'offered' by France and the costs to be borne by CERN were negligible). We have therefore decided to treat the two cases separately from this date onwards. 2.3.1 THE COMPLICATIONS SURROUNDING GARGAMELLE AND THE FINAL SOLUTION, FEBRUARY-DECEMBER 1965 The most urgent thing to do in March and in April as far as Gargamelle was concerned was to finalise the drafting of the convention. A first version, suggested by the services of the CEA, was circulated at CERN at the beginning of February. The idea was to submit the text to the Finance Committee in May for a final decision by the Council in June. (Let us remember that it was the Finance Committee that first studied legal questions which were then passed up to the Council.) On 16 April, after a visit to Saclay by G. Hampton, CERN's Director of Administration, a new version of the text was sent to Geneva^^. Notes: p. 62

50

Gargamelle and BEBC

Broadly speaking, this text stipulated that the construction of the chamber, which was the responsibiUty of the CEA and which would be done in France, would be supervised by a mixed committee in which the two partners (CERN and France) would be equally represented. It added that the costs of construction would be charged to the CEA, CERN contributing a capital sum of 5 MSF (distributed over four years). Finally it recognised that 'CERN shall be solely responsible for [the] operation [of the chamber] under CERN regulations, in accordance with the scientific programmes defined by the Director-General'29. The Finance Committee was satisfied with these arrangements and, at its meeting on 3 and 4 May, it approved the principles underlying the text. The following day the SPC also gave its blessing to the operation, Bernardini declaring 'that he considered the Gargamelle project to be an excellent example of co-operation'. The Scientific Policy Committee even stated that 'it would prefer to cut the [money for the construction of the experimental] East area rather than [for] Gargamelle' in the event that the reduction of the 1967 budget by 8 MSF demanded by the Finance Committee forced a choice between the two items^^. It only remained for the Council meeting in June to go along with this unanimous point of view once the provisional budgets for CERN for 1967 and 1968 had been voted on. Weisskopf was optimistic in a letter that he wrote to Perrin dated 25 May. CERN's final agreement would certainly be given during the summer, he said, and there was no need to interrupt the studies already under way regarding the site (i.e., where and in which experimental hall to instal the chamber) and the necessary equipment for analyzing the photographs taken by Gargamelle-^ ^ As it so happened the hope that there would be a definite decision in June was not fulfilled. The budgetary crisis which had beset CERN for several months persisted, and was not resolved during this Council session. And without any budgetary provisions for the years to come, the Council refused to take any position on future investments. Somewhat unexpectedly then all was blocked, and there seemed little hope that the tendency would be reversed easily. Clearly, there were major problems which transcended the simple question of Gargamelle^^. Three months later, however, a very simple, and definite, solution was found by the organisation's management. As we have said no scientist wanted to delay a project which was ready, which was of limited cost, and which they judged to be scientifically important. Thus Weisskopf and Gregory decided to commit the money themselves, within the normal framework of CERN budget, and without any concern for the final sum which the Council would vote for the forthcoming years. Believing that to manage was above all to exercise the art of choice (even when resources were uncertain), they were sure that they would find a way of installing the chamber in Geneva under suitable conditions and that they could pay the 5 MSF promised to the CEA. To simplify matters, the latter in fact offered a loan to CERN to cover the instalment due for 1966. At the start of autumn the technical liaison between the groups at CERN, at the CEA and of Lagarrigue was thus normalised again. The final contract between the CEA and the CERN management was signed on 2 December 1965. For the first time in CERN's history

51

The decision and the construction of Gargamelle

an investment which was initially thought to require a decision at the level of the Council was approved by the Director-General using his existing executive authority^^. 2.3.2 THE PRINCIPLE DATES IN THE CONSTRUCTION OF GARGAMELLE Even though our study is not intended to cover the construction and the preparation of the experimental programmes for the chambers, we will give here some summary information on the more important events during these phases. Here they are for Gargamelle, a chamber entirely constructed at Saclay, under the responsibility of the 'Departement Saturne'. The design of such a chamber, an unusually sophisticated piece of equipment, underwent notable changes between the end of 1965 and its commissioning at CERN in December 1970. Let us mention here only two components where there were major innovations: the chamber's optics, which was completely rethought when scotchlite was discarded, and the expansion system. The idea of having a single piston was abandoned because the chamber was long (4.8 m for a diameter of 1.9). To keep the chamber's Uquid homogeneous, and to avoid the creation of waves, it was replaced by two four-meter long membranes which were activated by 44 valves. There was also an important delay during the construction phase. While the contract foresaw that the chamber would first be assembled and tested at the Centre d'Etudes Nucleaires at Saclay, then dismounted and transported to CERN during the first months of 1969, the chamber was in fact directly assembled at Geneva, the first photographs were only taken in December 1970 and the first important run only occurred in March 1971. This delay of about two years does not however appear to have been a major catastrophe, since the competing hydrogen chambers also suffered important delays. Since there is no 'absolute time' for carrying out instrumental work - what counts above all for the scientific community is to be the first and to succeed - it is the maintenance of a lead which really counts. In any event the chamber was the decisive element in the neutrino experiments at CERN which were done between 1971 and 1974. These experiments provided the first evidence for weak neutral currents, certainly the first very important discovery made in the history of CERN. It was realised at the CEA in January 1968 that a delay in the construction of Gargamelle might well occur. According to the work plan which had been adopted, the body of the chamber ought to have been delivered by industry in June 1968, and the tests should have occurred between July and November. Difficulties with the process of fabrication of this part of the chamber, however, upset the initial plan and led Lagarrigue to suggest, in November 1968, that the chamber should perhaps not be assembled at Saclay. Rather, its body should be delivered directly to Geneva and the assembly done on the spot. Lagarrigue made the official proposal to Gregory on 27 January, who accepted it two months later. Everyone hoped then that the chamber body would be delivered in the summer of 1969^^. By October, this key component was still not delivered and the CEA made an official complaint to the suppUer, the Compagnie des Ateliers et Forges de la Loire (the CreusotNotes: pp. 62 ff.

52

Gargamelle and BEBC

Loire group). This was one of the best metallurgical industries in France and also the CEA's and CERN's normal supplier. The director of the company justified the delay by appealing to 'social difficulties' in France since 1968, but also because they were dealing with 'a very complex piece of equipment which was difficult to construct because of its tendency to lose its shape after having been welded'. He promised to deliver the item at the end of March 1970. This time the delay was negHgible and the chamber was subjected to its first tests at CERN before the end of the year^^. The preparation of the experimental programme raised two different kinds of problems. The first, which was dealt with very early on, was that of the data handling faciUties, notably the scanning tables necessary for reading Gargamelle's photographs. It was essential to rethink the procedure for treating thefilms,as well as the computer programmes associated with them, since the optics of the chamber was extremely complicated and involved the use of eight cameras. This issue was at the focus of many meetings at the European level from early 1966, and the matter was settled by building a new series of scanning tables^^. The second problem was the classical one of deciding what particle beams should be fired at the chamber and what experiments should be done first. The issue was first raised in a memorandum to the TCC drafted in common by Lagarrigue and by Ramm, who was responsible for heavy Uquid chambers at CERN. It was then discussed regularly in the socalled Gargamelle Users Committee. This body was modelled on other experimental committees at CERN, and it met for the first time on 29 November 1967. Its task was to discuss proposals for experiments coming from different European groups and to elaborate a coordinated programme for Gargamelle which satisfied and reconciled as many users as possible^^. As we have already mentioned, the first important experiments done with the chamber were those with a neutrino beam. Their results were of fundamental importance, as is explained in more detail in other chapters of this book. 2.4 The decision to construct BEBC and the CERN-Franco-German convention, Summer 1965-July 1967 Between summer 1965, when the study group was set up and the technical groups began to start working in Geneva, and February 1966, when a first report was submitted to the SPC, those responsible for the big hydrogen chamber were primarily concerned with scientific and technical matters. In the agreement reached between Jentschke, Perrin and Weisskopf on 4 May political questions had been provisionally resolved. Now the main objective was to define technically the ideal and multi-purpose detector which would be submitted to the member states for financing. The bubble chamber specialists were certainly convinced that the best chamber to build would be a classic one of the type that Shutt had proposed, and that it was this kind of chamber that should first be studied. At the same time they could not but Usten to the views of Weisskopf and of the physicists

The decision to construct BEBC and the CERN-Franco-German convention

53

doing electronic experiments and to compare their preferred option with other types of detectors. There were at least two reasons why they had to broaden their field of investigation. On the one hand, they did not really have a choice, we might say. They had to meet the demands coming from the rest of the community, even if only formally. Given the high costs of a very big hydrogen chamber it was essential that the specialists in electronic detection should at least not oppose the project in political circles. On the other hand, they had to reassure themselves, and to study closely alternatives which could improve the performance of the system. Granted the strong competition in the field, they would certainly be held responsible for any bad choices if other devices were in a better position to make important discoveries in the future. Rivals with better detectors could eventually steal their glory, fame, and recognition and as a consequence limit their means for continuing to do top-level research. 2.4.1 TECHNICAL DISCUSSIONS AROUND THE VARIOUS POSSIBILITIES, JUNE 1965-FEBRUARY 1966 To get the technical work under way, the study group defined two major directions during its first meetings in June 1965. Firstly, and in the light of 'information recently received from the United States', they opted for a superconducting magnet. As this was still a rather novel technique the CERN group needed to deal with rather basic questions like trying to establish whether it was better to have an iron yoke with the superconducting coils or not. Secondly, the study group defined a first set of parameters for its preferred option, a very big hydrogen chamber. On 8 June the committee fixed 'for the moment, a diameter of 4.5 metres and a height of 3.3 meters, it being understood that [...] one would examine the economic implications for 4 and 5 meters'. As for the interior of the chamber, it was still assumed that one would instal plates for detecting the TI:^, though their thickness and orientation were still to be defined. The optics also had to be carefully studied ('can a large volume of hydrogen be photographed? Will photography through a large volume of hydrogen allow precise measurements?' etc.)^^. In parallel and as a response to Weisskopf s remarks, the committee also considered the possibility of having mixed chambers with the same magnetic volume as the conventional chamber. Studies done at Saclay in 1964 on high repetition rate chambers were taken up again^^, and two variants of the mixed chambers were studied during the summer. One was a 3.5 m^ hydrogen chamber linked to a spark chamber, the whole being placed inside a 5 meter magnet. The other comprised the same rapid cycling chamber this time associated with a circular spark chamber which was placed inside 2.5 meter superconducting coils. Spark chambers surrounded the whole. Initiated in July, these exploratory studies led in their turn to new variants whose details were presented during the months of November and December^. The range and variety of questions which were still open for discussion during this period is clear from a reading of the documents produced for the end of the year. To vary Notes: p. 63

54

Gargamelle and BEBC

our account and not to linger on mixed chambers, we can note for example that the position of the axis of the chamber - and we are now speaking of the classic Shutt type chamber - became in its turn an object of discussion. A variant with a horizontal axis, and with a vertical window 3.5 meters in diameter and weighing 7 tonnes, was chosen. Its advantages were that it required 'classical' optics, that temperature control was 'good', and that the relationship between the useful and the total volume was 'favourable'. On the other hand, the mechanical construction was 'complex' because of the 'asymmetry' arising from the fact that the piston was on a horizontal axis. In another 'improved' version of the Shutt chamber with a vertical axis, the detector retained a 'simple' mechanical structure and was fitted with 'more conventional' optics. Here though the group feared that there would be temperature inhomogeneities in the chamber and that it would be difficult to protect it against cosmic rays. In January 1966 both variants were still being considered while in February a horizontal variant with a vertical piston was being envisaged"^*. It was not only the technology of the chamber that was discussed during these eight months. In parallel, a number of questions relating to the physics that could be done with it were raised. What was needed was to compare the performance of different kinds of detection as regards specific questions in physics. Thus on 17 January the members of the committee and of the working group met in Geneva, along with physicists like Armenteros and Lagarrigue, to debate five or six essential points related to the practice of bubble chamber physics. Their discussions were informed by three preliminary reports prepared by the study group. A comparison was drawn between three types of detectors: a classic 5 meter chamber with plates inserted, and two mixed chambers of different types and of 1.7 and 2.5 meters. These were studied in terms of their advantages for the detection of TT^S and of neutrons, for research with high statistics, for their precision in the measurement of trajectories, etc"*^. Finally in 1966, partially because more money was available and partially because the study group had grown in size and had been divided into seven specialised sub-groups, a number of experimental studies began in conjunction with the more theoretical approaches. At this stage they were predominantly concerned with the optical properties of scotch-lite through varying depths of hydrogen and with the modes and the speed of bubble formation in the chambers'*^. 2.4.2 THE BUDGET AGAIN AND THE DRAFTING OF THE REPORT ON THE BIG HYDROGEN CHAMBER, FEBRUARY-OCTOBER 1966 This first phase came to an end towards the end of February 1966. The final recommendation was to abandon mixed chambers and to concentrate on a classical big hydrogen chamber. This is not to say that the studies had arrived at a 'necessary conclusion'. We now know that this never happens, that there is never an inevitable conclusion because all studies are limited in their objectives and in their means. It was simply that the members of the committee and of the working group judged that the time had now come to reduce the number of possible alternatives, and that one system was more

The decision to construct BEBC and the CERN-Franco-German convention

55

promising than the others. Of course it was true, as Peyrou put it in March after the second meeting on the physics aspects of the project, that 'the opinion of physicists remained divided between two possible solutions', and that 'the mixed system [...] would enable one to gain a factor of 4' from the point of view of statistics. All the same the classical chamber seemed to the bubble chamber physicists on the committee as the solution. As a result they decided that, unless there were unforeseen novelties, all studies henceforth and until September would concentrate on two variants of a big chamber without any electronics organically associated with it. One design would have a vertical axis and the other a horizontal axis with a vertical piston"^. The second reason for devoting the resources available to one single solution was that it was essential not to delay the practical implementation of the project any longer. In May 1965 the study committee hoped to arrive at a clear result before the end of the year — a result which could be submitted to the Council and to the member states for their approval and financing. In autumn, as the number of options multiplied, this date had to be put back by six months. Now, in February 1966, it was deemed urgent to invert the rhythm and to arrive at a definite conclusion. As a result September 1966 was fixed as the target date. By this date, it was decided, the final report describing the technical and financial aspects of the project had to be submitted to the SPC, and to an international conference of experts which would meet in Heidelberg in October. In the interim the committee submitted an intermediate report to the SPC proposing the principle of a big chamber, which the committee approved^^. In March, the study committee drafted a note concerning the cost of the chamber. Translating the most recent figures from BNL into those appropriate for a European situation, it concluded that the costs had initially been underestimated. It was probably necessary, it said, to simpHfy the design if one wanted to remain within the order of magnitude put to governments fifteen months before. The use of large glass surfaces, for example, seemed to introduce a prohibitive cost overrun. Similarly, the plates which Shutt had proposed to introduce into the chamber to faciUtate the detections of gammas and of neutral particles were costly, and they had disappeared from the most recent designs at Brookhaven^^. As far as the committee was concerned, these cost increases meant that the space in which they could manoeuvre was reduced and that thenceforth they necessarily had to associate technical designs and cost estimates more closely. As they were now moving to the last stage in the conception of the chamber there was no longer any sense in putting forward technical solutions without at the same time estimating their costs. As a result they proposed to restrict themselves to the study of a chamber of about 3.5 meters in diameter whose cost seemed to be about 72 MSF. The choice of the figure 72 corresponded to the fact that there had been a 're-evaluation [in the light of inflation] of the initial cost' of 66 miUions submitted in March 1965 to Weisskopf, Perrin, Jentschke and to poHtical circles. And since scientists rarely restrict themselves when adopting solutions in the highly competitive field of high-energy physics, the committee recommended that all the same Notes: p. 63

56

Gargamelle and BEBC

one should still examine the impUcations on the final cost of increasing the diameter of the chamber to 4.5 meters and to 5 meters^^. In the autumn 1966 the contours of the project that would be submitted to governments began to emerge. In October, the Study Group for a Large European Bubble Chamber produced a report of about 100 pages. Here it proposed a cylindrical chamber 3.5 meters in diameter and about 3 meters in height with a vertical axis, and a useful volume of 20 m^. Its piston which was 2 meters in diameter was situated underneath the chamber and four cameras were placed on top of the cyHnder to photograph the volume through lenses with an aperture of 105°. The magnetic field of 35 kGauss was produced by two liquid helium cooled superconducting coils. As for the much debated problem of the detection of gammas, the report did not propose a definite solution. Instead it suggested that various alternative solutions and their costs should be studied, 'such as various metal plate arrangements and neon-hydrogen chamber fillings"*^. As for planning, the report estimated that the chamber would be working in 1971 if the decision to build it was taken at the start of 1967. Financially, studies made in Europe with industries had led to the conclusion that the cost of construction would be high, and of the order of 84 MSF 'which represents 27% more than the 66 foreseen [...]'. As Charles Peyrou wrote, defending the project, '[it] is certainly not a preposterous increase between a superficial evaluation and a careful one', especially if one took inflation into account. All the same the most important thing to be done now by the protagonists of the project was to convince the German and French governments of this fact, as well as the scientific opponents who were looking closely at the project in the light of this last-minute cost increase. Providing his friends with arguments which they could use if they had to reply to those who 'expressed doubts as to whether the chamber should be built at all', Peyrou suggested that one should remember that 'counter physics has also a long-range investment which is much bigger and is called storage rings"*^. 2.4.3 FINANCING THE CHAMBER AND ITS COST INCREASE, DRAFTING THE CONVENTION, AND SETTING UP THE GROUP TO CONSTRUCT IT, OCTOBER 1966-JULY 1967 From the time of the SPC meeting in November 1966 it was clear that the most delicate question was the additional cost of the chamber. In the case of CERN, for example, the final budget provisions made for the years to come were based on an estimation of 66 MSF. To get around this problem Director-General Bernard Gregory^^ proposed to spread the construction of the chamber over an additional year. 'Since the amount required for one year of construction was about the same as that necessary for one year's operation', he wrote, it was not even necessary to allocate additional funds for the device. The SPC, unhappy at the prospect of another complication, accepted Gregory's proposal, adding all the same that the size of the chamber should not be reduced^ ^ A final agreement between Gregory, Jentschke and Perrin was reached early in 1967. They accepted to share the cost of construction equally, and agreed that the time for

The decision to construct BEBC and the CERN-Franco-German convention

57

building the chamber should be extended so as not to exceed the contributions foreseen for the first four years. In February the German minister for scientific research, Dr. Stoltenberg, was contacted for his final agreement, which was more easily given by the French CEA. The Study Group, confident that the project would now go ahead, decided to start designing the experimental equipment that was needed. The most important were a onemeter diameter model of the chamber and a test bank for superconducting strips. All that now remained in the weeks ahead was to finalise the text of the convention^^. The drafting of the convention between CERN, France and Germany got under way in the summer 1966. On 18 July, after a meeting of scientists held in Geneva, Peyrou drafted a first version which was sent to the CEA and to the Bundesministerium fur Wissenschaftsforschung (BWF)^^. On 12 October 1966 this version was drastically modified after a meeting of legal experts. Here two major problems emerged, both connected to possible industrial spin-off's from the project. Both France and Germany wanted the convention to guarantee them a sort of 'juste retour' (fair return) linked to their important financial contributions. Germany's main concern, however, was industrial contracts^^. It wanted the text of the convention to state clearly that these would be distributed equally between the partners - a point resisted by CERN and by all the member states bar Germany and France on the grounds that it violated the existing policy of awarding contracts competitively to the best bidder. For France, on the other hand, the main problem was the protection of the inventions which the project could generate. Here again, CERN was opposed on the grounds of the current practice which held that the organisation did not take out patents^^. After two additional meetings in February and March 1967, a text was agreed for submission to the Finance Committee and to the CERN Council. In substance the agreement stipulated that the chamber would be CERN's property from the very beginning and that it would be constructed by 'a joint team from the three parties'. The chamber's cost was officially fixed at 84 MSF in 1966 prices. This was a definitive price and no additional money could be claimed from France or from Germany. Any cost overrun would be paid for by CERN. The convention stipulated that if this cost overrun was below 10 per cent, 'CERN would meet the extra cost' automatically, but if it was in excess of 10 per cent, the CERN Council was to be consulted about how best to handle the problem. The management of the project was to be in the hands of a 'Steering Committee consisting of a representative of each party', with CERN being represented by its DirectorGeneral. The Steering Committee, which would take its decisions by unanimity but would only meet several times a year, was to designate a Project Committee and to nominate a Project Leader. Its task was to approve the annual budget, to define a poUcy on patents if or when that became necessary, and to study the attribution of contracts worth more than 2 MSF. Contracts of a lower value would be dealt with by the Finance Committee and by CERN. The Project Committee, for its part, comprised two technical experts per partner. It was to monitor the technical aspects of the construction and to advise the DirectorGeneral on the organisation and the progress of the work. As for the distribution of contracts, and 'in so far as is compatible with technical and economic requirements', the Notes: p. 63

58

Gargamelle and BEBC

Director-General was to ensure that this was as equitable as possible. In short, a more or less clear commitment was taken to satisfy the specific demands made by France and by Germany, without formally questioning the overall policy of the organisation^^. The debates in May and in June in the FC and in the Council were rather difficult. There were two main reasons for this. Firstly and above all there was 'the fact that CERN was committing itself to providing any extra funds necessary in the course of the construction', a fact which disturbed certain delegations who saw in it an open-ended commitment to building the chamber. Secondly there was the question of 'the adjudication procedure for large contracts'. Here it was the German delegation who insisted that it should be the Steering Committee who had the last word and not the CERN Finance Committee. We will not enter into the details of the subsequent negotiations here. It is simply worth noting that everyone wanted to arrive at a suitable solution as quickly as possible, and that the final agreement was ratified by the Council on 14 and 15 June 1967. Only minor changes were made to the text during this final phase, though certain delegations did openly express their reservations on some points. On 21 July Bernard Gregory, CERN's Director-General, Hans von Heppe, Secretary of State to the Federal Republic of Germany and Robert Hirsch, Administrateur General of the CEA officially signed the agreement at CERN in Geneva^^.

2.5 Some remarks about the construction of BEBC, 1967-1972 The first meeting of the Steering Committee was held on 20 September 1967. It was composed of three well-known personalities, namely, Bernard Gregory, Wolfgang Paul and Francis Perrin, and it quickly confirmed a number of steps taken unofficially since the start of the year. The most important was the appointment of R. Florent as the sole head of the project - a decision that had been in the offing for quite some time to avoid the imbroglio of 1965. The second was the confirmation of the members of the Project Committee - Peyrou and Schmeissner for CERN, Teucher and Filthuth for Germany, Levy-Mandel and Meyer for France - a list reflecting the wish for stabiHty^^. Around this time about 50 people were in the team building the chamber (it would reach a maximum of 90 by 1971). Its main tasks were to test superconducting material and to construct a one-meter diameter model of the chamber. The latter was needed particularly to study the thermodynamics of the expansion system and the sources of optical distortion in the detector. In addition the group had to look into the characteristics of scotch-lite and of photography through several meters of liquid hydrogen - this work had been under way for over a year and was being done at Saclay and at DESY - , into magnetic shielding requirements - this work had also started the preceding year at Saclay - , and into the most suitable mixture of hydrogen and of neon, the aim here being to arrive at a means of detecting TT^S using a technique simpler than that of integrating plates into the body of the chamber^^. In December the Steering Committee accepted the final revision of the parameters of the system. A new idea put forward by Florent's group seemed to allow for an effective

Some remarks about the construction of BEBC, 1967-1972

59

increase in the chamber diameter by 20 cm and so of its useful volume by about 10% without any significant increase in the cost. Towards the middle of 1968, a number of calls for tender were made, notably 'for 45 km of stabilized superconducting material' for 'the stainless steel vessels (350 tons of stainless steel)', the magnetic shielding and the cooling system. In parallel the construction works got under way on the site at CERN. As regards the one meter diameter model, which was working during the autumn, it led the designers to prefer a chamber having a piston made of fibre-glass epoxy^^. Towards the end of 1968 an important point of friction began to emerge. It was the fact that the contracts were rather badly distributed between the partners, notably to the disadvantage of Germany whose representatives claimed that the agreements were not being respected. The reasons for the disequilibrium, according to Teucher in a letter which he wrote in January 1969, was that 'at present German industrial companies are not extremely eager to get orders for special equipment'. Reporting to Gregory on the rather unhappy experiences he had had with the industrialists in his country, Teucher concluded that 'it is sometimes really hard work'^^. In summer 1969, with the situation not improving notably, a new argument was used to placate the German authorities^^. It was pointed out that if one deducted the contracts of no technical interest, like those for the construction of the buildings or for the deUvery of the shielding, the distribution passed from 53% to 37% for France, and it increased from 23.8% to 33.5% for Germany. The other participating states then received 29% of the contracts. It was also noted that a considerable effort had been taken by the builders vis-a-vis German firms. Florent thus stressed that it was often 'necessary for us to insist strongly that the German prices become more competitive during second and third calls for tender', the calls being repeated to try to improve the distribution of the awards. He added that 'if we had simply gone ahead and placed orders on the basis of the first call for tenders, the present global distribution would give 8.6% for Germany and 68.5% for France ...'^^. From the end of 1969 onwards it became increasingly clear that a number of industries would not be able to respect their deUvery dates. By the winter 1970/71 the overall delay was estimated to be more than one year and it was hoped 'that commissioning would begin at the end of 1971 or at the beginning of 1972'. Six months later it was financial considerations which further slowed down the BEBC completion programme. At the same time the initial experimental programme of the chamber was the object of repeated and extremely complex controversies because the accelerated rate of construction of the 300 GeV machine was interfering with the organisation of work in certain experimental zones on the site at CERN^"^. Finally in the summer of 1972 (June and July) the first tests of the Big European Bubble Chamber got under way - operations being immediately halted by serious leaks in the vacuum tank of the magnet. Tests got under way again in mid-January 1973. In about a dozen days the magnet was cooled down by 20,000 litres of helium, 'and when operating temperatures were reached, current was fed to the superconductor increasing in steps towards the design level'. Notes: pp. 63 ff.

60

Gargamelle and BEBC

The instrumentation and the expansion system were then tested, and a map of the magneticfieldwas drawn up. Around 23 and 24 February a current of 5000 Amps was reached and thefieldwas 3.1 Tesla in the chamber. Now it was the turn of the chamber itself to be cooled. The helium cooUng the magnets was temporarily decanted into the reserve dewars, the idea being that only one operation should be performed at a time. On 3 May 38,000 Utres of liquid hydrogen were in the chamber and the first photographs of particles were taken. The final phase of testing ended by the simultaneous operation of the magnet and the bubble chamber. After certain necessary modifications and repairs had been made, notably to the expansion system, new tests were undertaken in June and July and again in October 1973, after another shut-down. In December, a first run was made in which 25,000 photographs were taken in a K~ beam of 9 GeV/c. 'Somewhat drastic surgery' was however felt necessary by January 1974 after some inexplicable phenomena had been observed during the charging and discharging of the magnet. Thus for the next ten months the chamber was once again dismounted and totally overhauled, with new tests getting under way in December 1974. It was only in the following six months that the chamber finally fully entered into operation and took more than 400,000 photographs. Its running-in was thus rather long and particularly laborious^^. 2.6 Some words by way of conclusion The first striking fact about these decisions is how much they differed from those taken towards the end of the 1950s for the first generation of bubble chambers at CERN. In those early years there was no collaboration between the CERN teams and those in the member states, and choices were made independently in France, in Great Britain, in Italy and at CERN. Now the new chambers (Gargamelle and BEBC) were the subject of a European-wide discussion. This evolution is not surprising and reflects an important change in social practice. It was a symptom of the consolidation of the European bubble chamber community since the time when the 25 GeV PS was commissioned. In 1958/59 each national group was in fact independent and it constructed the chamber for which it had adequate financial and human resources. It was only after this had been done that the question of installing the detector in Geneva was raised. It was then that the national groups came up against the physicists at CERN, who themselves wanted to instal their chambers in their laboratory and who were not particularly keen to collaborate, believing in their superiority and preferring to keep outsiders on the margins of experimental work. Hence the dialogue of the deaf which we described in volume 2, hence the incomprehensions. After one or two years of working together under the supervision of the 'levelling' committee that was the Track Chamber Committee, and with everyone now satisfied with the functioning of the system of collaborations, attitudes were very different. And quite naturally the questions were posed in joint terms in 1964/65, and at the European level.

Notes

61

This remark leads to a second. Even if the senior members of the community were thinking about the problem at the European level and were determined to establish collaborative solutions from the very start, the fact remains that conflicts between individuals and between institutions were real once the phase of concrete realisation started. This competition on the ground is rather banal, however, since it is part of everyday life. We will simply add, then, that these oppositions were rather easily dealt with and that they did not lead at any moment to a questioning of the rights of access to CERN's heavy equipment, which was governed by rules established in the first years of the TCC. Both BEBC and Gargamelle were thus declared CERN property from the beginning and nobody objected to their utiUsation being organised by the CERN experimental committees. This position was adopted even though everyone knew from experience that the builders would have certain de facto privileges during the definition of the first experimental programmes. Similarly, the relation between bubble chamber specialists and specialists in electronic detection techniques was not affected by this decision-making process. In fact the two communities remained more or less separate from each other, each collecting its own resources and defining its own projects. Certainly Weisskopf and Gregory tried to interest the community in hybrid projects and to have mixed chambers studied, but as we have seen there was little enthusiasm for them. While it was 'normal' for the director of a laboratory to see things globally and to try to facilitate cross-fertihsations which he thought would increase the efficiency of his laboratory, it was also only to be expected that the different professional and technical milieux would remain attached to their own fields of technical expertise. Nor should we be surprised by this mutual unwillingness of the two groups to mix with each other when we remember the important technical differences which separated the two traditions of detection, bubble chambers and visual modes of detection versus electronic apparatus and binary techniques'^. Translated by John Krige

Notes 1. For these two paragraphs, see A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN, volume II. Building and Running the Laboratory (Amsterdam: North-Holland, 1990), chapter 8; Note by R. P. Shutt, 30/ 1/64 (DG 20569), CERN archives, for this and all similar references. I would particularly like to thank Professors Harigel, Levy-Mandel, Peyrou and Rousset for their very useful comments on the first version of this chapter. 2. Letter Lagarrigue to Weisskopf, 14/2/64 (DG 20568); Rapport sur un projet de chambre a liquides lourds by Lagarrigue, Musset, Rousset, February 1964 (DG 20569); report by Fiorini, Guerriero, Mannelli, Negri, Scotoni, undated (DG 20567); letter Rousset to Pestre, 11/1/93. 3. Letter Lagarrigue to Hine, 3/4/64 (DG 20568); Record of a meeting..., UjAjeA (DG 20568) from which these quotes are taken; SPC/182/Add., 20/4/64. 4. Record of a meeting..., XAjAj^A (DG 20568) from which the quote is taken. Notes: p. 64

62

Gargamelle

and

BEBC

5. Letter Gregory to Rousset, 24/6/64 (DG 20568). The formal responsibility was in the 'Departement Saturne', which ran the 2-3 GeV PS of the French CEA. 6. See in particular Hermann et al. (note 1), chapter 12. 5 and 12. 6. 7. Hermann et al. (note 1), chapter 8.4.1. 8. Memorandum Peyrou to Gregory, 2/10/64 (DG20562); Projet [...] presente par le LPCHE..., 16/10/64 (DG20562); letter Florent to Gregory, 16/10/64 (DG20562). 9. Letter Florent to Gregory, 16/10/64 (DG20562). See below for Shutt's new ideas. 10. CERN/SPC/189, 13/10/64, for the quotes. 11. Letter Gregory to Berthelot, 6/11/64 (DG20562). 12. Report sent by six physicists to the Bundesministerium, 16/11/64 (DG 20822); Letter Gottstein to Weisskopf, 27/11/64 (DG 20822). 13. BCPW Group, First meeting, 14/12/64 (DG20562) from which the quotes are taken. 14. Given the events of 1965, it is probable that Jentschke played a central role in this agreement, but we do not have any exact information for 1964. 15. However, see Resume de la conversation du 9 decembre avec Berthelot, 11/12/64 (DG20562); Council 15-16/ 12/64, Minutes, p. 48. 16. BCPW Group, Second meeting, 5/1/65 (DG 20562); letter Florent to Gregory, 5/1/65 and Projet d'accord..., edited by Florent, 4/1/65 (DG20562). 17. Letter Gregory to Teucher, 15/1/65, from which the quotes are taken (for the two preceding paragraphs). 18. CERN/SPC/194, 10/2/65. 19. Comments to the SPC..., by the DG, SPC/195, 10/2/65, from which the quotes are taken (for the two preceding paragraphs). 20. CERN/SPC/199/Draft, 26/4/65. 21 Memo TC/ChP/sm, 20/1/61 (DG 20562). 22. For the broad outHne of the negotiations, letters Gregory to Jentschke, 9/3/65, Gregory to Teucher, 8/4/65 (DG20562), CERN/TC/StG 5000 65-1, 15/6/65 (DG20031), letter Weisskopf to Perrin, 25/5/65 (DG20562), CERN/TC/StG 5000 65-3 and 65-4, 16/6/65 et 22/7/65 (DG20031). 23. See for example letter from Gregory to Perrin of 13/9/65 (DG20562), which gives the compositions of the study group (six names without Burger), or the note from Florent to Gregory of 8/11/65 (DG20561) which gives the list of the study group and asks: *Should the name of its Chairman and Secretary appear, and that of Burger'. 24. Schmeissner was a top CERN staff-member and represented the organisation. In the previous scheme for a two-headed management (Florent-Schmeissner), the latter would have been '[taken] off the CERN pay-roll and [made] a pure German', according to Weisskopfs formulation in his letter to Jentschke, 15/4/65 (DG20822). The quote is from Florent, Note..., 9/12/65 (DG20562). 25. Three non-official meetings were held in the presence of these six persons and Burger on 24/3, 23/4 and 18/5, CERN/TC/StG 5000 65-1 and 65-3, 15/6/65 and 16/6/65 (DG20031); letter Weisskopf to Perrin, 25/5/65 (DG20562). 26. Note..., drafted by Florent for the CEA, 9/12/65 (DG20562). 27. The question of the rivalry between national groups has already been analysed in volume 2 with regard to the great debate in 1959 over bringing nationally constructed chambers to CERN (chapters 8.2 and 8.3). 28. Gargamelle, Grandes lignes d'un projet de convention, 2/2/65 (DA20257); letters Gregory to Perrin, 9/3/65 (DG20562); Hampton to Levy-Mandel, 14/4/65 (DG20568); Goure (CEA) to Gregory, 16/4/65 (DG20568); Hampton to Goure, 26/4/65 (DA20257). 29. Broad outline of..., FC/770, 23/4/65. 30. CERN/SPC/203, 4/5/65; memo Gregory, 13/5/65 (DG20568). 31. Letter Weisskopf to Perrin, 25/5/65 (DA20257). 32. Council, 16-17/6/65, minutes. 33. Letters Goure to CERN, 28/10/65, Fleischmann (CEA) to CERN, 2/12/65 (DA20257).

Notes

63

34. Letters Lagarrigue to Gregory, 15/11/68 and 27/1/69 (DG20568 et DA20257), Levy-Mandel to Gregory, 24/ 2/65, and reply, 19/3/69 (DG20257). 35. Letters Pascal (CEA) to Malcor (CAFL), 3/10/69 (DA20257), Malcor to Gregory, 25/11/65 (DA20257), Hampton to Levy-Mandel, 3/5/71 (DA20257). 36. See for example Progress Report on the Data Handling Facilities Necessary for GARGAMELLE, 29/8/1967 (DG 20569). 37. On the establishment of the committee, see Minutes ofGargamelle users meeting held on 29th Nov. 1967 (DA 20257) and Gregory's refinements, letter to Burhop, 21/12/1967 (DG 20568). The practical implementation differed very little from that described in volume 2, chapters 8.5 to 8.7, with regard to bubble chamber collaborations. 38. CERN/TC/StG 5000 6 5 ^ , 22/7/65 (minutes of the meeting of 8/6/65). 39. The 'working speed' of a chamber is measured by the number of expansions it can make per second (each expansion is associated with a photographic exposure). In order to profit fully from the advantages the electronics offer it is essential to increase the chambers' repetition rate. Hence the reactivation of the French studies made the previous year (Projet de chambre a haut taux de repetition, mars 1964, DG20561). Add Etudes sur [...] chambre mixte a haut taux de repetition, 1/9/65 (DG20561). 40. CERN/TC/StG 5000 65-5 to 65-10, 65-13, 66-3, resp. 28/7/65, 31/8/65, 22/9/65,4/11/65,18/11/65, 29/11/65, 23/12/65, 12/1/66 (DG20561). 41. CERN/TC/BEBC 65-1 to 65-3, December 1965 (DG20561). 42. CERN/TC/BEBC 66-12, 15/2/66 (DG20561). 43. CERN/TC/BEBC 66-12, 15/2/66 (DG20561). 44. SPC/218, 2/3/66; CERN/TC/BEBC 66-29, 13/4/66 (DG20561) from which the quotes attributed to Peyrou are taken. The fact that the bubble and electronic communities were deeply divided is eminently evident from this final decision. This point was already dealt with in volume 2, chapter 8.4. 45. Note..., Considerations sur le cout du projet, TC/RF/mk, 14/3/66 (DG20561); SPC/218, 2/3/66; CERN/TC/ BEBC 66-29, 13/4/66 (DG20561). 46. Note..., Considerations sur le cout du projet, TC/RF/mk, 14/3/66 (DG20561). 47. CERN/TC/BEBC 66-29, 13/4/66 (DG20561). 48. CERN/TC/BEBC 66-75, 9/11/66 (DG20561); CERN/SPC/231 and 231/Add., Annex 2, for the meeting of 27/9/66; CERN/SPC/233, 18/11/66, describing the chamber and from which the quote is taken. 49. Add to the previous references Peyrou's report, CERN/SPC/236, prepared for the meeting of 29/11/66, and his letter to 'Dear Friends' of 27/10/66 (DG20562), from which the quotes are taken. 50. Bernard Gregory was CERN Director-General from 1 January 1966. 51. CERN/SPC/231 (meeting of 27/9/66); CERN/SPC/236 (meeting of 29/11/66), quote on page 7. 52. Letter Gregory to Schulte-Meermann, 8/2/67 (DG20563); CERN/SPC/239 (meeting of 15-16/3/67); D. Ph.II/BEBC 67-13, 8/2/67. 53. In June 1966, the CEA had already circulated a first version. See letter CEA, Contracts Office, to CERN, 17/ 6/66 (DG20562). Add letter Peyrou to Goure (CEA), 18/7/66 (DG20562). 54. An added German concern was the question of language. This was solved by drafting a text in three languages and agreeing to do the same for future texts Hnked to BEBC (CERN's official languages are English and French). 55. Contract/letter no 8.424/r, 16/9/66 (DA20258); Reunion au sujet de la convention..., 12/10/66; Projet de convention resultant des discussions..., 12/10/66; letter Goure to Hampton, 5/12/66 (DA20258). 56. The text is in FC/943, 10/5/67. 57. CERN/FC/951, 11/5/67, 5 for the quotes; CERN/FC/964, 13/6/67; Council, 14^15/6/67, minutes, 31-32; Press release, 21/7/67 (DA20259). 58. EBC/5, 12/10/67 (minutes of the meeting of 20/9). J. Meyer had replaced Gregory in the Study Committee as the latter had been nominated DG of CERN. R. Levy-Mandel was head of the CEA's Saturne Department.

64

Gargamelle and BEBC

59. EBC/2, 5/9/67 {Progress Report). The idea was to replace the plates by a transparent hydrogen target in the mixture of neon and hydrogen. 'In this way, it was thought possible with the same photograph to observe the primary interactions in the target and, in the mixture, the electron pairs produced by conversion of gamma from n^ decay' (EBC/2, 5/9/67, 4). 60. EBC/STC/9, 4/12/67; EBC/12, 4/3/68; EBC/STC/14, 12/3/68; EBC/19, 29/5/68 EBC/22, 23/10/68. It is to be noted that this choice of a piston of fibre-glass epoxy would not turn out to be the best one in practice. 61. EBC/29, 1/4/69; letter Teucher to Gregory, 3/1/69 (DG20563). 62. Though it was accepted by the German delegates themselves. Cf EBC/35, 18/11/69, 10. 63. EBC/STC/32, 11/6/69 and memo Florent, 18/6/69 from which the indicated figures and the quotes are taken. 64. It is impossible to Hst the numerous sources used here. See for the construction EBC/47, 23/10/70; EBC/51, 12/3/70; EBC/56, 17/11/70; for the experimental programme, letters Rousset to Cresti, 1/7/71, Perkins to Dear colleagues, 8/7/71, to Jentschke, 9/7/71, Hine to Perkins, 19/7/71, Peyrou to Lehr, 23/8/71, to Jentschke, 2/9/71, etc. 65. These three paragraphs are based on the CERN annual reports and the Courrier CERN. 66. For the last two paragraphs, see Hermann et al. (note 1), chapter 8.

CHAPTER 3

The Difficult Decision, Taken in the 1960s, to Construct a 3^00 GeV Proton Synchrotron in Europe Dominique PESTRE

Contents 3.1 The situation in 1965, when the decision on the ISR was taken 3.2 Revival, slippages caused by the American decision, and sudden halt, 1966-1967 3.2.1 Drafting the new convention 3.2.2 The choice of the site 3.2.3 The brutal setback of November and December 1967. The resolution passed by the German Atomic Energy Advisory Committee 3.3 1968, the year of paradoxes 3.3.1 Rebuilding confidence during the spring, and reorienting the project after the British refusal 3.3.2 The site question in 1968 and at the December Council meeting 3.3.3 On the growing autonomy of the member states vis-a-vis CERN and its Council 3.4 Adams's first attempt to revive the project and the setback in January 1970 3.4.1 Adams's way of posing the problem 3.4.2 The new 300 GeV programme and the decision-making procedure foreseen by Adams 3.4.3 The German refusal 3.5 Adams's second scheme for reviving the project: towards a Genevan solution 3.5.1 Adams's new project: build something cheaper at Geneva 3.5.2 The reactions of physicists: let's increase the energy 3.5.3 The adoption of a revised Adams project 3.6 Conclusion Notes

65

67 70 70 71 74 76 77 79 80 82 83 84 86 87 87 90 91 92 93

In Volume 2 of the History of CERN we published a study on the decision, finally taken by the Council in 1965, to construct the Intersecting Storage Rings, a technically sophisticated machine which was fought for, above all, by the engineers. The preparatory studies and controversies we described there lasted for nearly a decade, and included the prehistory of the machine with which this chapter is concerned^. In that volume, we sketched the method which we considered best suited to the study of decisions on very large equipment for high-energy physics. It was derived from two research traditions which have both proved very fruitful and have been extended into new fields of investigation. The first is that pursued by political scientists who have been working, since the 1960s, on the complexity of the political or military decision-making processes. Allison's study, published in 1971 on the functioning of the American government machinery during the Cuban missile crisis is one of the best examples of this genre. The second tradition is that of British sociologists of science who, in the 1970s and 1980s, revitalised the study of how scientific knowledge is produced. One of their most important tools for doing so was to concentrate on scientific controversies at the frontier of knowledge^. What emerges from both approaches, and is particularly pertinent for us, is the injunction to follow events as they 'actually unfold', to analyse their sequence as 'locally' as possible, and to avoid at all costs comforting anachronisms which overrationaHse human actions. One is to describe in detail the behaviour of individuals and of groups, to explore the situations in which they find themselves and which they help to define. One must not hide the messiness of the world, one must not simplify the intricacy of reasons and motivations nor impose too much a posteriori coherence on the account. At each stage of the historical process which is being analysed it is important to try to identify the chief protagonists and their reciprocal relationships, to describe the issues at stake as perceived by each of them, and to pick out those who, at any given time, are able to impose the 'rules of the game'. In this way one can follow the constant shift of interests and aUiances, one can see how the process evolves, and how the 'choice' takes shape. Within this logic the ultimate result, that which we still call 'the decision', is seen as the final operative moment in a temporal sequence of events, and it often emerges as partly 'unexpected' rather than as the realisation of an ever-present and controlling 'objective' or goal. It is thus important not to treat such processes as point-like decisions in which an optimal-rational choice could be made from an exhaustive Hst of well-studied and defined possibilities. The decisions on very large equipment in complex settings (like CERN) should not be approached as if they were logical choices made at one moment by one group of people who successively 66

The situation in 1965, when the decision on the ISR was taken

67

- define its objectives unambiguously, - consider all the means which could satisfy them, - make, as a result, the only necessary choice. On the contrary, it is essential to remember - that decisions of this kind are spread over long periods of time, that they are the final outcome of a series of micro-decisions which progressively reduce the field of possibilities and the freedom of the actors, rather than being one choice made at a given moment, - that the micro-decisions taken by the actors are often (and perhaps always) taken on the basis of alternatives which are limited in number, unequal in quality, and perceived in the light of the context of the time. In brief, the information at the disposal of the actors is locally evaluated and is never exhaustive nor systematic, - that the actors are not necessarily the same at the beginning and at the end of the process, and that they have their own criteria of what is the right way of handling things. In other words, there is not one rationaUty which dominates the whole process, but several, each peculiar to a group and to a time period, and often in conflict with one another. Speaking very generally, the history we are going to recount here - that of the 300 GeV decision - seems particularly 'chaotic', and subject to quasi-Brownian zig-zags. In this case the partisans of the project, noteworthy for their extraordinary tenacity, had to contend with open opposition and with indifference, had to deal with demands whose simultaneous satisfaction seemed hardly possible, and had to manage economic and political situations which were constantly changing and which differed sharply between member states. To return to the themes we have just adumbrated we can say that here the temporal dimension is more important than ever, that specifically local actions and compromises were dominant, and that no one could ever have more than a partial control on the evolution of the whole process. The element of contingency was ever present in each microdecision, and objections and refusals arose from different, unexpected and changing quarters.

3.1 The situation in 1965, when the decision on the ISR was taken By way of introduction, and somewhat abstractly, we could say that the Council and the CERN management had three problems to solve if they were to sell the 300 GeV project to member states' governments with a reasonable chance of success. The first was to offer a precise technical description of the machine that they wanted. Around 1965 CERN's Director General had such a solution to offer, a solution that had been first spelt out in a report published at the end of 1964 after three years of work. This choice for a classical strong focusing synchrotron of 300 GeV was contested by nobody: the eUte of the European high-energy physics community, the physicists and engineers at CERN, and the national delegates to the Council were all apparently quite happy with it^. Notes: p. 93

68

3-400 GeV Proton Synchrotron in Europe

The second problem that the CERN management had to deal with was the redrafting of the organisation's convention. The reason was that, at the time, more or less everyone thought that the 300 GeV machine would require the building of a new laboratory. The original text which had been drawn up for a single laboratory in Geneva had then to be modified. Two ways of doing this could be considered. The first involved creating a new organisation with its own Council to supervise the 300 GeV centre as the existing Council watched over the Geneva laboratory. In this case it would be necessary to draft a new text and to have it ratified by the member states' parliaments. The alternative was to modify the existing convention to allow for a single organisation, and to have an unchanged CERN Council supervise the two laboratories. The Council, quite sure of itself, appealed to efficiency, simplicity, and coherence in the management of European high-energy physics, and only seriously considered the second alternative"*. The third problem, and the one that seemed to many to be the only difficult one to resolve, concerned the site of the future laboratory. At issue were questions of national prestige and the belief, widely spread at the time, that economic advantages were to be had from having large items of research equipment on one's soil (through industrial contracts, technological fall-outs and so on). One index among others of the importance attached by governments to this is the large number of site proposals made in 1964 and 1965. Nearly all countries offered a site, the countries with federal structures (like Italy or Germany) proposing several alternatives^. In March 1965, with the decision to finance the ISR apparently assured at governmental level, the Council President proposed that a Steering Committee be set up to look into the matter of the other accelerator proposed by the European physics community, the 300 GeV machine. According to current estimates two or three more years would be needed to get the member states to agree to fund this machine^. A year earlier the bulk of the European physicists had strongly criticised this estimate. Since the 300 GeV synchrotron was for them the only interesting accelerator, and since they did not want CERN to risk having governments refuse it on the grounds that they had just funded the ISR, the physicists had proposed that member states be asked either to fund both machines simultaneously, or to drop the ISR programme altogether. In spring 1964, and after consultation with the Council, Victor Weisskopf had decided to disregard this opposition and had chosen to 'sell' the ISR to the member states before initiating the procedure for funding the 300 GeV^. Throughout 1965 the Steering Committee set up to deal with the 300 GeV machine looked into the problems of the convention and of the site. It seems, however, that its members' main concerns remained elsewhere. The financing of the PS improvement programme (elaborated by European physicists to ensure that their machine remained competitive with Brookhaven's AGS) and that of the ISR (just then in its final phase) were of paramount importance. The decision to build the ISR, taken after long and intense lobbying, had immediate effects on the 300 GeV programme. As the physicists had feared, it suddenly became difficult even to find the extremely modest sums of money required to enable a working group to continue its study. At that point, it was Germany which emerged as the most

The situation in 1965, when the decision on the ISR was taken

69

recalcitrant member state. In December its delegates announced to the Council that they were not prepared to vote the finance needed for the additional studies. The short-term consequences were negligible, however, as the Council, in its usual fashion, found a way around this minor obstacle and so had the working group funded^. By contrast the long-term effects of the German position raised considerable concern and the CERN lobby decided to embark on what one may call a policy of revival. In every decision-making process there are always periods of inertia, one of the ways most frequently used by administrators who do not want to refuse head-on a project being to try to wear out its protagonists. To revitalise a project its champions must therefore periodically refloat their ideas, they have to find new paths, new arguments which permit them to make their requests again. The first quarter of 1966 was dedicated to preparing the ground for this kind of renewal of interest. This policy involved action on three fronts. First, the Council and the CERN management tried to constitute the European physics community as a group of independent experts. The aim was to offer to member states an 'independent' estimate of Europe's needs for a new machine. This part of the policy of revival was set in motion by the Director General and by Edoardo Amaldi, and it took the form of the reactivation, in the first quarter of 1966, of ECFA, the European Committee for Future Accelerators created by Weisskopf in 1963. Meetings of ECFA attended both by young physicists and by the hallowed establishment of European physics thus took place throughout 1966^. The second front to cover was to start individually lobbying delegates from the most reluctant member states, or wherever any danger to the project might surface. There were thus discussions about the best way to tie German interests more closely with the 300 GeV project (the Director General, for example, asked Amaldi if he could not perhaps nominate a German physicist as ECFA's Vice-Chairman), and close contact was maintained with Perrin and with Teillac to ensure that the French 45 GeV accelerator project did not interfere with the CERN machine. In this country, traditionally in favour of joint projects, a group of physicists was emerging who felt that national interests should not always be sacrificed to collective ventures - particularly when their British and German colleagues appeared to have no such scruples. Indeed new machines were being commissioned in these two member states, some claimed, so that both countries were less than enthusiastic about the 300 GeV project - and France risked losing on both fronts, nationally and at the European level^^. Finally, it was felt necessary to define a global strategy, to fix the order in which the various questions had to be tackled. It was, for example, desirable to settle the site at the last moment to avoid any member state using blackmail of the kind: we will not participate since our site was not chosen. The CERN lobby thus decided to begin by drafting the new convention. And the question of the site was reduced simply to paying systematic visits to the different places proposed by the European countries.

Notes: p. 93

70

3-400 GeV Proton Synchrotron in Europe

3.2 Revival, slippages caused by the American decision, and sudden halt, 1966-1967 3.2.1 DRAFTING THE NEW CONVENTION The meetings of the Council and of the Committee of Council in June and July 1966 adopted a timescale for the steps to be taken in the medium term in the member states. The first thing to be done was to redraft the convention. Having agreed that the only way to proceed was to have a single organisation managing the two laboratories, the Council invited the CERN management to formalise the results of its debates as quickly as possible so that the changes to be made to the convention could be circulated by the end of the summer. It was made clear that modifications to the original text, adopted in 1953, should be kept to a strict minimum. CERN's existing convention had worked satisfactorily and the Council wanted as little fuss as possible created around this issue^^ On 9 September 1966 the Council President sent a formal letter to the European member states of CERN. After describing the present state of the 300 GeV project, the President asked governments for two things. Firstly, to agree at the Council session in December on the idea of keeping one single organisation managing two laboratories. Secondly, to take a first look at the proposed amendments with a view to agreeing on a final text in 1967^^ In December 1966 no delegation was opposed to the principle of having one single organisation, and the Council took this as a sign that it could continue its work along the envisaged lines. It discussed again the articles and the amendments of the text at its session in June 1967 and set up a Drafting Committee under the Council President to finalise the text. This committee of four met in Stockholm in June, it asked a group of legal experts to consider its work in August, and it presented the text of the new convention to Council delegates during an extraordinary Council session held in September. The final text was adopted by the Council at its meeting in December 1967 by nine votes in favour and none against, though there were five abstentions (Germany, Spain, and the Scandinavian countries). A resolution was also passed inviting the member states to adopt these amendments - which meant, in most cases, a procedure of parliamentary ratification^^. The key point to remember about this new convention is that it remained very close to the spirit of its predecessor, which was analysed in detail in Volume I of the History of CERN. In particular it kept the principle of having several programmes running in parallel, each member state choosing the programmes in which it wished to participate. This had proved an essential element in CERN's functioning since it prevented one or two recalcitrant states from blocking a new initiative which they disliked. This allowed, for example, the 300 GeV project to be launched even if some member states did not want to contribute to it. Only one of the 'traditional' procedures for the functioning of the Council was changed in the new draft, that of the budget vote. The text accepted in 1953 very liberally required that a simple majority suffice to have a budget adopted. That proposed in 1967 raised the threshold to two-thirds. This was a concession to member states' governments. It is

Revival, slippages caused by the American decision, and sudden halt, 1966-1967

71

nevertheless remarkable that no right of veto was introduced - since unanimity was not required - and this despite more restrictive procedures adopted in the early 1960s in ELDO and in ESRO^l 3.2.2 THE CHOICE OF THE SITE As we mentioned earlier almost all of those involved in the 300 GeV negotiations assumed that the accelerator would be built at a site other than Geneva. Two kinds of 'reasons' lay behind their conviction. Firstly it was thought that the machine would be built on the surface (and not in an underground tunnel), mainly to save money and to facilitate the use and maintenance of the equipment. This effectively excluded the existing CERN site. A machine of 2.4 km diameter could not easily be built there as the site was too narrow (it was bounded by the Franco-Swiss border, for example), too heavily populated, and had several topographical and geological disadvantages. The possibility of using the 28 GeV as an injector for the 300 GeV was considered at ECFA meetings in March 1966, but it was also discarded on the grounds that the scheme would seriously perturb the work at the PS during the years of construction without offering substantial economies in the construction costs^^. Another (and perhaps more important) reason for rejecting the CERN site was a cluster of more or less tacit but shared assumptions. To begin with, the future of CERN as a laboratory was guaranteed by the construction of the ISR, so that the 300 GeV could be built somewhere else without risk to the centre at Geneva. Then it was thought to be poUtically more astute not to concentrate all of Europe's resources in one place, and that a different site would be diplomatically preferable. Finally it was felt to be only correct that a region other than that around Geneva should benefit from the technological spin-offs which these big centres were supposed to generate. In brief the establishment of a new laboratory seemed the ideal solution from every point of view^^. This does not mean that no one ever defended the Geneva site. For example, Colin Ramm, the head of one of CERN's divisions, did so repeatedly from 1961 onwards but he remained isolated. (He tried in fact to convince his colleagues that such a solution was materially possible, something often denied.) Geological samples were also taken in the Geneva area and ECFA considered the matter in its sessions in 1966, as we have said. All the same, there was Uttle enthusiasm for the Geneva solution, interest in it never really rose - and the 'results' of every study or sample only tended to confirm what everyone knew in advance: That it was better to install the 300 GeV machine somewhere else^^. The specifications for the choice of a new site were given to the member states in June 1964. They concerned both the topography and the nature of the ground ('Strict requirements on stability, size and flatness have been imposed'), and 'the necessary supplies and services which would have to be provided' (amount and cost of electricity, for example). During the following twelve months 22 offers were received from nine member states, a sure sign of the interest of governments in the scheme. The 300 GeV Steering Committee then drew up a set of guidelines for the decision. First, each country was only Notes: p. 94

72

3^00 GeV Proton Synchrotron in Europe

to submit one offer (the number of proposals was thus reduced to ten). A 'purely facinar report which did not try 'to assess the relative merits of individual sites' (our emphasis) was then to be prepared. Thirdly, the Council was to define 'the machinery to be used for the process of site selection before the comprehensive report was issued'. Finally an intergovernmental meeting was to be arranged to make the final choice^^. The inescapably political character of the decision began to emerge in June 1966 after the debates in the Committee of Council and the SPC. As CERN's Director of Applied Physics put it, even if one or two sites 'could be definitely put lower technically', 'there would still be left a large number among which technical pros and cons could easily be outweighed by economic, political or other factors'. This emerged clearly at the end of the spring: despite the cautious remarks made at the CC meeting by the CERN group asked to study the sites, the member states whose proposals were found less satisfactory reacted strongly (notably Britain). To reassure them the Council accepted the idea that each country nominate one or two experts in geology or soil mechanics. Their task was to facilitate contacts between the Council and the member states' governments, and all relevant files would be put at their disposal. The newly appointed experts met for the first time with the CERN group in Geneva in October 1966^^. This arrangement did not serve to dispel the misgivings, on the contrary. Three months later, in December 1966, the Council President proposed that a restricted committee be set up. It would comprise three people whose authority was beyond doubt and who would be selected from each of the countries which had not offered a site. Rebaptised the Site Evaluation Panel, it first met in February 1967, and was composed of J. Bannier for The Netherlands, J.K Boggild for Denmark, and A. Chavanne for Switzerland. All three men were very influential Council members. (Bannier, for example, was the immediate past President of the Council.) The Site Evaluation Panel was officially instructed to consider 'the most suitable way of submitting the [final] report' to the member states. Its function though was above all to guarantee the impartiality of any assessment and to convince a prion suspicious governments^^. At the December Council session the President also suggested a set of rules for taking the final vote on the site. The procedure was to remain internal to the Council to avoid the terrifying prospect of having nine member states each defending its own site at an intergovernmental conference and so paralysing progress. There were to be two steps. Firstly, a choice would be made to reduce the number of sites to three. This would be settled by a simple majority vote of the Council delegates, each delegation being called on to list the three sites it preferred. Thereafter, and once the member states participating in the 300 GeV programme were known, the choice between the three would be made by taking a second vote^^. The Site Evaluation Panel got down to work in spring 1967. It quickly adopted a more 'technocratic' line which distanced it from the diplomatic caution current until then. By this we mean that it defined its task more ambitiously, aiming to collect and to order the data so as 'to lead to a grading of sites in order of merit, or at least to the production of a short list of the best sites from which a choice can safely be made by Governments without

Revival, slippages caused by the American decision, and sudden halt, 1966-1967

73

further detailed justification and argument' (our emphasis). To do this the panel first identified the several factors shaping the choice. In the autumn they suggested grouping together 'those relating to the construction and development of the Laboratory on the site', 'those relating to the technical operation of the laboratory' and 'those affecting the willingness of people to come and to work in the Laboratory and the way in which families can live there'^^. These broad categories established, the Panel then defined 'a way of grading each individual factor which will allow for rejection of a site failing to reach an acceptable minimum, and which will give a site a bonus for better performance'. Regarding 'the flatness of the site', for example, it thought to take 'the total volume of rock to be excavated as a score', this being normalised once all the sites had been visited. Finally, 'the resulting scores for each factor' were to be 'combined in a rational way [...] and the resulting total or totals used to provide an over-all ranking'. Using the scheme in conjunction with the three broad categories just mentioned, the Site Evaluation Panel, in a report pubUshed in December 1967, assessed the nine sites in competition. It concluded in fact that no site was the best in all three sections simultaneously (a happy result, and one that was probably politically unavoidable). Only two sites obtained the best mark in two categories however (those in France and in Italy), and one site, that in Greece, was at the bottom of the Ust three times^^. The Panel recommended that the Council treats its findings with all necessary prudence. Indeed this exercise in classification was extremely dangerous. In the Council in September 1967 the new President G.W. Funke - whose role called for a mastery of diplomacy stressed that 'the meaning which Mr. Bannier gives to the word 'evaluation' requires some clarification, since each of the thirteen member states will have its own views on the criteria to be applied for the choice of a site' (our emphasis). The Italian delegate, for his part, again stressed that while the Panel's report would undoubtedly be useful, 'it was the Member States who would decide [in the last resort]'. Finally, in the December Council meeting, after having been showered with praise and the usual thanks, the final report of the Site Evaluation Panel was noted without any discussion whatsoever - which was tantamount to 'burying' it. This happened because a new and major problem had been raised by Germany, in the face of which the report was a political obstacle rather than a help^^. Before discussing the main features of the German delegation's position at the December Council session, it seems useful to stop briefly to consider how the site question was handled at CERN. Very schematically we can say that it oscillated between two poles. On the hand, it was recognised that such a choice was above all a poHtical affair to be treated as such since the member states were convinced that a matter of strategic interest was at stake. On the other hand, there was the idea that it was possible to draw up rules and to define more 'objective' criteria which would enable the sites to be ranked and the choice made on 'rational' grounds. The first, pragmatic approach saw the solution to the problem lying in diplomacy, the second placed its faith in experts. The first accepted that, whether one liked it or not, any objective judgement could always be disputed by the member states if they chose to do so, while the second was based on the hope that a certain Notes: p. 94

74

3-400 GeV Proton Synchrotron in Europe

amount of goodwill was available to be tapped and that a minimum of rationality could be imposed on the choice. The senior CERN management and members of the Council had one main concern throughout these negotiations - that the first pattern of behaviour would too obviously dominate the process. This would effectively place them at the mercy of the member states' governments and make them vulnerable to the wishes of national administrations - a situation that the management and the Council had consciously manoeuvred to avoid for fifteen years. Hence they preferred to push the alternative approach to its limits. For one thing it was more in keeping, they felt, with the nature of the place. The vitality and efficiency of CERN, they believed, derived from the fact that, unlike other European scientific centres, it had never been used as a political football in interstate rivalries. For another the scientific community 'spontaneously' tended to think that technical solutions could be found and that political considerations were nothing other than perturbations which muddied the otherwise clear waters. The policy followed by the leading CERN engineers and the Site Evaluation Panel consisted thus in trying to impose a technical rationality on the debate, in trying to make the decision a choice between numbers arrived at by experts, in trying to reduce to the minimum the direct intervention of the member states by keeping the debate in the 'depoliticised' context of the Council. In short their aim was to try to classify the sites according to (their) neutral criteria and to stop the issue falling prey to the give and take, and blackmail of political horsetrading^^. 3.2.3 THE BRUTAL SETBACK OF NOVEMBER AND DECEMBER 1967. THE RESOLUTION PASSED BY THE GERMAN ATOMIC ENERGY ADVISORY COMMITTEE In parallel with the debates on the convention and the future site of the laboratory, the Council sought to obtain member state finance for the 300 GeV project. To this end in May 1967 the CERN management published the final results of its scientific, technical and budgetary studies undertaken since the project had been revived in 1966. Three reports were produced. The first was an addendum of some 100 pages to the 1964 'Design Study of a 300 GeV Proton Synchrotron' which gave a technical description of the machine. Then there was a three-volume, 750-page report entitled 'Study of the Uses of a 300 GeV Proton Synchrotron'. These described the experimental programme of the future machine as envisaged by the physicists at the time. The volumes dealt with detection techniques as well as the layout of experimental halls and the beam transport systems. Finally there was a general report from ECFA which was presented to the Council by Edoardo Amaldi at its June 1967 session. Reviewing the studies made during 1963 and 1964, these reports claimed that the initial choices were still valid, and that 'the 300 GeV accelerator, as presently conceived, should do what is asked of it and that the experimental layouts envisaged are wellsuited to its efficient exploitation'-^^. If these reports were pubhshed more or less simultaneously in May 1967 it was because it was thought that a decision would be possible in the months to come. This assumption

Revival, slippages caused by the American decision, and sudden halt, 1966-1967

75

was reinforced by Belgium's official statement, in July, of its wish to participate in the project, by an expression of similar sentiments by Austria and by France in the autumn, and by the fact that Mr Francis himself told the Council in June that 'the United Kingdom hoped to be in a position to take a decision in December, if not before'. The British position, we should add, was probably Hnked to the tour of European capitals then being undertaken by the new Labour Prime Minister Harold Wilson with a view to the UK joining the European Community^^. There was also a second, conjunctural but strategic reason, for this acceleration of the pace. After intense battles the site of the competing American project had been chosen (the laboratory was to be built near Chicago), the funds for the project had been guaranteed in the spring, and Robert Wilson had been nominated as the director. In short Europe risked once more being left behind in the competition with the USA if a similar decision was not soon taken in favour of the 300 GeV European project. During the summer of 1967, however, the appointment of Wilson had effects other than simply creating anxiety. No sooner had he taken up the job than the director of the new American laboratory reviewed all the existing designs for the accelerator and proposed a series of radical technical modifications. These, he claimed, would lead to a superior machine (i.e. an increase in its operating energy) at a reduced cost. Naturally the news quickly spread to Europe and after returning from a trip to the United States, Amaldi and Jentschke explained how impressed they were by the highly-energetic Bob Wilson^^. The sudden brake on the 300 GeV project arrived from Germany at the end of November. Justifying their doubts by appeaUng to the new concepts suggested by Wilson, the German Atomic Energy Advisory Committee insisted that CERN radically redesign its machine. In a two-page text which it released after its meeting on 14 November the committee stated 'that the decision to build [the European 300 GeV] accelerator should not be taken under pressure of time and should take into account all aspects of the project'. More specifically it asked (according to the 'translation' made by the Director General) whether 'modern techniques [were] used in the present CERN design' (mentioning for example 'superconducting magnets' and 'beam handling [techniques] by computer'), and to what extent 'an advanced design and close cost calculation may [not] help to cut construction costs of the accelerator'. Suggesting that the machine's conception was obsolete, that it incorporated outdated techniques, and that its cost was excessive and unjustifiable, the Atomic Energy Advisory Committee proposed that the accelerator be rethought. In short its text effectively put a stop to any hopes that a decision could be taken in December^^. The immediate reaction in CERN and in ECFA was to reject firmly the criticisms of the German committee. People in Geneva took the objections one by one and tried to demonstrate that they were ill-informed and unjustified. Regarding the costs, for example, they remarked that new American figures could appear to be low to the unwary, but that in reality they overlooked expenditures which would be necessary, and which had already been included in CERN's estimates. 'Owing to the pecuharities of the US accounting system', said the Director General, 'considerable extra sums will be spent on development. Notes: p. 94

76

3^00 GeV Proton Synchrotron in Europe

experimental equipment and operating costs during the construction period'. In any event the difference between the cost of the two schemes, which had quite different specifications anyway, was of the order of 15% at most^^. As for the technical design of the European machine, CERN tried 'to show that the European builders were so well aware of the alleged 'recent developments' [those proposed by Wilson] that they had already incorporated some of them several years before'. According to Gregory and Amaldi 'the techniques of orbit correction [through 'pick-up stations, correction devices and computer'] is now standard practice on the CERN PS'. The separate function magnets (as proposed by Wilson for the US machine), they added, were already being used at CERN's electron storage ring CESAR, as well as at Frascati and at Orsay. Only one real concession was made regarding these magnets. In the December Council meeting Amaldi admitted that it might be a good idea again to consider using them for Europe's 300 GeV project^^ This debate obviously stopped the Council taking any decision on the European accelerator in December. Certain delegates were plainly irritated, even frustrated. Perrin, for example, said that he was 'most disturbed' by this new contre-temps, and let it be known that he was not particularly impressed by the arguments advanced by the German committee. After all, he pointed out, it is only after the money has been voted and the director appointed that a new push is given to a project and the design finalised. Before that the project can only be sketched in broad outline. He went on to remind the delegates that the strong focusing principle was only discovered after the money had been obtained for the 28 GeV PS in 1952/53, that this did not hinder its immediate integration into new plans for the machine, and that it was the nomination of Wilson himself that had introduced a new dynamic into the American process. It was surely necessary to stop dithering about, said Perrin, to make the funds for Europe's machine available as a matter of urgency, and to nominate the project director as soon as possible. The definite design could then be settled taking into account all the new ideas, to the satisfaction of everyone^^.

3.3 1968, the year of paradoxes The hopes of the protagonists of the 300 GeV programme were twice dashed in the space of the twelve months which separated the Council meetings of December 1967 and December 1968. In the closing days of 1967 it was the German authorities who seemed to want to block or at least to put a brake on the decision-making process, and general gloom prevailed at Geneva. The arguments used by the Atomic Energy Advisory Committee against the European project were technico-scientific. This was altogether novel in the history of CERN. Traditionally, member states opposed projects on the grounds of financial considerations. In fact the German delegation, by questioning CERN's technical excellence and the official view of the physics community as expressed through ECFA, had violated a major taboo. They had broken the tacit convention not to discuss pubhcly one's disagreements with technical choices put forward for the Geneva laboratory. By cutting

1968, the year of paradoxes

11

across the normal channels which enabled the European scientific community to speak with one voice, and in so doing by showing that the experts were not in agreement, the German Atomic Energy Advisory Committee gave member states' governments a new means of opposing the requests made by CERN and by the Council. The main activity at CERN early in 1968 was thus to try to close the breach, to try to restore the confidence of the member states, and to reconstitute ECFA (and the CERN Scientific Policy Committee) as the single expert groups whose views were not challengeable. After two or three months of discussion, and with all parties making the requisite concessions, the operation appeared to be achieving its objectives: in the spring, the Germans aligned themselves with CERN's arguments. At this point yet another thunderbolt struck from a sky that had seemed to be clearing. At the June 1968 Council meeting the British delegation reported that its government had refused to participate in the project. As Britain contributed about a quarter of CERN's budget, and often determined the vote of a certain number of countries (notably the Scandinavians), the project obviously had to be profoundly revised. In particular its budget would have to be reduced, as the countries who were going to participate in the programme certainly did not want to see their contribution increased. Let us explore these points in greater detail. 3.3.1 REBUILDING CONFIDENCE DURING THE SPRING, AND REORIENTING THE PROJECT AFTER THE BRITISH REFUSAL On 8 and 9 February 1968 a general meeting of ECFA was held at CERN in the presence of Robert Wilson. The questions asked by the German Atomic Energy Advisory Committee were on everybody's mind. Four days later the SPC in its turn met and agreed on an official resolution to be submitted to the Council. It stressed again that the differences between the two projects were far from being as important as some had been led to believe, and it reaffirmed the SPC's conviction that 'the technical studies and the present estimates' for the European 300 GeV constituted 'an altogether satisfactory base on which to take [Council] decisions'. The SPC recommended however that a Steering Committee be set up to assist the Director-General. Its task would be to keep an eye on new developments likely to appear in accelerator technology, and to address the extremely urgent question of the nomination of a project director. This Committee, comprised of six persons outside CERN, including Wolfgang Paul from Bonn, and three insiders, met on 15 March. It called for a new series of technical studies, particularly on the 'magnet design, with the aim of making a magnet model of a Wilson type'^^. At the extraordinary Council session of March 1968 the criticisms raised in November were no longer a major issue - at least officially. The German and the British delegations (who had supported the German request in December) stated that they had the impression that the replies given were 'complete, clear and entirely satisfactory', to use Brian Flower's formulation. Once again, then, attention was focussed on the task of getting governments to declare their intention to participate in the 300 GeV programme^"*. Notes: pp. 94 ff.

78

3-400 GeV Proton Synchrotron in Europe

The overriding impression given at the Council was that most of the small countries would not take a position until the four large ones had reached an agreement, and that there were still some hesitations amongst the latter. The inclination to oppose the project in Germany was attributed to Heisenberg, von Weizsacker and Maier-Leibnitz 'who propagate the idea that high-energy physics is so costly that one can no longer afford duplication'. Since the Wilson machine was already under construction, they claimed, one ought not therefore to finance the European 300 GeV machine. In Italy, on the other hand, the high-energy physicists strongly backed the project, the rest of the scientific community did not overtly oppose it - but one had to wait for the formation of a new government. As for the British, there were the fears arising from their financial difficulties and, above all, from their reactions to the veto, announced by General de Gaulle, against the entry of Great Britain into the Common Market^^. As we have already said the British response was negative and undoubtedly due to monetary and political considerations. It was announced to the June Council session by Professor Flowers. The British delegate, however, took an altogether unusual position in declaring publicly, but in his personal capacity, that he regretted the decision made by his government. The Science Research Council, he said, had made the 300 GeV a top priority, and he hoped that the project would start despite the decision taken in his country. At the same time British physicists would continue their eff'orts to persuade the government that their country should join the project at a later date. And since Wolfgang Paul declared that the German delegation regretted the British decision - 'all the more so since [his delegation] hoped to be in a position to give a positive reply' towards the autumn - the climate at the meeting, although somewhat troubled, was not altogether discouraging. The chairman of the SPC, for his part, declared that a small study group had already thought through the consequences of one country not participating in the project and he announced that the Committee would present, in September, a programme with its budget reduced by 2030%. It had been assumed, he pointed out, that 'the nominal energy and intensity of the machine should remain the same' so that the reductions would need to be made in the experimental areas or by spreading the time to construct the machine over a longer period36. Despite these positive signs it was important to prevent all risk of contagion (according to certain sources the British government was pursuing diplomatic initiatives to have the Germans refuse to sustain the project^^), and not to lose the momentum acquired since March. It was thus essential that France did not waver - even though it was in the midst of the major social crisis of May 1968. Lobbying also got under way again in Germany and in Italy, with tried and trusted friends being contacted once more. Positive results were rapidly achieved, and around August and September these two countries agreed to participate in the 300 GeV programme^^. In September, then, everyone was once again very optimistic, and the nomination of a director for the 300 GeV programme appeared to be the most pressing step to be taken. At its meeting in October 1968 ECFA agreed 'that a scientifically meaningful [300 GeV] programme can be realized within 75% annual expenditure compared to the one originally

79

1968, the year of paradoxes

foreseen', 'that a number of [technical] alternatives exist which [...] can be kept within the same financial limit and are [...] scientifically valid' but that the definite choices could only be taken by the future director. 'For this reason', the report proposed, 'ECFA urges that the nomination of the Director General of the new Laboratory should be taken as soon as possible'^^. Towards the middle of November and after a number of rapid consultations the Committee of Council and the Scientific Policy Committee unanimously chose John Adams for the task. Adams was of course the constructor of the 28 GeV PS at CERN in the 1950s, and now in charge of basic and industrial research for the British Atomic Energy Authority (which included the laboratories of Harwell and of Culham). Asked to take over immediately the direction of the 300 GeV programme within the framework of CERN, it was understood that Adams would become the Director General of Laboratory II as soon as it was officially set up, and that he would remain there throughout the construction phase of the accelerator"^^. 3.3.2 THE SITE QUESTION IN 1968 AND AT THE DECEMBER COUNCIL MEETING As we have already mentioned, in December 1967 the report of the Site Evaluation Panel was submitted to the Council. The Council took note of it without debating its contents, asking member states to comment on it if they chose. Within two months all governments - except that of France whose site emerged as the best one in the report - sent their criticisms to the Director-General. Overall the tone was critical and indicative of a refusal to accept the conclusions. On 23 February, for example, the Belgian delegation commented ironically on the techniques which the Panel had used. It wrote that 'to give a value simultaneously to the topography, to the uniformity of the terrain, to the hardness and resistance of the ground, [...], to the geographical location, to the social consequences of the climate or of the housing possibilities or of the attraction of the region, etc. ..., and to sum all these figures to arrive at a final value, necessarily implies an important subjective component'. While recognizing that the 'wise men' who had drafted the text 'had a number of remarkable qualities', the Belgian delegation declared that it could not consider their report as constituting an evaluation in the strict sense of the term, 'a judgment or an arbitration', but rather as a simple 'document providing information'^^ Twenty days later it was, for example, Austria's turn to reject radically the report. Austria's criticisms ranged from the refusal of the conclusions reached by the expert geologist appointed by CERN, the Norwegian Bjerrum, to the rejection of the cocktail of criteria used for the assessment. According to the Austrian delegation, the most important criteria had changed during the course of the study and yet they had been treated as if they were static. It did not take account for example of the improvements which could be made to the site notably in social and cultural terms from now until it was brought into use^^. In March 1968 a prudent Council thus invited the member states to take note of the comments received and to bear them in mind when making their own assessment. AH Notes: p. 95

80

3—400 GeV Proton Synchrotron in Europe

discussion of particular conclusions was avoided. Instead, the Council devoted its attention to the ballot procedure to be adopted for the final selection. Concerning the principle of having the choice made by states via two successive votes organised by the Council, it decided in favour of two public ballots"^^. From this time on it seems as though everyone understood very clearly that the question was very delicate, that there was no way of avoiding horsetrading between the states, that the final choice was clearly going to be at least as difficult as that in the United States. In October the Council therefore decided that 'no new study was really necessary to enable the governments of member states to take a decision on the site'. All the same, the Council could not but allow those states who were not satisfied with the report of the Site Evaluation Panel to ask for, or to carry out themselves, new expert studies. As the report was now public the Council necessarily had to communicate to all other governments new information which was sent to it by any of the concerned parties^. In December it was once again the question of how to organise the decision which was on everyone's mind. To simpUfy enormously, one can say that three questions constantly interfered with the debate making it extremely chaotic and disorganised. Firstly, should balloting start before a state had had an opportunity to improve the image of its site unjustly 'blackened' by previous reports? Secondly, was it possible to choose a site before the list of member states participating in the 300 GeV programme was definitely fixed? the advantage claimed for such a procedure being that the Director of Laboratory II could thus make an immediate start on the definitive study of the machine. Finally, what sites had the right to compete with each other and what delegations would be authorised to vote? - a major stumbHng block being those countries that had offered a site but had not yet indicated their definite wish to take part in the programme. The debate was long and concluded without any clear agreement being reached. It is true, all the same, that a new variable had just been introduced by the Council - the nomination of John Adams as project director - and that it was up to him, in his way, to come to grips with the problem as a whole"^^. 3.3.3 ON THE GROWING AUTONOMY OF THE MEMBER STATES VIS-A-VIS CERN AND ITS COUNCIL The episodes which we have just described illustrate one crucial point. This is that, during the negotiations around the 300 GeV project, the traditional relationships between the member states and the Geneva laboratory began to be dramatically changed. The nature of this relation until the mid-1960s was analysed in detail in Volume II of the History of CERN. The major conclusion reached there was that, for a number of conjunctural historical reasons, the CERN Council was rather the spokesman of the laboratory and of the European physics community before member state governments than what it was legally supposed to be: a committee comprising member states' representatives whose task it was to control the organisation in their governments' names.

1968, the year of paradoxes

81

We used three main arguments to justify this claim. Firstly, we showed that the 'representatives' of governments in the Council held their positions for a surprisingly, not to say abnormally, long time. It was the 'founding fathers' of CERN who were in key posts for almost twenty years. This enabled them to keep national administrations at arm's length and to defend before their governments the enfant prodige that was CERN. We also showed how the Council functioned as a highly structured pressure group, whose key members organised all decisions as they wanted them, in close consultation with the scientific management of CERN. At the core of this group, and without being exhaustive one finds Bannier for the Netherlands, Willems for Belgium, Funke for Sweden, Amaldi for Italy, Perrin for France and, to a somewhat lesser extent, Schulte-Mermann for Germany and Adams for the United Kingdom. Finally, we analysed in some detail certain events in the life of the organisation, events during which certain states - in fact the United Kingdom - tried to break this hermetically closed structure. The British government, for example, once tried to bypass the Council by subjecting it to instructions arrived at in direct negotiations between the relevant ministers in member states - but it had to capitulate to the resistance and the power of what we have called the CERN lobby"^^. From 1967 onwards the tone changed. Clearly, the state apparatuses became more weighty, the most effective of these being without doubt that of the Federal Republic of Germany. In contrast to what we find with France and with Italy, where the 'traditional' situation persisted - Amaldi and Perrin along with Gregory and Puppi, still elaborated and controlled rather well the French and Italian positions - the German delegates to the Council found it increasingly difficult to anticipate the line which they would have to defend. This change came through the German Atomic Energy Advisory Committee, a committee which comprised not only people from academia (among which high-energy physicists were in a minority!) but also industriaUsts and administrators. In 1967, the demands of the committee were three: minimise and better control expenditure, enforce what had then become the European rule of just return (i.e., spend in any country that proportion of the budget which it contributes), and ensure that industry has a direct role in the conception and construction of major equipment. The aim then was to reduce somewhat the autonomy of the 'CERN system' and to bring it more closely in line with the current norm (as prevailing in ELDO or ESRO for example), it was to give back all their power to the state bureaucracies which would now have a kind of right of veto, it was to reinsert CERN into the industrial context and to make it more useful socially. Several changes in the political and economic situations facilitated the expression of these new tendencies. Firstly, there were the growing economic difficulties, almost structural in the case of Great Britain, more differentiated for other European countries, difficulties which militated for stricter controls on all non-productive expenditures. Then there were the social and political conflicts which had broken out in the developed countries - of which the protests against the Vietnam war and the revolt of students in the spring of 1968 were two indices - and which often turned into a criticism of science, of its authoritarian attitudes, and of its compromises. Finally, there was the fact that physics, and high-energy physics in particular, was no longer regarded as being the most important Notes: p. 95

82

3-400 GeV Proton Synchrotron in Europe

scientific discipline in society. In the case of Germany, we should add the more general wish to have the new balance of forces which had been gradually set in place between European states recognised, and to put a stop to attitudes of exclusion or of condescension towards the country defeated in the previous war. We see this determination on the part of the German delegation in its crusade to have German recognised as the third official language of the Council, and regarding the site of the future laboratory: in 1967 and 1968 Germany appears as really determined to have its site of Drensteinfurt chosen. During these years, however, the success of these new tendencies remained somewhat meagre. It is true that the Atomic Energy Advisory Committee blocked the decisionmaking process in December 1967. On the other hand it withdrew most of its criticisms in February 1968 and accepted unanimously to recommend to its government that Germany participate in the 300 GeV programme. And although the insistence on industrial linkages and on the principle of just return were reaffirmed by the Committee in its new resolution, these were not preconditions nor even strongly insisted upon. By contrast they were central in the agreement between CERN, France and Germany, which was reached at the same time, to construct a big European bubble chamber. In this contract German was recognised as being a language on an equal footing with English and with French, just return was admitted more or less expHcitly for contracts on Germany's insistence, and industry was invited to participate in the construction of the superconducting magnet^^. It was also the first time that the British government carried out its threat to withdraw from a project. That said, we have also mentioned the very firm attitude of the British delegate, who publicly regretted the choice made by his country and exhorted other countries not to take it into account. This was hardly an uncontroversial gesture, yet it was not sanctioned in any way by a government which tried, on the contrary and in public, to soften the blow caused by its refusal. In conclusion there certainly was a real change in the atmosphere but a change still in the first phases of its development. While the CERN system had certainly been more seriously attacked than ever before, it was still largely in place.

3.4 Adams's first attempt to revive the project and the setbacli in January 1970 The newly nominated Project Director, John Adams, first exposed his ideas during a Committee of Council meeting in January 1969. A month later he submitted to the SPC and to the CC a new document. In the traditional CERN manner the happy few met the night before over dinner. Present on this occasion were Amaldi and Smoquina for Italy, Gentner and Haunschild for Germany, Kummer for Austria, Martin for France (Perrin could not come), Willems for Belgium, Chavanne for Switzerland, as well as Funke, the Council President, Gregory, Adams and Hampton, CERN's Director of Administration. John Adams's proposals were thus discussed and an overall plan of attack was elaborated^^.

Adams's first attempt to revive the project and the setback in January 1970

83

3.4.1 ADAMS'S WAY OF POSING THE PROBLEM The question of the technical choices to be made and of the comparison with Wilson's machine remained an implicit concern in member states' administrations, so the Committee of Council firstly recommended to Adams that he draft a policy document which discussed these in detail. This document of more than 40 pages long was ready in May, and it shows what was and what would be Adams' philosophy as Director of the 300 GeV project. To a first approximation we might say that it was pragmatic, that it confronted problems head-on, that it was open-minded, and that it sought to avoid easy and hasty decisions. Indeed the logic of the report is worth spelUng out as it throws considerable Ught on Adams's personality"^^. As the decision-making process had been going for a long time Adams began his text by summarising all that had taken place since the beginning of the 1960s. He ended this part of his expose by presenting the research done in 1968 by the Steering Committee on accelerating techniques at 300 GeV (seven European working groups had studied this question^^). In the second part of the report Adams tackled the question of the design study pubHshed in 1964 by CERN - the point of comparison being of course Wilson's new ideas. In this section, and contrary to what many of his colleagues had done, Adams chose not to defend systematically the proposals made by the European engineers, but to explain their approach, to illustrate the choices they had made - and to show that their results could not simply be dismissed with a wave of the hand. The conception of an accelerator begins by the choice of the type of magnet, John Adams reminded his readers. 'The closed H-type magnet or window-frame magnet [...] now proposed for the NAL [Chicago] design, was considered [at CERN at the beginning of the 60s]', he explained but it was 'discarded on the grounds of greater construction cost, limited access to the vacuum chamber and greater risk of radiation damage to the coils'. According to Adams the recent studies undertaken in the United States and at CERN did not raise any doubts about the vaUdity of this conclusion. On the other hand, he pointed out, the choice of a new objective could lead one to another conclusion. If one's goal was for example to increase the energy of the machine stepwise, as did Wilson, then the use of H-type magnets could be of some advantage. All the same Adams recommended prudence since the costs of maintenance and of use were often inversely proportional to those of construction. The gain made here thus risked being 'at the cost of more expensive operating conditions'. For the magnets chosen, continued Adams, it was the size of the vacuum chamber and the radius of the accelerator that were to be fixed, and therefrom the majority of the machine's parameters. Taking a pedagogic approach, he explained why 'aperture requirements together with the average radius determine so much of the cost' and how the choice here was essentially a matter of judgment in the Ught of two contradictory requirements. 'Overoptimism [...] may lead to attractive capital cost reductions for the initial installation', Adams wrote, but as a result one risked compromising flexibiUty and the future development of the machine. Going into considerably more detail than one would Notes: p. 95

84

3-^00 GeV Proton Synchrotron in Europe

expect for a report whose primary function was political, Adams showed how the design made in 1964 arrived at its proposals for the vacuum chamber, drawing attention to where assumptions were made and choices taken. In short, he did not present the decisions which were made as the only ones possible and preferred to re-open some black boxes. This allowed him to nuance the evidence favouring Robert Wilson's choice, to show where he had taken risks and where he had seemed to be rather conservative, to show in fact that the final choice was still an open question. In sum, Adams led his readers to see that the 1964 report did not in any way err on the side of conservatism - which was not to say that one should not consider with great attention the latest technical report from NAL. The systematic analysis of the work done by the Americans was undertaken in the third part of the report. It dealt with new technologies for accelerators 'which proved of some attraction to nuclear physicists and to the sponsors of the project'. The questions touched on here included the appUcation of cybernetics to accelerator control, superconducting coils, and electron ring accelerators. Adams's view, notably on the last two points, was that these techniques would not be feasible in the short term, and that they would be better exploited in the next generation of machines. These conclusions were reinforced strongly by the main scientific members of the Council at its June session. Thus Wilkinson reminded those present that, according to British experts, 'the development of superconducting magnets appropriate for this type of project would probably take from 5 to 10 years', that 'the application to accelerators of the principle of electron rings would only be possible at a date which could not now be foreseen' and that the costs of these projects were 'as uncertain as their time scales'^^ Whatever was done, Adams concluded, the final design could only be definitely fixed after the team of accelerator builders had been recruited. This required that the programme be officially accepted and that its budget be voted. For the moment Adams only chose to set up a Machine Advisory Committee comprising CERN engineers and European experts whose role was to keep in touch with all technical questions. 3.4.2 THE NEW 300 GeV PROGRAMME AND THE DECISION-MAKING PROCEDURE FORESEEN BY ADAMS The attitude adopted by John Adams during these first months of 1969 contrasted sharply to that adopted at CERN during the preceding years. Not only did Adams seem more open and less quick to justify systematically CERN choices, but he was also ready to admit that not everything was financially possible and that CERN and particle physicists were not necessarily entitled to everything that they wanted. Reassuring and very professional, his proposals were received with warmth, at least if one is to judge by the atmosphere which prevailed at the June Council meeting. It was nevertheless evident that the most deHcate issue, that of actually proceeding with the project, was still not settled. Happily for Adams all the elements required for a favourable decision seemed to be in place. The competing American programme was advancing rapidly, the parliamentary ratifications of the new convention were well under

Adams's first attempt to revive the project and the setback in January 1970

85

way, six member states who contributed nearly three quarters of CERN's budget had declared their intention of participating in the new programme - and Adams was the uncontested director of the project and his methods of working had been well accepted! The next step was thus to test successively all the links in the chain and to arrive at a final decision at an extraordinary Council meeting to be held in October^^. The first step was taken at the Council in June 1969. On this occasion Adams foresaw that the Council would accept 'the programme definition document [...] as a proper description of the 300 GeV programme'. This decision pertained to a 'programme which member states are invited to join and will be asked to approve in October'. In this programme, reduced to take account of the (temporary?) withdrawal of the British, the initial energy of the accelerator was fixed at 200 GeV, to be increased to 300 GeV in a second phase. A single experimental zone was foreseen, though the possibility of constructing a second was not excluded. Finally, the cost was reduced from 1776 MSF to 1335 MSF (at 1967 prices). The construction period was estimated to be at most eight years, to be reduced if more money was available. The first year would be devoted to the recruitment of personnel and to the final definition of the design^^. The second step, unofficial in terms of CERN's rules, was however the most important. Between June and October 'those Member States who intend to participate in the Programme would arrange amongst themselves high level meetings, possibly involving Ministers, to discuss and agree which of the present sites [...] is acceptable to them' (our emphasis). Once this potentially explosive question of the site was resolved between the countries who were participating in the programme, it would be advisable for them to obtain the support of the others, for example at a meeting of the Committee of Council. At this moment the definite text of the programme definition could be drawn up and officially submitted to member states. A brief remark is to be made here on Adams's pragmatism. Having seen what had happened during the previous four years, he openly admitted that a radical break with the rules and 'the spirit of CERN' was inevitable in this business. Since governments attached great importance to the question of the site he judged it preferable to recognise the fact and to leave them to take the decision between themselves. It was just too bad that that went against CERN's principles and the balloting procedures defined by the Council^"*. The official acceptance of the programme, the third and last step, would take place at the extraordinary Council meeting in October. 'The Programme Definition document would then be put to the vote in Council', Adams wrote, the two-thirds majority required by the Convention to create a new programme being certainly achieved. The letters of intention from the member states who wished to participate in the construction of the 300 GeV machine would then be officially submitted, the Director-General of the new laboratory would be officially appointed by the member state representatives, and the budget would be voted. The teams could then be recruited and the design reconsidered component by component^^. Everything took place as expected at the June Council session in an atmosphere of trust. Sweden was the only country to abstain from the programme proposed by John Adams. Notes: p. 95

86

3-400 GeV Proton Synchrotron in Europe

On 20 August, in a confidential letter sent to all members of Council, Adams nevertheless expressed his anxiety about the slow progress being made in Germany and in France. Minister Stoltenberg wanted to know what France's intentions were before asking the German cabinet to engage itself definitively, while Paris had fallen prey to post-GauUism. In particular the new President, Georges Pompidou, and his ministers wanted French participation in the 300 GeV project to be reconsidered in the light of the country's monetary situation, the franc having been devalued on 8 August. Fearing for the negative psychological effects of a Council meeting which could not move ahead, Adams suggested that the session in October should be suspended if phase 2 of his plan - the announcement of the participation of at least six countries and an agreement on the site - had not been achieved by mid-September. In the weeks which followed everyone came round to Adams's position, and the October Council meeting was effectively cancelled^^. Around 12 September the French delegates effectively let it be known that the major choices were being taken in their country but that the French decision would not be known until after the interministerial meeting which would be held around 10 November. To add to Adams's bad luck, the German government was to fall in its turn, and before having taken a decision. It seemed difficult to imagine that the new government would have the time to make its choice before the Committee of Council meeting on 13 November. Now it was even the possibility of a final decision at the December Council meeting which seemed to be in doubt! The ship being piloted by Adams seemed once again to have been deviated by the demons of inertia lurking in the depths^^. 3.4.3 THE GERMAN REFUSAL In fact the break - for there was going to be a break - was not caused by inertia or by the ups and downs of the political and economic life of the twelve member states, but by the intransigence of the new German government concerning the site. In December there was a slight improvement in the overall situation. On 11 November France confirmed its participation in the 300 GeV programme, Germany did so a month later, and the Swiss did so on 19 December. At the same time, the German government added, in its press release, a rather menacing phrase, a phrase carefully avoided by the others and which looked very much like blackmail. It was: 'Should a decision in favour of Drensteinfurt [the German site] not be reached, the Federal Cabinet will consider this matter again'. Cautious, and perhaps just a little bitter, and since anyway the matter could not now be settled except at a very high level, the December Council session discussed only CERNMeyrin and did not deal with the subject of the 300 GeV machine. It only 'took note' of a declaration read by the Council President. In it Funke stated that a last problem remained, that of the site. He had learned, he said, that a ministerial meeting of the six would shortly be held 'with the view to facilitate the decision to be taken', adding that he hoped that work on the programme could get under way at the beginning of the following year^^. Early in January the Swiss government organised for the 28th and 29th a meeting to be attended by ministers from Austria, Belgium, France, Germany, Italy and Switzerland. Its

Adams's second scheme for reviving the project: towards a Genevan solution

87

aim was of course to decide on the site of the future European synchrotron. From 7 January onwards, Adams began to plan the next steps in the campaign. He asked the four countries which had not yet submitted the instruments of ratification for the new Convention, namely Belgium, Italy, the Netherlands and Sweden, to do before the end of the month. In this way, an extraordinary Council session could be held at the end of February and the programme could be launched in March. On 15 January, the Swiss Departement Politique Federal officially announced to the press that the conference would take place, while a debate on the question was held the following day in the German federal assembly ^^. Ten days later the conference was cancelled, 'the minister of foreign affairs of the German Federal Republic [having] asked [the Swiss Departement Politique Federal] that this meeting be postponed to a later date'. It is still too early to have access to the archives which would allow us to identify precisely the motives of the various protagonists in this affair, but it seems as though the German government had understood that the site at Drensteinfurt would not be supported at the conference in Geneva. Certainly, deals were being struck behind closed doors. For example in their book published in 1967 Goldsmith and Shaw remark that there was an agreement made between Belgium and France, the latter accepting to support the Belgian site if Brussels agreed to purchase Mirage fighters. Certainly too, Germany wanted everybody to understand clearly that it attached enormous importance to this question. One point is clear, however: member state governments had now profoundly encroached on the traditional prerogatives of the Council. In fact, the latter had effectively been stripped of them^^.

3.5 Adams's second scheme for reviving the project: towards a Genevan solution In a certain sense everything was lost. A setback at this level, the level of ministers, was not easily overcome. Perhaps some measures could be taken after a few months or years to enable everyone to save face, but, in the short term, the situation was gloomy. All the more so since Robert Wilson was advancing with giant strides on the planes of Illinois, and interest in the European project was declining proportionately. In fact people began to say that one should reconsider from scratch the entire question of Europe's future accelerators. But this was not to take account of the imagination and of the sense of reality of a John Adams, paid to construct this machine, and aware of the shock which this first setback had caused at CERN. 3.5.1 ADAMS'S NEW PROJECT: BUILD SOMETHING CHEAPER AT GENEVA In the weeks following the cancellation of the ministerial conference in Geneva, and while the Machine Advisory Committee continued to work on a classical schema, Adams Notes: pp. 95 ff.

88

3-400 GeV Proton Synchrotron in Europe

began to completely change the way of looking at things. On 23 February, in a handwritten note sent to Gregory, he proposed for the first time a radically new solution^^. The starting point was the impasse on the site and the split between the member states into two groups - the six countries who wanted to participate in the construction of a 300 GeV machine and the others - a spHt which it was essential to overcome as soon as possible if one did not want to destroy CERN completely. Adams's proposal was to take seriously the feelings of governments confronted with difficult social and economic situations, and to propose to them a single budgetary envelope covering the programme both at Meyrin and for the 300 GeV machine. And to accept that the growth in the joint budget should not exceed 3-5% This choice would certainly have the unfortunate consequence of reducing the Meyrin budget in order to permit the construction of the new accelerator. On the other hand, it would once more enable all the member states to become involved in future programmes. What was Adams's concrete proposal? 'To build CERN II [the 300 GeV J adjacent to CERN I [Meyrin] using CERN I facilities to reduce the cost of the laboratory budgets and those for preparation for research'. Then, to exploit a new idea which had recently appeared in the Machine Advisory Committee, that of the missing magnet. On this scheme one began by placing only some of the magnets symmetrically around the ring while the others, which could be of a different type, would be installed at a later date, so allowing for an increase in the machine energy. Adams's precise proposal was to construct a tunnel 1.5 km in diameter (instead of the 2.9 km envisaged in December 1959) and to instal in it at first only half the magnets. In this way, an energy of 150 GeV could be attained at a reasonable cost whatever the future hypothetical possibiUties might be. This proposal had obvious advantages. Firstly, the question of the site was resolved at last, along with the future of the Meyrin laboratory. Then, the final energy of the machine was not irreversibly fixed. It was still an open question and could be adjusted in the light of technical developments in magnet material occurring in the next five to eight years. The energy would be doubled to 300 GeV if the new magnets installed were of the classic type, the additional cost being modest and of the order of 70 MSF. It could be pushed to 500 or 600 GeV if superconducting magnets were available. At the same time if one reduced the budget of CERN I from 330 to 290 MSF per year - a reduction to take place progressively over four years - and if one spread the construction of the new accelerator over eight years - its cost was estimated at 890 MSF for the 150 GeV phase - it was possible, according to Adams, to maintain the overall growth in the budget of the two laboratories at 4% This, said Adams, 'may be acceptable to all member states' and would also put the organisation back on its feet^^. Until mid-March Adams's idea remained confidential and was only discussed by a handful of people who tried to assess its strength and weaknesses. Their main fear was that it would be immediately rejected by the physicists - since the energy of the machine was reduced initially to 150 GeV - a rejection which would inhibit any in-depth study of the scheme. On 19 March the members of the Committee of Council were informed in their turn in a text drafted by Adams marked 'Personal and Confidential'. It was entitled 'An

Adams's second scheme for reviving the project: towards a Genevan solution

89

alternative way of achieving the aims of the 300 GeV programme'. In this text Adams' new project (called Project B) was compared item by item with the project studied by the Council the previous year (and labelled Project A)^^. Adams stressed two things in this text. Firstly, that the accelerator proposed in Project B, which was now 1.8 km in diameter, could be 'accommodated on a site adjacent to CERN-Meyrin, whereas the Project A machine certainly could not'. He claimed that for this circumference the ground adjacent to CERN was known to be good - after all, it was the same as that for the PS and for the ISR - , that it was sufficiently flat and that 'the boundary of the site does not include any villages, only a few farm buildings'. Then he pointed out that the costs of construction would be reduced, firstly by decreasing the size of the accelerator, then 'by making it possible to use the facilities of the Meyrin Laboratory during the construction and bringing into operation of the new laboratory'. Adams then gave again figures which were close to those mentioned in February: only an additional 750 MSF would be necessary, distributed over eight years. This was roughly half of what Project A required (1431 MSF in 1969 prices). Two new ideas were put forward in writing during the following three weeks. The first was that the machine would be buried about 30 metres below the surface. In this way only a few isolated buildings would be situated on the surface (for example the access points or the buildings containing the ventilation system) and the experimental zone which would only occupy a reduced area could be freely chosen. By burying the machine there would also be a greater latitude for its exact size and so its maximum energy, an advantage which could only satisfy the physicists. The second idea, expressed for the first time on 7 April in a note signed by Adams, proposed to use the CERN 25 GeV synchrotron, the PS built in the 1950s, as an injector for the 300 GeV accelerator. At the time the PS was being rebuilt and improved. Its use as the first stage in acceleration would permit a saving in the cost of construction estimated in May at about 200 MSF. This possibiUty was studied carefully in April, found to be viable in May, and definitively incorporated in the proposal submitted to the SPC and to the Council^^. Now confident in their new project, Adams and Gregory decided to present it to the scientists at CERN and to pubUsh a press release. The official presentation to the physicists was made on 20 April in Geneva by Gregory. On this occasion a new idea was proposed by J.V. AUaby and by C. Rubbia. Wanting to use the machine as quickly as possible at 150 GeV, and seeing an additional way of making an economic saving, the two physicists proposed that the West Experimental Hall (containing the big European bubble chamber and the Omega detector then under construction) should be the first experimental area for the new accelerator. 'Thus one is led to conclude', they summarised, 'that to start physics at 150 GeV/c one needs basically only to build the main accelerator, an injection system and an ejection system'. This ought to have allowed for an appreciable speeding up of the project. For physics at 300 GeV, they added, a more appropriate hall would be necessary^^.

Notes: p. 96

90

3-400 GeV Proton Synchrotron in Europe

3.5.2 THE REACTIONS OF PHYSICISTS: LET'S INCREASE THE ENERGY Other less imaginative suggestions than these were made during the following weeks. It was however the meeting of ECFA held on 9 May 1970 which was crucial, and it is on this meeting that we must now pause for a while. This was the main forum in which physicists could express their views (physicists understood in the strict sense of the term, as opposed to constructors for example). At this meeting a number of objections were raised which rapidly led to a reorientation of Adams's project^^. The overwhelming if not unanimous opinion of the physicists was that an energy of 150 GeV after some 5-8 years was totally unacceptable. Firstly, because the rival American laboratory would have 400 GeV in 1972 and an experimental hall suitable for working at this energy two or three years later. Then because physicists in six countries had already obtained governmental support and financing for a 300 GeV accelerator, and that it would be politically unwise to retreat now. On the other hand, all agreed that Project B 'broke the deadlock concerning the choice of a site', and the community supported 'the construction of the new laboratory next to Meyrin'. ECFA's recommendations were thus 'that the energy should not be less than 300 GeV and [...] that the largest radius at the Meyrin site should be chosen' - the idea here being to leave open the possibiHty of reaching energies of 400 or 500 GeV in a second phase. A third conclusion was that it was important to build the accelerator in six years, and not in eight, a goal which seemed possible if one used the PS as an injector and the West Hall as the first experimental hall. Finally it was suggested, in line with Adams's idea, to decide now for half the magnets, the other half being settled at the last moment. This was obviously done in the hope that superconducting magnets would be available and that one could in this way leapfrog the American laboratory^^. At its meeting on 11 and 12 May the SPC adopted the majority of these proposals and drafted a statement for the Council. Here it enthusiastically defended the idea of a project which it named B*, comprising a ring of at least 2 km in diameter using the missing magnet idea and separate function magnets, and taking the PS as injector. This accelerator, it thought, should be able to reach 300 GeV after five or six years of construction and would use the West Hall as its initial experimental area. A more appropriate experimental zone would be opened in the eighth year. On the financial side the SPC estimated that the project would have a cost 'close to the estimates for Project B' made by Adams in March. At the same time the first contacts were made with the French and Swiss authorities, since the machine would cross the border between the two countries. For their part, the CERN management explained to the elected authorities in the region that the machine would be underground, and would thus have no significant impact on local life. At its meeting in June the Council accepted warmly the proposal put forward by Adams and supported by the SPC and by ECFA, even if the majority of the countries which had already supported Project A registered their regret that it had been abandoned without any discussion. (This was notably the case for Italy, and to a lesser extent for Belgium and for France.) Sir Brian Flowers, in his turn, spoke of a new 'impetus' having been given to the 300 GeV programme and declared that the British physicists were 'extremely anxious to take part in the new project'^^.

Adams's second scheme for reviving the project: towards a Genevan solution

91

3.5.3 THE ADOPTION OF A REVISED ADAMS PROJECT From this moment onwards things moved rapidly. Still rather stunned by the events of the previous January, but relieved by the intelligent solution put forward by Adams, the Council delegates, and under their pressure the various state apparatuses, decided to step up the pace. In brief the Committee of Council met at the end of July and recognised that 'there seems to be a general agreement amongst delegates that CERN should in some way or another ask the governments of France and Switzerland whether the site proposed for Project B could be made available to the Organization'. This was done unofficially in the subsequent weeks, and a report with positive conclusions was presented to an extraordinary session of the Council called in October^^. At the start of September the Committee of Council approved, for presentation to the Council, the new Programme Definition document. The tendency now was to build a machine 2.2 km in diameter. This radius would permit the Europeans to obtain reasonably quickly, and using classical means, 400 GeV, namely, the energy of the American accelerator. This proposal was maintained in the final document submitted to the member states in December. In October all the delegations approved the text 'for presentation [...] to the Governments of the Member States' and gave their approval for an official request being made to the French and Swiss authorities^^. The final touch came on 4 December in the aftermath of the Conservative Party coming to power in Great Britain. In reply to a written question submitted to the government in the House of Commons 'Mrs. Margaret Thatcher, Secretary of State for the Department of Education and Science repUed: 'Yes. We have decided that the UK should participate with the other European countries which are members of the European Organisation for Nuclear Research, CERN, in building a 300 GeV accelerator [...]'. With Britain's participation added to the other six member states which had already confirmed their participation, 80% of the budget was now covered. Nevertheless, everything was not yet definitely settled at the Council meeting in December. Several governments, and notably the British government, insisted that all member states should participate. The session was just suspended until February when the Netherlands, Norway and Sweden in their turn announced their participation. Despite the defections by Denmark and by Greece the project was thus voted, Adams was nominated the Director-General of Laboratory II, and the recruitment of personnel as well as the construction could thus get under way^^. In mid-1973 it was finally decided not to use superconducting magnets, essentially for industrial reasons. Guarantees for constructing reUable magnets of this type in series could not be given. Adams thus proposed to the Council to instal classic magnets in the ring, thus enabling the machine to achieve 400 GeV directly. The Council accepted his proposal. On 17 June 1976 the superproton synchrotron accelerated protons to 400 GeV for the first time. On 25 October an intensity of 10^^ protons per pulse was achieved.

Notes: p. 96

92

3-400 GeV Proton Synchrotron in Europe

3.6 Conclusion We will conclude this study with a few brief remarks. Firstly on the unusual length of this decision-making process - it took longer than ten years - and on the fact that in order to succeed, it required the constant permanent presence of an extremely highly motivated group of people. This group had constantly to keep a large number of threads in their hands, had constantly to cope with defections on each and every point, and had never to lose hope. When everything seemed to have been settled in 1967, for example, for the participation by six member states, it was the German Atomic Energy Commission which, suddenly, questioned the scientific foundations of the choices made by CERN and blocked the decision. A year later it was the United Kingdom who announced that it would not participate, this time for more classic reasons, namely political and financial reasons. Finally in January 1970 it was the Federal Republic of Germany which again stopped, in a brutal and apparently irreversible manner, a process which seemed about to succeed. On this occasion it was because its partners did not want to concede that the new laboratory should necessarily be established on German territory. There were three main reasons behind the enormous difficulties which CERN people had in bringing this affair to a conclusion. Firstly, the social and economic difficulties of the time, and the new demands being made in the field of policy, notably as regards industrial policy. Then there was the gradual loss in the prestige of high-energy physics and its relative decline, coupled with the demands coming from other sectors of scientific research which until then had been all too easily overlooked. Finally, though this point is intrinsically linked to the two preceding ones, the difficulty which the CERN lobby had to maintain the autonomy which it had had and could enjoy in the early 1950s. The traditional space in which the Council's strategic core could manoeuvre had been reduced since particle physics was under attack, since the available resources were less, and above all since the state apparatuses had taken it upon themselves to manage science and technology. Of course the lobby still had considerable room to move, as a comparison with the situation in the domain of space makes all too clear. Nevertheless, it had far less freedom than was the case in the 1950s and the early 1960s when the Council could triumphantly oppose itself to the British wish to better control CERN's expenditure. Some words on the German attitude during this historic phase are also needed. While during the preceding period of CERN's history it was the United Kingdom, and to a lesser extent the Scandinavian countries, who most frequently created difficulties for the lobby, this time the dangers came from the Federal Republic of Germany. This is confirmed in the analysis on the decision of BEBC which we give in the following chapter. In their book on the SPS Goldsmith and Shaw advance an explanation for this. They claim that Germany was no longer prepared to be treated any differently to Britain or to France while it was making the most important contribution to the budget. These authors even interpret the episode in January 1970 as a signal intended to illustrate the new determination of this country.

Notes

93

Their observations seem to us to be correct, but perhaps call for an additional remark. One must not forget, in fact, that the German delegation to the Council did not have in its own country the aura which surrounded some members of the other delegations, that it did not enjoy the kind of freedom that some delegates had succeeded in keeping vis-a-vis their national administrations. Perrin for example, even if he had lost some of the autonomy which he had had ten years before, still exercised a major influence over the recommendations of his government. Another difference is that German physicists were no longer in the majority on the national bodies which were mandated to advise their government on CERN policy. As we have mentioned industrial circles had been given a new weight in these organisations, they now played a decisive role in CERN's decision processes, a role which they did not play in Italy or in France. Certainly there was the determination to make scientists more accountable in France and in Italy in 1970/1971 but the pressure put on them was far less important, and certainly far less systematic, than was the case in Germany^^. Translated by John Krige

Notes 1. See A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN, volume II. Building and Running the Laboratory (Amsterdam: North-Holland, 1990), chapter 12. 2. See for example, H.M. Collins, Changing Order. Replication and Induction in Scientific Practice (London: Sage, 1985), M J . Rudwick, The Great Devonian Controversy (Chicago University Press, 1985), S. Shapin and S. Schaffer, Leviathan and the Air Pump. Hobbes, Boyle and the Experimental Life (Cambridge University Press, 1985), and D. Pestre, 'Monsters' and 'CoUiders' in 1961: The First Debate at CERN on Future Accelerators, in F.A.J.L. James (ed). Laboratories: The Place of Experiment, Past and Present (London: Macmillan, 1989). 3. References in Hermann et al. (note 1), chapter 12, section 12.6. 4. The future constitution of CERN, Draft, 30/10/64, letter Hampton to members of the Steering Committee, 11/3/65, note of the President of Council's Steering Committee, 26/3/65 (DG20894). This, and similarly referenced files, can all be found in the CERN archives. 5. The different offers for a site (some of them pubUshed) can be found in file DG20895. A similar situation arose in the United States. Most regions of the country were keen to host the American 200 GeV machine. 6. Letter CERN/10.455, signed Bannier, President of the Council, 2/12/65. 7. Hermann et al. (note 1), chapter 12, section 12.6. 8. References in notes 4 and 6. For other examples of how the Council dealt with such obstructions, and for a partial analysis see Hermann et al. (note 1), chapter 7. 9. CERN/SPC/217/Draft, 1/3/66, CERN/ECFA 66/lA, 3/2/66, letter Gregory to Trumpy, 25/2/66 (DG20780), CERN/ECFA 66/2, 2/5/66, CERN/ECFA 66/7, 16/9/66 (DG20782). On the claim that ECFA was 'an independent organism composed of member states physicists nominated by national authorities', and 'who were thus entirely free to express opinions which were not necessarily those of CERN', see Amaldi, Council minutes, 15-16/6/66, 15, or Gregory, id., 18 (quotations are our translation from the French official minutes). 10. Letters Weisskopf to Amaldi, 22/12/65 (DG20780), Gregory to Blanc-Lapierre, 20/1/66, Van Hove to Gregory, 28/2/66, Confidential note from Van Hove, 28/2/66 (DG20785).

Notes: p. 96

94

3^00 GeV Proton Synchrotron in Europe

11. Council, minutes, 15-16/6/66, letters Hampton to Committee of Council members, 15/8/66 (DG20787), Hine to Bannier, 24/8/66 (DG20892). 12. Letter CERN/10978, Bannier to Ministers, 9/9/66 (DG20892). 13. Council, minutes, 14^15/12/66, 14-15/6/67, 21-22/9/67, 13-14/12/67, letter Gregory to Funke, President of Council, 21/8/67 (DG20894). 14. Revision of the CERN Convention, CERN/716/Rev. 5, 24/11/67. 15. ECFA/66/2, 2/5/66, 13. 16. On reading an earlier version of this text John Krige justifiably remarked that many CERN engineers probably saw in a new laboratory additional possibilities for top management posts. 17. Hermann et al. (note 1), chapter 12, section 12.3. As an example, add Amaldi, Council, minutes, 15-16/6/66, 16, who stated 'the Working Group [of the ECFA] estimated that owing to the improper nature of the ground at Meyrin, it would be extremely difficult and costly to build a 300 GeV machine'. 18. ECFA/66/2, 2/5/66, 6 for the first quote; Status of the Project..., report printed by CERN dated July 1966, 18 for the second. The others are taken from the Note of the discussion which took place at the President of Council's Steering Committee /.../, 26/3/65 et 9/7/65 (DG20894). Italy offered two sites, which explains the figure ten for nine countries. Note that holding an intergovernmental conference was only proposed as a possibility. 19. Quotes from letter Hine to Bannier, 5/6/66. Add Council, minutes, 15-16/6/66, CC/662/Draft, 16/9/66, letter Hine to Committee of Council Members, 8/8/66, note for the First Meeting of the National Experts, 20/10/66 (DG20894). 20. Council, minutes, 14-15/12/66, quotes page 40; Site Evaluation Panel, 1st meeting, SEC/1, 3/2/67. 21. Council, minutes, 14^15/12/66, 40. 22. Memorandum Hine to Director-General, 5/6/67 (DG20894), from which the first quote is taken; CERN/761, 4/12/67, 3 for the others. 23. The first quote is taken from Hine's report cited in the previous note. The report was submitted in December (CERN/761). 24. Council, minutes, 21-22/9/67, quotes on pp 52 and 53. 25. The fact that the Site Evaluation Panel itself was a committee of experts should not be ignored either. Its members tended in fact to make more 'technical' moves than they had done before their nomination. For example, Mr. Bannier became less 'political' once he chaired the Panel than he had been whilst presiding the Council. In other words, the institutional logic has to be taken into consideration. The sense in which we use 'depoliticised' is made clear in the concluding chapter of A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN, volume I. Launching the European Organisation for Nuclear Research (Amsterdam: North Holland, 1987). On the limits of the idea that CERN was rarely a factor in the quarrels between states, see Hermann et al. (note 1), chapter 7. 26. Respectively, CERN/702, 30/5/67 and CERN/700. Amaldi's presentation is reproduced in extenso in Council, 14-15, quote 11. 27. The letters of agreement sent by the Belgian (4 July) and Austrian (4 October) governments are in file DG20892; Council, minutes, 15-16/6/67, quote page 33. 28. Council, minutes, 21-22/9/67, 4 7 ^ 8 . 29. The quotes are taken from the Resolution passed by the German Atomic Energy Advisory Committee on 14 November 1967, except the second one which is Gregory's interpretation of it in Comments by the DirectorGeneral on the questions from the German Atomic Energy Advisory Committee, 13/12/67 (DG20787). The Germans also raised the question of long-term collaboration with the USA and the USSR and that of the financial consequences of the geological differences between the sites. 30. Comments by the Director-General on the questions from the German Atomic Energy Advisory Committee, niniei (DG20787). 31. The first quote is from Amaldi, Council, minutes, 13-14/12/67, 68, and the second from Gregory, same reference as in the previous note.

Notes

95

32. Council, minutes, 13-14/12/67, 69-70. 33. CERN/SPC/256, 30/4/68; letter Funke, President of Council, to delegates, 19/2/68, from which the first quote is taken, CERN/773, 15/2/68, Steering Group Meeting, 15/3, 3/4, 15/5,..., quote meeting of 15/3. Going back on the first reaction of the Director-General, it was now stated that the costs of the two projects corresponded very exactly; see for example Council, minutes, 14/3/68, 17. 34. Council, minutes, 14/3/68, pp. 16-19. 35. For Germany, letters Citron to Gregory, 9/4/68 (DG20894), Jentschke to Gregory, 3/7/68 (DG20892); for Italy, Steering Group Meeting, 15/5/68, 1, Motion sur le 300 GeV, INFN Council of Management, 25/6/68 (DG20892). 36. Council, minutes, 19-20/6/68, from which the quotes are taken. 37. On the subject of British diplomatic pressure that the Germans '[do] not insist on the project of the 300 GeV machine', see letters Gentner to C.F. Powell, 22/7/68 and Van Hove to Gregory, 30/7/68 (DG20893). 38. For France, letter Gregory to Aigrain, 21/6/68 (DG20787), for Germany, letters Gregory to Bannier, 12/7/68, Hine to Gregory and Hampton, 15/8/68, Stoltenberg to Funke, 4/9/68 (DG20892). For Italy, letter G. Smoquina to Gregory, 12/8/68 (DG20892). 39. ECFA 68/9, 11/6/69 (DG20781). 40. Letters Gregory to Members of Committee of Council, 2/12/68, Funke to Adams, 23/12/68 (DG20896); see also the correspondence between Weisskopf and Gregory and between Adams and Gregory in file DG20896. 41. Letter Willems to Director-General, 23/2/68 (DG20787). 42. Letter of the Delegation Permanente de VAutriche to Gregory, 13/3/68 (DG20787). 43. Council, minutes, 14/3/68. 44. Council, minutes, 2-3/10/68. 45. Council, minutes, 18-19/12/68. 46. See Hermann et al. (note 1), chapter 7. 47. For BEBC, see the previous chapter. 48. Letters Gregory to members of the CC, 23/1/69, Adams to Gregory, 27/1/69, 10/2/69, 11/2/69 (DG20894). 49. CERN/869, 30/5/69. 50. Working Groups on window-frame magnets, power supply, booster and RF systems, close orbit control, high-efficiency ejection, controls and collective ion acceleration (CERN/870, 28/5/69). 51. The quotes from the four previous paragraphes are taken from CERN/869, 30/5/69. Add Council, minutes, 19-20/6/69, 15. 52. Letters Adams to Committee of Council Members, 24/4/69 (DG20894), Adams to Willems, 24/4/69 (JB22729). 53. Letter Adams to Committee of Council Members, 24/4/69 (DG20894), CERN/871 and 873, Note, Ministere des Affaires Etrangeres (France), 16/7/69 (DG20893). 54. Letter Adams to Committee of Council Members, 24/4/69 (DG20894), CERN/874, Note, Ministere des Aff"aires Etrangeres (France), 16/7/69 (DG20893). 55. Letter Adams to Committee of Council Members, 24/4/69 (DG20894), Note, Ministere des Aff"aires Etrangeres (France), 16/7/69 (DG20893). 56. Council, minutes, 19-20/6/69, letter Adams to Committee of Council Members, 22/8/69. 57. Internal notes to the French government, Fran9ois OrtoH to Lucien Malavard, 12/9/69, Schumann to OrtoH, 17/9/69, Gregory to Malavard, 25/9/69 (DG20785), Summary of the discussions of the Committee of Council meeting, 15/10/69 (DG20893), letter Adams to Valloton, 16/10/69 (JBA22729). 58. The announcements of the various governments are in box DG20892; Council, minutes, 18-19/12/69. 59. Letters Departement PoHtique Federal to Gregory,6/1/70, Adams to Committee of Council Members, 7/1/70, Communique de presse, 15/1/70, Parliamentary Inquiry in the German Federal Assembly on 16 January 1970 (DG20893).

96

3-400 GeV Proton Synchrotron in Europe

60. Communique de presse, 26/l/70(DG20893), from which the quote is taken. See also M. Goldsmith and E. Shaw, Europe's Giant Accelerator. The Story of the CERN 400 GeV Proton Synchrotron (London: Taylor and Francis, 1977). 61. Note entitled CERN II, 23/2/10 (DG20893). 62. The quotes in the three preceding paragraphes are taken from Adams's note entitled CERN II, 23/2/70 and from that entitled An Alternative Way of Achieving the Aims of the CERN 300 GeV Programme, to Committee of Council Members, 19/3/70 (DG20893). 63. There are in fact two versions of Project A, and that of December 1969 already differs somewhat from the one presented in June. It takes into account, for example, the concept of the missing magnet and proposes, for the price accepted by the June Council, an accelerator whose energy would amount to 250 GeV in phase I. See the note entitled An Alternative Way of Achieving the Aims of the CERN 300 GeV Programme, to Committee of Council Members, 19/3/70 (DG20893). 64. Notes entitled Alternative Ways of Realising the CERN 300 GeV Programme, 6/4/70, The Use of the CERN 25 GeV Proton Synchrotron as an Injector for the Project B Machine, 1/4/10 (JBA22683). 65. Notes entitled Wider discussion of Project B, 1/4/10, Comments on the Potentialities ofMeyrin as a Site for the 300 GeV Accelerator (Allaby & Rubbia), 24/4/70 (DG28893). 66. CERN/ECFA/70/6, 2/6/70 (DG20782). 67. Quotes taken from CERN/ECFA/70/6, 2/6/70 (DG20782). 68. CERN/967/Draft, 18/9/70. 69. Letters Adams to Committee of Council Members, 11/8/70, 24/8/70 (DG20895), CERN/983, 26/11/70. 70. CERN/SPC/296, 29/10/70, CERN/983, 26/11/70, CERN/1008/Draft, 27/5/71. 71. Telex Gregory to Committee of Council and SPC Members, 4/12/70 (from which the quote is taken), letter Thatcher to Amaldi, 4/12/70 (DG20892), CERN/CC/993/Draft, 18/12/70, CERN/998/Draft/Extr., 7/1/71 (December Council Session), CERN/CC/999/Draft, 19/1/71, CERN/CC/1006/Draft, 3/3/71, CERN/1008/ Draft, 27/5/71 (February Council Session), letters Adams to Flowers, 15/121/70 (JBA22729), Adams to Weisskopf, 8/1/71 (DG20893). 72. Example in letter Gregory to Aigrain, no date (probably September 1970) (DG20893).

CHAPTER 4

The Intersecting Storage Rings. The Construction and Operation of CERN's Second Large Machine and a Survey of its Experimental Programme Arturo RUSSO

Contents 4.1 A few technical essentials about the ISR 4.2 Getting started 4.2.1 The problem of voting majority 4.2.2 The search for a compromise 4.3 Building the machine 4.3.1 General layout and engineering 4.3.2 The magnet 4.3.3 The vacuum system 4.3.4 The RF system and the stacking process 4.3.5 Controls 4.3.6 Running-in 4.4 Setting up the physics program 4.4.1 Organization and management of the ISR experimental programme 4.4.2 The definition of the first experimental programme 4.4.3 The SpUt-Field Magnet 4.5 Keyhole physics 4.6 Particle physics in the 1970s 4.6.1 Hard scattering, partons and quarks 4.6.2 The 'November revolution' 4.7 ISR physics 4.7.1 A 'brilliant start' 4.7.2 The need for big detectors 4.7.3 A difficult period 4.7.4 The last achievements 4.8 Epilogue Notes References

97

100 107 108 111 112 118 119 121 122 124 125 127 127 129 132 134 137 138 140 145 145 150 151 153 154 156 164

The Intersecting Storage Rings (ISR) project was unanimously approved by the CERN Council in June 1965^ It was the outcome of a long and controversial decision-making process which was analyzed in detail in the previous volume^. The construction of the machine started in early 1966 and it was commissioned for physics experiments in March 1971. The ISR was in operation for about 13 years, the last run being completed in December 1983. The ISR was a machine of a completely different design from standard proton accelerators. In the latter, in fact, a beam of accelerated protons collides with a target and the events produced by the collision are either studied as such or, more often, used to create secondary beams of particles (usually mesons) to study particular physical processes. In the ISR, on the contrary, two beams of protons each accelerated to energies up to 26 GeV by the CERN proton synchrotron were brought into virtually head-on collision. The ISR was actually the first proton-proton collider and it was to remain the only one. Before it there was only very limited experience on electron-positron colliders (ADONE in Frascati, Italy, and the e"*"e~ faciHty in Cambridge, Mass.). Subsequently, along with several e^e~ colliders, only two proton-antiproton colliders have been built, one at the CERN SPS and the other at the Fermilab Tevatron-^. Due to the novelty of the conception and to the sophistication of the technical design, the construction of the ISR was a challenging undertaking for CERN's engineers and accelerator physicists who had to obtain the best performance from all components of the machine. The operation of the facility was also a matter of considerable complexity and required a novel organization of experimental work. Physicists were not just confronted with a new accelerator but with a machine of a completely different kind from those with which they were familiar and they had to learn how to do physics with it. This was at one and the same time a fascinating prospect and a worrying unknown; ISR results could eventually provide a scientific break-through as well as bitter disappointment. The ISR was also CERN's second large machine. After more than eleven years of exploitation of the 28 GeV proton synchrotron (PS), a new facility was available to European particle physicists in their search for the ultimate laws of nature and in the competition with their American colleagues. The latter had also considered the idea of building a proton-proton collider in the United States but eventually abandoned it and directed all efforts towards the 500 GeV proton synchrotron under construction at a new national laboratory near Chicago (later called Fermi National Accelerator Laboratory, or Fermilab for short). This was commissioned in 1972, one year after the ISR. European physicists had also advocated the construction on this side of the Atlantic of a large proton synchrotron, the machine they considered by far the best option for the new generation of particle accelerators, but their expectations had been frustrated by political 98

99

A few technical essentials about the ISR

and financial constraints. Most of them did not like the ISR, which was on the contrary the favourite of CERN engineers and accelerator physicists, and they had eventually accepted the decision to build it only when it became clear that there was no way quickly to get the money they needed to build the 300 GeV proton synchrotron"^. The ISR promised a much higher centre-of-mass energy - it was equivalent to that available in a 2000 GeV fixed target accelerator. On the other hand, it suffered from major limitations in luminosity and in the kind of processes which could be investigated - actually only proton-proton collisions. Here was the challenge European physicists had to confront. The history of the ISR is certainly the history of a great technological success but the physics done with it can only be considered against the background of particle physics in the 1970s and with reference to the perception that particle physicists had of the evolution of their discipline. CERN's physicists were not only confronted with a completely new machine; they also had to tune their experimental programme to the rapid development of the field. In the period of operation of the ISR, in fact, particle physics passed through a dramatic change which reshaped both the theoretical framework and experimental practice. Hard-scattering experiments provided compelling evidence of an internal structure of the proton, thus giving an experimental foundation to the quark hypothesis. As a consequence, new theories of quarks and leptons began to be formulated within the context of a theoretical approach known as gauge theory. In particular, it was suggested that electromagnetic and weak interactions could be seen as manifestations of a single electroweak force. This electroweak theory was dramatically confirmed by the discovery of the weak neutral current, in 1973, and by the discovery of the charm quark, in 1974. At the same time, a particular gauge theory, called quantum chromodynamics (QCD), was also suggested for strong interactions of quarks, which proved to be capable of explaining the properties of hadronic phenomena and soon became the accepted theory of the strong interactions. In the late 1970s, Particle physicists were agreed that the world of elementary particles was one of quarks and leptons interacting according to the dictates of the twin gauge theories: electroweak theory and QCD^.

In order to cope with this changing landscape using the ISR, a new experimental philosophy had to be developed, based on large and sophisticated detectors and searching for rare phenomena at large angles. It took time, probably more than necessary, to understand that complex detectors of a new conception were needed at the ISR and this was the reason for the machine's missing important discoveries and being late in finding its proper place in the mainstream of experimental particle physics in the 1970s. Thus the history of the ISR must take account not only of a great technological success and of important physical results but also of malaise and disappointments. And when writing this history, one is inevitably reminded of two famous lines from Shakespeare which a leading theoretical physicist at CERN used as an introduction to his review of ISR physics when the machine was closed: Notes: pp. 156 ff.

100

The Intersecting Storage Rings The evil that men do lives after them, The good is oft interred with their bones^.

This chapter is organized in four main parts. After an introductory section describing the general characteristics of the ISR, the first part deals with the discussions and controversies within CERN's bodies to find a proper institutional arrangement for the ISR project. The second part will describe the construction of the ISR, dealing with the different aspects of the reaUzation of such an extremely demanding technological undertaking. In the third part, one can find a presentation of a few important aspects related to the organization of the research work at the ISR, beginning with the institutional framework set up to deal with the experimental programme (the ISR Committee). We continue with the description of the major experimental facility realized at the ISR, the so-called Split-Field Magnet (SFM). Then we will describe the experimental programme approved for the first phase of operation of the machine and, to close, we will discuss a few aspects of the early experimental approach to ISR physics (eventually called keyhole physics) which were to affect the overall scientific performance of the machine. The fourth part will discuss ISR physics, dealing in more detail with the first half of its lifetime. This discussion is preceded by a review of the development of particle physics in the 1970s which helps to understand the how and why of the ISR's achievements and setbacks.

4.1 A few technical essentials about the ISR In order to understand better the problems connected with the construction of the ISR and to its operation for physics experiments, it may be useful to give a short description of the machine and how it was operated^. A first aspect to be considered is the energy motivation for this kind of device. Experiments with conventional accelerators involve the analysis of the phenomena produced by a collision between a particle in the primary or in a secondary beam of the accelerator and a stationary particle in a target. The energy available for producing the phenomena of interest is the centre-of-mass energy of the system which, in this case, is only a fraction of the energy of the incoming particle. The rest is shared as kinetic energy among the particles which result from the interaction. At high energy, if the two colliding particles are the same, as in the case of a proton beam hitting a stationary hydrogen target (or protons inside heavier nuclei), the available centre-of-mass energy is given approximately by the formula: Ecm = y (2mc2E) where E is the energy of the beam, m the mass of the particle and c the speed of light.

A few technical essentials about the ISR

101

If, on the contrary, two particles of energies Ei and E2 collide head-on, all the energy given to them can go into the phenomena of interest of physicists, i.e. the transformation of particles and the creation of new particles. In this case, in fact, the centre-of-mass energy is approximately: Ecm = 2 v (E1E2) and, if the energy of the two colliding particles is the same (Ei = E2), the centre-of-mass energy is just twice this energy. The energy advantage of colliding beam devices can be appreciated by considering that if a 28 GeV proton beam of the CERN proton synchrotron bombards a stationary hydrogen target, the available energy is only 7.5 GeV while, if two beams of 28 GeV are brought to collide, the available energy is 56 GeV, that is the equivalent of a conventional accelerator of 1800 GeV. This gives one the possibility of studying some very high energy interactions at a much lower price than with a fixed-target accelerator of equivalent interaction energy. Against this energy advantage in colUding beam machines, there is a severe limitation in the range of phenomena which can be studied and in the rate at which the phenomena occur. First of all the particle density in a beam is much lower than in a stationary target. To obtain an interaction rate high enough to make coUiding beam experiments feasible, it is then necessary to build up very intense particle beams by a stacking process and to store the beams for long periods of time. A consequence is that only relatively stable particles can be used. Furthermore, in colUding beam devices, it is possible to study only phenomena produced in the colUsions of the circulating particles, proton-proton colUsions in the case of the ISR, while in conventional accelerators a copious supply of different particles can be provided in the secondary beams. The ISR consisted of two interlaced, slightly distorted concentric rings in which protons provided by the PS travelled in opposite directions and could be brought into colUsion in eight intersection regions denoted I-l to 1-8 (Fig. 4.1). Each crossing region was in the middle of a long straight section of about 17 meters and the angle of crossing was about 15°. The diameter of the rings was 300 metres, i.e. 1.5 times that of the PS. The two rings were quite independent; thus they could be run at different energies in order to make the centre of mass move in either direction at will. The rings were housed in a single underground tunnel located some 300 metres away from the PS. Beam-transfer Unes guided the protons ejected from the PS and bent them into either of the two rings. Table 4.1 Usts the main parameters of the ISR. In normal ISR operation, protons were accelerated in the PS to the required energy, normally between 11 and 26.5 GeV (with the possibiUty of further 'phase displacement' acceleration to 31.4 GeV in the ISR), and then they were injected into a transfer channel where magnets guided them towards one or the other of the rings. A fast injection system injected the protons initially into an orbit close to the inside wall of the ring vacuum Notes: p. 157

The Intersecting Storage Rings

102

Intersection region l-^^

xJ'^

LINAC

Fig. 4.1 Schematic presentation of the beam paths at the PS and the ISR. Protons are accelerated to 50 MeV in the Linac, further accelerated to 800 MeV in the Booster, transferred to the main ring of the PS and there taken to the desired energy (between 11 and 26.5 GeV) for injection into the ISR. Via the transfer tunnels TTl and TT2 they can be fed to one or other of the storage rings. Proton-proton collisions can then take place at the eight intersections: I-l to 1-8 (Ref. [74], p. 7).

chamber. A radio frequency system was used to get hold of the protons as they came in and to accelerate them slightly so that they moved horizontally across the beam pipe of the ISR to an orbit nearer the outside wall in order to leave the injection orbit free for another pulse of PS protons. This, in turn, was accelerated and moved to an orbit only a fraction of a millimetre from where the first pulse had been left. This stacking process was repeated again and again in order to create a stacked beam about 50 mm wide and of a sufficient intensity for physics experiments (Fig. 4.2). The time required to stack each ring with a beam current up to 20 A was slightly less than an hour. Colliding beam experiments could then be carried out for many hours before calling on the PS again for a refill. In order to keep beams of sufficient intensity for a long time, the vacuum chamber in which the protons circulated had to be evacuated to a very low

A few technical essentials about the ISR

103

Table 4.1 Main parameters of the ISR Physical parameters Design luminosity Design current per ring Maximum energy of each ring Geometrical parameters Circumference of rings Average radius of equihbrium orbit Maximum distance between inner and outer arc Intersection angle Straight section at intersection region Difference in beam level between ISR and PS

4 X 10^0 cm-2 s-^ 20 A 31.4 GeV 942.66 m 150.03 m 8.79 m 14.77° 16.78 m 11.80 m

Beam parameters Number of magnet periods Number of superperiods Stack width for 2.5% momentum spread Maximum height of beam profile Horizontal closed orbit distortions after correction Vertical closed orbit distortions after correction

48 4 ~ 50 ~ 15 ^ 6 ~ 4

mm mm mm mm

Magnet parameters (one ring) Field at equilibrium orbit (28 GeV/c) Maximum current to magnet coils Maximum power dissipation Total steel weight in blocks Total copper weight

12 3750 6.8 4350 560

kO A MW ton ton

R.F. system (one ring) Number of R.F. cavities Harmonic number Centre frequency (25 GeV/c) Maximum peak RF voltage per turn Minimum defined RF voltage per turn

7 30 9.53 MHz 20 kV 50 V

Vacuum system (one ring) Pressure Vacuum chamber material Vacuum chamber magnetic permeability Length of vacuum chamber Dimensions of elUptical chamber in magnets Diameter of circular chamber in intersections Number of roughing pump stations Number of sputter ion pumps Number of titanium sublimation pumps Number of Bayard-Alpert gauges

10-11 t o 10-12 tQj.^

low carbon stainless steel < 1.005 ~ 1 km 160 X 52 mm^ 160 mm 35 144 250 250

104

The Intersecting Storage Rings

V/////////A vacuum chamber

moQiietic field

V/////////A Fig. 4.2 Cross-section of the ISR beam-pipe in the magnet gap. In order to produce a highly uniform magnetic field, the distance between the pole pieces was made smaller than their width. This leads to a flat chamber and, consequently, to stacking in the horizontal plane. The small cross indicates the injection orbit and the area available for stacking accumulation is shaded (Hiibner [70], p. 8).

pressure (less than 10"^^ torr) so as to avoid collisions with gas molecules in the chamber resulting in the protons being scattered in the course of many millions of revolutions. Because of the high intensity and energy of the individual beams, the machine needed to be well protected against radioactivity hazards and special dumping systems were set up at intersection 1-3 by kicker magnets which gave the beams a vertical deflection into titanium alloy blocks. Intersection 1-5 was permanently used for machine studies, while at intersections I-l and 1-4 two large experimental halls were available. In the latter, in particular, a large magnet system was built, called the Split Field Magnet, and it was used as a general purpose facility for experiments. At other intersections, the setting up of experiments was possible in the available width of the tunnel. By early 1974, three years after the commissioning of the machine, the ISR operated for about 3000 hours per year, of which about 2200 hours was for colliding beam physics and the preparation for it, and the rest for studies of machine performance and development. Table 4.2 shows the distribution in time during 1973 for experiments at the standard operating momenta, and the values for beam currents and luminosities. Scheduling of ISR operation had to be co-ordinated with that of its injector, the PS, and special care had to be taken to minimize interference between the physics done with the two machines. Setting up normally took several hours. The first step was to eject the PS beam into the transfer line from where it was then injected into either of the two rings. Optimization of the injection trajectories in the rings generally took about one hour. The acceleration cycle was then adjusted and all secondary devices were adjusted. After setting up, the machine was ready for a development run or forfillingfor colliding beam physics. A machine development run took place once or twice per week and lasted 10 to 20 hours. It involved machine performance studies and tests of equipment and techniques aimed at improving performance and developing special conditions for physics experiments. Filling required a continuous draw of protons with definite energy from the PS and this operation was usually done in a beam-sharing mode whereby the ISR took only every third PS pulse

A few technical essentials about the ISR

105

Table 4.2 Operation of the ISR for colliding beam physics in 1973* Momentum GeV/c 11.8 15.3 22.5 26.5 31.4 Different in each ring

Running time percent 12.8 17.8 21.8 31.5 6.8 9.3

Beam current range

Luminosity Maximum

Amperes Ar-6

5-8 8-14 8-14 3-5 various

Average xlO^^cm-^s-^ 0.4 0.6 1.8 2 0.15

0.68 1.25 4 4.5 0.36 various

(*) From ISR [74], p. 26

SO that other PS users could continue their experiments simultaneously. The process went on until a beam with the desired intensity had been stacked, typically one hour. Each physics run was usually preceded by a luminosity measurement at lower intensity (around 5 A). Stacks with the desired intensity were then completed in both rings and their position in each intersection region carefully adjusted in order to optimize the interaction rate against background. Optimization work took about 1 to 2 hours and then the beams were declared stable and the machine was ready for experiments. These were coded in the form RINN, where R stands for Rings, I denotes the intersection where the experiment was carried out, and N N is the running number of the experiment. A physics run usually lasted between 10 and 40 hours, followed by a shut-down of about two hours to allow controlled access to the tunnel for experimenters to check and adjust their equipment. The machine was then started up again for a new physics run with the same or different beam conditions. This sequence was repeated on about a 24-hour basis for a period of 2 or 3 weeks. Figure 4.3 shows a typical weekly schedule for ISR operation^. An important aspect of ISR operation, unlike that of a standard accelerator, must be mentioned here. In the latter case, by making the accelerated particles of the primary beam hit a target, other kinds of particles are produced which can be used to build up secondary beams. These are taken out from the machine and driven to different experimental halls for various investigations. Each group can operate quite independently from the others: when the machine is working it can turn on and turn off its particular beam, arrange its experimental apparatus and organize the work of its members. This was not the case for the Intersecting Storage Rings where all experiments shared the same (coUiding) beams at the same time and possibly two, three or even four groups shared the same experimental area around one of the interaction regions. Moreover, all or most of the experimental equipment was inside the tunnel; as a consequence, work on any of the instruments could be done only after the ISR was turned oflF, and the run could be resumed only after the rings had been recharged from the PS. The experimental activity around the ISR was then Notes: p. 157

1 s PHPSICCS-OPERATION

WEEK

This schedule i s definitive at time of publimion. Eng.-irrCharge

20

(

4215

- 431s;

For later changas see

SBC.

Fig. 4.3 ISR operation in May 1975 (CERN Archives file EWDS 22321).

Getting started

107

an integrated set of operations, whose planning and management involved at the same time the definition of the experimental requirements, the technical operation of the machine, its coordination with the PS, the coordination of the different experimental groups, and the optimization of the use of time, space and technical faciUties. In a certain sense the ISR had the characteristics both of an accelerator serving several independent experimental groups and of a big experimental facility used jointly by them. This required a special kind of organization and management of the experimental activity around the machine and a high degree of integration of technical and scientific operations. At the same time this also stimulated much collaboration and a continuous exchange of information among the various teams involved in ISR experiments, which openly shared their problems and findings, as well as between them and the theorists. This was soon institutionalized in the form of a series of TSR discussion meetings between experimentalists and theorists' which were held more or less regularly every two or three months on a particular subject and represented a novel and probably unique phenomenon at CERN^.

4.2 Getting started The ISR project, aimed at building CERN's second big accelerator faciUty, was approved as a supplementary programme according to article 2 of the CERN Convention, which distinguished between the 'basic' programme, involving the construction and operation of the laboratory and its first accelerators (the 600 MeV synchro-cyclotron and the 28 GeV proton synchrotron), and any additional 'supplementary' programme, covering projects and initiatives to be decided on in the future. While the former had been agreed by all Member States and all were financially responsible for it, the starting of a supplementary programme required the approval of a two-thirds majority of Member States though only those who decided to join it were financially responsible for its implementation^^. After December 1964, when an agreement to build the ISR was finally reached at scientific and political level, it required almost one year to settle all the legal and financial aspects related to the establishment, management and control of such a supplementary programme within the institutional framework of CERN. For the first time since the creation of the laboratory, a new big machine, new major equipment, new research programmes were to be added to it and, in principle, not all Member States were to become involved in the undertaking. Moreover, one must recall that the building of the ISR involved the crossing of the Swiss-French border, which posed delicate legal problems. This happened at a very critical phase of CERN's administrative and financial history, when the new budgetary procedures set up after the recommendations of the Bannier Working Party were passing their first test under the urgency of decisions on the future development of the organization after the fulfillment of its initial programme^ ^ Laborious negotiations were necessary to agree on the formalities required for adhesion of Member Notes: p. 157

108

The Intersecting Storage Rings

States, on the conditions under which a Member State could join the programme at a later date or withdraw from it during the construction period, on the procedures for establishing and approving the budget, on the relationship between the supplementary programme and the basic one, and on the means of managing and controlling both. These negotiations caused some stress and even seemed to jeopardize the project itself before it got under way. 4.2.1 THE PROBLEM OF VOTING MAJORITY In order to cope with institutional and legal problems and to present solutions within the framework of the Convention, a special working party of legal experts was created by the Finance Committee in February 1965^^. The issues, however, proved to extend well beyond the legal limits when a number of Member States, led by Italy and the United Kingdom, stressed that, with the addition of the ISR project to the already growing basic programme budget, there should be a tighter control over future expenditure^^. As a consequence, the extraordinary Council meeting called in March to decide on starting the ISR supplementary programme could do nothing but register the negative attitude of Italy and the United Kingdom and refrain from taking any decision before the whole matter was first discussed and settled in the Finance Committee^"^. G.H. Hampton, CERN's Director of Administration, took charge of the difficult task of working out a procedure for the control of the ISR supplementary programme acceptable to national delegations without undertaking the long and complex procedures required to amend the Convention. He was quite aware that the main difficulties would come from the United Kingdom and he therefore first sought approval from the Italians before confronting the British. As he wrote to the German delegate and chairman of the Finance Committee, W. Schulte-Meermann: I would prefer to tackle the question this way because I am afraid that if we put the British and the Italians together, then there is a danger of Italy supporting the most restrictive policy, which will undoubtedly be that recommended by the U.K. If, on the other hand, I can persuade the Italians (as I think I can) to accept this present proposal, I may also be able to prevail separately upon the British in the same way'^.

Hampton's proposal stated that, together with the supplementary programme, the Council should approve a document estabHshing the procedure for its control, including a financial plan with the estimated total cost of the project and annual expenditures for the construction period. This implied that any deviation from the principles listed in the document required fresh consideration by the whole Council and approval by a two-thirds majority, while normal budget decisions were still to be taken by a simple majority, in accordance with the Convention and with the so-called 'Bannier procedure'^^. At the Finance Committee meeting of 3-4 May, 1965, the philosophy of Hampton's proposal was generally accepted - Italy in particular expressed its satisfaction with it - but the U.K. presented an alternative proposal which defined rules for much stricter financial

Getting started

109

control. Two points were stressed in particular: the first established a Unk between the basic and the supplementary programmes, requiring that the financial plan of both programmes should be approved for the construction period of the ISR; the second aimed at introducing the principle of the so-called two-thirds qualified majority, namely that any budget decision had to be taken by a majority of two-thirds of the Member States representing not less than two-thirds of the total contributions. The British delegate, R.St. J. Walker, went as far as to point out that 'the acceptance of two-thirds majorities would be a most important factor in the United Kingdom's decision to participate in the storage rings programme'^^. Occurring just a few weeks before the June Council meeting where the ISR programme was to be finally approved, the British position posed a major problem. Considering that Germany would have approved the ISR programme only on condition that its contribution did not exceed 25% (the so-called 25% rule), and that smaller Member States, on the contrary, were unable to approve it if the 25% rule was enforced because of the resulting financial burden on them, the only way to adopt the programme was to get the participation of nearly all Member States and in particular all major ones. In this case, as Bannier put it. T h e 25% rule would only have a marginal effect and the Netherlands Delegation [and presumably other smaller Member States' delegations] might then be able to accept it as a matter of fact though not as a matter of law'^^. The menace of the withdrawal of the United Kingdom from the ISR project at this stage could have definitely jeopardized the project itself. In order to find a solution before the Council meeting, a special working group was set up by the Finance Committee, including Schulte-Meermann, Walker, A. AUine (France), C.E.I.M. Hoogeweegen (Netherlands), and Hampton. The group met in Bad Godesberg on 14 May and the outcome of the meeting was a revision of Hampton's original proposals that Hampton himself was asked to draft. In particular, following one of the British requests, it was decided that the financial plan of the basic programme during the construction period of the ISR should also be included in the document to be approved by the two-thirds majority of the Council as part of the decision of principle to build the ISR^^. No agreement could be reached, however, on the problem of the voting majority for annual budgets. The U.K. insisted on having a two-thirds quaUfied majority both during the construction period and later; in particular, as the Convention established that the budget should be voted by the Council with a simple majority, they suggested that the Council should approve a special instruction to the Finance Committee by which any budget recommended to the Council by the Committee itself had to be supported by a two-thirds quaUfied majority. The other members of the Working Group, on the contrary, were of the view that 'this question called for more thorough examination than was possible before the June Council session, and that this could be done as part of the study which is now being made of a revised convention to take account of the 300 GeV accelerator project'^^. The members of the Finance Committee were also confronted by strong reservations from the CERN administration. Considering, in fact, that 'the document now presented Notes: p. 157

110

The Intersecting Storage Rings

[was] in effect a proposal from Member States rather than from the Administration', Hampton felt obliged to make clear to the Finance Committee and to the Council what the views were 'in the house' on the proposal itself^^ A severe criticism, in particular, was addressed to the British proposal for a qualified two-thirds majority for the approval of annual budgets. The arguments stemmed from long-time experience infinancialdebates as well as from sound pragmatism: Experience has shown that it is not easy to reach a recommendation within the Finance Committee about future budget figures, and it seems improbable that this will be made simpler by demanding a larger majority before a recommendation may be made to Council. The most likely result would be that, even more often than at present, a decision would have to be taken in Council, where a simple majority would prevail. There is, moreover, no evidence that in those organizations where qualified majorities exist, decisions are more easily taken or are of better quality. CERN has behind it ten years of successful operation unrivalled in any other organization, and one is tempted to feel that this is due in no small measure to the spirit in which the Council has resolved the differences which have arisen in the past. This has rarely been done by recourse to voting majorities, but rather by a readiness to take full account of the positions of individual Member States. This has perhaps been encouraged by the fact that only a simple majority was normally required for such decisions. The more formalistic approach which is implied by the use of qualified voting, particularly in the proposition that this should be applied in the Finance Committee to normal budgets, may well damage this spirit^^.

On the eve of the Council meeting the situation was at a deadlock and those attending the meetings of the Finance Committee, where the revised document was discussed, and of the Committee of Council, where a further discussion took place, could only acknowledge it^^. It was finally decided to submit to the Council a resolution by which it just approved 'in principle' the ISR supplementary programme, with no reference to financial control. Member States willing to participate in it were to decide by the time of the December meeting of the Council, when a document fixing the financial plan and the procedures of budget control would also be approved. In the meantime the Finance Committee would continue the discussions and find an agreement on this topic. Later that same day, at the official session of the Council, Sir Harry Melville declared, to the great rehef of all delegations and of the CERN management, that he was 'happy to announce that Her Majesty's Government has decided in principle that the United Kingdom should participate in the ISR project provided that the project commands general acceptance.' The resolution was unanimously approved and the President, while thanking all those who had had a role in this successful outcome, felt obliged 'to pay tribute especially to the United Kingdom Delegates, for whom this decision had posed particularly difficult problems'^"*.

Getting started

111

4.2.2 THE SEARCH FOR A COMPROMISE As a matter of fact, while the ISR programme was now definitely approved 'in principle', the legal and financial problems were far from being solved, and the members of the Finance Committee had to confront them again when they met in July to continue the discussion on financial control procedures. The opposed positions on the voting procedures arose again as harsh as ever. The British delegate insisted that 'the adoption of the principle of the qualified two-thirds majority for the two programmes was of vital importance for the decision his Government would take in December in connection with the storage rings'; the French delegate, on the contrary, objected that 'there had never been any question of accepting a two-thirds majority of votes and of contributions as proposed by the United Kingdom'^^. He continued arguing that 'the objection raised by the French Delegation to the United Kingdom proposal was one of principle [because this] proposal was completely at variance with the provisions of the Convention.' All other delegations shared this opinion, even though most of them declared that they would eventually accept a simple two-thirds majority, namely a majority of two-thirds of the Member States present and voting, only for the ISR programme. Again, no agreement could be reached. Just before the following meeting of the Finance Committee, the delegates from the four major countries met to find a last-minute compromise. However, they did not understand each other on the main issue. In fact, at the official meeting. Walker said that a compromise had been agreed by which annual budget figures should be approved in the Finance Committee by a two-thirds simple (not qualified) majority for both programmes. To this the French delegate objected strongly, arguing that agreement had been reached that this procedure would be required only for any departure from the estimates in the supplementary programme^^. The ItaUan and German delegates supported this statement. At this point, Hampton reported to Bannier, 'the Finance Committee broke up in a certain amount of confusion, because by then no-one was clear who had agreed with what.' He went on to inform the President of the Council that 'the British are completely unable to accept simple majorities in the Finance Committee for the budget decisions and if they are not given more than this, then they will press for an amendement to the Convention with the consequent delays which would then result'-^^. In fact, the real British worry about budget control was not so much the construction period as the operating period after 1971, when the budget would be running at levels around 300 milUon Swiss francs per year, namely nearly twice as much as in 1965. On the other hand, on the request of the Chairman of the Finance Commmittee, the French delegation issued a document explaining the principles which they, as well as the Germans and the Italians, supported^^. It was clear that the Finance Committee was unable to find a solution for what had become a hard political issue and a tough confrontation of rather rigid positions. It was then decided to arrange for the discussion to continue after the meeting of the Committee of Council, in order to reach a conclusion following directions from higher poUtical levels. Hampton himself kept negotiating informally with the parties involved^^. Notes: p. 157

112

The Intersecting Storage Rings

By the time the Committee of Council met, on November 9th, the British position had been accepted, notwithstanding the fact that all other delegations represented in the Committee would have preferred the method of simple majority^^. In fact, this was somehow an inevitable choice if they wanted to keep the U.K. in the ISR programme. It was agreed, however, that, in case the Finance Committee should eventually be unable to make budget recommendations by the required two-thirds simple majority, it would be up to the Council to reach a final decision in accordance with the provisions of the Convention (i.e. by a simple majority). The document which laid down the financial plan of the ISR programme and the agreed procedures for its control was finally approved by the Finance Committee, submitted to the Council and eventually approved, together with a resolution requesting the Finance Committee to ensure that any figures for budgets recommended to the Council should be supported by a two-thirds majority of Member States represented and voting^^ At the same time all CERN Member States bar Greece announced that they would participate in the programme and the budget for 1966 was approved, thus giving the green Hght to the construction of the ISR.

4.3 Building the machine The design study of the ISR had been worked out by CERN's Accelerator Research Division since 1961 by a special Study Group on New Accelerators led by K. Johnsen. The final report of this Group, issued in May 1964, formed the basis for the eventual implementation of the project^^. Figure 4.4 shows the general layout of the ISR and its association with the CERN PS, as presented in this report. Three experimental halls were foreseen in the project: two of them, at intersections 1-4 and 1-5, were for colliding beam experiments; the third, around I-l, was mainly intended to increase and improve the facilities of the PS for experiments with 25 GeV protons. The protons circulating in one of the ISR rings, in fact, could be used up in a target or extracted, much as in the PS, but at a steady controllable rate rather than being tied to the cycle of the accelerator. The same hall would be used for assembly work during the construction period^^. Facilities (access, floor pit, etc.) were foreseen at all other intersections in order to allow colliding beam experiments in the available width of the tunnel. The original design did not undergo major modifications during the construction phase. After the approval of the project several discussions took place among physicists about the possibility of head-on or near head-on collisions, and the question was raised whether this could be achieved in the ISR project as proposed. It was then decided to reconsider the question of the crossing angle and, as a consequence, of the entire magnet structure of the ISR. In autumn 1965 the Study Group analysed this problem and concluded that no structure with a crossing angle smaller than 9° was practicable^^. Both in this case and in the original 15° crossing, strong magnetic fields over a long distance were needed in order to reach 0° coUisions in good experimental conditions, which would have been feasible

Fig. 4.4 CERN proton-synchrotron and the ISR as presented in the original project (Ref. [72], Fig. 11.1).

c c

u

114

The Intersecting Storage Rings

with superconducting magnets if significant progress had been realized in this field. While the 9° structure required a weaker magnetic field and had in fact certain technical advantages, it was more expensive and caused a significant reduction in flexibility from the experimental point of view, in particular because it reduced the space available for experimental apparatus in the region between the two rings. Following further discussions with physicists, it was recognised that there was no strong clear-cut argument in either direction, but that altogether the original 15° structure had been studied best and thus it was to be preferred. While the structure of the rings remained essentially unmodified, two significant changes in the general layout of the ISR were decided at an early stage of the project development, following discussions between the constructors of the machine and future users^^. The first was the moving of the 25 GeV experimental hall to the opposite side of the rings. In the original position, in fact, a proton beam could be transferred from the PS to this hall only yia the ISR, with the great disadvantage that no beams of any kind could be sent to the hall while installation or maintenance work took place in the ISR tunnel or while colliding beam experiments were being performed in the machine. This significant limitation in the time available to potential users would have seriously reduced the usefulness of the hall. In the new layout, protons from the PS and from the ISR reached the hall, later known as the 'West Hair, by separate and independent channels. The gain in running time largely compensated the sHght disadvantage that this configuration did not allow the mode of operation with internal targets. The West Hall was completed in 1968 and during the construction of the ISR it was used by the ISR Division for assembling and testing the various components of the machine. The second change regarded the colliding beam experimental halls. As we have seen, only two had been envisaged (at intersections 1-4 and 1-5), a choice motivated by economic reasons as well as by prudence due to lack of experience about colliding beam experiments. Both these halls were buried under heavy earth shielding, thus making any material modifications difficult and time-consuming. Moreover, these halls were very similar in character, being very suitable for the detection of particles emerging close to the magnets of the machine. On the contrary, they did not offer the possibility of moving far from the interaction region, as required for time-of-flight experiments, particularly at large angles. The interest in having two experimental halls with different characteristics and greater flexibihty was stressed by the physicists in their discussions with the ISR builders and so it was suggested to suppress hall 1-5 and to construct a colliding beam hall at intersection I-l, in place of the original 25 GeV hall. Due to the topography of the site at I-l, it was possible to provide free access to the hall from both sides of the ring and a considerable amount of flat open space^^. Figure 4.5 shows the agreed final layout of the ISR. According to Johnsen, the ISR project leader from the start, *the ISR construction proceeded fairly uneventfully, although those involved experienced considerable anxiety at times'^^. As a matter of fact, because of the novelty and the complexity of the design of the new machine, the people involved in the construction were well aware that it was 'a daring and bold project', which required tight tolerances and the highest performance for all

Fig. 4.5 The final configuration of the ISR with the beam transfer channels from the PS to the rings and to the West Hall (on the left). The experimental halls at intersections 1-1 and 1-4 are also visible (Keil [85], p. 15).

116

The Intersecting Storage Rings Table 4.3 Staff of the ISR Division at the end of each year of the construction period*

Staff

1965

1966

1967

1968

1969

1970

88

162

216

284

313

320

C) From CERN Annual Reports 1966-1970

components. The reorganization of the structure of CERN at the beginning of 1966, approved by the Council after a proposal of the new Director General B. Gregory, helped to provide an institutional context particularly suitable for the successful realization of the project^^. In the new framework, in fact, an ISR Construction Department was created, which gave its director Johnsen a place in the CERN Board of Directors. Johnsen was also leader of the new ISR Division, which was independent from the Accelerator Research Division^^. The ISR Division was also responsible for the technical study of the 300 Gev accelerator because of the important part played in both projects by some of the key personnel in it. When the division was created, on 1 January 1966, it consisted of 88 staff; thisfigureincreased to 162 by the end of the year and kept rising during the construction period (Table 4.3). Responsibility in CERN top management, institutional autonomy within CERN's organization, andfinancialautonomy as a supplementary programme, were all factors which significantly contributed to the smooth implementation of the ISR project. This, in particular, was completed within the budget and the construction of the rings was completed four months ahead of schedule, certainly a remarkable achievement in the field of high technology devices in international organizations (Tables 4.4 and 4.5). In order to understand the outstanding performance of the ISR Construction Department one must consider two other important aspects. The first is that the project had been carefully studied for several years and eventually implemented by an already experienced team most of the people, in fact, had been involved in the construction of the proton synTable 4.4 Breakdown of annual costs for the construction of the ISR, compared with original estimates* (in units of million Swiss francs)

Estimates (at 1965 prices) Expenditure (at 1965 prices) Actual expenditures

1966

1967

1968

1969

1970

1971

Total

21.7

68.6

73.3

74.6

67.1

26.7

332.0

20.3

66.0

72.4

78.6

68.2

20.1

325.6

21.1

71.1

79.8

88.9

81.4

25.0

367.3

(*) From CERN/FC/1572, 2/5/73. Estimates as in CERN/613, 25/11/65.

Building the machine Table 4.5 Breakdown of ISR costs compared with original estimates* (in units of million Swiss francs at 1965 prices) Item or Group

Actual Costs

196546 Estimates

35.6 5.4

Staff Expenses General Expenses Installation Labour General Overheads Direction and General Services General Layout (plant and buildings) Magnet Magnet Power Supply R F and Beam Observation Vacuum Beam Transfer General Engineering Survey Controls Preparations for ISR Experiments General Studies Group

25.1 2.3 102.2 47.1 5.4 7.4 27.3 22.3 12.2 0.7 20.7 11.6 0.3

35.0 4.6 13.0 25.0 1.5 97.0 66.5 9.1 7.0 28.9 14.7 8.1 0.5 10.5 10.6 --

TOTALS

325.6

332.0

-

-,-+

-

v) From CERN/FC/1572, 2/5/73.

(+) 7.9 MSF for installation labour is included in the actual costs

for the various groups (mostly the Controls Group).

chrotron. The second is that, while formally engaged in an independent, supplementary programme, nevertheless they could largely avail themselves of the facilities and technical expertise already established at CERN. It is significant, in this respect, that most savings were realized in the magnet system, where these two aspects could play a major role. Johnsen organized his department on the basis of the experience gained in the construction of the PS. Working groups were created with responsibility for the different components of the machine (Table 4.6). The group leaders (the 'Parameter Committee', as it was called) met regularly on Mondays and the system worked as a 'guided democracy', according to Johnsen's a posteriori recollection^^^. An important aspect of the construction of the ISR was that, due to the high sophistication of the design and the strict requirements on the components, all project development was made in-house, every part of the machine was carefully designed and tested at CERN while industries received final blueprints with very tight tolerances. In 1969 a special Beam-Equipment Interaction Committee was created to monitor, at the design and prototype stage, all components that could interfere with the beams. According to Johnsen, 'this was a difficult task but an extremely important one [and] this foresight avoided much potential t r ~ u b l e ' ~ ' . Notes: p. 158

118

The Intersecting Storage Rings Table 4.6 The ISR Parameter Committee (Group leaders and consultants) K, Johnsen CJ. Zilverschoon W. Schnell G. Schaffer L. Resegotti B. de Raad S. Van der Meer F. Bonaudi E. Fischer E. Keil J. Gervaise H. Horisberger M.H. Blewett H.G. Hereward

Director of the ISR Department Deputy Director Radio frequency and running-in Controls and computers Magnets Beam transport and injection Power supply General layout and civil engineering Vacuum Theoretical studies Survey and setting of magnets Technical engineering and installation Secretary, administration, budgets and planning Special consultant on accelerator problems

In the following sections I will review the most significant aspects of the construction and commissioning of the ISR. 4.3.1 GENERAL LAYOUT AND ENGINEERING Three groups (Survey, General layout, and Technical engineering) took care of all complex problems related to the civil engineering work on the site, the definition of the general layout of the machine and its facilities and the correct installation of technical systems. Invitations for tenders on the main civil engineering work were sent to about 30 firms in the Member States in October 1965 and, after a long phase of negotiations, a contract was signed in September 1966 and the contractor started excavation work on the site. Work on the 10,000 m^ West Hall started in May the following year. The construction of the circular tunnel where the ISR rings were to be housed resulted in a very complex enterprise because of the special geometry of the machine and of its requirements. The tunnel, in fact, was much wider (15 m) than that of a standard accelerator because it had to contain two rings which, in the centre of each octant, were as much as about 9 m apart. Moreover, it had to house many facilities and devices such as injection and ejection systems, experimental halls, etc. Finally, one must recall the severe requirements on shielding against radiation background in a machine characterized by high energy and intensity of the beams. The ring building was closed in November 1969; by that time the beam transfer tunnels had been completed as well as all construction accessory to the machine, and the installation of machine components was already in progress. An important aspect of the construction of the ISR was that of the proper Unking up of the rings with the PS and the correct positioning of the magnet system in order to provide the very precise field configuration required to guide and focus the beams along the 4 km

Building the machine

119

of tunnels in the booster, the PS, the transfer tunnels and the two rings of the ISR"^^. The expression 'accelerator metrology' was used at CERN to indicate this kind of activity. An accurate triangulation was made of the whole site which assured the self-consistency of the coordinates of the markers within ±1.5 mm throughout the entire perimeter of the ring. For this a special, automatic measuring device (distinvar) was developed, capable of assuring an accuracy of 14.7 /^ over a distance of 50 m^^. Its data were then checked by a special instrument for the optical measurement of distances (mekometer) originally designed and developed at the National Physical Laboratory, Teddington, U.K., a prototype of which was built at CERN and was ready to be used by May 1969. Unfortunately, on the 16th of that month, the Metrology Group's speciaHst for the electronics of the CERN mekometer was killed in a heUcopter crash. As it was impossible to readjust the CERN instrument, two specialists from Teddington were invited to come and make the planned measurement, which they did, however, rather unsatisfactorily due to haste. The positioning of the magnets and other scientific equipment within the framework provided by the triangulation required a much more refined accuracy as some 2000 components had to be positioned in relation to each other with an accuracy of the order of a tenth of a milUmetre. This was achieved by a careful positioning of the magnets with respect to a reference figure made of a double row of 64 survey monuments along the ISR tunnel. By the end of 1970, when the magnets were all in place, measurements of the radial deviation between the measured value of the orbit and the theoretical value was as low as ±0.02 mm for magnets close to a pair of monuments and ±0.06 mm for magnets in the centre of the reference figure. A similar measurement of the vertical deviation gave, on ring 1, a value of ±0.07 m m ^ . 4.3.2 THE MAGNET The aim of the main magnet system of the ISR, as in any strong-focusing, alternatinggradient synchrotron, was to keep the high energy protons on the exact radii of curvature and to provide an alternating focusing and defocusing force (resulting in a net focusing gain) on the beams. In the case of the ISR, however, much stricter requirements were imposed on the stability and correct position of the orbit. Focusing (F) and defocusing (D) bending magnet units were arranged along the circular vacuum chamber together with compensating magnets such as skew quadrupoles (to prevent coupling of radial and vertical oscillations), Terwilliger quadrupoles (to focus protons of different energies at four of the intersection regions in order to reduce the beam cross section and increase luminosity), sextupole lenses (to compensate the restoring forces so that protons of different momenta had the same betatron frequency), and radial field magnets (to steer the beams in the vertical plane in the intersection areas). A great deal of flexiblity had been designed into the magnet structure in order to allow fine adjustments and to correct orbit distortions. In particular, pole-face windings with 12 independent circuits were provided on each magnet unit and a good number of them also had auxiliary windings placed between the main coils and could be moved up and down by Notes: p. 158

120

The Intersecting Storage Rings

remotely controlled screw jacks. In each ring there was a total of 68 focusing and 64 defocusing units, 28 skew quadrupoles, 48 TerwilUger quadrupoles, 16 sextupoles, and 20 correcting radial field magnets. Finally, the beam transfer between the PS and the ISR constituted another large magnet system consisting of bending and focusing magnet units, with special septum magnets and fast kicker magnets at injection points. In the magnet system too, allowed tolerances were extremely tight. The magnet field could not vary by more than 5 x 10""* from unit to unit. To achieve this, the mechanical tolerance on the profiling of the magnet pole faces was ±0.01 mm. The magnet units had to be put in the right place to a precision of about 0.2 mm horizontally and 0.1 mm vertically. The power supply had to have a long-term stabiUty of 10"^ with a short term stability of 3 x 10~^. These accuracies were achieved, commented Johnsen with a sense of pride that can be understood^^. As early as 1964 a first magnet model was ordered and magnetic measuring techniques were developed by Johnsen's group; measurements with this model started in the fall of the following year. In the same period extensive investigations were made for the choice of steel for the magnet cores. By August 1966 the Magnet Group had sent detailed specifications to 38 steel firms, twelve of which gave preliminary positive answers, and then started technical discussions with prospective manufacturers. The specifications of the cores and the invitations to tender were issued by the end of that year and all main components of the magnet system were ordered during 1967^. In the summer of 1968 the first elements of the series production of the magnet system started to arrive at CERN and the Magnet Group staff* moved into the new West Hall to assemble and test all magnet units before installation in the ring tunnel. The systematic, careful measuring programme was made possible by two precision benches of black diabase equipped with probes and electronic readout and by the use of an on-line computer for the immediate reduction of magnetic measurements. Special vehicles were designed and built for the transport of the different units in the ring tunnel and in the beam transport lines. Assembly and measurements of the main magnet units were finished in March 1970 and in May all 264 units were installed in the ring tunnel. By the middle of the same year, all auxiliary magnets had been delivered and measured and their installation and cabling proceeded together with the installation of the corresponding vacuum elements. The system was provided with a specially designed 'field-display system' for monitoring magnetic fields and gradient during operation. The result of the Magnet Group's work, after the commissioning of the machine, was summarised in a few lines of the CERN Annual Report for 1971: All magnets have performed without failure, no change in magnetic behaviour has appeared, and the influence on the proton beams corresponds well with forecasts based on previous magnetic measurements. The field display system has proved reliable and accurate, and is regularly used as a reference to define central momentum and for setting the excitation of the main magnets and their auxiliary windings^^.

Building the machine

121

4.3.3 THE VACUUM SYSTEM It was clear from the very beginning that the vacuum problems were 'of the most severe technological ones [to be expected] in the construction of the ISR"*^. In fact, proton scattering in the residual gas affected the performance of the ISR in two respects: the lifetime of the circulating beams and the interaction rate in colliding beam experiments. It had been calculated that an average pressure of 10"^ torr was required along the whole length of the vacuum chamber while a still lower pressure, less than 10"^^ torr or even 10"^^ torr, was required in the colliding beam areas where one wanted to observe scattered protons'*^. As a comparison, one can consider that in conventional accelerators, pressures around 10"^ torr were considered adequate and that values less than 10"^ torr were feasible only in small bench-models when the ISR was designed. In this case the total length of the vacuum vessel in the two rings was almost 2 km with thousands of joints. In fact, the ISR was to be by far the biggest ultra-high vacuum system in the world^^. For the design of the vacuum chamber and of the pumping system, the ISR people could avail themselves of the experience gained with the CERN Electron Storage and Accumulation Ring (CESAR), a machine which had been designed and built in the early 1960s to study experimentally some of the basic problems of the proton storage rings^^ The design pressure of CESAR was 10"^ torr: in fact it succeeded in achieving a working pressure of 5 x 10"^^ torr for most of its life, up to a mean pressure of 7 x 10"^^ torr in its final phase (June-December 1967). Three aspects were to be considered for the proper management of the vacuum problem: the structure of the vacuum chamber, the baking process, and the pumping system. The vacuum chamber of each ring of the ISR was composed of many sections of different type, joined by more than 6000 demountable flange seals with bellows and metal gaskets^^. One type of chamber section was that included in the magnet gaps: it had an oval cross section of internal dimensions 160 x 52 mm and 2.3 mm wall thickness. A normal chamber for straight sections was cylindrical with a diameter of 160 mm and a wall thickness of 1.5 mm. Special wide chambers were also provided in straight sections at RF acceleration stations, pick-up stations, and so on. All these chamber sections were made from seam welded, high temperature (1000 °C) vacuum annealed stainless steel sheet with low magnetic permeability (// < 1.004) and low desorption rate. All parts of the system were designed and tested to resist a baking temperature up to 300 °C. In order to allow the separation of one given sector of the system for repair or modification without exposing the whole chamber to atmospheric pressure, a set of special sector valves was foreseen between the eight outer arcs, the eight inner arcs and the eight interaction regions. These valves had to be capable of withstanding baking at high temperature in both the open and closed states and had to be so tight that either of the two rings could be operated with ultrahigh vacuum while the other one was partly or wholly exposed to air. Such valves did not exist on the market and in fact they were at the limit of what was technologically possible. Their development resulted in one of the most difficult aspects of the whole vacuum system^^. Notes: p. 158

122

The Intersecting Storage Rings

All parts of the vacuum chamber were degassed by heating at about 250 to 300 °C in a helium tank for 2 hours and then, after installation in the rings, there was a final bake-out under vacuum at 300 °C for 24 hours. This, in fact, was the procedure as originally foreseen. During the construction period new bake-out procedures, which seemed satisfactory in laboratory tests, were tried in order to limit the duration of a shut-down of the machine involving the vacuum system^"*. The method adopted consisted in baking-out at 200 °C for 5 hours. The first year of operation of the ISR revealed, however, that the circulating beam led to drastic pressure increases, which in turn limited the maximum current that could be stored. It was understood that the beam created ions from ionization of the residual gas; these ions bombarded the chamber walls liberating gas molecules which were a further source of ions. As a consequence of this avalanche phenomenon, a 'pressure bump' was created once a certain current level was exceeded^^. It was then decided to go back to the original baking-out procedure as well as to improve the surface treatment for critical chamber sections before installation by glow-discharge cleaning. Moreover, more pumping capacity was added in the form of hundreds of titanium sublimation pumps all around the rings^^. On this occasion the great flexibility embedded in the ISR design proved decisive: in fact, the addition of these powerful additional vacuum pumps was possible because the vacuum vessel was accessible, particularly in the sideways open long bending magnets. Without this unforeseen facility the circulating beam intensity would have been limited to very modest values ( « 1 A) giving in turn totally unsatisfactory luminosities for the physics experiments^^. The pumping system of the ISR was in three stages. The first one, designed to rough down the system to 10"^ torr, consisted of 35 turbomolecular pumping stations per ring. The pressure was then taken down to about 10"^^ torr by 144 sputter-ions pumps per ring. The third stage included titanium sublimation pumps at critical places. At the beginning of operation these were 34 around either ring; later these were about 500 in the whole system. As a result of these efforts to improve the vacuum system, an average pressure value as low as 1.5 X 10"*^ torr was achieved in the first period of operation while, during the following years, average pressures of almost one order of magnitude lower were attained, with values as low as 10~^^ Torr in experimental areas (Fig. 4.6). 4.3.4 THE RF SYSTEM AND THE STACKING PROCESS The purpose of the radio frequency (RF) system of the ISR was to pick up the bunches of protons arriving from the PS, to accelerate them from the injection orbit to the stacking orbit, and to deposit them there without affecting the existing ribbon of stacked protons. This process had to be synchronised in such a way that the frequency of the accelerating field was in tune with the arrival frequency of incoming bunches of particles and out of tune with the circulating frequency of the stored particles. Thanks to a phase-lock system, the bunches of protons from the PS were trapped in the RF 'bucket of stability' in phase space and moved bodily across the tube to the stacked ribbon. The radio-frequency system, designed to achieve this process of acceleration and stacking, consisted of seven

123

Building the machine

lO^-f

ISR

VACUUM - Average Pressure •

RING 1

o RING 2 3

0

(x7

•

ex o

8

0

•

sj

•

0

1d"-j

• 0

8

8

9

•

•

Balctou \s

200-^300*C Subl. Pumps

0

•

3J 2]

id

71

GLow DISCHARGE

^

»

•'

•

•

73

I

H —

75

V

s

8 •

1

1

0

•

0

•

•

~i

CLEANING

77

•

¥'

79

1

81

-4--.

• H —

1983

Fig. 4.6 The average pressure of the ISR vacuum for the years 1971-1983 (Johnsen [81], p. 9).

accelerating cavities in each ring, arranged in two groups of four and three units respectively, with a centre frequency of 9.55 MHz (i.e. the frequency of the PS at maximum energy) and capable of delivering accelerating voltages from about 20 kV down to 50 V. Apart from the usual highly sophisticated technical development, the main, improvement in the RF system during the construction of the ISR came from a theoretical suggestion, the so-called 'stacking with missing buckets' scheme, originally proposed by W. Schnell after a suggestion of A. Schoch^^. The starting point is to consider that a pulse from the PS normally consists of 20 bunches and that the circumference of the ISR is 3/2 times that of the PS. As the frequency of the two machines must be the same it follows that there are 30 buckets in the ISR, only 20 of which are occupied by a train of bunches. In other words, a pulse from the PS would fill only 2/3 of one ISR ring. Therefore, during each stacking cycle, the 10 empty buckets would enter the ribbon of stacked particles as a sort of 'beam hole' in the phase space, causing a dilution of the beam intensity. In order to overcome this limitation in the stacking efficiency the RF system was designed so as to chop the signal following the passage of the last bunch in a pulse until the arrival of the first bunch of the next pulse. Among the tasks of the RF Group there was the realization of highly sophisticated diagnostic equipment to control the stacking process and the quaUty of the beams. More Notes: p. 158

124

The Intersecting Storage Rings

than a hundred stations for beam position monitoring were installed around the vacuum chamber, coupled with a video system for displaying information on oscilloscopes. Orbit distortions of about 0.1 mm could be detected. 4.3.5 CONTROLS The Controls Group was established in the middle of 1966 and it soon devoted particular attention to the possible appUcation of an on-line process computer for the machine control system. This sounds obvious today but it was, in fact, a matter of research and development in the mid-1960s. The Group also had responsibility over the development of the beam dump system and over the personnel protection system. At the end of 1970, when the installation of most of the control and other signal transmission cables was finished, the total length of installed cable was nearly 1000 km and more than 20,000 individual cables and over half a million individual connections had been made^^. Among the various aspects of the control of the machine performance, special attention was paid to the remote control of the magnet units, to the monitoring of the vacuum system, and to the monitoring of the beam quality. The control system set up for the ISR enabled the operators in the control room to use computer terminals to record and adjust the currents of about 300 magnet power supplies as well as to adjust the vertical position of individual magnet units to a precision of 1/100 mm^. As to the control equipment for the vacuum system, 300 ionization gauge control units were ordered in 1968 as well as 325 power supplies for the sputter-ion pumps. The following year a system to control the turbomolecular pumping system was designed and tested and an order was placed to manufacture 80 complete systems. Finally, in 1970, 120 subUmation pump control units were purchased. The monitoring of the temperature of all parts of the vacuum chamber during the bake-out of one sector was provided by four scanning systems. We have already described the attention paid to the development of highly sophisticated beam diagnostic equipment. In fact, all information about the quality of the beam was available on-line in the ISR control room. In particular, the beam monitoring system, for both the beam-transfer system and the storage rings, included 23 luminescent-screen monitors, ten of which were observed via radiation-resistant TV cameras, and 16 secondary-emission monitors for measuring beam phase-space ellipses. The pulsed beam current in the beam-transfer system and at injection could be monitored and read out in the control room to an accuracy of better than 1 % while a special d.c. current monitor measured the circulating beam in the storage rings in the range from about 100 //A to 20 A, with the current values displayed on digital voltmeters or plotted on a paper recorder. The beam diagnostics system continued to be improved after the commissioning of the ISR and, in the words of Johnsen, 'this development belonged to the most exciting experiences at the ISR'^^. The most important result in this field was the use of the so-called 'Schottky noise' as an element in beam diagnostics. This phenomenon consists in the statistical fluctuations in the beam current and beam centre of gravity due to the finite

125

Building the machine

number of circulating protons. These fluctuations are very small and had not been observed in accelerator beams before they were observed in the ISR in 1972. The Schottky noise soon became extremely important not only as a tool for diagnostics in the ISR and other coUiders but also for the practical development of stochastic cooling^^. 4.3.6 RUNNING-IN On 29 October 1970, the ISR team was ready to inject the first protons into one of the rings. Here is how Johnsen summarized the event to CERN's Scientific PoHcy Committee: At 8.00 p.m., when the test was due to start, all was in readiness. [...] At 8.32, with all stops taken out, a pulse from the PS was sent along the beam-transfer hne and injected into Ring 1. It circulated at once and stayed in the ring until kicked out by the dumping system. Before any adjustments were made, the first Ufetime test took place between 8.58 and 9.19 p.m. The dumping was stopped and the pulse allowed to circulate for 21 minutes. During this time, the total loss was 22% and only 0.5% per minute at the end of the test. The average pressure around the ring was about 3 X 10"^ Torr, nitrogen equivalent. [...] At 11.00 p.m., rather ahead of the planned schedule, came the turn of the RF group. After a few adjustments, but with no attempts of proper tuning, the beam was captured at once. Then the pulses were accelerated across the aperture. Although no plans had been made for doing any stacking of the pulses, it was decided at 00.28 on 30 October to attempt this and the first stack of 55 mA was obtained. [...] At 2.00 a.m. (the end of the run), another Hfetime test was made with intermediate current, only 80 mA (one 20-bunch pulse), and it was found that the beam loss was less rapid than at the higher intensity. [...] During this first test, every component of the ISR had been in use, everybody in the ISR Division had been involved and so all had good cause to feel pleased with the results^^.

Applause burst out at the end of Johnsen's report and the acting chairman of the SPC, F. Perrin, expressed his hope that 'full intensity would soon be reached as it would be most important for ISR physicists to start before the Batavia accelerator operated at 500 GeV'^. The test runs were resumed in January 1971 and Ring 2 also went into operation. On 27 January, beams at momenta of 15 GeV/c were stacked in both rings with no measurable loss and two successive runs were made, the first one with four bunches, the second with the full PS intensity of 20 bunches. For these runs, two teams of physicists had set up counter telescopes at crossing points 1-4 and 1-5 and, 'happy as children on Christmas day', announced that colliding beam events were observed^^. With a beam-energy of 15 GeV in the rings, the equivalent accelerator energy was close to 500 GeV: Johnsen could proudly announce to the SPC that 'the main conclusion of the day was that the ISR can provide an effective facility for research at the highest centre-of mass energies available anywhere in the world'^^. While rightly satisfied with the successful start of their machine, the builders of the ISR had also to confront the first technical problems. In particular, during the very early Notes: pp. 158 ff.

The Intersecting Storage Rings

126

operation of the accelerator, it was observed that when they tried to stack beam currents higher than about 3 A, instabilities occurred that resulted in beam losses. Johnsen called this phenomenon the 'Brick Wall'^^. This came as a surprise because this kind of instabiUty, associated with large coherent transverse oscillations, had been taken into account, and a sextupole field component had been built into the magnet profile to avoid it for currents much higher than 3 A. In the event, it was recognized that the stability requirement was violated in parts of the beam while holding for the entire beam on average. It required a great deal of theoretical work and extreme accuracy andflexibilityof the components involved to compensate the effect and to incorporate a proper feedback system in the machine. In fact, this development continued over many years and led to a gradual increase of the stabiUty limit to around 60 A. The highest stacked current ever seen in a single beam was 57 A, while normal currents during high-luminosity runs were 30 to 40 A. As a consequence, the maximum luminosity of the machine kept rising over the years, reaching the value of 10^^ cm~^ sec~^ almost two orders of magnitude higher than the design value (Fig. 4.7)^^. After further tests with increasing beam energies, the first pilot run, under conditions suitable for colUding beam physics, was successfully carried out during the night of 24-25 February, when beams of about 700 mA were left circulating in each ring for 6 hours: 1.4 ij

Maximum ISR luminosity during physics runs

1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4

Design luminosity 4xl0^cmH •

OJ

1-8 sclow-^

0.2 !• 0.1 0

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

Fig. 4.7 Maximum ISR luminosity during physics runs. One can see the dramatic effect of the insertions of low-P sections at intersections I-l and 1-8, the latter with superconducting quadrupoles (Johnsen [81], p. 18).

127

Setting up the physics program At the end of this time, the loss had been 1 mA in one ring and 11 mA in the other, and it had been proved that the ISR was ready to receive thefirstexperimental teams on the floor. Consequently, [...] 1st March was taken as the end of the construction period^^.

The ISR was ready to be used by physicists and they were in fact actively using it when the machine was officially inaugurated, on 16 October, 1971. As V.F. Weisskopf said on that occasion, quoting I.I. Rabi, The ISR does not ask questions of nature; it grabs nature by [the] throat and forces her to speak'^^. 4.4 Setting up the physics program Even though limited to proton-proton coUisions, the new machine opened up a new and wide range of energies for experimentation, until then accessible only with cosmic ray experiments. On the other hand, the non-conventional design of the ISR and the novelty of doing physics with colliding beams presented a technical challenge to European physicists. Early in 1968 a special Working Party was set up within the ISR Department to discuss the problems involved in experimenting with the new machine. The aim of the Working Party was to help define an experimental programme for the first period of ISR operation and to design a large, general purpose magnet system for one of the intersecting regions. Regular meetings with CERN physicists were organized by E. Picasso and K. Winter, attended on average by about 40 people, where both the characteristics of the ISR and possible physics experiments were presented and widely discussed^K In June 1968, when the ISR project was approaching the mid-point of the construction period, an ISR Users' Meeting was called which was attended by about 300 scientists and represented the first occasion when proposals for experiments with the ISR were publicly discussed^^. Four broad areas of investigation were identified for the first phase of operation, namely total cross section, elastic scattering, diffractive and exchange processes, and particle production^^. After the meeting many groups from outside CERN expressed their interest in participating in the experimental programme at the ISR and by the end of October the ISR coordination group had been contacted by experimental teams from 21 European laboratories: ten from the United Kingdom, three from Sweden, two each from Germany and Italy, and one each from France, The Netherlands, Denmark and Norway^^. 4.4.1 ORGANIZATION AND MANAGEMENT OF THE ISR EXPERIMENTAL PROGRAMME Around this time a lively debate arose inside the CERN Directorate about the kind of organization to set up for the management of the ISR and the definition of its experiNotes: p. 159

128

The Intersecting Storage Rings

mental programme^^. On the one hand, G. Cocconi, then leader of the Physics I Department, had suggested creating a strong autonomous group of people, working almost full time on the ISR, and attached to the Physics I Department. The role of this group was to design and build general facilities for the experimental areas, to conceive and perform experiments at the ISR and to study experiment proposals from outside users in order to assess their feasibility and submit them for the approval of CERN's Nuclear Physics Research Committee (NPRC). Cocconi's proposal reflected the main role that experiments with electronic detectors (the domain of the Physics I Department) were expected to have at the ISR as well as the desire of CERN physicists to keep control over the new facility. At the Board of Directors, Cocconi himself wanted to stress 'the difficulty of finding space for visitors on the ISR experimental programme'^^. An alternative proposal was advanced by the leaders of two other departments, C. Peyrou, head of the Physics II Department (dealing with bubble chamber experiments), and M.G.N. Hine, leader of the Applied Physics Department. In their opinion, the 'proposal and preparation of specific experiments should be left open to the free market for groups of physicists of Physics I and Physics II and outside, as is done for the PS'^^. The discussion and selection of proposed experiments should be the task of a Committee made up of physicists from both physics departments as well as from outside CERN. Finally, the preparation of large general purpose experimental equipment and facilities had to be left to a group of the ISR Department, possibly assisted by a working party of physicists interested or involved in ISR experimentation. Peyrou also stressed the potential interest of bubble chamber physicists in the ISR and therefore the need to encourage them 'to do that sort of physics [in order to] make of the ISR a less restricted gadget than they appeared at the beginning'. He then concluded: If I am completely wrong in my prediction and my optimism and if physics at the ISR is better done by some happy few grouped in a strong group or in a small division, then we better attach it, right away, to the ISR Department.

The difference of opinions echoed the problems and difficulties encountered a few years before in the organization of the experimental work around the PS and reflected the contradictory relations between CERN's physicists and visitors^^. Peyrou and Hine's proposal was eventually accepted. By the time of the second Users' Meeting, on 2 and 3 December 1968, it had been decided to leave to the ISR Department the responsibility for building experimental facilities at the ISR and for preparing the approved experiments in collaboration with the experimental groups. It was also agreed to create an ISR Experimental Committee (ISRC) with the task of examining experimental proposals for the ISR and recommending a coherent experimental programme to the NPRC^^. W. Jentschke, then at DESY, Hamburg, was chosen as the chairman of the Committee, which included five members from outside experimental groups, four members from CERN experimental groups and three (later four) members from the ISR Construction Departments^.

129

Setting up the physics program

This decision was probably suggested by a proper consideration of the pecuUarity of the ISR, namely the need of strong coupUng between the experimental activity and the management of the facility. This had at least three aspects: firstly, any large experimental facility would interfere with the machine operation and would require proper coupling with its components; secondly, the succesful running of experiments depended critically on the correct performance of the machine and on the fine adjustment of all its parameters; finally, after the commissioning of the ISR, an ongoing research activity on 'machine development' would be required to deal with the problems which arose in such a novel device and to improve its performance. The arrangements were also probably influenced by established CERN practice in the definition of the experimental programmes. In fact, two committees already existed, the Track Chamber Experiments Committee (TCC) and the Electronic Experiments Committee (ECC), devoted to the study and selection of experiment proposals with bubble chambers and electronic techniques respectively. They reported to the NPRC which had the overall responsibility for decisions on CERN's research programme. All three of these committees included members from both inside and outside CERN and, while the chairman of the NPRC was CERN's Director General, the chairmen of the other two were always eminent outside physicists. Thus the choice eventually made for the ISR fitted into an already tried framework for handling the sentitive issue of decision-making procedures for research programmes. However, unUke the two other committees, the ISR Committee was based on a machine rather than on a detector system. In this respect, the ISR was opening a distinct new tradition of research management in particle physics, based on the use of colliding beam accelerators. Following the example of the EEC, the ISR Committee held both open and restricted meetings. The former were devoted to the presentation and discussion of experiment proposals and progress reports on the programme; in the restricted meetings, the Committee decided on its recommendations to the NPRC. At the ISR Committee's first meeting, on 13 January 1969, it was decided to call for experiment proposals to be arranged in the four intersections made available for physics experiments during the initial period of operation (I-l, 1-2,1-4,1-6). By November, about 30 proposals had been studied and revised and the Committee was in a position to make recommendations to the NPRC for experiments to be distributed at intersections 1, 2, 6^^ Intersection 4 was reserved for a large magnetic analysis system, the so called Split-Field Magnet, whose construction was to start soon and that we will discuss later. 4.4.2 THE DEFINITION OF THE FIRST EXPERIMENTAL PROGRAMME The definition of an experimental program at the ISR was not just a matter of choosing between different proposals coming from several laboratories. It also required dealing with the problems arising from the simultaneous running of several experiments. The ISR Committee had to cope with this kind of problem from the very beginning of its activity Notes: p. 159

130

The Intersecting Storage Rings

and recognized that careful consideration of questions concerning the compatibility of groups of experiments was prior to definite conclusions about individual proposals^^. The Committee recommended that the experimental groups that had suggested similar arrangements of auxiUary equipment should agree on some form of common apparatus and it stressed that 'experimental equipment [should] be designed for relatively easy removal in order that experiments can use the region in fairly rapid succession, or on an alternating basis'^^. As an example of this search for compatibiUty among different experiments, and also as an example of the decision-making process in this early phase, we can consider how the first experimental programme was arranged in two intersections, 1-2 and 1-6, the first devoted to the study of stable particle production, the second to proton-proton total cross section and proton-proton scattering^^. The study of particle production in proton-proton collisions at ISR energies was independently suggested by several groups, following the call for proposals from the ISR Committee at the beginning of 1969. The most ambitious one, aimed at investigating the production spectra at low energy around 90°, was proposed by the so-called 'Scandinavian Collaboration', a group of physicists from the universities of Bergen, Copenhagen, Lund, Stockholm, and Uppsala^^. A significant aspect of the proposed experimental set-up was a large magnet providing a magnetic field of about 1 Tesla around the interaction region and parallel to the colUding proton beams. This field did not affect the beams while allowing momentum analysis of the secondaries in a 2n solid angle with cylindrical symmetry around the beam direction. This magnet was considered with interest by the ISR Committee because of the possibility to use it 'for further and more refined experiments'^^. Three other groups proposed experiments on particle production: a 'British Collaboration', suggesting to search for intermediate bosons; a CERN Team, suggesting to measure multiparticle spectra; and a CERN/Holland-Lancaster/Manchester collaboration, which wanted to study particle production at large angles. The Committee urged the four groups to discuss the possibility of a common apparatus and, following a meeting of their representatives, a report was presented to the Committee which acknowledged that 'the British and Dutch proposals are not only compatible with each other but a combination of them at the same intersection would be desirable for both parties' and suggested intersection 1-2 as suitable for the two combined experiments^^. The Scandinavian experiment, on the other hand, could not be combined with them since it completely surrounded the interaction region. It was then suggested to arrange this experiment in intersection 1, provided that the experimental equipment was designed so as to be easily movable in order to share the available running time with another possible experiment. As to the CERN proposal, it was recognized that this experiment depended on the availability of a kind of magnet which was not expected to be available in the near future, so it was suggested that the CERN team should join the Scandinavian Collaboration. It required more than two months and three ISR Committee meetings to examine concretely all the proposals in the light of compatibility among groups of experiments

131

Setting up the physics program

which could be carried either simultaneously or alternately. At its sixth meeting, early in June 1969, the ISR Committee decided to reject the Scandinavian Collaboration's magnet and asked the Collaboration: To examine the possibilities for use of this magnet in a wider scope than that of their original proposal, what features of the magnet would make it valuable as a generalpurpose facility, and to compare it with other designs (for example, a central-field magnet) in providing complementary use with the spHt-field magnet^*.

The Committee then asked K. Winter to explore the possibiUty of arranging all experiments on particle production at intersection 2, including one more experiment proposed by a collaboration from the Universities of Bologna and of Michigan^^. Following a meeting of representatives of all interested parties it was finally agreed that different groups should be responsible for different angular regions: the CERN/HoUandLancaster/Manchester Collaboration for the small angle region, up to 150 mrad; the Bologna/Michigan Collaboration for the medium angle region, starting at 100 mrad in order to reduce the overlap with the small angle spectrometer; the British Collaboration and a team of the Scandinavian group for large angles (from 300 mrad to njlf^. Opposite the large angle spectrometer, the British could install their muon detector to search for the intermediate boson. In fact, since the search for large-angle muons required a good knowledge of the spectrum of the pions, this experiment had to rely on the data collected by the other groups in the same region. The arrangement, in fact, did not satisfy the Scandinavians who, while expressing their wiUingness to collaborate with other groups at intersection 2, insisted that their 'main interest continues to be the study of particle correlations, which requires a detector of large soUd angle.' They also suggested a new experimental set-up of their original proposal and reiterated their request for intersection I-l^^ They did not succeed, however, as this intersection had already been committed with three other experiments, and the ISR Committee finally decided to recommend to the NPRC the arrangement suggested in Winter's report^^. The NPRC approved this arrangement and the four experiments, labelled R201 to R204, started at the very beginning of ISR operations'^. A somewhat similar pattern was followed for intersection 6. Here it was advised to set up the experiments on elastic scattering and total cross section, following the proposals of three groups, namely: a group from the University of Pisa (later in collaboration with a group from Stony Brook) who proposed to measure the total cross section; a CERNGenova-Torino Collaboration (later with a group from Aachen) who proposed to measure the elastic scattering cross section; and a Rome (Istituto Superiore di Sanita)-CERN Collaboration who proposed to measure the elastic scattering cross section in the angular region of Coulomb scattering (i.e. at small angles)'^. A meeting between the representatives of the three groups was held, together with F. Bonaudi and G. Cocconi, and a possible scheme of operation was suggested according to which the Pisa experiment on total cross section alternated with a combined set-up of the two elastic scattering exNotes: pp. 159 ff.

132

The Intersecting Storage Rings

periments running simultaneously and taking data in different angular regions, within and beyond the region of Coulomb scattering respectively^^. From the practical point of view, the hodoscope of the Rome experiment could remain permanently installed while the apparatus of the other two experiments had to alternate over a period of a few months and a change-over time of 3-4 days. Further discussions among all future experimenters at the interaction region 6 helped to design a proper arrangement for the several instruments and to plan the experimental programme^^. The scheme, however, proved unworkable: a few months before the start of operations the three groups became aware of the difficulties and conflicts involved in running their respective experiments in a single interaction region and therefore the ISR Committee suggested that a new intersection, 1-8, should be opened to arrange the Pisa-Stony Brook experiment on total cross section^^. The Committee wanted to emphasize, however, that this was *an emergency measure [which] should not be interpreted as an opening up of this region for other experiments'. This underlining appeared opportune as a previous request to open another interaction region for experiments had been turned down because of budgetary and other difficulties with respect to the overall CERN programme^^. In the event, intersection 8 was definitely added to 1, 2, 4, and 6 as one of those exploited from the very beginning of ISR operations^. 4.4.3 THE SPLIT-FIELD MAGNET It was soon recognized that one of the interaction regions at the ISR had to be reserved for a large general purpose magnet system, capable of momentum analysing most of the secondary particles produced in proton-proton collisions. In order to avoid any perturbing effect on the beam orbits in the rings, a system of magnetic fields had to be designed which compensated each other in some way by suitable alternation of sign, so that the circulating protons, although deflected whilst passing through the system, reverted to their equilibrium orbit as they left the device. A few designs meeting this requirement were discussed early in 1968 at the open meetings of the Working Party on the experimental programme and a special Study Group for large magnet detectors was set up^^. At the first Users' Meeting, in June 1968, several possible arrangements for general purpose magnetic systems were presented and extensively discussed. All of them considered vertical fields, so that deflections occurred in the horizontal plane, but could be divided into two classes: the first included a central analysing magnet, namely a magnetic field across the centre of the interaction region; the other had only downstream fields. In the words of the reviewer. It depends on the experimental programme which is preferable. Extrapolation from known interactions and perhaps speculation about unknown interactions should be decisive. Once the question about the central magnet is settled, it is believed that the sorting out of the remaining variants is readily obtained^^^.

Setting up the physics program

133

In fact, while downstream magnets were necessary to analyse the many secondary particles emitted at small angles with respect to the direction of the colliding protons, a central field was useful if one wanted mainly to analyse particles produced at large angles. It depended on what one expected from proton-proton coUisions in the ISR to make a choice between the two alternatives. By the end of the year attention had concentrated on three systems, two of which were based on a central magnet with uniform field covering the interaction region while the third foresaw a large magnet providing fields of opposite polarity on either side of the interaction region and zero field at the crossing point itself (split-field magnet, hereafter SFM)^^^. In order to study these proposals in detail and to make a choice, a special working party was set up by the Director General of CERN, which eventually submitted a report^^^. Behind the technical comparison between the three designs, the real issue was the choice between two radically different experimental interests. On the one hand, the main proponent of the spUt-field magnet system, CERN's physicist and later Nobel Prize winner J. Steinberger, could claim that all experimental evidence so far confirmed that hadronic collisions produce secondary particles (pions and other hadrons) largely concentrated at small angles and that therefore that was the region to be privileged in investigations at higher energies^^^. On the other hand, the main supporter of central field systems, the American physicist G. O'Neill (who was also one of the fathers of the storage rings idea), stressed the importance of covering as much as possible of the solid angle around the intersection region as well as the necessity of making good momentum measurements both on charged hadrons and on electrons and muons^^^. O'Neill's suggestion was to prove more far-sighted, as we shall see, but it did not succeed. At the 3rd meeting of the ISR Committee, in fact. Director General B. Gregory reported that it had been decided to build 'a simplified version of the so-called spUt-field magnet'^^^. No explicit reason for this choice could be found in the files, but one may venture to suggest that the prestige and influence of Steinberger, on the one hand, and a kind of sound conservatism which led to look at the ISR in terms of extrapolation from known results, on the other, determined the decision of CERN's directorate. This decision did not please O'Neill, however, and as his following proposal for an experiment based again on a special magnet was also rejected by the ISR Committee, he decided to drop any collaboration with CERN^^'^. The Magnet Group of the ISR Department was charged to build the magnet proposed by Steinberger while G. Charpak and A. Minten were to coordinate a working group on the detection apparatus and other equipment to be associated with the magnet, 'both in the Ught of the proposed experiments that may use this magnet and in the light of what may be needed for the entire system to be used as a general facility'^^^. A set of large multiwire proportional chambers developed by Charpak was eventually chosen as the basis for the experimental apparatus at the SFM^^^. In the event, the ISR Committee felt it should not commit itself too much with CERN's physicists in the future exploitation of the SFM facility and asked Charpak and Minten's group to request wider collaboration outside CERN^^^. Two groups, in particular, had Notes: p. 160

134

The Intersecting Storage Rings

expressed an interest in participating in the building and testing of SFM detectors and they then joined the CERN group in a test and survey programme which was approved by the ISR Committee^^^ In spring 1971, just after the commissioning of the ISR, the ISR Committee held an open session to review the progress of work on the SFM faciUty and called for experiment proposals for using it^^^. In October several proposals were on the table and, after discussion at an open meeting, the ISR Committee approved a number of experiments to be run in the first phase of SFM operation^^^. At the same time, the Committee suggested that CERN appoint an SFM co-ordinator for planning and managing the experimental programme at this facility, taking as a model the co-ordination of experiments for the Omega Spectrometer. In the event, K. Tittel was appointed as the first SFM co-ordinator. In May 1973, the 1000 tons complete magnet was carried from the assembly hall to intersection 1-4 and accurately positioned. The first physics run of the SFM faciUty was then successfully performed at the end of August and the first experiments started taking data. By the end of the year, the SFM facility had been in operation for about 300 hours for physics, with beams at all standard energies and beam currents from 3 to 7.5 A^^"*.

4.5 Keyhole physics The experimental programme set up for the first phase of operation of the ISR clearly reflected a policy aimed at offering as many experimental groups as possible the opportunity to work with CERN's new accelerator. The ISR Committee and the CERN estabUshment did not want to give one group the monopoly of experimentation at one of the intersections or the exclusive right of pursuing a specific scientific objective. This policy was in the tradition of CERN and derived from the laboratory's multinational personality. At the same time, the experimental programme at the ISR also reflected the lack of experience with collider physics. Physicists designed ISR experiments with the same approach used with fixed target accelerators where, due to the kinematics of the collisions, one has the compression of most of the solid angle in the centre-of-mass into small laboratory angles with respect to the beam. The particles emitted at large angles are mainly fragments of the target hadrons while most secondary particles are produced in the forward direction. Therefore it appeared reasonable to allot each experiment one small wedge in the imaginary sphere surrounding the collision point with a strong bias towards small angles. This is what was eventually called 'keyhole physics'^^^. It was realized too late that, due to the kinematics of head-on colHsions and to the newly discovered phenomena, the entire laboratory solid angle was important and a completely different approach was required. Experiments had to be based on detectors covering as much as possible of the region around the collision point in order to investigate events occurring at large angles, which are usually mixed up with those at small angles in fixed target collisions, and to study correlations among secondary particles.

Keyhole physics

135

Among the very first experiments proposed at the ISR, that of the Scandinavian Collaboration provided an example of what would have been a more suitable approach to ISR physics. As a matter of fact, the axial field magnet proposed by the Scandinavians represented a completely different experimental philosophy with respect to the vertical-field magnet systems under discussion at that time for intersection 1-4. The ISR Committee could not accept it as a specific experiment for it would have monopolized a whole intersection; on the other hand, it did not feel up to accepting it as a general facility in competition with the SFM. The decision not to accept the magnet proposed by the Scandinavians, a political as well as a scientific decision in the light of the above considerations, appears a posteriori as an opportunity missed to have this kind of magnet spectrometer available at the very start of ISR operations. One would be tempted to ascribe the timidity and delays in equipping the ISR with big detectors to some 'strong element of conservatism in the early experiments and in the experimental selection procedures'^^^. As a matter of fact, some cultural inertia and conservatism is always present in big science and it is hard to expect the management of a large international laboratory to undertake revolutionary steps. Project proposals with quite a new experimental technique are always richer and riskier than the set of approved projects and extrapolation usually prevails over speculation. In the case of CERN, there was the established tradition to give many experimental groups a chance to work at the laboratory's accelerators and any big equipment was intended as a faciUty open to interested users. But it was not only a matter of policy and management. Running the ISR was a scientific novelty and a technical challenge from the experimental point of view. Most physicists with experience in the study of hadronic interactions at fixed target accelerators approached the new machine with their cultural biases and designed their experiments according to their standard practice. By the end of the 1960s, when the first experimental programme at the ISR was defined, there was no adequate theory of strong interactions and the new machine had been built without any specific scientific goal other than to probe much higher energies where some kind of asymptotic behaviour was expected. Most physicists interested in strong interactions looked at p-p colUsions at the ISR as they were used to do at the PS: study of particle production at small angles and measurement of cross sections. The people who were interested in large angle were those who searched for rare events Uke the production of electrons or muons from the decay of the intermediate vector bosons W^ and Z°^^^. Another factor that probably affected negatively the timely development and implementation of large detectors for the ISR was the rather lukewarm interest of many physics leaders towards this accelerator. This machine had been strongly advocated by accelerator physicists and engineers but particle physicists had tolerated it only as an intermediate step towards their favourite project for a 300 GeV accelerator^ ^^. We may remember, for example, the strong opposition of L. Van Hove to the ISR and we can guess that when he became CERN's Director General for Research, in 1976, this attitude had something to do with the decision of the Research Board, in November that year, not to Notes: pp. 160 ff.

136

The Intersecting Storage Rings

follow the recommendation of the ISR Committee to build a big solenoid as a new magnetic faciHty^^^. The case of this solenoid is interesting. By May 1975 an ambitious proposal to build a large axial field spectrometer, based on a superconducting solenoid, was presented by a collaboration of seven scientific institutions. The aim was to investigate the production of hadrons with high transverse momentum, the most important phenomenon discovered at the ISR^^^. After considerable discussion, extending over three meetings, the ISR Committee decided not to recommend this proposal^^^. The issue of a new magnetic facility for the ISR remained, however, and a special Working Party was formed to study possible designs. Two alternative devices were discussed in detail, a solenoid magnet and a toroidal magnetic field, and the ISR Committee recommended the solenoid. As we have anticipated, the CERN Research Board decided, however, not to follow this recommendation and dropped the project^^^. Eventually, a less ambitious project was approved, based again on an axial field magnet associated with a drift chamber detector and a uranium calorimeter. This facility was built at intersection 1-8 (experiment R807) but it started to operate only in 1980, when the 300 GeV was already providing spectacular results and the future of the ISR was definitely endangered^^^. A second case which reveals the unwillingness of the laboratory management to undertake the construction of big detectors is the story of the large calorimeter proposed by C. Rubbia in 1972. Rubbia was certainly among those who understood from the beginning the novelty of collider physics and, in particular, the need for large detectors surrounding the intersection. In November 1972 he and his collaborators presented a proposal for 'a large An detector to investigate multibody events at the ISR'^^^. The physics motivation and the experimental philosophy of the proposed experiment expressed a radical departure from established practice: One of the most striking features of the ISR energy range is the spectacular complexity of the events. [...] How can we visualize the physics contained, for instance, in a fifty or more prong event? Single particle spectra, two or more particle correlations of course are very Hkely averaging over a greater fraction of the information. Evidently the single particle behaviour is probably irrelevant and one must concentrate on more global properties of each event. [...] A main experimental problem is the one of selecting with good efficiency the relevant type of events out of the fantastically large number of p-p interactions. This is possible only provided several physical quantities like transverse momenta, multiplicity etc. are directly accessible to very fast decision-making electronics^^^.

The apparatus was based on a An total absorption calorimeter consisting of a large segmented sphere, filled with liquid scintillator, completely surrounding the intersection. This was an instrument of which the 'unconventional nature' and 'unusual size' was explicitly acknowledged and that was presented as 'completely complementary' to the Split-Field Magnet ^2^.

Particle physics in the 1970s

137

The proposal was discussed at the ISR Committee at the beginninng of 1973, together with two others also suggesting total absorption detectors. All were rejected^^^. A new design was then worked out by Rubbia's group, based on a hybrid device in which two small calorimeters were used to study the forward jets and the large angles were covered by the magnetic spectrometer installed at intersection 1-6 for experiments R602 and R603. Compared with the original proposal, the new detector was much smaller and lighter and considerably less expensive. The ISR Committee discussed the new project in August 1973 and encouraged the group to continue studies for this experiment; almost one year later, however, the proposal was definitely rejected^^^. Keyhole physics at the ISR was to predominate until 1977-1978, when new wide-angle magnetic spectrometers started operation. In particular: the superconducting solenoid detector at I-l and the magnetic toroid spectrometer at 1-2 for lepton-pair studies; the Axial Field Spectrometer and argon calorimeter at 1-8 for large transverse momentum phenomena; the upgraded Split-Field Magnet. After the important results of the first period of operation (1971-1974) and the difficult period when the ambitious detectors which were needed were not yet available (1974-1978), ISR physics could again find a respectable place in the highly competitive terrain of particle physics^^^.

4.6 Particle physics in the 1970s The period of operation of the ISR coincided with a dramatic change in high energy particle physics and, in order to better understand the merits and limits of the physics made at the Rings, a short review of this research field in the 1970s is useful^^^. By the late 1960s particle physics was dominated by the study of strong interactions, with its multitude of data on cross-sections and resonances. Protons were regarded as extended objects and their colUsions were essentially soft, producing secondaries mostly concentrated in a very limited soUd angle along the direction of motion of the coUiding particle. The quark model had been suggested to explain the resonance population while the Regge-pole theory provided a general framework for hadronic phenomena. Going to higher and higher energy in hadron physics seemed to be the most promising path to simpUcity^^^ Ten years later, after electron and neutrino deep scattering experiments, the discovery of charmed particles and the merging of the concept of quarks and the concept of partons, a new tradition had been firmly established, based on the Standard Model of quantum chromodynamics and unified electroweak interactions. In the new framework, protons, while still extended and complicated objects, were made of point-Hke constituents, and the most interesting phenomena could be observed at wide angle by detecting leptons, photons and hadrons, isolated or correlated in jets, which are produced by the interactions of these constituents. Hard scattering experiments involving leptons and partons seemed the new Promised Land of experimental particle physics. Notes: p. 161

138

The Intersecting Storage Rings This almost about-turn in our approach towards hadron physics [...] took place as research at the ISR was already well under way and, to some extent, benefiting from it with the discovery of an anomalous high production of hadrons at large transverse momentum, in 1972. The history of physics at the ISR, as one is now able to contemplate with some hindsight, indeed appears to be characterized by this mutation of what is more fundamental in hadronic interactions^^^.

4.6.1 HARD SCATTERING, PARTONS AND QUARKS At the beginning of the transition between particle physics in the 1960s and the 'new physics' of the 1970s there was an important result obtained at the Stanford Linear Accelerator Center (SLAC) in 1969. Experiments performed at the new 22 GeV, two-mile long, linear electron accelerator showed that energetic electrons were inelastically scattered from protons at large angles with a probability much larger than one would expect if the charge of the proton were smoothly distributed over its volume. These data were interpreted by J.D. Bjorken as a manifestation of the scaling phenomenon and, after a suggestion by R. Feynman, this phenomenon was explained in terms of a structure of pointlike constituents of the proton called partons. In the parton-model explanation of scaling, the deep inelastic electron-proton scattering was visualised as a process wherein the incoming electron interacts with a single free parton in the proton by the exchange of a photon (Fig. 4.8)^^^ The discovery of point-like structures inside the proton was soon connected with the quark hypothesis. The latter, however, was a highly abstract theoretical model which had been introduced in the old physics of resonance phenomena as a possible classification scheme of hadrons. It required a good deal of theoretical effort to put quarks and partons in a coherent framework which included gluons and a quark-antiquark 'sea' as components of the hadrons ^^^.

e"

p{; parton' Fig. 4.8 Deep inelastic scattering in the Bjorken-Feynman parton model.

Particle physics in the 1970s

139

iW*

»{;

^S^

X

Fig. 4.9 Neutrino-proton scattering in the quark-parton model.

The quark-parton model drew its early empirical support from electron-scattering experiments; other processes on which experimental information became available in the late 1960s and early 1970s were conceptuaUsed in terms of the quark-parton model and came to constitute important strands of particle physics in the 1970s. In particular, the neutrino scattering experiments with CERN's new large bubble chamber Gargamelle, which led to the discovery of neutral currents, confirmed the vaHdity of the model also in the domain of weak interactions and stimulated the rapid growth of neutrino physics (Fig. 4.9)^^^. Other processes involved the production of lepton pairs (e+e" or fi^fi~) in protonproton collisions. The first important experiment in this field was made in 1968-69 at the Brookhaven AGS by a Columbia University group led by L. Lederman^^^. The primary aim of Lederman's experiment was the search for intermediate vector bosons (IVB) by detecting the //^jU" pairs expected to be their decay products. They failed, of course, to find any IVBs (the energy was far too low) but, as Lederman recalled later, their results 'stimulated a flood of theoretical attempts to account for one feature of the data - a continuum distribution of dimuon masses [...]. When the dust had settled, the most often quoted and used model was that of Drell-Yan'^^^. According to this model, a lepton pair (electrons or muons) emerged from a virtual photon created by the annihilation of a quark from one of the protons with an anti-quark from the other (Fig. 4.10).

Fig. 4.10 Lepton-pair production in the quark-parton model. Notes: p. 161

140

The Intersecting Storage Rings

Fig. 4.11 Electron-positron annihilation to hadrons in the quark-parton model.

Lederman's results, interpreted in terms of the Drell-Yan model, placed experiments on inclusive lepton-pair production in the stream of the new ideas and perspectives opened by the deep-inelastic electron scattering experiments ^^^. This kind of experiment, however, was very hard to perform because the few lepton pairs expected had to be detected in the high background of hadrons produced in proton-proton collisions. The same phenomenon could be studied in a much cleaner way in electron-positron collisions (the inverse process. Fig. 4.11) and, in fact, e"*"e" colliders became the topical machine for this kind of investigation in the 1970s^^^. 4.6.2 THE ^NOVEMBER REVOLUTION' By the end of 1974, the new experimental traditions on hard scattering processes were still a minority compared with the dominant soft-scattering traditions^^. From the theoretical point of view, the discovery of neutral currents in 1972-73 had confirmed the validity of unified gauge-theory models of electro weak interactions but, on the other hand, the gauge theory of coloured quark and gluons named quantum chromodynamics (QCD) received relatively Uttle attention from the point of view of phenomenological applications because of its weakness in explaining the strict confinement of quarks and gluons inside the proton. In November 1974 the discovery was announced of a new, very massive (3.1 GeV) particle which, due to its simultaneous revelation in two different laboratories, received and kept a double name: J/i/^. It was discovered at the Stanford electron-positron colUder SPEAR by a SLAC-LBL collaboration led by B. Richter and G. Goldhaber {xj/) and at the Brookhaven AGS by an MIT group led by S. Ting (J). The former were investigating e"^e~ annihilation to hadrons; the latter were investigating e"^e~ pair production by hadrons^"^^. In the following months, evidence for the existence of further particles belonging to the same family came from electron-positron machines and, by mid-1976, it was generally accepted that the new particles were manifestations of a new quark, carrying the charm quantum number which had been postulated in the framework of the unified electroweak gauge theory^^^. This theory thus became the standard model upon which all subsequent experimental programmes on weak interactions were organized: the rise to prominence of

Particle physics in the 1970s

141

electron-positron annihilation physics and of neutrino physics was amongst the most important effects arising from the 'November revolution'. The charm explanation of the new particles also represented a successful application of quantum chromodynamics and encouraged further theoretical elaboration: as a consequence, the existence of quarks as components of hadrons was put beyond dispute and QCD became the basis of a new hadron spectroscopy. Again, this caused a significant shift in experimental practice at proton synchrotrons: existing experimental programmes on hard-scattering were reinforced and new programmes were designed to investigate the production and properties of charmed particles using photon, neutrino and hadron beams. A brief analysis of the experimental apparatuses used in 1974 at Brookhaven and Stanford to detect the J/i/^ particle can give an idea of the new paths of experimental particle physics which the ISR scientific management were called to develop. At the Brookhaven 33 GeV proton synchrotron. Ting and his collaborators were aiming at the same objective as Lederman's, namely to search for massive particles which decay into lepton pairs, in this case electron-positron pairs. The problem was to detect these rare e+e~ pairs and to measure their physical parameters in the large hadronic background. The apparatus built by the MIT group, which drew from Ting's early experience at DESY, consisted in a very sophisticated double-arm spectrometer, each arm including three magnets, 8000-wire proportional chambers, Cerenkov counters and lead-glass calorimeters (Fig. 4.12). A pure electron beam for calibration and shielding consisting of 10,000 tons of concrete, 100 tons of lead, five tons of uranium and five tons of soap completed the experimental setup. Owing to its complexity, the detector required six physicists to operate it and, before each data-taking run, about 100 hours were spent ensuring that all the detectors worked with 100% efiiciency. According to Ting, During the construction of our spectrometer, and indeed during the entire experiment, I encountered much criticism. The problem was that in order to gain a good mass resolution it was necessary to build a spectrometer that was very expensive. One eminent physicist made the remark that this type of spectrometer is only good for looking for narrow resonances - and there are no narrow resonances. Nevertheless, since I usually do not have much confidence in theoretical arguments, we decided to proceed with our original design^"^^.

It is interesting to remark that Ting's ambitious programme included the installation of three experimental apparatuses: one at the electron synchrotron DESY at Hamburg for small mass values (0.5 to 2 GeV), one at the Brookhaven AGS for intermediate mass values (1.5 to 5 GeV) and a third at the ISR for high mass values (10 to 40 GeV). After discussing Ting's proposal, the ISR Committee 'expressed its interest in the physics of this experiment' but eventually rejected it, a decision 'motivated in part by the heavily loaded program for the SFM facility^"*^'. At Stanford, the SLAC group led by Richter and the Lawrence Berkeley Laboratory group led by Goldhaber built a huge magnetic detector, called Mark I, which completely surrounded the point where the electron and positron beams of the SPEAR storage ring Notes: p. 162

The Intersecting Storage Rings

142

... ^ . j j i f i ^

•

^

-

-<e^

(a) Plan view

0 \m 2m (b) Side view

Fig. 4.12 Schematic diagram of the experimental set-up of Ting's experiment in which the J particle was discovered. Mo, Ml and M2 are dipole magnets; AQ, A, B and C are 8000-wire proportional chambers; a and b are each 8x8 hodoscopes; S designates three banks of lead-glass and shower counters; Q , Q and Cg are gas Cerenkov counters (Ting [113], p. 239).

came into collision (Fig. 4.13)^"^^. The Mark I magnet produced a solenoidal field, coaxial with the beams, of about 4 kG throughout a volume of 20 m^. Particles moving radially outward from the beam-interaction point passed successively through a trigger counter, 16 concentric cylindrical wire chambers, a cylindrical array of 48 scintillators, a cylindrical array of 24 lead-scintillator shower counters and an additional array of spark chambers to separate muons from hadrons^"*^. From this description of the apparatuses which were responsible for the most important and dramatic discovery in particle physics in the 1970s, one can easily understand how major future experiments in this research field would be characterized by highly sophisticated electronic triggers and An detectors. The following quotation from a well docu-

Particle physics in the 1970s

143

MUON SMRK CHAMBERS FLUX RETURN

TRIGGER COUNTERS Sn\RK CHAMBERS PIPE COUNTER

-COMPENSATING SOLENOID -VACUUM CHAMBER -LUMMOSmr MONITOR

) MUON WIRE CHAMBERS IRON ( 6 In.) - S H O W E R COUNTERS ( 2 4 ) IL TRIGGER COUNTERS ( 4 8 )

Fig. 4.13 Schematic diagram of the magnetic detector Mark I at SPEAR (Schwitters & Strauch [108], p. 125).

Notes: p. 162

144

The Intersecting Storage Rings

merited historical account of particle physics gives an idea of the implications of the 'November revolution' from the experimental point of view: Whilst e+e~ machines had the advantage in producing a very clear signal of the existence of massive long-lived particles, other machines had the advantage in energy, intensity, and variety of quantum numbers which could be produced. [...] Thus three general categories of experiment moved to the centre of attention during the period from 1974 to 1976: e'^e" annihilation; neutrino scattering; and general investigations of heavy particle production using lepton or hadron beams. The experimental tradition which was least affected by this transformation was that which was most productive: high energy hadron scattering at proton synchrotrons. Certainly charm searches did get under way at these laboratories, but these in no sense provided for full utilisation of the available facilities. In hadronic scattering the old-physics traditions of experiment persisted, so too did the old theoretical traditions which fed upon them. In the event, though, the old-physics traditions of experiment soon went into decline^*^.

From 1976 onwards, in spite of persisting difficulties, the new physics was estabUshed: 'Experimenters sought to isolate and explore the rare, small cross-section processes of particular significance in the gauge-theory world-view [and] the properties of the new particles were held to demonstrate the reality of quarks*'*^'. The Weinberg-Salam electroweak model and hadron spectroscopy based on quantum chromodynamics were estabhshing themselves as the new paradigm in particle physics*"*^. And in 1977 a second important discovery was made which confirmed the validity of the paradigm: the discovery of the Y particle by L. Lederman and his collaborators at Fermilab^^^. Lederman, who had missed the discovery of the J/i/^, had installed an experiment similar to Ting's but they searched again for n^iT pairs instead of e"^e~ pairs. The new particle revealed the existence of a fifth quark, the b-quark, that was a member of a doublet whose existence was required by theoretical considerations. By the late 1970s, experimental activity in high energy particle physics was essentially planned within the framework of the new physics and could avail itself of a new generation of sophisticated electronic detectors and of the new set of e"^e~ coUiders especially designed for it: PETRA at DESY (1978), CESR at Cornell (1979), VEPP-4 at Novosibirsk (1980) and PEP at SLAC (1980). At Fermilab, plans were started to install superconducting magnets in order to reach 1 TeV energy (the Tevatron, inaugurated in 1984). At CERN, Rubbia's project to transform the SPS into a pp collider was approved and the new facility started operations in 1981. In that same year, the project for LEP entered the development phase. To the process which caused a mutation of particle physics in the course of the 1970s, the ISR contributed one important discovery and a set of significant results but it could not be a main protagonist of the change: 'As a purely hadronic machine, the ISR was the hardest of hard cases for the new physics^^^' It produced proton-proton coUisions when the best machines for the new physics were electron coUiders; it allowed higher centre of mass energies but its lower luminosity compared to fixed target machines impeded the

ISR physics

145

analysis of the most interesting rarer events of the new physics. It required highly sophisticated detectors to investigate the new phenomena but when they became fully operative at the rings the forthcoming opening of the new SPS pp collider promised (and started to give) more spectacular results. The ISR could only follow in the wake of the main scientific events of the transition process rather than create them. Its importance lay less in the results it obtained than in the invaluable experience that it gave for the next generation of CERN coUiders, the SPS pp coUider and the LEP.

4.7 ISR physics The period of operation of the ISR covered about 13 years, from March 1971 to December 1983. The experimental programme which developed at the Rings included 63 experiments, many of them corresponding to a research programme extending over several years and covering several topics. The number of groups involved in ISR experiments was well over 200, of which there were 44 from CERN, 119 from Member State institutions and 58 from institutions in the rest of the world (45 in the United States)^^^. It is not possible to cover here the whole of this programme. Extensive reviews have been published and some of the most significant results are dealt with in others chapters in this volume, devoted to the development of physics at CERN in this period^^^. I will limit myself to discussing a few aspects which I consider more significant and to make reference to those experiments which help to place ISR physics in its proper historical context. 4.7.1 A 'BRILLIANT START' The early ISR experimental programme was essentially a beam survey programme based on the traditional 'old physics' approach to the study of pp collisions^^'*. Three experiments (R601, R602, R801) were devoted to measurements of the total cross-section and to investigating elastic scattering, with the aim of studying the high-energy asymptotic region expected in the framework of the Regge theory. At intersection 2, three experiments (R201, R202, R203) shared the experimental hall to study particle production at small, medium and large angles respectively. One experiment (R103) can be considered as definitely belonging to the territory of the 'new physics'^^^. The aim of the experiment, designed by a CERN-Columbia-Rockefeller Collaboration, was to study the production of electron pairs (e"^e~) at large angles and it was, in fact, the follow-up of Lederman's Brookhaven experiment. The idea of repeating this experiment at the ISR had been suggested by CERN's physicist L. Di Leila after a visit to Lederman's laboratory at Columbia University^^^. The ISR experiment differed from that at Brookhaven in that it looked for electron pairs instead of muon pairs and allowed a better mass resolution. It differed from other ISR experiments on particle production in that its detectors covered a large fraction of the solid angle around the intersection: they consisted of two symmetric arrays of wire Notes: p. 162

The Intersecting Storage Rings

146

spark chambers, plastic scintillators and lead-glass counters at 90° with respect to the beams' direction. The ISR's beginning was 'a brilUant start'. In spite of its highly sophisticated technology the machine worked outstandingly in all components; the luminosity rose rapidly by two orders of magnitude, reaching the design value of 4 x lO^^cm^-^s"^ in about two years; the particular organization required for experimental work around the rings worked smoothly and important results were obtained which brought to light unexpected features in proton-proton interactions at very high energy. Two of them have deserved a place in textbooks on particle physics. The first derived from the experiments on total cross-section and elastic scattering^^^. Two groups, as we have seen, had set up experiments on this topic at intersection 6 and one at intersection 8, the latter limited to measurements of total cross-section. They found that the total cross-section rises with energy after passing through a broad minimum near 100 GeV equivalent laboratory energy. The total cross-section, in fact, was found to rise by about 10% over the ISR energy range and this came as a surprise as data obtained at lower energies seemed to indicate a constant asymptotic value (Fig. 4.14)^^^.

10000

•f»t

o OENISOV el ol

%

30

D CHAPMAN et ol O CHARLTON at ol A DAO el ol

25

(SERPUKHOV)

I

10

V HOLDER

el ol

rsR

• • AMALOI el ol

NAL

•

AMENDOLIA e( al

100

1000

LABORATORY MOMENTUM (GeV/c) Fig. 4.14 Total cross section measurements by 1972 (CERN Annual Report 1972, p. 13).

10000

ISR physics

147

The second important discovery was the surprisingly copious production of pions with large transverse momentum (px), with cross-sections many orders of magnitude greater than had been empirically predicted on the basis of pre-ISR data. The transverse momentum is the momentum component in the direction perpendicular to that of colliding protons, and lower-energy experiments had shown that inclusive pion production, i.e. interactions like P + p - ^ TT + X

where X is anything else produced in the interaction, presented cross-sections rapidly decreasing with the transverse momentum of the pion. The transverse momentum distribution, in fact, fell exponentially, with a mean value of 0.35 GeV/c. Evidence for a marked departure from this exponential fall-off was observed by three groups at the ISR in 1972 (R102, R103, R203), whose results were pubHshed in 1973^^^ Departure from the expected exponential behavior was already evident at 1 GeV/c and became orders of magnitude greater than the extrapolated value at higher px (Fig. 4.15). The excess production of large-px hadrons in high energy pp interactions was indeed the most important discovery of ISR physics. It was immediately interpreted as evidence for partons also in strong interactions and prompted a distinctive tradition of hard hadron scattering experiments to investigate large transverse momentum hadronic processes both at the ISR and, later, at Fermilab and the CERN SPS^^^. Quite paradoxically, the important discovery which gave the ISR a ticket to enter the new territories of hard-scattering particle physics also brought to light its intrinsic weakness. Two aspects are relevant in this respect, the first related to the study of large-px hadron production in hadron interactions, the other related to lepton physics. With regard to the first aspect we must consider the physical interpretation of large-px phenomena in the quark-parton, hard-scattering model (Fig. 4.16)^^^ According to this picture, an observed large-px particle should be considered as a member of a jet of hadrons strongly coUimated in the direction towards the trigger detector with an associated jet somewhere in the other direction. It was an obvious consequence to design experiments aimed at analysing the structure of final states of large-px processes. The key point was to study the correlations among large-px particles but instrumentation at the ISR was inadequate to make such correlation studies. These, in fact, required complex detector arrays surrounding the interaction region and sophisticated electronic triggers in order to pick out interesting events in the typical large background of hadronic interactions. We should recall that the SFM had been specifically conceived to study events producing secondary particles at small angles and, in the words of an experimenter, for large angle events, 'the SFM was a nightmare.'^^^ At large angles, in fact, the magneticfieldwas very weak (actually zero at 90°) and with rapidly changing directions. It thus required a long and patient effort to develop highly sophisticated detecting systems and software for track reconstruction in order to study large-px events. By 1975, the problems and limitations of the SFM were quite evident and a proposal was also suggested to rotate the Notes: pp. 162 ff.

I

x.0

._

on#K

nIW

a A

23.5 30.6

0

44.8

v

52.1

0

621

v v

"5 o-* 2

k) a

\

€

\

, , , , , , , , , , , 3 A

f

. . . . . . . . . . . . . . . . . . . . . . 5

8

7

8

9b

Fig. 4.15 Pion production with large transverse momentum in p p collisions as reported by: (a) Banner et al. [14] and (b) Biisser et al. [23].

1 , ~ 9

ISR physics

149

(a)

(b)


/

o \ \

(c)

V - ^ : %

/ \

^ %

Fig. 4.16 The quark-parton model visualized in three different high-energy processes: (a) lepton-hadron interaction; (b) e+e" annihilation; (c) hard-scattering hadron-hadron coUision. In the latter case it is assumed that constituents a and b of the two coUiding hadrons scatter into constituents c and d which result in hadron jets at wide angle. The observed large pj particle h is a member of a jet (Field and Feynman [51], p. 2591 (with minor modification)).

magnets by 90°. A working group was formed to study this proposal and then, 'after considerable discussion', the proposal was rejected though a programme for upgrading the faciUty was eventually implemented^^^.

Notes: p. 163

150

The Intersecting Storage Rings

4.7.2 THE NEED FOR BIG DETECTORS In spite of difficulties, from 1973 to 1976, a long series of correlation studies at the ISR provided good evidence for the validity of the hard-scattering model and contributed important results^^. Significant progress, however, was only possible by using hadron calorimeters to trigger on the energy of a whole jet rather than on a single large px particle. From an analysis of the ISR correlation data, in fact, it was predicted that, for a given value of the transverse momentum, the triggering rate with a suitable calorimeter should be some two orders of magnitude greater than with a single particle^^^. It took a long time to implement calorimeter experiments at the ISR, however. This was due not only to a certain 'conservative mode' of the ISR Committee (remember the rejection of Rubbia's proposal in 1972-73) but also to intrinsic technical difficulties: At the ISR [...] the implementation of a jet trigger is a difficult experimental problem. Hadron calorimeters have lower performance at smaller energies. Systems having the same transverse momenta have much larger laboratory energies at Fermilab than at the ISR. In addition none of the existing ISR detectors could conveniently accommodate such a calorimeter'^.

It was at Fermilab that the first calorimeter experiments were performed which permitted a more detailed analysis of jet production^^^. The first ISR calorimeter detector optimized for large-pT hadron events came into use only in 1980 (experiment R807), as a part of the Axial Field Spectrometer (AFS) facility. By the time the ISR started to give interesting results with this new facility, however, more spectacular results were already being obtained by the SPS pp collider. The second aspect, as we have mentioned, regards the use of the ISR for lepton physics. One of the groups which discovered the large high-pj hadron production was the CERNColumbia-Rockefeller (CCR) Collaboration of the dilepton experiment R103. As we have remarked, the detectors for leptons had been placed at large angles where, due to the known exponentially falling p -dependence, the hadron background was expected to be small and relatively easy to cope with. The discovery that this was not the case represented, of course, a setback for this kind of investigation. The reaction was along two lines: on the one hand to improve the existing apparatus in order to investigate the new phenomenon while still keeping the original aim of the experiment; on the other hand, to propose a new experiment with more sophisticated, wide-angle lepton detectors. Regarding the former, the CCR Collaboration joined the group from Saclay which ran experiment R102 in the same intersection I-l. The calorimeter of R102 was added to the detectors of R103 forming the new experiment R105 which started taking data in February 1973^^^. As for the latter, a proposal to continue the search for electrons with increased sensitivity, together with large-px hadrons, was presented early in 1973 by the CCR Collaboration which a group from Oxford joined in 1974^^^. It was based on a superconducting solenoid magnet providing a field along the proton beams, a configura-

ISR physics

151

tion particularly suited to study the production of particles at large angles with azimuthal symmetry. At its 39th meeting, in July 1973, the ISR Committee expressed 'its interest in the physics of this experiment and agreed that lepton physics at the ISR should receive emphasis.'^^^ The Committee recommended studies on the effect of this solenoid on the ISR and on prototype detectors and approved the proposal in March 1974 as experiment R108^^^. After more than three years of building and testing, the experiment started to operate in 1977 and gave its first significant results in 1978^^^. By that time other sophisticated, wide-aperture magnet detectors were also operative for lepton pair studies: in particular the toroid spectrometer R209 to study muon pair production and the 'lampshade magnet' detector R606 to study electron pair production. The former originated from a proposal presented in 1973 by S. Ting on behalf of a GenovaHarvard-MIT-Pisa Collaboration^^^. The experiment was originally approved for installation at intersection 1-8 (experiment R804) by 1975 but, due to scheduUng problems, its installation was delayed until 1976 when it was decided to move it to intersection 1-2^^"^. The latter originated from a proposal to improve the experiment R605 run by an AachenCERN-Harvard-Munich-Riverside collaboration led by C. Rubbia^^^. In 1978 the upgrading of the SFM was also completed, with two experiments, R415 and R416, taking data on electron pair production. The first derived from a proposal of Zichichi's CERN-Bologna collaboration; the second had been proposed by a C E R N CoUege de France-Heidelberg-Karlsruhe collaboration joined eventually by groups from Annecy (LAPP) and Warsaw. In this case too, it took a long time for the ISR Committee to discuss and approve the two experiments together with the upgrading of the SFMi^6. At last the ISR was well equipped with a set of powerful wide angle detectors. It was too late. 4.7.3 A DIFFICULT PERIOD The specific features of the ISR and the dramatic discovery that there was a lot of hadronic physics going on at large angles had posed the problem of building a new generation of detectors at the very beginning of ISR operation. On the one hand it was recognised that the whole angular region around the intersection was worth investigating; on the other hand, more sophisticated and selective triggering systems were required in order to discriminate among different kinds of events. Whether because of technical and financial difficulties or to the slowness of most CERN physicists to tune their practice to the new trends of particle physics, it took a rather long time, as we have seen, to build the new experimental facilities which were needed. One must also remark that, at that time, large electronic detectors were slowly taking the lead over bubble chambers in experimental particle physics and, in the words of an ISR experimenter, 'people did not think as big in those days.'^^^ 1974 to 1977 was, according to M. Jacob, a somewhat difficult period at the ISR: Notes: p. 163

152

The Intersecting Storage Rings One had to make do with existing devices (combining spectrometers or spectrometers and hodoscopes) exploiting particularly the SFM, which eventually became a powerful, though not ideal, instrument only by means of a long and patient effort at both the hardware and software levels ^^^.

This period, continued Jacob, 'was marked at both ends by the two setbacks of leaving the discovery of the J/i/^ (1974) and the discovery of the Y (1977) to other laboratories'. The news of the discovery of the J/i/^ caused much frustration among CERN physicists^^^. In fact, Di Leila and Lederman's CERN-Columbia-Rockefeller collaboration of experiment R103 had the same objectives as Ting's and they had caught the beginning of the very narrow peak of the J/i/^. Due to the unexpected high hadronic background which saturated their data acquisition system, they had to put the threshold of their detecting apparatus just above what proved to be the mass value of the J/i/^ (3.1 GeV against 3.097 GeV) and then missed the discovery by a few thousandths of a GeV^^^. In the event, after the announcement of the discovery of the J/i/^, the CERN-Columbia-Rockefeller-Saclay Collaboration of experiment R105 adjusted its detectors and quickly observed a few J/i/^ events^^^ Just one month after the announcement of the discovery of the J/i/^, a rather nervous meeting of the ISR Committee was held, where a host of proposals to search for the new charmed particles was discussed ^^^. The CERN-Columbia-Oxford-Rockefeller Collaboration urged a new scheduling for their superconducting solenoid (R108) and presented as well a new proposal for a search for high mass states decaying into two electrons^^^. A proposal to search for charmed particles was also presented by a CERN-Saclay Collaboration and, 'in the discussion following these presentations, mention was made of the use of the SFM facility as a muon spectrometer and the possibilities of using it as an electron detector.'^^"^ The ISR Committee recommended the CERN-Saclay proposal as experiment R702 and this, in due time, obtained beautiful data on the J/i/^ and related phenomena. At the same meeting, Zichichi's Bologna-CERN collaboration presented its proposal 'to transform the SFM into a powerful electron detector', which also considered the possibility of rotating the whole magnet by 90°^^^. As we have already said, this proposal was rejected and a project to upgrade the SFM was started instead. In spite of the strong engagement in lepton searches at the ISR since 1975, this kind of investigation kept being hampered by the large-pj hadronic background and by the very low cross-sections of these processes. In fact, in comparison with experiments at fixed target accelerators, collider physics suffered two major difficulties regarding lepton pair studies: the relatively low luminosity and the very wide solid-angle spread over which lepton pair production may occur. On standard accelerators, they are concentrated forwards by the motion of the centre-of-mass. Lacking sophisticated detectors surrounding the interaction point, the ISR could not compete with Fermilab and then with the CERN SPS. And it was at Fermilab, in fact, that Lederman discovered the Y particle, his revenge after missing the ijxj/ at Brookhaven and at the ISR^^^. Even when the discovery had been announced, it took several months to collect evidence for this particle at the ISR, in spite

ISR physics

153

of the fact that the cross-section for Y production at the ISR turned out to be two orders of magnitude larger than at Fermilab. By 1976-1977, 'physics at the ISR [had] lost much of its past glamour to many,' as Jacob has put it^^^. The new detectors were still under construction and the start-up of the SPS offered a very tempting alternative. There were more and more rumours at CERN that the ISR would be shut down to free resources for the new 300 GeV proton synchrotron and to build a new accelerator. As early as October 1975, in fact, a confidential 'Note for discussion on the long-term future of CERN' was sent by J.B. Adams to members of the future Directorate of CERN. Here, after discussing the financial boundary conditions of the Laboratories, it was stated that, in order to start a new major project in the 1980s, the ISR had to be closed down by about 1980^^^. Opinions on this question were split, of course, but the uncertainty about the future of the ISR certainly did not help those who advocated the need to exploit the machine in the best way. In 1976 and 1977 a two-session Workshop on future ISR physics was held which bears witness to these difficulties even though it was acknowledged that the installation of the new detectors, the rise in luminosity to be obtained by the insertion of superconducting low-j8 sections, and the possible use of antiprotons might produce a significant improvement in the experimental programme. The possibilities of associating the ISR with the SPS and of upgrading the ISR in energy by the introduction of superconducting magnets were also suggested and discussed^^^. After the workshop there was, in fact, a new surge of scientific interest in ISR physics but everybody knew that the ISR's days were probably numbered. 4.7.4 THE LAST ACHIEVEMENTS The latter period of the ISR (1978-1983) was not devoid of important results. The availability of proper detectors finally allowed for the full exploitation of the information contained in the events produced by the collisions, and the machine proved to be a wonderful tool for experimenting. By the insertion of superconducting low-^ sections at intersection 1-8, the maximum luminosity grew dramatically to over 10^^ cm"-^ sec"^. This permitted the optimal use of the axial field magnet detector. The improvement of the vacuum and the highly sophisticated control system gave physicists working at the Rings extremely stable beams for their experiments and very long uninterrupted physics runs could be provided, of 50-60 hours if desired, with a very high fraction of stable operation^^^. The versatiUty of the ISR was also revealed when it was decided to use it to store other kinds of particles. Antiprotons, deuterons and a particles were successfully stored in the Rings and the results of experiments performed with these particles complemented those obtained by pp collisions with regard to global features of hadronic interactions^^^. Finally, the continuing progress of research in accelerator physics which was made possible at the ISR, in particular the development of the technique of stochastic cooUng on anti-protons, provided invaluable knowledge for the implementation of the SPS pp ColUder and the LEP. Notes: pp. 163 jf.

154

The Intersecting Storage Rings

Among the achievements of the last period of operation of the ISR one must recall the results on jet production, where useful data were obtained which complemented those being obtained at the SPS Collider, the study of charmed hadrons and the investigation of charmonium states. The most important result, however, was the discovery of prompt photons at large transverse momentum. The emission of single energetic photons at large PT in hard proton-proton collisions had been theoretically anticipated within the framework of quantum chromodynamics. As the photon can emerge without interacting further, unlike quarks or gluons which give rise to jets, it provides a window through which one can get direct information about the primary scattering of proton constituents. The results obtained in 1979-1980 by experiments R806 and R108 confirmed the validity of the theory and represented an important first at the ISR^^^. Experiments on this topic then continued at intersection 1-8 with experiment R808 and at intersection I-l with experiment RllO. Correlations between single-photon events and associated charged secondaries were studied by experiments R806 and R807.

4.8 Epilogue The end of the ISR came on 23 December 1983 at 6.30 a.m., when the last two beams of protons were dumped. The machine was working satisfactorily and still providing good results within an active physics programme. In fact, the ISR had to be closed down in order to free resources to be used for CERN's new undertakings and this justified a premature termination which, in some cases, left a 'half-finished job'^^^. Some sweet and sour notes, which revealed physicists' mixed feelings about the ISR, could be heard at the two meetings that were 'the formal end of a glorious chapter of CERN history'*^'^. These were the last meeting of the ISR Committee, on 27 January 1984, and the official closure ceremony of the machine,fivemonths later. At the former meeting, M. Jacob wanted to put as an epigraph to his review of the ISR physics the first lines of Mark Antony's famous funeral oration from Shakespeare's Julius Caesar: I come to bury Caesar not to praise him; The evil that men do lives after them, The good is oft interred with their bones; So let it be with Caesar*^^

The evil of the ISR was, of course, the missed discovery of the 'two gems of physics in the seventies', namely the J/i/^ and the Y. 'Physics at the ISR', remarked Jacob, 'is, in many people's mind, marred by this shortcoming with lepton pairs, and this had to be mentioned first as an evil that lives on long after.' The bright results which actually originated from experiments at the ISR, the 'good' of the machine, inevitably remained in the shadow of this setback and were almost forgotten as such as they became part of the general background in particle physics.

Epilogue

155

Shakespeare's verses echoed also at the closure ceremony of the ISR, on 26 June 1984. Here, CERN's Director General H. Schopper wanted to stress that he had come 'to bury the ISR and to praise it.' The funeral, in his words, 'should not be too sad, since the deceased has had a very glorious Ufe.'^^^ After him, V. Weisskopf, a long time supporter of the ISR and probably the main person responsible for its approval in 1965, preferred to claim that he had come 'to praise ISR and to leave it to others to bury it' The former Director General went on to argue that, to the 'famous question' of the missed discovery of the J/i/r and of the Y, one had but to answer: It can be explained as being due to the fact that one had to develop the necessary instrumentation and this has taken much time. It is too bad, and we have probably missed one or two Nobel prizes, but let me say one thing. Does it really matter so much? If the J/psi and the upsilon [had] been discovered here, it would not have changed the landscape of high energy physics: it is not so important where it is discovered. The really important thing about the ISR is its success as an instrument, because that fact did change the landscape of high energy physics^^^.

This is hard to take at face value. As a matter of fact, physicists do value the who and where of important discoveries. With less rhetoric, the last chairman of the ISR Committee, G. Bellettini, acknowledged that Although one might admit that no specific discovery of historical importance was made here, still our views of the behaviour of strong interactions at high energies have changed quahtatively because of the work done at the ISR - and this is of historical importance^^^.

This is probably the most that can be said for the physics done at the ISR. At both meetings, Johnson's was the only triumphant note. The ISR project, in the words of its builder, 'started as accelerator research [and] it continued as accelerator research' and the ISR 'has continually carried out an accelerator physics programme which also got high priority on the machine and really paid off handsomely.'^^^ After listing the long series of results obtained at the ISR, Johnsen concluded: [The ISR] has been about the finest instrument one can imagine for research in accelerator physics. [...] Before the ISR, everyone talked about fixed-target machines, but nowadays it is essentially on the coUiders that people base their hopes for the future. This is really a fantastic development for those of us who remember the reluctance of many to accept the idea of coUiders as a physics tool before the ISR was launched^^^.

He was right, we believe. Even the most severe critics of the ISR had to acknowledge the splendid performance of the machine and its crucial contribution to CERN's glamorous achievements with the SPS Collider and the LEP. This is the real historical value of the ISR, at least for CERN. Notes: p. 164

156

The Intersecting Storage Rings

The ISR is no longer there: unlike its predecessors, the proton synchrotron which is still in operation and the cyclotron which was closed only in 1991, the ISR has been completely dismantled and only a large annular hillock on the French part of CERN's site marks the place of the tunnel where the hundreds of magnets, detectors and other apparatus of the machine and of its experiments had been busily working for 13 years. Physicists always tend to forget their past: each step of evolution of their discipline is considered by them as a new starting point from which previously acquired knowledge must be used without any consideration of how and why it was obtained. So it is for the ISR. Physicists did not love the ISR and, due to technical difficulties or to lack of imagination, they were not able to get important discoveries from it. Its good results soon became a part of the new general framework of particle physics in the 1980s while the machine as such has remained the one that missed the J/i/< and the Y. 'Exploit technique, physique pauvre', is the judgement of a particle physicist who has written a history of his discipline: Prouesse technique, modele pour projects ulterieurs, les ISR ont ete une machine d'ingenieurs plutot que de physiciens. En ce sens ils sont un exemple frappant de la croissance du poids des ingenieurs et des appareils techniques des grands laboratoires dans le developpement de la physique des particules^^'.

This is, in a certain sense, the ISR paradox. Its construction was strongly advocated by the engineers as a technical challenge and was eventually accepted by most physicists as an unfortunate compromise. It did prove to be not the best choice from the point of view of physics but, in the Hght of following developments, it was fortunate for CERN that it was built. In fact, it proved to be a necessary technical step in the path to the following successful CERN colliders, the SPS pp Collider and the LEP^^^. It depends on personal feeHngs and experience whether one prefers to stress the good or the evil of the ISR.

Notes 1. All documents cited in this paper can be found in CERN's central archive except for a few that were still stored in the archive of the former ISR Department when this chapter was written but which were due to be moved to the central archive. The most important set of documents is the series of documents of the ISR Committee (ISRC), coded as CERN/ISR/yy-nn, where yy is the year of issue and nn is a running number. A copy of these documents, including the minutes of meetings of the ISRC, can be found in K. Potter'sfilesat CERN's central archive. The author is greatly indebted to CERN's archivist R. Rahmy for her help and cooperation. While the author bears all responsibility for the opinions expressed in this paper, he would like to acknowledge helpful information and comments from several people involved in the history of the ISR: M. Albrow, U. Amaldi, F. Bonaudi, L. Camilleri, P. Darriulat, L. Di Leila, G. Goggi, M. Jacob, K. Johnsen, B.W. Montague, F. Pastore, B. de Raad, J. Steinberger, V.F. Weisskopf, K. Winter. Last but not least, the author would like to acknowledge J. Krige's collaboration throughout the duration of this work. 2. Pestre [98].

Notes

157

3. The project for a second pp collider, called Isabelle, had been discussed since 1972 at Brookhaven and construction began in 1978. Due to technical difficulties and cost escalations, and also because it became redundant after CERN commissioned the pp coUider, the project was abandoned in 1983. 4. Pestre [98]. 5. Pickering [100]. 6. Jacob [75]. 7. This description is essentially based on ISR [74]. 8. A complete set from February 1972 to August 1976 can be found in file EWDS 22321. 9. Reports on these meetings are in the ISR archive. 10. For this distinction see Krige [87], p. 246-249. 11. Krige[88]. 12. Finance Committee, 65th meeting (10/2/65), CERN/FC/753/Draft, 16/3/65. See also CERN/FC/745, 20/1/ 65, and CERN/538, 13/5/64. The Working Group met in Paris on 2-3 March 1965 and its report (CERN/ FC/LWP/2, 16/3/65) is annexed to the document CERN/FC/757, 17/3/65. Handwritten minutes of this meeting and a first draft of the final report can be found in file DIRADM 20104. 13. Finance Committee, 66th meeting (23/3/65), CERN/FC/766/Draft, 26/4/65. 14. Council, 29th session (25/3/65), CERN/590. 15. Letter Hampton to Schjilte-Meermann, 6/4/65, DIRADM 20305. See also Hampton's letter to D'Andrea (adviser of the Italian delegation), 5/4/65, ibidem. About the critical role of Britain in advocating the need to limit and control CERN expenditure and in defending lower budget figures ever since 1957, see Krige [88]. 16. Hampton's proposal is in CERN/FC/769, 23/4/65, and CERN/586 Draft, undated. The very first draft of this document is appended to Hampton's letter to D'Andrea. The 'Bannier procedure' (CERN/442, 29/5/62) was based on the principle of a four-year rolling budget approved each year, namely the budget for the first year, a 'firm budget determination' for the second year and a 'provisional determination' for the following two. The firm determination could be changed only without dissent in the Council. On this topic, see Krige [88], p. 604^623. 17. Finance Committee, 67th meeting (3^/5/65), CERN/FC/777/Draft, 3/6/65, p. 7. The British document is CERN/FC/773, 3/5/65. 18. Committee of Council, 48th meeting (16/6/65), CERN/CC/605/Draft, p. 4. The 25% rule, namely the proviso that no member state should pay more than 25% of the costs of a programme, had been exphcitly included in the Convention for the basic programme but not for supplementary programmes. According to the report of the Working Party of legal experts, the Council could introduce such a rule for a particular supplementary programme such as the ISR programme. 19. CERN/FC/769/Rev, 24/5/65, and CERN/586/Draft/Rev, undated. See also the correspondence of Hampton with Walker and Schulte-Meermann in file DIRADM 20305. 20. CERN/769/Rev, 24/5/65, p. 1. 21. Letter Hampton to Walker, 3/6/65, file DIRADM 20305. The Administration's document is CERN/599, 2/ 6/65. 22. CERN/599, 2/6/65, p.3. 23. Finance Committee, 68th meeting (15/6/65), CERN/FC/785/Draft, 7/7/65; Committee of Council, 48th meeting (16/6/65), CERN/CC/605/Draft, 20/8/65. 24. Council, 30th session (16-17/6/65), CERN/604, p. 24^25. 25. Finance Committee, 69th meeting (12-13/7/65), CERN/FC/790/Draft, 27/8/65, p. 9-10. See also CERN/ FC/788, 12/7/65. 26. Finance Committee, 70th meeting (28/9/65), CERN/FC/799/Draft, 27/10/65. 27. Letter Hampton to Bannier, 30/9/65, file DIRADM 20305. 28. CERN/CC/611, 2/11/65. 29. Letter Hampton to Martin, 14/10/65; letter Gregory to Hampton, 15/10/65; letter Martin to Hampton, 19/ 10/65; file DIRADM 20305. Notes: p. 164

158

The Intersecting Storage Rings

30. Committee of Council, 49th meeting (9/11/65), CERN/CC/623/Draft, 8/12/65. 31. Finance Committee, 71st meeting (10/11/65), CERN/FC/816/Draft, 24/11/65; 72nd meeting (25/11/65), CERN/FC/825/Draft, 13/12/65. 'Procedure for the estabhshment and control of a supplementary programme for the construction of Intersecting Storage Rings', CERN/613, 25/11/65. Council, 31st session (1516/12/65), CERN/634, annex II (also CERN/614). 32. ISR [72]. 33. Hine [68]. 34. Johnsen et al. [84]. 35. Johnsen & Van Hove [83], in particular Appendices III and IV. 36. Johnsen & Van Hove [83]. Discussions with physicists are reported in 'Minutes of discussion on ISR experimental areas and buildings, 18 March 1966', 24/4/66, and 'Notes on discussions of the ISR Working Party', 11/5/66; file NP 22897. 37. Johnsen [81], p. 4; Johnsen [82], p. 168. 38. See introduction to this volume. 39. The Accelerator Research Division was not incorporated into any department while the ISR Division was in fact the only division of the ISR Construction Department and practically coincided with it. 40. Interview with A. Russo and J. Krige, 30/8/90-1/9/90. 41. Johnsen [81], p. 5; Johnsen [82], p. 169. 42. Gervaise [58] and [59]. 43. The distinvar is a measuring device based on the accurate length measurement of an invar wire stretched between two points. The model developed and used at CERN is described in Gervaise [57]. 44. CERN, Annual Report, 1970, p. 108-109. 45. Johnsen [80], p. 212-213. 46. CERN, Annual Report, 1966, p. 116; 1967, p. 121. 47. CERN, Annual Report, 1971, p. 107. 48. Johnsen [79], p. 4. 49. ISR [72], p. 136 ff. 50. Fisher [52]. 51. CESAR [28]. 52. Samuel [104]. 53. ISR [73]; CERN, Annual Report, 1969, p. 115. 54. CERN, Annual Report, 1969, p. 115. 55. The phenomenon was first reported by K. Johnsen at the 64th SPC meeting of 11 May 1971, CERN/SPC/ 307/Draft, 30/7/71, p. 20-22. 56. CERN, Annual Report, 1971, p. 104^106; 1972, p. I l l ; 1973, p. 109-110. 57. I wish to thank F. A. Ferger for bringing this aspect to my attention. 58. Schnell [105] and [106]. See also Ruggiero [103]. 59. CERN, Annual Report, 1970, p. 108. 60. Johnsen [80]; CERN, Annual Report, 1969, p. 116. 61. Johnsen [81], p. 14; Johnsen [82], p. 177. 62. Van der Meer [114], Schnell [107]. It is well known that the technique of stochastic cooling developed by S. Vand der Meer was essential for the realization of the pp collider at the CERN SPS. For this contribution Van der Meer shared the Nobel Prize with C. Rubbia in 1984. 63. Scientific Policy Committee, 61st meeting (10/11/70), CERN/SPS/298/Draft, 1/2/71, p. 10-11. The event is vividly described in CERN Courier, 10:11 (November 1970), 344-347. 64. Scientific Policy Committee, 61st meeting (10/11/70), CERN/SPC/298/Draft, 1/2/71, p. 15. 65. 'Premieres colHsions de faisceaux', CERN Courier, W.l (February 1971), 32-36, p. 34. The technical report of the event, signed by W.C. Middelkoop and B. de Raad, is ISR running-in, runs 15 and 16. First observation of colliding beams events, ISR-BT/BdeR/EEK, 3/2/71, ISR Archive.

Notes

159

66. Johnsen's report at the 62nd meeting of the SPC (9-10/2/71),CERN/SPC/ 303/Draft, 8/3/71, p. 5. 67. The term was used for the first time in a report on the start of ISR operation to the CERN Directorate. Johnsen also reported on it at the 62nd meeting of the SPC. See also Johnsen [81], p. 6-7; Johnsen [82], p. 170-171. 68. Such high values of the luminosity were also achieved thanks to the insertion of superconducting low-)S sections which greatly reduced the vertical dimension of the beams, Johnsen [81] and [82]. 69. Johnsen [80], p. 214^215. 70. Inauguration of the Intersecting Storage Rings, 16.10.1971, CERN, 1971, p. 7. 71. Agenda and summaries of these meetings can be found in file DIRADM 20307. 72. The meeting was held on 10-11 June 1968; its programme is in file NP 22898. 73. Minten [96]. 74. E. Picasso and K. Winter, circular for the second ISR user's meeting, 21 Oct. 1968, file DIRADM 20306. 75. This presentation is based on reports of meetings of the Board of Directors of 17/9/68,17/10/68 and 22/10/68 and on two memoranda, respectively by K. Johnsen and C. Peyrou, both dated 23/10/1968. These documents are in files DGR 21355 and DG 20864. Johnsen's and Peyrou's memoranda are also in file DIRADM 20306. 76. Board of Directors, meeting of 17/9/68, CERN/DIR/410, 24/9/68. 77. Peyrou's memorandum cited in note 75, p. 2. 78. Pestre [99]. For the relations between CERN physicists and external users, see also Krige, Chapter 5, see also in this volume. 79. CERN/ISRC/69-1, 15/1/69. This was originally a circular letter by W. Jentschke (first chairman of the ISRC), a copy of which can be found in files NP 22898 and NP 22907. See also B.P. Gregory's letter to G. Cocconi (and other appointed members of the ISRC), 18/12/69, file NP 22899. 80. The initial membership of the Committee included W. Jentschke (DESY, Hamburg), F.F. Heymann (University College, London), C. Franzinetti (University of Turin), P. Marin (Laboratoire de I'Accelerateur Lineaire, Orsay), E. Lillethun (University of Bergen), G. Cocconi, G. Charpak, K. Winter (CERN, Physics I Dept.), B. French (CERN, Physics II Dept.), M.H. Blewett (from April 1969), F. Bonaudi, K. Johnsen, L. Resegotti, (CERN, ISR Dept.). 81. Scientific Policy Committee, 56th meeting, CERN/SPC/284/Draft, 22/1/70. The figure of 30 proposals for experiments was quoted there by the Director-General on behalf of Jentschke, who was unable to attend the meeting, and probably includes also informally presented proposals. As a matter of fact, only 19 formal proposals had been received and filed by the ISRC in 1969. This is also the figure quoted by K. Potter in his Memorandum on ISRC statistics prepared on 8 June 1979: Potter's files, folder 'Summary of proposals. ISRC statistics'. 82. ISRC, 6th meeting (3^/6/69), CERN/ISRC/69-40, 9/6/69. 83. ISRC, 5th meeting (20-21/5/69), CERN/ISRC/69-35, 23/5/69, p. 3. 84. The general layout of the planned ISR experiments just before its commissioning was presented in CERN/ ISRC/71^, 20/1/1971. A set of tables presenting the experiments at the ISR from 1971 to 1976, prepared by the ISR coordinators and coded CERN/ISR/EXP/1 to CERN/ISR/EXP/10, is in file EWDS 22324. 85. The experiment proposal is presented in three documents: CERN/ISRC/69-2, 24/1/69; CERN/ISRC/69-16, 17/3/69; CERN/ISRC/69-17, 17/3/69. Also: Report ISRSc-ERL-69/13, 16/9/69 (CERN, K. Potter's files). 86. ISRC, 2nd meeting (11-12/2/69), CERN/ISRC/69-10, 12/2/69, p. 1. 87. CERN/ISRC/69-18, 17/3/69, p. 1. 88. ISRC, 6th meeting (3^/6/69), CERN/ISRC/69^0, 9/6/69, p. 5. 89. CERN/ISRC/69-7, 17/2/69. 90. CERN/ISRC/69^W, 20/6/69. 91. CERN/ISRC/69-48, 1/7/69. 92. ISRC, 7th meeting (3/7/69), CERN/ISRC/69-49, 3/7/69. 93. Experiment R201 (particle production at small angles) was on the floor from August 1971 to March 1974; experiment R202 (particle production at mediimi angles) from May 1971 to September 1971; experiment

160

94. 95. 96. 97. 98. 99.

100. 101. 102. 103. 104. 105.

106. 107.

108. 109. 110. 111.

112.

The Intersecting

Storage

Rings

R203 (particle production at large angles) from July 1971 to December 1971; experiment R204 (search for the intermediate vector boson) from June 1971 to December 1973 (information from documents in files EWDS 22302 and EWDS 22324. ISRC, 6th meeting (3-4/6/69, CERN/ISRC/69-40, 9/6/69. These experiment proposals are, respectively, in CERN/ISRC/69-12, 14/3/69; CERN/ISRC/69-19, 16/3/69; CERN/ISRC/69-20, 24/3/69. CERN/ISRC/69^6, 30/6/69; ISRC, 7th meeting (3/7/69), CERN/ISRC/69-49, 3/7/69. CERN/ISRC/69-53, 12/9/69. The programme was eventually approved at the 8th meeting of the ISRC (2324/9/69), CERN/ISRC/69-56, 26/9/69. CERN/ISRC/70-27, 16/11/70; ISRC, 17th meeting (17-18/2/71), CERN/ISRC/71-11, 4/3/71. ISRC, 12th (2-3/6/70) and 13th (13-14/10/70) meeting, CERN/ISRC/70-12, 5/6/70, and CERN/ISRC/7023, 16/10/70. See also CERN/ISRC/70-17, 29/9/70. The Pisa-Stony Brook experiment became R801 and stayed on the floor from September 1971 to December 1974; the CERN-Rome experiment, code named R601, was on the floor from May 1971 to December 1972; the CERN-Aachen-Genova-Torino experiment (with the addition of groups from the University of California, Harvard, Munich, North Western, Riverside), was code named R602 and stayed on the floor in two phases from May 1971 to July 1974 (information from documents in files EWDS 22302 and EWDS 22324). Discussions on this subject were at meetings No. 1, 5, 8, and 9. The conclusions of the Study Group were discussed at the 13th meeting. F. Krienen, 'Review of proposed magnetic analysis systems for ISR reactions', report presented at the first ISR User's Meeting (10-11 June 1968), p. 10, file NP 22989. French et al. [53]; Hyams & O'Neill [71]; Steinberger [110]. See also Resegotti [101]. Winter [117]. According to L. Di Leila's recollections, G. Cocconi used to say: 'Let's forget 90°. Nothing happens at 90°'; interview with A. Russo and J. Krige, 29/8/90. G. O'Neill, A detector with large solid angle, paper presented at the second ISR User's Meeting (2-3/12/68), CERN/68 ISRU/119. The interest in looking for electrons and muons at large angles derived from the fact that they were expected to be decay products of intermediate vector bosons (IVBs). ISRC, 3rd meeting (18-19/3/69), CERN/ISRC/69-21, 25/3/69, p. 2. O'Neill's proposal is in CERN/ISRC/69-23, 31/3/69, and CERN/ISRC/69-30, 21/4/69. It was discarded at the 6th meeting of the ISRC (3-4/6/69), CERN/ISRC/69^0, 9/6/69. See also Gregory's letter to O'Neill, 6/ 6/69, in CERN Archive, K. Potter's files. The possible involvement of O'Neill in the experimental programme had been discussed since the end of 1965 (the relevant correspondence can be found in file MGNH 22007). After the choice of the split-field magnet and the dropping of his experiment proposal, O'Neill had been invited to join the group which was building the detectors for the SFM to perform a survey programme of test esperiments before the installation of the magnet: CERN/ISRC/69-54, 15/9/69; CERN/ISRC/70-05, 17/4/70; ISRC, 7th meeting (3/7/69), CERN/ISRC/69^9, 3/7/69; ISRC, 8th meeting (23-24/9/69), CERN/ ISRC/69-56, 26/9/69; ISRC, 12 th meeting (2-3/6/70), CERN/ISRC/7(>-12, 5/6/70. ISRC, 4th meeting (22-23/4/69), CERN/ISRC/69-33, 23/4/69, p. 3. Charpak et al. (1968). See also Gambaro, this volume. ISRC, 5th meeting (20-21/5/69), CERN/ISRC/69-35, 23/5/69. ISRC, 12th meeting (2-3/6/70), CERN/ISRC/70-12, 5/6/70, p. 4. See also CERN/ISRC/69^5, 2/7/69. The groups involved were a CERN-Miinich-Princeton Collaboration and a CERN-Hamburg-Orsay-Vienna (CHOV) Collaboration. Their original proposals are CERN/ISRC/69-8, 10/3/69, and CERN/ISRC/69-14, 14/3/69, respectively. Princeton's contribution in the first collaboration was that of O'Neill who eventually disappeared. The test and survey programme is described in CERN/ISRC/69-54, 15/9/69, and CERN/ ISRC/70-5, 17/4/70. ISRC, 19th meeting (28/4/71), CERN/ISRC/71-20, 5/5/71. The report on the situation of the SFM is CERN/ISRC/71-19, 28/4/71. By that time, only one proposal had been accepted, namely that presented in

Notes

113. 114. 115. 116. 117. 118. 119. 120.

121.

122. 123.

124. 125. 126. 127.

128. 129. 130. 131. 132. 133. 134. 135. 136. 137.

161

1969 by the CHOV collaboration (CERN/ISRC/69-14, 14/3/69). Another proposal, presented by a group led by A. Zichichi and aimed at quark searching, had been rejected (CERN/ISRC/70-31, 8/12/70, and Add. 1, 14/5/71). ISRC, 23rd meeting (19-20/10/71), CERN/ISRC/71-44, 21/10/71. See also CERN/ISRC/72-21, 13/7/72. CERN, Annual Report, 1973, p. 119. Jacob [75], p. 35. C. Rubbia's harsh criticism against keyhole physics is reported by Taubes [112], p. 45-46. Albrow [2], p. 745. Albrow's opinion has been questionned by Di Leila [39]. We shall deal with these ISR experiments later. The intermediate vector bosons required a much higher energy than that at the ISR and were eventually discovered at the SPS pp collider. Pestre[98]. ISRC, 69th meeting (10/11/76), CERN/ISRC/76-33, 16/11/76. Research Board, 11th meeting (25/11/76), CERN/RB/11. The proposal was described in CERN/ISRC/75-18, 12/5/75; CERN/ISRC/75-21, 25/6/75; CERN/ISRC/ 75-37, 30/9/75. The collaboration included three Scandinavian Institutions (the Universities of Bergen and Lund and the Niels Bohr Institute in Copenhagen), three American institutions (the Universities of Harvard and Illinois and the Lawrence Berkeley Laboratory) and the Rutherford Laboratory (U.K.). ISRC, 58th meeting (11/7/75), CERN/ISRC/75-23, 14/7/75; 59th meeting (10/11/75), CERN/ISRC/75-35, 11/9/75; 60th meeting (15/10/75), CERN/ISRC/75-40, 16/10/75. In the minutes of these meetings no reason for this rejection was explicitely given. Report of the ISR Working Party JdirnxdiTy-Kugusi 1976, in file DGE 21561. ISRC, 69th meeting (10/11/76), CERN/ISRC/76-33, 16/11/76. Research Board, 11th meeting (25/11/76), CERN/RB/11. The proposal was presented by a CERN-Lund-Copenhagen-Rutherford Collaboration: CERN/ISRC/7636 (P 95), 10/1/77; CERN/ISRC/77-7, 8/3/77; CERN/ISRC/77-11, 15/4/77. ISRC, 70th meeting (12/1/77), CERN/ISRC/77-3, 13/1/77; 71th meeting (16/2/77), CERN/ISRC/77-5, 17/2/77. The detector is described in Fabjan et al. [46]. The proposal was worked out by an Aachen-CERN-Harvard-Grenova collaboration and was described, with successive modifications, in CERN/ISR/72-32, 9/11/72, and add. 1-5, 16/2/73 to 14/10/73. CERN/ISRC/72-32, 9/11/72, p. 1, 3. CERN/ISRC/72-32, 9/11/72, p. 10, 16. ISRC, 34th meeting (24/1/73), 25/1/73, and 35th meeting (21/2/73). The two other proposals were presented by P. Darriulat, on behalf of the Aachen-CERN-Miinchen Collaboration already involved in experiment R701, and by the American W.J. WiUis, of Yale University and Brookhaven National Laboratory: CERN/ ISRC/72-30, 10/11/72 (with add. 1 and 2, 10/1/73); CERN/ISRC/73-1, undated. ISRC, 40th meeting (7/8/73), CERN/ISRC/73-25, 9/8/73; 41th meeting (16/10/73), CERN/ISRC/73-31, 18/ 10/73; 49th meeting (28/6/74), CERN/ISRC/74-32, 2/7/74. For this periodization see Jacob [75]. Useful historical reviews are Pickering [100], Crozon [34], Cahn & Goldhaber [26]. See also Watkins [115]. For a review of Regge theory, as it was applied to hadronic processes by the early 1970s, see Collins [32] and Horn [69]. Jacob [75], p. 26. Bloom et al. [19]; Breidenbach et al [20]; Bjorken [17]; Bjorken & Paschos [18]; Feynman [49]. See also Kogut & Susskind [86] and Yan [118]. Kuti & Weisskopf [90]; Drell & Yan [41]; Friedman & Kendall [54]; Kogut & Susskind [86]; Feynman [50]. Eichten et al. [42]; Deden et al. [36]; Musset & Vialle [97]. Excellent historical analyses of the discovery of neutral currents are Gahson [55] and GaUson [56], 135-241. See also Winter, this volume. Christenson et al. [30]; Christenson et al. [31]; Lederman [91]. Lederman [91], p. 153. Drell & Yan [40] and [41]. It must be noted that a 'curious protuberance between 3 and 4 GeV had been observed in the smooth curve found by Lederman, which was the first signal of the J/i/^ particle, not recognized at that time and then discovered in 1974, as we shall see.

162

The Intersecting Storage Rings

138. Lederman [91], Craigie [33], Stroynowki [111]. An inclusive experiment is one in which one is interested in detecting one particular product of the reaction regardless of others. An exclusive experiment is one in which one wants to study all events produced in a particular reaction. This distinction was introduced by Feynman [48]. Inclusive experiments based on the use of electronic detectors became more and more characteristic of the new particle physics in the 1970s. 139. Early experimental information on electron-positron annihilation with regard to the quark-parton model came from the e+e~ collider ADONE which began operation at Frascati, Italy, in 1967. Petween 1972 and 1980 seven e+e" coUiders started to operate: SPEAR at SLAC (1972), DORIS at DESY (1974), DCI at Orsay (1976), PETRA at DESY (1978), CESR at Cornell (1979), PEP at SLAC (1980), VEPP-4 at Novosibirsk (1980). 140. Pickering [100], p. 235-238, reviews the situation in the Ught of the proceedings of the 17th International Conference on High Energy Physics, held in London in July 1974. 141. Augustin et al. [13]; Aubert et al. [12]. Personal recollections of this discovery are Ting [113] and Richter [102]. Two weeks later, the SPEAR experimenters found a second member of this family, at 3.7 GeV, which was called \j/'\ Abrams et al. [1]. 142. Glashow, IHopoulos & Maiani [62]. 143. Ting [113], p. 241. Indeed, the J/^ resonance proved to be very narrow. 144. Ting's ISR proposal was in CERN/ISRC/73-9, undated, with add. 1, 2, 3. The proposal was discussed by the ISR Conmiittee at its 39th meeting (10/7/73) and rejected at its 40th meeting (7/8/73): CERN/ISRC/73-22, 11/7/73, p. 3; CERN/ISRC/73-25, 9/8/73, p. 4. It should be noted that Ting's group claimed that they intended to run their large detector outside the SFM, without interference with its operations. See also Crozon [34], p. 234^235. 145. Richter had been the moving force behind the construction of the SPEAR electron-positron storage ring at SLAC. This facihty started operation in 1972. After the small e''"e~ faciHties in Frascati (ADONE) and in Cambridge, SPEAR marked the real arrival of e'^e" physics. 146. Richter [102], p. 253. 147. Pickering [100], p. 271-272. An important aspect discussed by Pickering is that the 'November revolution' actually reconciled experimental particle physics with the theoretical work of field theorists involved in the construction of gauge theories of weak and strong interactions. See also Crozon [34], p. 265-285. 148. Pickering [100], p. 353 and 254. 149. I use this concept in the sense of Kuhn [89]. In 1979 S. Weinberg, A. Salam and S.L. Glashow shared the Nobel Prize for their seminal theoretical work on electroweak unification. 150. Herb et al. [65]. See also Ledermann [92]. 151. Pickering [100], p. 352. 152. Jacob [75], p. 74. 153. Reviews on ISR physics are Giacomelli & Jacob [61], Jacob [75]. 154. Jacob [75], p. 33. 155. Actually, two other experiments can be classified in this category: R102, designed by a Saclay-Strasbourg Collaboration, aimed at studying interactions producing gamma rays and electrons with large transverse momentum; R204, designed by a collaboration of British universities, aimed at detecting muons with large transverse momentum as a search for intermediate vector boson. The latter did not give any significant result; the former contributed to the discovery of large transverse momentum phenomena, as we shall see in the following. 156. L. Di Leila, interview with J. Krige and A. Russo, 29/8/90. 157. The total cross-section is a measure of the probability that two protons interact anyhow; elastic scattering is the process by which the interaction between the two particles is just a rebound of one against the other, as between two billard-balls. 158. Amaldi et al. [5], AmendoHa et al. [7], Amendolia et al. [8]. A review of ISR results on the total cross section is in Amaldi & Schubert [6]. A review on total cross section results is Giacomelli [60].

Notes

163

159. Banner et al. [14], Biisser et al [23], Alper et ai [3]. 160. Jacob & Landshoff [77] and Darriulat [35]. 161. This hard-scattering model (Berman et al. [15], ElHs & Kislinger [43], Field & Feynman [51]) is what eventually proved to be correct. Other models were proposed by 1973 but were discarded when more data became available: see Sivers et al. [109]. 162. G. Goggi, interview with the author, 11/4/91. 163. A discussion on the SFM was held at the 58th meeting of the ISRC (11/7/75), CERN/ISRC/75-23, 14/7/75. The proposal to rotate the magnet in order to transform the SFM into 'a powerful electron detector' was suggested by a Bologna-CERN collaboration led by A. Zichichi and was presented in CERN/ISRC/74-53, 22/11/74, and CERN/ISRC/75-3, 31/1/75. The setting up of the working group, co-ordinated by F. MuUer, was decided at the 56th meeting of the ISRC (25/4/75), CERN/ISRC/75-17, 28/4/75 and its results were discussed at the 59th meeting of the ISRC (10/9/75), CERN/ISRC/75-35, 11/9/75. 164. For a review and references see Jacob & Landshoff [77], Darriulat [35]. A review of knowledge about large transverse momentum phenomena by 1976 is ElHs & Stroynowski [44]. 165. Jacob & Landshoff [77], p. 292. About calorimeters see Fabjan & Ludlam [45]. It must be stressed that much cleaner data on jet production could be obtained by e+e" annihilation experiments (Fig. 4.16). The first significant result in this respect came in 1975 from the SPEAR facihty at SLAC: Hanson et al. [63]. The start of operation of the new e+e" colliders PETRA at DESY (1978) and PEP at SLAC (1980) opened up the possibility of performing experiments at much larger energies. 166. Darriulat [35], p. 166. 167. Bromberg et al. [21]; Bromberg et al. [22]. 168. CERN/ISRC/72-13, 16/5/72, with add. 1 and 2. A proposal to study large transverse momentum phenomena was first suggested by the Saclay group and was approved by the ISRC as experiment R105 at its 31st meeting (23/8/72), CERN/ISRC/72-25, 24/8/72. Then, in November, a joint proposal was presented by Saclay and the CCR Collaboration and was approved by the ISRC in January 1973 (34th meeting, CERN/ ISRC/73-4, 25/1/73). 169. CERN/ISRC/73-13, 14/5/73, with add. 1, 8/10/73, and CERN/ISRC/73^, 25/1/73). 170. ISRC, 39th meeting (10/7/73), CERN/ISRC/73-22, 11/7/73, p. 3. 171. ISRC, 46th meeting (26/3/74), CERN/ISRC/74-18, 28/3/74. 172. AngeHs et al. [9] and [10]. 173. CERN/ISRC/73-28, 1/10/73, with add. 1, 9/11/73. ISRC, 42nd meeting (20/11/73), CERN/ISRC/73-35, 22/ 11/73. 174. ISRC, 65th meeting (5/5/76), CERN/ISRC/76-16, 6/5/76. 175. CERN/ISRC/75-33, 29/8/75; CERN/ISRC/75-42, 4/11/75; CERN/ISRC 75-43, 3/11/75. In the following phase, groups from Holland and from Northwestern University joined the collaboration. 176. The R415 proposals is in CERN/ISRC/74^53, 22/11/74; CERN/ISRC/75-3, 31/1/75; and CERN/ISRC/7613, undated. The R416 proposal is in CERN/75-41, 30/10/75. They were approved by the ISRC at its 65th meeting (5/5/76), CERN/ISRC/76-16, 6/5/76. Status reports on the first phase of data taking are CERN/ ISRC/78-12, 1/5/78, and CERN/ISRC/78-11, 2/5/78, respectively. 177. Interview of L. Camilleri with J. Krige, 10/9/90.1 wish to thank J. Krige and L. Camilleri for allowing me to use the tape recording of this interview. 178. Jacob [75], p. 35. 179. Taubes [112], p. 25-26, gives a rather vivid description, with no documentation though, of this frustration. 180. Di Leila [39] and interview with A. Russo and J. Krige, 29/8/90. see Biisser et al. [24]. 181. Biisser et al. [25]. 182. ISRC, 53th meeting (11/12/74), CERN/ISRC/74^59, 12/12/74. Other proposals were also presented at the following meeting. 183. CERN/ISRC/74-56, 25/11/74.

164

The Intersecting

Storage

Rings

184. ISRC, 53rd meeting (11/12/74), CERN/ISRC/74-59, 12/12/74, p. 1. The CERN-Saclay proposal is in CERN/ISRC/74-51, 18/10/74, and CERN/ISRC/74-55, 26/11/74. A group from Zurich eventually joined the collaboration. 185. CERN/ISRC/74^53, 22/11/74, and CERN/ISRC/75-3, 31/1/75. Zichichi's proposal was presented by T. Massam and discussed at the open session of the following ISRC meeting (19/2/75), CERN/ISRC/75-10, 20/2/75. 186. Herb et al [65]. 187. Jacob [75], p. 35. 188. A copy of this document, coded Lab II-DI/JBA/pd and dated 23/10/75, can be found among Johnsen's papers in the ISR Archive at CERN. 189. The conclusions of the two sessions of the ISR workshop are reviewed by B.G. Pope and by M. Jacob, respectively, in CERN/ISRC/76-32, 2/11/76 and in CERN/ISRC/77-20, 26/9/77. These and other documents related to this workshop are in file DGE 21561. The conclusions of the workshop were discussed at open meetings of the ISRC: 68th meeting (15/10/76), CERN/ISRC/76-29, 18/10/76; and 74th meeting (2122/9/77), CERN/ISRC/77-19, 23/9/77. 190. Johnsen [81]. 191. The first proposal to use particles other than protons (actually deuterons) in the ISR was presented in July 1976 from a CERN-Pavia Collaboration, CERN/ISR/76-17, 10/6/76. The proposal was approved by the ISRC at its 67th meeting (1/9/76), CERN/ISRC/76-24, 2/9/76, and became experiment R417: Mantovani et al [93, 94]. General reviews are Faessler [47], Camilleri [27]. 192. Diakonou et al. [37] and [38], Angelis et al. [11]. Pioneering work on direct single-photon production had been done by experiment R107. 193. Jacob [75], p. 36. 194. CERN's Director General H. Schopper at the last meeting of the ISRC, cited in G. Bellettini's preface to Jacob & Johnsen [76], p. vi. 195. Jacob [75], p. 24^25. 196. H. Schopper in Closure Ceremony of the Intersecting Storage Rings, 26/6/1984, CERN, January 1985, p. 2, underlined in the original text. 197. Closure Ceremony, p. 5 and 7, underlined in the original text. 198. Closure Ceremony, p. 14. 199. Closure Ceremony, p. 11. Accelerator physics at the ISR is reviewed in Johnsen [81] and [82]. 200. Closure Ceremony, p. 13. 201. Crozon [34], p. 204. 202. A crucial technical element for the realization of the pp collider that derived from the ISR was the possibiUty to obtain high intensity antiproton beams in the Antiproton Accumulator (AA).

References [1] G.S. Abrams, D. Briggs, W. Chinowsky, C.E. Friedberg, G. Goldhaber, R.J. Hollebeek, J.A. Kadyk, A. Litke, B. Lulu, F. Pierre, B. Sadoulet, G.H. Trilling, J.S. Whitaker, J. Wiss, J.E. Zipse, J.-E. Augustin, A.M. Boyarsky, M. Breidenbach, F. Bulos, G.J. Feldman, G.E. Fischer, D. Fryberger, G. Hanson, B. JeanMarie, R.R. Larsen, V. Liith, H.L. Lynch, D. Lyon, C.C. Morehouse, J.M. Paterson, M.L. Perl, B. Richter, P. Rapidis, R.F. Schwitters, W.M. Tanenbaum, F. Vannucci, 'Discovery of a second narrow resonance in e^e" annihilation', Physical Review Letters 33 (1974), 1453-1455. [2] M. Albrow, 'Protons in coUision', New Scientists 8 December 1983, 743-745. [3] B. Alper, H. Boggild, G. Jarlskog, G. Lynch, J.M. Weiss, P. Booth, J.L. Carroll, J.N. Jackson, M. Prentice, G. Von Dardel, L. Jonsson, G. Damgaard, K.H. Hansen, E. Lohse, F. Bulos, L. Leistam, A. Klovning,

References

[4] [5]

[6] [7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15] [16]

165

E. Lillethun, B. Duff, F. Heymann, D. Quarrie, Troduction of high transverse momentum particles in p-p collisions in the central region at the CERN ISR', Physics Letters 44B (1973), 521-529. G. Altarelli, Tartons in quantum chromodynamics'. Physics Reports 81 (1982), 1-129. U. Amaldi, R. BiancastelH, C. Bosio, G. Matthiae, J.V. AUaby, W. Bartel, G. Cocconi, A.N. Diddens, R.W. Dobinson, A.M. Wetherell, 'The energy dependence of the proton-proton total cross-section for centre-of-mass energies between 23 and 53 GeV, Physics Letters 44B (1973), 112-118. U. Amaldi, K. Schubert, 'Impact parameter interpretation of proton-proton scattering from a critical review of all ISR data'. Nuclear Physics B166 (1980), 301-320. S.R. Amendolia, G. Bellettini, P.L. Braccini, C. Bradaschia, R. Castaldi, V. Cavasinni, C. Cerri, T. Del Prete, L. Foa, P. Giromini, P. LaurelU, A. Menzione, L. Ristori, G. Sanguinetti, M. Valdata, G. Finocchiaro, P. Grannis, D. Green, R. Mustard, R. Thun, 'Measurements of the total proton-proton crosssection at the ISR', Physics Letters 44B (1973), 119-124. S.R. Amendolia, G. Bellettini, P.L. Braccini, C. Bradaschia, R. Castaldi, V. Cavasinni, C. Cerri, T. Del Prete, L. Foa, P. Giromini, P. Laurelli, A. Menzione, L. Ristori, G. Sanguinetti, M. Valdata, G. Finocchiaro, P. Grannis, D. Green, R. Mustard, R. Thun, 'Total cross-section measurement at the ISR', Nuovo Cimento 174 (1973), 735-755. A.L.S. Angelis, B.J. Blumenfeld, L. Camilleri, T.J. Chapin, R.L. Cool, C del Papa, L. Di Leila, Z. Dimcovski, R.J. HoUebeek, L.M. Lederman, D. Levinthal, J.T. Linnemann, L. Lyons, N. Phinney, B.G. Pope, S.H. Pordes, A.F. Rothenberg, A.M. Segar, J. Singh-Sidhu, A.M. Smith, M.J. Tannenbaum, R.A. Vidal, J. Wallace-Hadrill, T.O. White, J.M. Yelton, 'A measurement of inclusive n° production at large p j from p-p coUisions at the CERN ISR', Physics Letters 79B (1978), 505-510. A.L.S. Angelis, H.-J. Besch, B.J. Blumenfeld, L. Camilleri, T.J. Chapin, R.L. Cool, C. del Papa, L. Di Leila, Z. Dimcovski, R.J. HoUebeek, L.M. Lederman, D.A. Levinthal, J.T. Linnemann, C. Newman, N. Phinney, B.G. Pope, S.H. Pordes, A.F. Rothenberg, R.W. Rusack, A.M. Segar, J. Singh-Sidhu, A.M. Smith, M.J. Tannenbaum, R.A. Vidal, J.S. Wallace-Hadrill, J.M. Yelton, K.K. Young, 'A measurement of the production of massive e''"e~ pairs in proton-proton collisions at v ^ = 62.4 GeV, Physics Letters 87B (1979), 398-402. A.L.S. AngeHs, H.-J. Besch, B.J. Blumenfeld, L. Camilleri, T.J. Chapin, R.L. Cool, C. del Papa, L. Di Leila, Z. Dimcovski, R.J. HoUebeek, L.M. Lederman, D.A. Levinthal, J.T. Linnemann, C. Newman, N. Phinney, B.G. Pope, S.H. Pordes, A.F. Rothenberg, R.W. Rusack, A.M. Segar, J. Singh-Sidhu, A.M. Smith, M.J. Tannenbaum, R.A. Vidal, J.S. WaUace-HadriU, J.M. Yelton, K.K. Young, 'Search for direct single-photon production at large p j in proton-proton collisions at y ^ = 62.4 GeV, Physics Letters 94B (1980), 106-112. J.J. Aubert, U. Becker, P.J. Biggs, J. Burger, M. Chen, G. Everhart, P. Goldhagen, J. Leong, T. McCorriston, T.G. Rhoades, M. Rhode, S.C.C. Ting, S.L. Wu, Y.Y. Lee, 'Experimental observation of a heavy particle J', Physical Review Letters 33 (1974), 1404-1406. J.-E. Augustin, A.M. Boyarsky, M. Breidenbach, F. Bulos, J.T. Dakin, G.J. Feldman, G.E. Fischer, D. Fryberger, G. Hanson, B. Jean-Marie, R.R. Larsen, V. Liith, H.L. Lynch, D. Lyon, C.C. Morehouse, J.M. Paterson, M.L. Perl, B. Richter, P. Rapidis, R.F. Schwitters, W.M. Tanenbaum, F. Vannucci, G.S. Abrams, D. Briggs, W. Chinowsky, C.E. Friedberg, G. Goldhaber, R.J. HoUebeek, J.A. Kadyk, B. Lulu, F. Pierre, G.H. Trilling, J.S. Whitaker, J. Wiss, J.E. Zipse, 'Discovery of a narrow resonance in e+e~ annihUation', Physical Review Letters 33 (1974), 1406-1408. M. Banner, J.L. Hamel, J.P. Pansart, A.V. Stirling, J. Teiger, H. Zaccone, J. Zsembery, G. Bassompierre, M. Croissiaux, J. Gresser, R. Morand, M. Riedinger, M. Schneegans, 'Large transverse momentum particle production at 90° in proton-proton coUisions at the ISR', Physics Letters 44B (1973), 537-540. S.M. Berman, J.D. Bjorken, J. Kogut, 'Inclusive processes at high transverse momentum'. Physical Review D 4 (1971), 3388-3418. S.M. Berman, M. Jacob, 'Connection between inelastic proton-proton reactions and deep inelastic scattering'. Physical Review Letters 25 (1970), 1683-1686.

166

The Intersecting Storage Rings

[17] J.D. Bjorken, 'Asymptotic sum rules at infinite momentum', Physical Review 179 (1969), 1547-1553. [18] J.D. Bjorken, E.A. Paschos, 'Inelastic electron-proton and gamma-proton scattering and the structure of the nucleon'. Physical Review 185 (1969), 1975-1982. [19] E.D. Bloom, D.H. Coward, H. H.DeStaebler, J. Drees, G. Miller, L.W. Mo, R.E. Taylor, M. Breidenbach, J.I. Friedman, G.C. Hartman, H.W. Kendall, 'High-energy inelastic e-p scattering at 6° and 10°', Physical Review Letters 23 (1969), 930-934. [20] M. Breidenbach, J.I. Friedman, H.W. Kendall, E.D. Bloom, D.H. Coward, H.H. DeStaebler, J. Drees, L.W. Mo, R.E. Taylor, 'Observed behavior of highly inelastic electron-proton scattering'. Physical Review Letters 23 (1969), 935-939. [21] C. Bromberg, G. Fox, R. Gomez, J. Pine, S. Stampke, K. Yung, S. Erhan, E. Lorenz, M. Medinnes, J. Rohlf, P. Schlein, V. Ashford, H. Haggerty, R. Juhala, E. Malamud, S. Mori, R. Abrams, R. Delznero, H. Goldberg, S. Margulies, D. McLeod, J. Solomon, R. Stanek, A. Dzierba, W. Kropac, 'Observation of the production of jets of particles at high transverse momentum and comparison with inclusive single-particle reactions'. Physical Review Letters 38 (1977), 1447-1450. [22] C. Bromberg, G. Fox, R. Gomez, J. Pine, S. Stampke, K. Yung, S. Erhan, E. Lorenz, M. Medinnes, J. Rohlf, P. Schlein, V. Ashford, H. Haggerty, R. Juhala, E. Malamud, S. Mori, R. Abrams, R. Delznero, H. Goldberg, S. MarguHes, D. McLeod, J. Solomon, R. Stanek, A. Dzierba, W. Kropac, 'Production of jets and single particles at high PT in 200 GeV hadron-beryUium coUisions', Nuclear Physics B134 (1978), 189214. [23] F.W. Biisser, L. Camilleri, L. Di Leila, G. Gladding, A. Placci, B.G. Pope, A.M. Smith, J.K. Yoh, E. Zavattini, B.J. Blumenfeld, L.M. Lederman, R.L. Cool, L. Litt, S.L. Segler, 'Observation of n° mesons with large transverse momentum in high-energy proton-proton collisions', Physics Letters 46B (1973), 471-476. [24] F.W. Busser, L. Camilleri, L. Di Leila, G. Gladding, A. Placci, B.G. Pope, A.M. Smith, J.K. Yoh, E. Zavattini, B.J. Blumenfeld, L.M. Lederman, R.L. Cool, L. Litt, S.L. Segler, 'A search for electron pairs at the CERN ISR', Physics Letters 48B (1974), 377-379. [25] F.W. Busser, L. Camilleri, L. Di Leila, B.G. Pope, A.M. Smith, B.J. Blumenfeld, S.N. White, A.F. Rothenberg, S.L. Segler, M.J. Tannenbaum, M. Banner, J.B. Cheze, J.L. Hamel, H. Kasha, J.P. Pansart, G. Smadja, J. Teiger, H. Zaccone, A. Zylberstejn, 'Observation of high mass electron-positron pairs produced in proton-proton colHsions at the CERN ISR', Physics Letters 56B (1975), 482^86. [26] R.N. Cahn, G. Goldhaber, The Experimental Foundations of Particle Physics (Cambridge: Cambridge University Press, 1989). [27] L. Camilleri, 'Proton-antiproton physics at the CERN Intersecting Storage Rings', Physics Reports 144 (1987), 51-115. [28] Cesar Group, The CERN Electron Storage and Accumulation Ring (CESAR), CERN 68-8, 6/3/68. [29] G. Charpak, R. Boucher, T. Bressani, J. Favier, C. Zupancic, 'The use of multiwire proportional counters to select and localize charged particles'. Nuclear Instruments and Methods 62 (1968), 262-268. [30] J.H. Christenson, G.S. Hicks, L.M. Lederman, P.J. Limon, B.G. Pope, E. Zavattini, 'Observation of massive muon pairs in hadron coUisions', Physical Review Letters 25 (1970), 1523-1526. [31] J.H. Christenson, G.S. Hicks, L.M. Lederman, P.J. Limon, B.G. Pope, E. Zavattini, 'Observation of muon pairs in high-energy hadron colhsions'. Physical Review D 8 (1973), 2016-2034. [32] P. ColHns, 'Regge theory and particle physics', Physics Reports 1 (1971), 103-204. [33] Craigie, Lepton and photon production in hadron colhsions. Physics Reports 47 (1978), 1-108. [34] M. Crozon, La Matiere Premiere (Paris: Editions du Seuil, 1987). [35] P. Darriulat, 'Large transverse momentum hadronic processes'. Annual Review of Nuclear and Particle Science 30 (1980), 159-210. [36] H. Deden, F.J. Hasert, W. Krenz, J. von Krogh, D. Lanske, J. Morfin, K. Schultze, H. Weerts, G.H. Bertrand Coremans, J. Sacton,W. VanDoninck,P. Vilain,D.C.Cundy,D. Haidt,M. Jafrre,S.Natah,J.B.M.Pattison, D.H. Perkins, A. Rousset, W. Venus, H. Wachsmuth, V. Brisson, D. Degrange, M. Haguenauer, L. Kluberg,

References

[37]

[38]

[39] [40] [41] [42]

[43] [44] [45] [46]

[47] [48] [49] [50] [51] [52] [53] [54]

167

U. Nguyen-Khac, P. Petiau, E. Bellotti, S. Bonetti, D. Cavalli, C. Conta, E. Fiorini, C. Franzinetti, A. PuUia, M. RoUier, B. Aubert, L.M. Chounet, J. Gandsman, P. Heusse, L. Jauneau, C. Longuemare, A.M. Lutz, C. Pascaud, J.P. Vialle, F.W. Bullock, M.J. Esten, T.W. Jones, J. McKenzie, A.G. Michette, G. Myatt, W.G. Scott, 'Experimental study of structure functions and sum rules in charge-changing interactions of neutrinos and antineutrinos'. Nuclear Physics B85 (1975), 269-288. M. Diakonou, C. Kourkoumelis, L.K. Resvanis, T.A. Filippas, E. Fokitis, C. Trakkas, A.M. Cnops, J.H. Cobb, E.G. Fowler, D.W. Hood, S. Iwata, R.B. Palmer, D.C. Rahm, P. Rehak, I. Stumer, C.W. Fabjan, T. Fields, D. Lissauer, I. Mannelli, W. Molzon, P. Mouzourakis, K. Nakamura, A. Nappi, W.J. Willis, 'Direct production of high pr single photons in pp collisions at the CERN ISR', Physics Letters 87B (1979), 292-296. M. Diakonou, C. Kourkoumelis, L.K. Resvanis, T.A. Filippas, E. Fokitis, C. Trakkas, A.M. Cnops, E.G. Fowler, D.W. Hood, R.B. Palmer, D.C. Rahm, P. Rehak, L Stumer, C.W. Fabjan, T. Fields, D. Lissauer, L Mannelli, W. Molzon, P. Mouzourakis, W.J. Willis, 'A measurement of direct photon production at large px at the CERN ISR', Physics Letters 91B (1980), 296-300. L. Di Leila, 'ISR Physics' (letter). New Scientist, 9 February 1984, 49-50. S.D. Drell, T.M. Yan, 'Massive lepton-pair production in hadron-hadron colHsions at high energies'. Physical Review Letters 25 (1970), 316-320. S.D. Drell, T.M. Yan, 'Partons and their applications at high energies'. Annals of Physics 66 (1971), 578623. T. Eichten, H. Faissner, R.J. Hasert, S. Kabe, W. Krenz, J. von Krogh, J. Morfin, K. Schultze, G.H. Bertrand-Coremans, J. Sacton, W. Van Doninck, P. Yilain, D.C. Gundy, D. Haidt, M. Jaffre, S. Natah, P. Musset, J.B.M. Pattison, D.H. Perkins, A. PuUia, A. Rousset, W. Venus, H. Wachsmuth, V. Brisson, B. Degrange, M. Haguenauer, L. Kluberg, U. Nguyen-Khac, P. Petieau, E. Bellotti, S. Bonetti, D. CavaUi, G Conta, E. Fiorini, C. Franzinetti, M. RoUier, B. Aubert, L.M. Chounet, P. Heusse, L. Jauneau, A.M. Lutz, C. Pascaud, J.P. Vialle, F.W. Bullock, M. Derrick, M.J. Esten, T.W. Jones, J. McKenzie, A.G. Michette, G. Myatt, W.G. Scott, 'Measurement of the neutrino-nucleon and antineutrino-nucleon total cross sections'. Physics Letters 46B (1973), 274^280. S.D. EUis, M.B. Kislinger, 'Implication of parton-model concepts for large-transverse-momentum production of hadrons'. Physical Review D 9 (1974), 2027-2051. S.D. EUis, R. Stroynowski, 'Large px physics: data and the constituent models'. Reviews of Modem Physics 49 (1977), 753-775. C.W. Fabjan, T. Ludlam, 'Calorimetry in high-energy physics'. Annual Review of Nuclear and Particle Science 32 (1982), 335-389. C.W. Fabjan, J. Lindsay, F. Piuz, F. Ranjard, E. Rosso, A. Rudge, S. Serednjakov, W.J. WiUis, H.B. Jensen, J.D. Petersen, 'A drift chamber vertex detector for intersecting storage rings'. Nuclear Instruments and Methods 156 (1978), 267-274. M. Faessler, 'Experiments with alpha particles at the CERN Intersecting Storage Rings', Physics Reports 115 (1984), 1-91. R.P. Feynman, 'Very high energy coUisions of hadrons'. Physical Review Letters 23 (1969), 1415-1417. R.P. Feynman, Photon-Hadron Interactions (Reading, Ma.: Benjamin, 1972). R.P. Feynman, 'Structure of the proton'. Science 183 (1974), 601-610. R.D. Field, R.P. Feynman, 'Quark elastic scattering as a source of high transverse momentum mesons'. Physical Review D 15 (1977), 2590-2616. E. Fischer, Two kilometres at 10~^^ torr: the CERN Intersecting Storage Rings for protons, CERN, ISRVA/71-55, 10/11/71. B. French, F. Krienen, T. Hassam, M. Morpurgo, A proposal for an open magnet system for the ISR experimental region, CERN, NP internal report 68-5, 11/3/68. J.I. Friedman, H.W. Kendall, 'Deep inelastic electron scattering'. Annual Review of Nuclear Science 22 (1972), 203-254.

168

The Intersecting Storage Rings

[55] P. Galison, *How the first neutral current experiments ended', Review of Modern Physics 55 (1983), 477509. [56] P. Galison, How Experiments End (Chicago: University of Chicago Press, 1987). [57] J. Gervaise, *Mesure de distances de haute precision au fil d'invar en micro-geodesie', Geometre, No. 12 (1965), 28-55. [58] J. Gervaise, Un example d'implantation de haute precision: le complexe synchrotron a protons et anneaux de stockage a intersections du CERN, CERN, ISR-SU/70-1, 26/1/70. [59] J. Gervaise, Positioning of the Intersecting Storage Rings: The Geodetic Approach, Geneva: CERN 70-18, 30/6/1970. [60] G. GiacomeUi, Total cross sections and elastic scattering at high energies'. Physics Reports 23 (1976), 123235. [61] G. GiacomeUi, M. Jacob, Thysics at the CERN-ISR', Physics Reports 55 (1979), 1-132. [62] S.L. Glashow, J. lUopoulos, L. Maiani, *Weak interactions with lepton-hadron symmetry'. Physical Review D 2 (1970), 1285-1292. [63] G. Hanson, G.S. Abrams, A.M. Boyarski, M. Breidenbach, F. Bulos, W. Chinowsky, G.J. Feldman, C.E. Friedberg, D. Fryberger, G. Goldhaber, D.L. Hartill, B. Jean-Marie, J.A. Kadyk, R.R. Larsen, A.M. Litke, D. Liike, B.A. Lulu, V. Liith, H.L. Lynch, C.C. Morehouse, J.M. Paterson, M.L. Peri, F.M. Pierre, T.P. Pun, P.A. Rapidis, B. Richter, B. Sadoulet, R.F. Schwitters, W. Tanenbaum, G.H. Trilling, F. Vannucci, J.S. Whitaker, F.C. Winkelmann, J. Wiss, 'Evidence for jet structure in hadron production by e+e" annihilation'. Physical Review Letters 35 (1975), 1609-1612. [64] H. Harari, 'Quarks and leptons'. Physics Reports 42 (1978), 235-309. [65] S.W. Herb, D.C. Hom, L.M. Lederman, J.C. Sens, H.D. Snyder, J.K. Yoh, J.A. Appel, B.C. Brown, C.N. Brown, W.R. Innes, K. Ueno, T. Yamanouchi, A.S. Ito, H. Jostlein, D.M. Kaplan, R.D. Kephart, 'Observation of a dimuon resonance at 9.5 GeV in 400-GeV proton-nucleus collisions', Physical Review Letters 39 (1977), 252-255. [66] A. Hermann, J. Krige, U. Mersits, D. Pestre, History of CERN, vol. 1 (Amsterdam: North Holland 1987). [67] A. Hermann, J. Krige, U. Mersits, D. Pestre, History of CERN, vol. 2 (Amsterdam: North Holland 1990). [68] M.G.N. Hine, A short description of the project for Intersecting Storage Rings at CERN and their place in European physics, CERN, DIR/AP/143, 30/11/64. [69] D. Hom, 'Many-particle production'. Physics Reports 4 (1972), 1-65. [70] K. Hiibner, ISR Performance for Pedestrians, CERN 77-15, 1977. [71] B. Hyams, G.K. O'Neil, A momentum analysis system for ISR reactions, CERN, NP internal report 6830, 11/9/68. [72] CERN Study Group on New Accelerators, The design study of Intersecting Storage Rings (ISR) for the Cem Proton Synchrotron, CERN, AR/Int. SG/64^9, 12/5/64, re-numbered as CERN/542. [73] Intersecting Storage Rings, CERN, Technical Notebook No. 5, May 1969; [74] Intersecting Storage Rings, Technical Notebook No. 5, CERN/PIO 74^2, January 1974. [75] M. Jacob, 'The role of the ISR in the development of particle physics', in ref. [76], 21-81. [76] M. Jacob, K. Johnsen, A review of accelerator and particle physics at the CERN Intersecting Storage Rings, Geneva: CERN 84-13, 30/11/84. [77] M. Jacob, P.V. Landshoff, 'Large transverse momentum and jet studies', Physics Reports 48 (1978), 285350. [78] K. Johnsen, 'The CERN Intersecting Storage Rings Project', 5th International Conference on High Energy Accelerators, Proceedings (Frascati 1965), Roma: CNEN, 1966; pre-print in ISR Archive, CERN. [79] K. Johnsen, 'The CERN Intersecting Storage Rings Project', 6th International Conference on High Energy Accelerators, Proceedings (Cambridge 1967), Cambridge, 1967, 58-63. [80] K. Johnsen, 'The CERN Intersecting Storage Rings', Nuclear Instruments and Methods 108 (1973), 205223.

References

169

[81] K. Johnsen, T h e ISR and accelerator physics', in ref. [76], 1-19. A substantially identical version of this paper is [82]. [82] K. Johnsen, 'The ISR and accelerator physics', in Particle Accelerators 18 (1986), 167-182. This is a revised version of [81]. [83] K. Johnsen, L. Van Hove, Status report on ISR, CERN/SPC/226, 12/5/66. [84] K. Johnsen, E. Keil, B. de Raad, L. Resegotti, Alternatives to the presently proposed ISR structure, CERN, AR/Int. SG/65-21, 29/11/65. [85] E. Keil, Intersecting Storage Rings, Geneva: CERN 72-14, 21/7/72. [86] J. Kogut, L. Susskind, T h e parton picture of elementary particles'. Physics Reports 8 (1973), 75-172. [87] J. Krige, 'Case studies of some important decisions', chapter 8 in ref. [66], p. 237-292. [88] J. Krige, 'Finance policy: the debates in the Finance Committee and the Council over the level of the CERN budget'. Chapter 10 in ref. [67], 571-635. [89] T.S. Kuhn, The Structure of Scientific Revolutions, 2nd ed. (Chicago: Chicago University Press, 1970). [90] J. Kuti, V. Weisskopf, 'Inelastic lepton-nucleon scattering and lepton pair production in the relativistic quark-parton model'. Physical Reviev^^ D 4 (1971), 3418-3439. [91] L. Lederman, 'Lepton production in hadron coUisions', Physics Reports 26 (1976), 149-181. [92] L. Lederman, 'The upsilon particle', Scientific American 239:4 (1978), 60-68. [93] G.C. Mantovani, M. Cavalli-Sforza, C. Conta, M. FraternaH, G. Goggi, F. Pastore, A. Rimoldi, B. Rossini, 'First results on diffraction dissociation of neutrons at the ISR', Physics Letters 64B (1976), 4 7 1 474. [94] G.C. Mantovani, M. CavaUi-Sforza, C. Conta, M. Fratemah, G. Goggi, F. Pastore, A. Rimoldi, B. Rossini, 'Observation of neutron-neutron interactions with double diffraction dissociation at the ISR', Physics Letters 65B (1976), 401^04. [95] W. Marciano, H. Pagels, 'Quantum chromodynamics'. Physics Reports 36 (1978), 137-276. [96] A. Minten, 'Plans for physics with the Intersecting Storage Rings', in Proceedings of the 1969 CERN School of Physics, Leysin, CERN 69-29, 19/11/69, 97-122. [97] P. Musset, J.P. Vialle, 'Neutrino physics with Gargamelle', Physics Reports 39 (1978), 1-130. [98] D. Pestre, 'The second generation of accelerators for CERN, 1956-1965: the decision-making process', in ref. [67], 679-780. [99] D. Pestre, 'The organization of the experimental work around the Proton Synchrotron, 1960-1965: the learning phase', in ref. [67], 429-502. [100] A. Pickering, Constructing Quarks (Edinburgh: Edinburgh University Press, 1984). [101] L. Resegotti, Progress report on the Split-Field Magnet for the ISR, CERN, ISR-MAG/69-58, September 1969. [102] B. Richter, 'From the psi to charm: the experiments of 1975 and 1976', Nobel Lecture, Reviews of Modern Physics 49 (1977), 251-266. [103] A.G. Ruggiero, Beam stacking with suppressed buckets in the ISR, Geneva: CERN 68-22, 4/6/68. [104] R.L. Samuel, 'La grande enceinte a ultra-vide des I.S.R. du CERN', Industries Atomiques, No. 7/8, 1970, 3-13. [105] W. Schnell, Stacking with missing buckets, another way of gaining the ISR/CPS circumference factor, CERN, ISR-RF/66-34, 10/11/66. [106] W. Schnell, 'Stacking in proton storage rings with missing buckets', 6th International Conference on High Energy Accelerators, Proceedings (Cambridge 1967), Cambridge, 1967, 85-89. [107] W. Schnell, About the feasibiUty of stochastic damping in the ISR, CERN, ISR-RF/72^6, November 1972. [108] R.F. Schwitters, K. Strauch, 'The physics of e+e~ coUisions', Annual Review of Nuclear Science 26 (1976), 89-149. [109] D. Sivers, R. Blankenbecler, S. Brodsky, 'Large transverse momentum processes', Physics Reports 23 (1976), 1-121.

170

The Intersecting Storage Rings

[110] J. Steinberger, in CERN, NP internal report 68-34 (1968). [Ill] R. Stroynowski, 'Lepton pair production in hadron collisions', Physics Reports 71 (1981), 1-50. [112] G. Taubes, Nobel Dreams. Power, Deceit, and the Ultimate Experiment (New York: Random House, 1989). [113] S.C.C. Ting, 'The discovery of the J particle: a personal recollection', Nobel Lecture, Reviews of Modem Physics 49 (1977), 235-249. [114] S. Van der Meer, Stochastic damping of betatron oscillations in the ISR, CERN, ISR-PO/72-31, August 1972. [115] P. Watkins, Story of the W and Z (Cambridge: Cambridge University Press, 1986). [116] F. Wilczek, 'Quantum chromodynamics: the modern theory of strong interactions', Annual Review of Nuclear and Particle Science 32 (1982), 177-209. [117] K. Winter, A summary of discussions on a large analysis system of ISR reactions, CERN, NP Internal Report, 69-2, 14/2/69. [118] T.M. Yan, 'The parton model'. Annual Review of Nuclear Science 26 (1976), 199-238.

CHAPTER 5

The Relationship Between CERN and its 'Visitors' in the 1970s John KRIGE

Contents 5.1 The underlying causes of outside users' discontent in the early 1970's 5.2 The setting up of ECFA Working Group 3. A brief chronology 5.3 First point of friction: the construction of big equipment 5.4 Second point of friction: CERN's indefinite contract policy 5.5 Third point of friction: visitors' participation in decision-making 5.6 Fourth point of friction: the working conditions of visitors at CERN 5.7 Fifth point of friction: salary differentials between CERN staff and outside users 5.8 The visitors question: a quick survey of later developments 5.9 Concluding remarks Notes

171

173 176 178 182 185 190 193 196 199 200

*....The physicists of the European High Energy Physics Community, which are the users of CERN, [...] [look] at CERN as their laboratory, and not as an ivory tower for a select body of physicists on site. [...] I feel that, in spite of the budget difficulties of CERN, we have discussed today, the even greater difficulties of the home laboratories render the ideal of CERN as the laboratory of us all even more essential.' From the farewell address by the Chairman of ECFA, Guy von Dardel, to CERN Director General W. Jentschke (emphasis in the original)^.

From its very inception it was understood that CERN would have to open its doors to CERN physicists who wanted to make use of its unique facilities for doing research^. Funded by a 'conglomerate' of nations, the bulk of which could not afford to build anything comparable on their own, it was assumed that the laboratory would serve a community whose size far exceeded those employed by CERN itself. In terms of access CERN was supposed to be quite different to, say, a university laboratory whose equipment 'belonged' to those who had acquired it. It was meant to be a European laboratory, and as such the entire European high-energy physics community was seen to have a right to exploit the potential of its machines. In the late 1950s and early 1960s the CERN staff and management negotiated a number of arrangements with the outside users aimed at protecting the visitors' right to work around the machines. A committee structure was set up for deciding on the experimental programme on which visitors were well-represented. A suitable scheme for using beams and distributing photographs was worked out by bubble-chamber physicists once the big equipment built by groups in France and at CERN had been installed and was running. Finally, an equilibrated mix of CERN teams and outside groups using electronic modes of detection had been established by 1964/65. In 1961 five out of six groups doing electronic experiments at the CERN PS were composed of CERN staff only, plus the odd individual visitor. By 1965 only three out of twelve teams were built like this. There were eight mixed teams of CERN staff and outsiders working at the machine, and one team composed of visitors only^. Little was to perturb the modus vivendi established between the CERN staff and the outside users for the next five years. The experiments committee structure remained intact, to the extent that both Gregory in 1965 and Jentschke in 1970 left its basic core unchanged, coping with new developments (like the ISR experimental programme) by accretion to the existing system rather than by transformation. Bubble chamber physicists continued to decide among themselves how to organize their work. And the swing in favour of electronic experimentation by outside teams at the PS continued. In mid-1969 there were only three 'pure CERN' groups working at the machine out of a total of 22 teams, the balance being made up of ten mixed teams and nine visitors-only teams^. 172

The underlying causes of outside users' discontent in the early 1970's

173

This relatively harmonious situation was not to persist for long, however. By the early 1970s rumbhngs of discontent among the visitors were once again being heard. No longer satisfied to be treated as 'customers' of a faciUty which was 'owned' and controlled by others, they wanted CERN to belong to them in the same (restricted) sense that it belonged to the physicists based in Geneva. The point came up again and again, we are told, in an informal meeting held with visitors in January 1973. They stressed, the author wrote, 'that they should not be considered as visitors at CERN but they thought they had a right to be fully integrated into the CERN machinery'^. In other words, experimentalists in the member states wanted to aboUsh any distinction between 'host' and 'visitor' with the differences in property-rights and power that that entailed. Correlatively, they felt that any arrangement which embodied such distinctions between physicists was discriminatory and degrading. In this chapter we shall describe in more detail some of the grievances expressed by visitors to CERN in the 1970s and their causes. The problem will be studied primarily through the deliberations of a working group set up by ECFA (the European Committee for Future Accelerators) in 1973 to look into, inter aUa, the visitors question. Having briefly identified the factors precipitating ECFA's enquiry in the first place, we go on to study five specific points of friction between outside users and the host laboratory which were widely debated in this period. We then briefly survey the situation about a decade later. It emerges that many of the complaints made by visitors in the mid-1970s were still being made in the mid-1980s. In conclusion we discuss some of the reasons for the persistence of these difficulties.

5.1 The underlying causes of outside users' discontent in the early 1970's ECFA's idea of setting up a working group to study the relationship between CERN and institutes in the member states was sparked off by the decision, taken officially in February 1971, to build a 300 GeV 'Super Proton Synchrotron' in Geneva. The negotiations over the design, funding, and siting of this machine had dominated CERN Council meetings throughout the late 1960s. At this time it had been assumed that the new machine would not be built in Geneva. However, early in 1970 John Adams, the recentlyelected 300 GeV Project Director, and his team, showed that this was in fact technically, geologically, and financially feasible, not to say advantageous. With that, the CERN Council rapidly agreed to pay for an SPS built on an extension of the existing CERN site^. The European high-energy physics community was deUghted, of course: now, at last, they were guaranteed the machine that would enable them to compete with the faciUties under construction at Fermilab near Chicago. But they were also concerned: for the Council's decision inevitably signalled an even greater concentration of the European high-energy physics effort at CERN. The writing was already on the wall. At the end of 1966 about 52% of the European high-energy physics community not paid by CERN was 'dependent' on the Geneva laboratory in the sense that they were working exclusively on taking data at Notes: pp. 200 ff.

174

The Relationship Between CERN and its 'Visitors' in the 1970s

CERN, or on analysing data obtained there. By 1970 the percentage of physicists depending on CERN hadrisento 58%^. During the 1960's outside users in at least the four big CERN member states could do useful physics at their 'own' national laboratories. With the commissioning of the ISR and, above all, the SPS, these would soon be obsolete. Hence the demand by visitors that they be better integrated into CERN, that CERN become the common property of the entire European high-energy physics community. Coupled with this - and this is the second factor explaining the new 'militancy' among the users in the early 1970s - , was the increase in the number of outside users at CERN caused by the growing importance of electronic methods of detection. In the early 1960s the bubble chamber had been the dominant detector in thefield.However, it gradually lost ground to electronic detectors - spark chambers, counters, and later wire chambers, drift chambers, etc. ECFA figures indicated that in October 1966 there were 607 European experimentalists doing bubble chamber physics and about the same number, 594, using counters and spark chambers. Four years later the balance had swung distinctly in favour of electronic detectors. Provisionalfiguresfor 1970 gave 986 counter and spark chamber physicists in Europe, and 708 bubble chamber physicists, a ratio of almost 3:2^. This trend was coupled with a growth in the user population actually present on the CERN site. For technical reasons physicists using electronic devices were obliged to spend far more time at the host laboratory than were those using conventional track chambers^: • a bubble chamber was basically a piece of heavy engineering; physicists had little to do with its construction and installation. An electronic detector, by contrast, was basically a combination of separate components, some of which required heavy engineering, others of which could be made in a local workshop or bought off the shelf; physicists took part in the construction of the detector and their presence was essential during the assembly on the experimental floor; • the experimental parameters did not change during a bubble chamber run; physicists, in so far as their presence was needed at all during the data-taking phase, played a supervisory role. With an electronic device, on the other hand, the experimental parameters were continually modified during a run; the physicists' relationship to their detector was interactive, and it was imperative that they be present while taking data; • finally, the results of a bubble chamber experiment were recorded on film, and were extracted after a run, and away from the experimental area. Some of the results of electronic experiments, and often the most important and exciting ones, were acquired during a run (though much analysis could also be done after the data was taken, and away from the experimental floor). In short, whereas bubble chamber physicists would generally expect to have rather weak links with the technical staff" of the host laboratory, and to spend most of their time at their home institutes (if they had adequate scanning and measuring instruments and computers), the converse was true for electronic experimentaUsts. They had to work closely with the laboratory staff"- as Goldschmidt-Clermont put it, 'The symbiosis CERN-outside group(s) has to be rather close for electronic experiments, where much work occurs on the spot at the time of the exposure, and where

The underlying causes of outside users' discontent in the early 1970's 175 apparatus has to be built and assembled [...]' - and they could count on spending many days, even months at the host laboratory during the course of an experiments^. In consequence as this form of experiment grew more important in the late 1960s and early 1970s so the pressure mounted on CERN to meet the day-to-day needs of a fast-growing, insistently present, population of outside users. Figure 5.1 illustrates both the concentration of resources at CERN in the 1970s, and the growth in the number of outside users on the site^^ The curves are indicative only: it is difficult, if not impossible, to get strictly comparable data across such a wide time scale. Yet the trends are clear: a marked increase during the 1970s in the proportion of the European high-energy physics community using CERN, and a rapid, even exponential growth in the users on site, with particularly sharp increases in about 1969 (preparation for the ISR, commissioned early 1971) and in 1975 (preparation for the SPS, commissioned early 1977). These technico-demographic transformations triggered the events we shall now describe.

2000

I

B NP only « NP + TC D EP 4 All users

1000 H

1960

1980

Fig. 5.1 Visitors to CERN from the member states in the NP (electronic detectors) and TC (track chambers) divisions (until 1975) and in the EP division (from 1976 onwards). The curve marked 'all users' gives the size of the European outside user community (regardless of technique) exclusive of those paid by CERN and (in 1978) of those using DESY. Data from different periods, and for different divisions, is not always strictly comparable. For more details, see note 11.

Notes: p . 201

176

The Relationship Between CERN and its 'Visitors' in the 1970s

5.2 The setting up of ECFA Working Group 3. A brief chronology On the 30 November 1972 the ECFA held an information meeting intended to keep the European particle physicists in touch with important developments at CERN and elsewhere^^. The fifth item on the agenda concerned the relationship between the 300 GeV accelerator and the national laboratories and universities. It was introduced by ECFA secretary Dick Harting, who for several years had been responsible for compiling statistics on the European high-energy physics community. Harting began his address by pointing out that the increasing tendency to concentrate the high-energy research effort in Europe at CERN 'had already given rise to a considerable amount of discussion'. He then went on to give some data illustrating this situation. For example, in 1966 CERN had accounted for 30% of the total European highenergy physics budget. This had climbed to 39% in 1970, and to 46% in 1972. The proportion granted to the national laboratories had decreased accordingly. And the situation in universities seemed to be even worse. 'Of the total budget of 374 MSF for the CERN-independent laboratories in 1970', said Harting, '311 MSF had been granted to the national laboratories employing 321 physicists and only 63 MSF to the universities employing 408 physicists'*^. 'Although the decision to build the 300 GeV accelerator was to be welcomed by the whole European physics community', said the Secretary, 'the structural problems of co-operation in the field of high-energy physics should be closely examined both by CERN and by ECFA'. Acting chairman Giorgio Salvini took a step in this direction the following day, when ECFA held its fourteenth plenary meeting*"^. An item dealing with the issues raised by Harting's report was added to the agenda at the last minute. Salvini opened the debate on it by mentioning some of the concerns that he felt - the need for every European highenergy physicist to spend some of his time at CERN, the need for a 'proper balance' between a visitor's duties at CERN and his obUgations at his home institute, 'action to increase the impact of physics research activities on European culture', etc. Other items were added in the subsequent discussion. To conclude, Salvini proposed that a summary of the discussion together with the terms of reference of a future working group be sent to ECFA members for their comments. Three weeks later Salvini and Harting circulated a letter to all members of the plenary ECFA presenting the argument for 'a careful study of the relations CERN-National Laboratories/Universities', and calling for suggestions for the members of a working group. They then went on to explain why they thought this study was needed. The Geneva laboratory, they said, was 'an absolutely necessary institution', but it 'could not exist alone' - 'for we could not justify its solitary existence to our governments, and it [was] difficult to imagine three hundred millions of Europeans ready to finance a huge splendid enterprise for the enjoyment of a selected class of persons, with thousands of technicians working for them'. National laboratories and universities, 'the transmission belt of the scientific culture from one generation to the other', were needed too: the image was that 'of a triangle, with currents circulating through the vertices'. The authors then listed some of

The setting up of ECFA Working Group 3. A brief chronology

177

the problems faced at home by visitors to CERN from the universities, concluding that 'it [would] be the task of ECFA and its Working Groups to discuss all these topics in detail'i^ The Salvini-Harting letter elicited some dozen replies from the members of the plenary ECFA. About half of them simply proposed candidates for the envisaged working group. A few went further, suggesting issues that needed looking into, sometimes using strong language. Two respondents complained that at CERN 'Visitors [were] treated as secondrate physicists [...]'. One letter even questioned the vaUdity of the enterprise as a whole: 'HEP [was] a patriarchal ivory tower', its author said. 'We should think about integrating in society rather than make [sic] HEP still more exclusive'^^. At its fifteenth plenary meeting on 4 May 1973 ECFA estabUshed a working group whose task it was to explore these issues in greater depth (Working Group 3). Professor J.C. Gunn of the Department of Physics at Glasgow University was appointed Chairman. There were 16 other members drawn from the spectrum of the CERN member states, and five CERN representatives. Harting and Salvini were ex officio members of the panel and its Secretariat was provided by J.M. Valentine and D.J. Baugh. The group's terms of reference invited it to look into the relationships between the 'constituent parts' of the particle physics community, and between that community and the physics community as a whole^^. The working group held its first meeting in the CERN Council Chamber on 15 June 1973. The chairman, who had prepared a tentative Ust of topics, called for a wideranging discussion on the aims of the study. Salvini broke the ice. 'At a certain moment', he said, 'a community [felt] something and [...] it was important to check this and establish its real content. It was important to bring to the level of careful analysis what [was] whispered or discussed in a disorderly way in a community'. This was followed by what Hine afterwards described as 'a well conducted exchange of views and a general consensus that h.e.p. in Europe was at another turning point [...]'. It was also agreed, Hine went on, that 'there could be no useful discussion until the factual background to questions was established [...]'. In line with this idea, all delegates were asked to consult widely (25 written statements were ultimately submitted to the group) and to provide information for the next meeting on a select number of topics^^. The working group set up four sub-committees to deal with these several topics when it met for the second time on 17 September 1973. Sub-committee 1, chairman H. Faissner, was to report on demographic problems. Sub-committee 2, chairman A. Donnachie, had responsibility for the problems faced by visiting groups from the CERN member states. The third sub-committee, chaired by Gunn himself, dealt with the relationship between CERN and the national laboratories. Finally, sub-committee 4, chairman J. Geheniau, was asked to make recommendations on how to improve the Unks between high-energy physics and European science or, more generally, 'the community'^^. The provisional findings of the subcommittees were outUned by Gunn in a progress report to the sixteenth plenary meeting of ECFA held on 22 February 1974^^. The final report of Working Group 3, dated 1 August 1974, was laid before ECFA when it next met Notes: pp. 201 ff.

178

The Relationship Between CERN and its 'Visitors' in the 1970s

in January 1975. It solicited a lively debate in which quite a few people, including some non-CERN scientists who had served on the working group itself, again criticized various practices and attitudes at CERN, and indicated that they felt that the report's recommendations were not strong enough. The report was accepted 'subject to the inclusion of the remarks made during the present meeting', and the new ECFA chairman, Guy von Dardel, closed the debate by suggesting that its findings 'be constantly kept before ECFA so that it could see where action remained to be taken'^^. The central theme throughout these discussions was that the resources and facilities for European high-energy physics were becoming concentrated at CERN, at the expense of activities in the member states' laboratories. 'I feel strongly' wrote one user 'that we [i.e. national groups] must resist forces that completely centralise all life and initiative in the subject' at CERN^^. To that was coupled a concern, a resentment even, among the outside users of the laboratory that this concentration of resources was going along with a concentration of privileges for the in-house staff, that CERN was becoming an 'oasis' cut off from its base in the national laboratories and the universities. These twin concerns were translated into a number of specific complaints in the early 1970s. Some of these complaints were to recur again and again in later years. Some of them have been raised by physicists using facilities in the United States. In short, taken as a whole, they may be regarded as exposing problems which are intrinsic to the practice of high-energy physics today, a practice in which accelerators have necessarily become national, or international facilities, a scarce resource serving a large and demanding community, and in which friction between 'in-house staff and 'outside users' is commonplace.

5.3 First point of friction: the construction of big equipment One of the major concerns of the member states' physicists in the early 1970s was that their national laboratories should be given every opportunity and encouragement to build big equipment for use at the SPS. Electronics experiments were not only growing in popularity, but also in complexity and in scale. Consider, for example, the increase in the size of the teams. Table 5.1, presented by Jentschke at a 300 GeV Study Week in September 1972, illustrates the situation as it evolved from 1966 to 1970, with the Director General's estimates for 1976 (the year the SPS was expected to start)^^. We see a 50% growth in size from 1966 to 1970, and an expected doubling over the decade 1966-1976. The equipment used became correspondingly 'heavy'. In 1961 spark chambers were presented as extremely easy to construct - 'anyone can build one in the basement and make it work' - and cheap and versatile - '[...] you can build a device for a particular experiment and give it away, store it in the basement, or forget it and build another one for the next experiment'^"*. By contrast one of the first experiments being installed at the SPS in 1976 was a six-team, 26 physicist affair, and its proposed apparatus, which extended over 25 m on the experimental floor, consisted of'a beam telescope of proportional wire chambers, a liquid-hydrogen target surrounded by a An solid angle anticoincidence counter arrange-

First point of friction: the construction of big equipment

179

Table 5.1 The increase over time in the size of teams doing electronics experiments at CERN

Number of physicists in electronics experiments Number of groups doing electronics experiments Physicists per group

1966

1968

1970

1976 estimate

271

460

630

900

17

20

27

30-36

16

23

23

25-30

ment [...], and a forward spectrometer equipped with two magnets giving a total bending power of 3Tm, wire spark chambers with a resolution better than 0.3 mm, two large aperture Cerenkov hodoscopes, a trigger system and anticoincidence counters for the detection of charged particles and neutral pions'^^. These was clearly a good deal of work in the field of detector-construction for applied physicists and engineers. But who would doit? The general feeling among outside users was that CERN wanted to 'hoard' important, big-equipment projects for itself^^. As one visitor put it in a written statement to WG3 in 1973, he had been struck by some 'rather startling comments' made by CERN senior staff at a meeting of the SPS Experiments Committee. 'The question asked by a senior CERN physicist', the correspondent went on was 'whether all major experimental projects at the SPS should come under the control of CERN paid project leaders'. Two arguments were put forward by CERN for this poUcy. Firstly, the laboratory had the requisite technical and engineering capacity for building big, complex equipment. Secondly, it was claimed that such projects should come under the 'neutral' control of CERN, rather than be built by any national group. This was because, by virtue of their size and complexity, they were not just one-off experiments but general long-term faciUties which should be available to the whole physics community^^. In line with these ideas D G Jentschke told ECFA in December 1972 that 'big experimental equipment projects were usually financed by CERN', and that it was planned 'to spend about 50 MSF on major equipment for SPS physics in the West Area [...]'^^. Against this, visitors from the member states felt that, whenever possible, big experimental equipment should be built in the national laboratories. For one thing, they had the infrastructural resources, employing together about 4500 people and dispensing funds of about 500M Swiss francs per annum. This compared favourably with the manpower and expenditure figures for the more capital-intensive CERN programme of some 3500 people and a budget of 570M Swiss francs in 1973^^. For another they had the technical capability and skills deriving essentially from the fact that they had built accelerators of their own. To give some examples. Saclay in France had constructed and installed a 7 m^ hydrogen bubble chamber, Mirabelle, for use at the 70 GeV machine in Serpukhov, and had also Notes: p. 202

180

The Relationship Between CERN and its 'Visitors' in the 1970s

built a variety of scanning and measuring set-ups. As for counter experiments, to quote Berthelot in May 1972, 'physicists [were] assisted by engineers and technicians who [had] acquired a large amount of experience both in very fast electronics, on-line computers, and construction of all kind of equipment involved such as spark chambers, wire chambers, scintillators, Cerenkov counters, etc...'^^. At Frascati in Italy there were groups specialized in magnets, in cryogenics, in ultra-high vacuum techniques, and in electronics. There was also a workshop in which about ten people built detectors for electronics experiments counters, light pipes, spark chambers, etc^^ Finally (and unfortunately we have no comparable information for Germany) the Rutherford Laboratory in England had 'a strong appHed physics support programme', covering the development of superconducting magnets and RF separators, polarized and track sensitive bubble chamber targets, and fast cycling vertex detectors. They had also built a special camera system (the so-called Plumbicon) for the Omega project^^. In brief, national laboratories were well equipped to build major equipment for use at the SPS and, in one visitor's view, 'it would be a madness to ignore this capacity [...] and to go instead to a further rehance on CERN engineering and technical faciUties'^^. Three other arguments were advanced by 'outsiders' to bolster this Hne of thinking. Firstly, it was recognized that detector development required and extended strategically important skills and knowledges in those involved in 'technically advanced projects'. Member states had 'a legitimate desire' to see those skills fostered in their technicians and engineers-^"*. Secondly, there were the advantages to be gained by the universities in those countries that had national laboratories. On the one hand the latter had the resources and the know-how to turn good ideas into useful devices - and the most oft-quoted example here was the Plumbicon, which had been built at the Rutherford Laboratory though the 'initial thinking' had been at Westfield College, London^^. At the same time, they could simplify the working arrangements of electronics experimenters based in physics departments. They provided 'a local, easily accessible, centre for the preparation of apparatus and for subsequent data analysis'. As such they could help reduce the time university physicists had to spend away from their families and their normal teaching duties^^. Finally, and perhaps most important of all, the construction of big equipment for highenergy physics provided something of a guarantee for the long-term survival of the national institutes. During the late 1950s and early 1960s all the large member states built national accelerators which, though not comparable in energy to the biggest Europe could offer, the 28 GeV CERN PS, could still do useful high-energy physics work. However, the costs of financing the construction of, first the ISR and then, immediately afterwards, the 300 GeV-SPS, coupled with the enormous increase in energy that these machines represented over other accelerators in Europe, inevitably entailed a refocussing of activities at the national level. Two lines of action were envisaged. Firstly, machines that could no longer compete in the high-energy field were to be decommissioned. At the end of 1973 France, for example, was planning to do all its high-energy physics at accelerators outside the country (CERN, Serpukhov, Fermilab), and to concentrate on nuclear structure physics -

First point offriction: the construction of big equipment

181

Saturne had in fact already been converted to a nuclear structure programme. In Britain, for its part, there were plans to close NINA, the 5 GeV electron synchrotron at Daresbury by 1977 or 1978, transferring some of the staff to a nuclear structure faciUty, and to turnoff the 7 GeV PS Nimrod around 1979 - in fact NINA was closed down in 1977 and Nimrod in 1978^^. The second approach taken by national laboratories was to envisage building high-energy accelerators that were 'complementary' to what CERN had, realizing that if they did not the money would flow out of high-energy physics into other fields. However, the strongest, and indeed the only serious candidate for this role from a physics point of view was a 10-20 GeV electron-positron colHding beam machine - and in 1973 three national laboratories had plans to build one (the 14 GeV per beam EPIC at Rutherford, the 15 GeV PETRA at DESY, and the 10 to 12 GeV Super ADONE at Frascati). The Working Party realized that 'to attempt to build more than one would be quite unrealistic, political and financial suicide for the high-energy physics community' to quote Mulvey^^. Put differently the ECFA-inspired image of a pyramid of European accelerators with CERN at the peak, resting on a base of high-energy machines in the member states, was now obsolete. And national laboratories needed to carve out a new niche for themselves to ensure their survival. The construction of heavy equipment for use at CERN was seen to be one important way of keeping them in business. In fact it was even suggested that they might do this on 'some sort of contractual basis for CERN, providing equipment not only for their own user groups but in a more general way'^^. To simpHfy, why not have CERN build accelerators and the national laboratories build the heavy equipment to exploit them (rather as was done for the two big bubble chambers, BEBC and Gargamelle)40? How sympathetic was CERN to these arguments? We have no direct evidence for answering this question but it is safe to say that no formal attempt would have been made by CERN to coordinate its detector-building activities with those in the Member States. More precisely, the kind of suggestion made by visitors to the effect that 'CERN should rely more on specialist techniques developed in the National laboratories rather than maintaining comparable specialist groups at CERN [...]' (our emphasis) would probably have fallen on deaf ears^^. This was partly for the simple reason that CERN had a large number of appUed physicists and engineers on its staff (550 not counting mathematicians and programmers in December 1974, 398 of them on indefinite contracts) and it was management's responsibiUty to secure interesting and challenging work for them^^. It was also because the CERN staff had every intention of building 'their' laboratory into the best of its kind in the world, and wanted to have all the equipment and expertise that was needed to achieve this goal at hand and under their control. There was no question then of CERN suppressing scientifically and technically important and challenging activities just because there were groups engaged in doing similar work in the member states. This does not mean, of course, that there was no technical collaboration between CERN groups and outside groups in detector construction for electronic experiments. What we suspect though is that, just as in the case of the organization of work with bubble chambers in the early 1960s, this happened informally rather than as a matter of deliberate Notes: pp. 202 ff.

182

The Relationship Between CERN and its 'Visitors' in the 1970s

policy, and in response to the concrete needs of the parties concerned. In fact, as detectors got bigger and more expensive, and were of modular construction, it became normal for visiting groups to develop and build their own piece of the apparatus using in-house facilities in national laboratories and universities. These are points we shall return to later. 5.4 Second point of friction: CERN's indefinite contract policy In the late 1950s and early 1960s the CERN management successfully argued that certain categories of staff should be given indefinite contracts, a concept equivalent to tenure in a university. Initially seen as something of a privilege to be awarded to a few individuals whose services were highly prized, this practice gradually evolved into standard laboratory policy. By the end of 1971 about 60% of the CERN staff had indefinite contracts'*^. Table 5.2 shows how these contracts were distributed among scientific staff a few years later. We see that almost three-quarters of applied physicists and engineers and about half the experimentalists had indefinite contracts at this time. CERN's policy of granting physicists, in particular, a 'job for Ufe' after they had been employed on afixed-termcontract for several years was strongly opposed by some of the outside users in the early 1970s. Indeed it was the one issue on which certain ECFA delegates felt that the working group's final recommendations were not firm enough with CERN. Its report recommended that CERN 'should be asked to examine critically the balance of its temporary and tenure appointments in both pure and appHed physics [...]'. In fact, as was pointed out by H. Faissner, who had chaired the subcommittee most directly concerned with this question, 'there was a strong opinion in the Working Group that the number of tenure appointments in pure and applied physics at CERN should not be allowed to increase'. This opinion, he said, had been 'insufficiently stressed' in the final recommendation - apparently to accommodate CERN's claim that the laboratory had already adopted a no-growth policy"*^.

Table 5.2 Number of CERN scientific staff with indefinite contracts (IC) around the end of 1974"^ Category Experimental physicists"^ Theoretical physicists"^ Applied physicists* Mathematicians, programmers Engineers* Notes "" = Ason 1.1.75 * = As on 31.12.74

Total staff

Staff, IC

Percent

77 19 197 138 353

36 12 147 68 251

47% 63% 75% 49% 71%

Second point offriction: CERN's indefinite contract policy

183

The main objection that the visitors had to this poUcy was that it seriously impeded mobility through CERN, so that the knowledge and experience to be gained by working in Europe's most important laboratory were becoming concentrated in the hands and minds of a privileged few who were based there. Indefinite contracts discouraged scientists from leaving CERN. 'European physicists must spend at CERN a part of their Hfe, but not all their life [...]', otherwise 'a deadly stagnation develops'. Indefinite contracts led CERN staff" to be closed in on themselves, indifferent to building contacts with colleagues in national laboratories and universities, and reluctant to spend extended periods of time away from Geneva. 'One reason why collaboration [with CERN] was easier in research than on the technical side was the fact that all applied physics staff" held indefinite contracts and thus had no incentive to maintain outside contacts'. Indefinite contracts impeded the flow of outsiders through the laboratory. 'Anybody who scientifically deserves it [should have] an opportunity to spend a period at CERN. To improve the situation in this respect I see only one way: to shorten the admissible stay of visitors at CERN, and to stop the creation of new permanent positions'^^. Behind these objections, and increasing the strength of feeling in ECFA on this question, lay the prevailing situation in the universities, and the difficulties that high-energy physics was experiencing at the time, both of which were demoralising younger people in the field and turning potential recruits away from it. Firstly, and most concretely, it seemed that 'in most countries the physicists' career prospects [had] recently changed dramatically [...]' in the universities'^^. There was a growing tendency to give tenure, not only to those in very senior positions, but also to relatively young, junior staff", so that in some countries it looked as if only one PhD graduate out of ten could hope for a permanent appointment in the foreseeable future. At the same time, there appeared to be a declining number of technical or computing jobs in high-energy physics. In short, all indications were that the boom of the 1960s was coming to an end in the universities, and that the field as a whole was reaching a 'steady state', both in terms of money ('The expected financial future in different countries [was] typically one of constant budgets [...]'^^') and of manpower ('The number of positions in high energy physics [would] stay approximately constant'^^). Hence the need to improve the circulation of staff" between CERN, the universities, and the national institutes, and 'Not to increase the number of permanent positions at CERN and at the National Labs'^^. A second factor increasing anxiety about the long-term future of high-energy physics was 'the current antiscientific tendencies among young people'^^ This was associated with the general wave of student unrest which swept through many European and American universities in the late 1960s. A focal point of student protest was the involvement of scientists in the Vietnam war, a war in which the USA's role was vehemently opposed by many of the young, and which exposed, in their view, the shallowness of claims that scientific research was 'objective' and 'disinterested', its results 'value-neutral'. At a famous meeting of the AAAS in Chicago in December 1970 'Dr Teller, father of the American H-bomb, had to share his platform with placards proclaiming him a war criminal; Dr Glenn T. Seaborg, chairman of the Atomic Energy Commission [...] fled the Notes: pp. 203 ff.

184

The Relationship Between CERN and its 'Visitors' in the 1970s

room rather than hear himself indicted for the crime of 'science against the people'; the president of the National Ac5ademy of Sciences, Dr Philip Handler, escaped lightly in being called a lackey of the ruling class by a speaker who usurped his podium [...]'. As one of those present explained, 'Because science is used for war, we have lost the respect of the people and there is a revulsion against scientists [...]'^^. Similar, though perhaps less spectacular, protests were also common in Europe, where they were coupled with a fundamental challenge from below to the prevailing power-relationships in many walks of Ufe, including the universities, and the demand for more participation in decision-making procedures'^. Some members of ECFA were alarmed to the point of despair: 'In my country', wrote Morpurgo from Genoa, 'the future itself of the Universities as a place where research of any kind can be done is, in my opinion, strongly in doubt. We have assisted', he went on, 'in the past 6 years to a progressive unbehevable deterioration of the standards of our Universities, which has proceeded in parallel with a demagocic [sic] set of laws aiming, partially, to hit the so called 'meritocracy'''^. Even the sober-minded Nature felt it apposite to ask 'Can and Should the Universities Survive?'^'. In this embattled atmosphere, with science under attack, and with poor career prospects in high-energy physics, the working group felt that every effort should be made to improve the public image of their discipline, and to provide young researchers with a taste of the excitement and the challenge of the field which only a place like CERN could offer. CERN's position on these questions rested on two main planks. Firstly, it reiterated the scientific need for indefinite contracts. Many experimental projects, as GoldschmidtClermont pointed out, could take five years or more from conception to completion - and here he mentioned large experimental facilities like BEBC, Gargamelle, the Split Field Magnet and the Q, spectrometer by way of examples. Obviously 'some long-time continuity' was required for a number of the people working on these projects, and this was not compatible with a rapid turnover of staff, he claimed. CERN's second main argument was that, unless its employment policies were compatible with those being applied in the member states, it could not recruit and keep good people. 'Many staff feel strongly that CERN policies and practices should parallel those found in the Member States [...]', noted the Working Group on Appointment Policy which reported in August 1972, and this meant that CERN too had to yield to the pressure to grant long-term job stability. 'The idea of a guaranteed job in the same organization from the age of 25-30, with a pension to follow, is now a commonplace, and mobility between employers becomes more and more difficult after the age of about 30-35'^^. As Goldschmidt-Clermont explained to Faissner, if the laboratory's policy for awarding indefinite contracts did not reflect these realities, 'some of the best candidates for work at CERN may be discouraged to join its staff''^. This did not imply that CERN was against a greater deal of mobility among the three vertices of the triangle CERN-national laboratories-universities. On the contrary, it 'favour[ed] sabbatical years in the member states and support[ed] extended leaves for its senior staff with indefinite contracts. If these possibiHties had not been used very much to date, it was not for any lack of goodwill on CERN's part. Indeed the laboratory's sci-

Third point offriction: visitors' participation in decision-making

185

entists and engineers would welcome the opportunity to teach some advanced courses at universities, but they found it difficult to do so 'due to a lack of available positions in the member states'^^. In line with these considerations, and despite the protests from its users, CERN continued to apply an active policy of awarding indefinite contracts to its staff. Indeed the 1972 CERN Working Group on Appointment Policy effectively ignored the outside users' pleas. It proposed that research physicists be given 2-3 ICs per year, that 50% of mathematicians and programmers, and 50% of applied physicists and engineers recruited for development work should be awarded indefinite appointments, and, finally, that 50-60 applied physicists and engineers on fixed-term contracts who were in non-developmental work should also be given the appropriate job security^^. This was a far cry from the appeal to stop all such awards which was made by some people in ECFA's WG3.

5.5 Third point of friction: visitors' participation in decision-making One of the classic sites of conffict between a host laboratory and its outside users is the extent to which the latter are involved or, at least, feel involved in decisions which affect them, notably decisions concerning the experimental programme^^. In the early 1960s the CERN management set up structures which took account of this demand for consultation, a demand which was that much more insistent because the laboratory was supposed to serve the entire European high-energy physics community. The committees set up at that time, after some difficulty one should add, were still essentially intact in the early 1970s, with the addition of two new bodies to handle the experimental programmes on the ISR and the SPS. One of the tasks of Working Group 3 was to see if visitors were satisfied with the way such committees were functioning at CERN and in the national laboratories (though the latter were not, in fact, studied in any depth). By way of introduction to the issue let us first survey the committees involved in laying down the experimental programme at CERN^^ In 1973 there were four experiments committees deaUng with the machines then operating, the Track Chamber Experiments Committee, (TCC), the Electronic Experiments Committee (EEC), the Physics III Committee (Ph.IIIC, primarily concerned with work at the Synchro-cyclotron), and the Intersecting Storage Rings Committee (ISRC). A fifth committee was preparing the experimental programme for the Super Proton Synchrotron, then under construction (the SPSC). Overall responsibilty for the laboratory's research programme was vested in the Nuclear Physics Research Committee (NPRC), and ultimately in the hands of the Director General. Broadly speaking the experiments committees functioned along similar lines, holding both open and restricted meetings (the exception was the PhlllC, where the community was sufficiently small (c^ 140 people) that restricted meetings were not necessary). Open meetings were held roughly once a month, and could be attended by all physicists interested in the technique or machine concerned - as for numbers, as Hine put it, 'the Notes: p. 204

186

The Relationship Between CERN and its 'Visitors' in the 1970s

document circulation lists add[ed] up to several centimetres of computer print out'^^. At these meetings those present would hear and discuss proposals for experiments, reports on the progress of the programme, information on problems to be expected in the future, and so on. At the more restricted meetings, attended basically by the official committee members (typically 10-20 people, see below), the proposals were analysed in more detail, their infrastructural needs were identified, and a consistent programme for the months ahead was laid down. While all committees combined open and closed sessions, the relationship between the two forums for discussion, and the mechanism for transmitting recommendations to the NPRC differed between them. In the EEC and the ISRC the restricted meeting formulated its recommendations after hearing the discussions in the open session. In the TCC the proposals were first prepared in the restricted meeting (the TCC 'bureau'), and then submitted to the open session for possible modification and formal approval, before being passed on to the NPRC. As for the SPSC, at the end of 1973, it was, in Hine's view, 'following the EEC schema rather than the TCC'^^ It was up to the NPRC to approve the proposals laid before it which came up from below. Generally speaking these were already compatible with one another technically, this having been settled previously with those responsible for the accelerators and the beams. Only exceptionally did the NPRC have to choose between various proposals. Its main task was to legitimate the decisions already taken by the 'lower' committees, and to fix 'the future frame in which the other committees should plan their programmes (numbers of shifts available, times of shut downs, sharing between Experimental Areas or between kinds of beam and detector, use of new ejection faciUties etc. etc.)'^. Table 5.3 illustrates the distribution of membership of the five main experiment committees towards the end of 1973. The chairmen of the experiment committees were always eminent outside physicists, and were formally appointed by the Director General, who was himself chairman of the overarching NPRC. The often large contingent of ex officio CERN staff* included the secretaries of the committees, senior members of the division most directly concerned, technical people from the accelerators, etc. (whose membership lasted 'as long as they [were] involved in the work'^^) and the physics 'coordinators' who were responsible for the day-to-day running of the programmes (and who were changed annually). The rest of the membership, including the chairman, were generally appointed for two years. What did the visitors feel about these arrangements? After investigating the situation, the working group found that, by and large, outside users were satisfied with them. Their anxieties, it seems, had been based on a misunderstanding, a lack of information about the precise composition of the committees, how members were chosen, the rate of rotation of membership, and so on^^. With these points clarified, as Hine put it, the tone of their remarks became 'much more understanding and favourable than the initial attitudes had been'^^. At the same time the visitors did feel that there was room for improvement. What particularly disturbed them was the number of ex officio CERN members, which was extremely high in committees Hke the SPSC and the NPRC (see Table 5.3). To counteract

187

Third point of friction: visitors' participation in decision-making Table 5.3 The composition of the main experiment committees at CERN in October 1973, as distributed between CERN staff and visitors^^ Committee Type of Membership

EEC

TCC

ISRC

SPSC

NPRC

Visitor CERN staff CERN staff, ex officio Chairman

6 3 2 ManeUi (Pisa)

9 1 5 Cresti (Padova)

6 5 7 Schopper (DESY)

9 4^ 10 Lehmann (Orsay)

7 1 14 Jentschke (DG)

Note "^: Rubbia (CERN, Harvard) has been counted as CERN staff here.

this they would have liked to increase the external membership (accepting, for want of a better idea, that CERN should continue to appoint the outside members). At the same time, they realized that there were, in fact, very few 'active' CERN physicists in these bodies. Seen from this point of view, it was the CERN physicists' representation which was unsatisfactory^^. In the event the working group conceded that it was necessary to have CERN staff with knowledge and responsibiUty for running the experimental programme, as well as the appropriate division leaders, present at meetings and accepted that there were already enough external members on most committees. Their main recommendation was simply that the balance between external and internal membership be kept under review^^. The visitors' views on the committee system prompt a number of remarks. Firstly, it is important to realize that if they were basically satisfied with the structure, it was because they had, and almost always had had, an important role in it. The CERN management had been made aware very early on in the laboratory's Ufe that they would have to include outsiders in decision-making at this level, - witness the policy of having non-CERN staff as chairmen for example - and this obviously reduced and redirected any tension that there might have been between the laboratory and its users in this area^^. Secondly, it must also be admitted that these committees had a very particular, and rather limited, kind of power. Most crucially, their main aim was not to settle priorities in the research programme, it was not to make important choices between proposals for experiments (although originally Weisskopf, for example, had thought that a committee like the NPRC would do this). Their task was essentially to give the seal of approval for the carrying out of decisions already prepared before the committees met. As Hine put it - and the Report of Working Group 3 uncritically repeated this phrase almost word for word - with the effective spreading of information and discussion prior to formal meetings, most decisionmaking at CERN became 'the necessary formality of giving authority to those responsible for execution for actions already agreed upon'^^. As Wolfgang Paul explained to the SPC on a different occasion, 'Although relatively few proposals were rejected at the Committee stage, a substantial number were never put forward after discussions between the physiNotes: p. 204

188

The Relationship Between CERN and its 'Visitors' in the 1970s

cists concerned and Professor Cocconi, Professor Preiswerk or himself [the three senior physicists in the NP division]'^^. The experiments committees were thus not the site of titanic battles with winners and losers in which it was important to have as many likeminded people on one's side as possible. They had power, but they did not use their power to decide but to confirm. They did not choose between experiment proposals, they legitimated 'choices' already made in the pre-committee stage. This probably explains why the outside users were so concerned about the number of ex officio members on these committees. Here was the executive arm in person, the group which had earlier played a dominant role in eliminating certain proposals as unpractical, in persuading some groups to join up with others, in suggesting when certain experiments might be scheduled and how much priority they should be given, and so on. What the committees were doing, in effect, was to 'rubber stamp' the decisions that the beam and accelerator people, the division leaders and the coordinators had worked out beforehand in consultation with the physicists who had made the proposals. What the visitors sought in reducing their weight in the meetings was a clearer line of demarcation between the 'legislative' and the executive, a greater freedom to discuss, among a core of active physicists, the experimental proposals that were before them without having the debate dominated by the practicalities and pressures of implementation - and by the CERN staff responsible for doing so. One other committee, apart from the experiments committees, was singled out for criticism by the visitors. This was the Data Handling Policy Group, chaired by Mervyn Hine, whose task it was to advise on major computer installations. Visitors objected strongly to the absence of an outside contingent of users and computer experts on this committee (it had 14 members in October 1973, the bulk of them being CERN staff)^'^, and were determined to be properly represented on it, and any other similar body dealing with computer policy. Behind this objection was the feeling that the services given by the Data Handling Division at CERN were not particularly good. As one person who was not an outsider reputedly put it, they were 'much less convenient to the users than those at the Rutherford Laboratory and at the Max-Planck Institut in Munich'. The main cause of the difficulty seems to have been the poor performance of the new central computer. In 1969-70, after user representatives had made two surveys of future needs, and a panel of experts had been invited to assess various possibilities, it was decided to acquire a CT>C 7600 for CERN rather than an IBM^^. This machine was deHvered in 1972, when it was found that there were major deficiencies in the software, particularly for the processing of large volumes of data on magnetic tape. With more and more electronic experiments storing their information in this form (see below), this weakness - which was still not ironed out at the end of 1973 - was causing considerable irritation to the physics community^^. A more fundamental reason why visitors wanted to be fully consulted on data-handhng policy was the growing importance that big computers were playing in electronic experiments. Big facilities like the Split Field Magnet and the Q spectrometer were recording their data on tapes as bubble chambers had produced film, a new generation of electronic

Third point offriction: visitors' participation in decision-making

189

detectors suitable for fast data capture, like 'Charpak' or wire chambers, was coming into use, and increasingly large and sophisticated experimental set-ups were being proposed for use at the ISR and the SPS. In 1972, Hine reported, about 87% of the used computer capacity in Europe was dedicated to data analysis, 52% for bubble chamber film, 35% for electronics experiments. Overall computer usage was expected to grow 2-3 times between 1972 and 1975, and the amount of data to be stored (mostly on tapes), was expected to grow by a factor of 3 to 5 over the same period. This could mean that in a few years a large centre like CERN would be holding 100,000 tapes or more^^. CERN alone could not carry this load; indeed it was central to its policy that datahandhng be shared Europe wide^^. The need to be able to transfer data on tapes between computers at CERN, the national laboratories, and the universities, and the new possibilities being opened up for this by using telephone lines, made it essential for outside users to keep in touch with all major developments at the CERN computer centre^^. These criticisms fell on fertile ground at CERN. Early in 1976 Leon Van Hove, newlyappointed D G for Research, reported to ECFA that 'improvements' were being made to the committee structure. 'A strict rotation rule' was being imposed on the experiments committees. And the Data HandUng Policy Group was being aboUshed. In its place there would be a Computing and Data Handling Policy Committee. It would be advisory to the CERN management, and its membership would be made up of two ex officio CERN staff, two ordinary CERN members, four external users (physicists using CERN and computer centre managers) and a secretary^^.

So far we have concentrated on the need which outside users felt for adequate representation in formal, rather high-level committees. However many of them beUeved that this was not sufficient, that a participation in internal decision-making at the less formal and working level was just as crucial. As one outsider put it, what was 'very poorly catered for [at CERN] [was] for visitors to get involved in the day-to-day dialogue on what physics to back and what projects to start. This is not my view alone', he went on, 'but to my experience a frequent complaint of visitors'^^ Of particular concern were laboratory decisions to invest in major faciUties Uke the Split Field Magnet. These called for important investments in time and money which, while opening new horizons, also set important constraints on the physics that could be done by staff and by users. More generally, visitors wanted 'a much better integration' into the routine life of the laboratory, being included, for example, in selection committees for staff appointments^^. Participation at this level, plugging people into the CERN system 'from a cultural or organizational point of view', finding ways of involving 'even the quieter visitor into the discussion and even some of the decision-making that goes on here' was more difficult to arrange than having visitors represented on experiments committees^^. It involved not simply a change of rules - rules for the selection of chairmen, for the rotation of membership, etc. - but a change of attitudes on the part of the CERN staff- the building of a relationship based not 'only on the need of the outsiders to get better service but on a genuine co-operation [...]'^^. Notes: pp. 204 ff.

190

The Relationship Between CERN and its 'Visitors' in the 1970s

One remark by way of conclusion to this section. The debate between CERN and its outside users over the question of participation in decision-making, while raising an important point of principle, was also very much a child of its time, and followed the classic pattern of the day. On the one side, the visitors, those who felt excluded from the structures of power and influence, demanding to have a greater say in the running of aff'airs which affected them directly. On the other, the CERN management, tending to reduce the problem to one of a 'lack of information', and to treat the complaints as misguided and 'emotive'. Inevitably too the mechanism set up to deal with the conflict, a committee of enquiry, clarified misunderstandings, reduced tensions, proposed certain measures for improving relationships - and did not really come to grips with a number of deeply felt, vaguely articulated objections and misgivings which visitors had. Objections which had less to do with the inadequacy of formal mechanisms than with informal assumptions about the role of CERN and its responsibilities to its user community.

5.6 Fourth point of friction: the working conditions of visitors at CERN The relatively long periods of time that visitors using electronic detectors had to spend at CERN, and away from their home institutes, raised a number of new problems for outside users in the early 1970s. Two general kinds of complaint emerged in the debates stimulated by the enquiry of ECFA Working Group 3. Firstly, there was concern about access to CERN facilities which, said chairman Gunn, people felt to be 'prejudiced in favour of CERN-based groups rather than visitors'^^. These facilities ranged from office accommodation ('of low quality', according to one source), through secretarial and administrative support ('minimal' according to the same source^^), to technical support and workshop arrangements. The other area of concern was the social and personal problems of people coming to work temporarily in Geneva. We shall reserve our discussion of them to the next section. To understand the complaints about the assistance being given to outside physicists doing experiments at CERN, we need first to describe the services and support available at the laboratory in the early 1970s. We shall focus on the arrangements made inside the NP division, as it was the needs of electronic experimentalists that particularly caught the working group's eye^^. In 1973 there were nine 'technical and service groups' in the NP division which helped experimentalists 'at close range'. Goldschmidt-Clermont regrouped them by task into six. Three of these dealt with the development, construction, assembly and, if need be, operation of heavy equipment: polarized targets (11 people), magnets and beams (26 people), and technical equipment of a mechanical nature (23 people). The other three dealt with electronic equipment. One group of 33 people was concerned with development (e.g. prototypes of fast electronics and readout systems for wire chambers, prototypes of CAMAC and general computer interfacing). Another, of 38 people, concentrated on the maintenance of electronic units built by CERN or by industry, on running the electronics

Fourth point offriction: the working conditions of visitors at CERN

191

pool for the experimental groups and projects, and on building prototypes and small series for the electronics development groups (the electronics workshop). Finally, there was a group of 16 people providing small on-Hne computers and programming assistance. CERN groups and visiting groups did not have equal access to these resources, even when they were part of the same collaboration. Let us take the CERN groups first. Each contained typically one to three CERN staff physicists, and two CERN-paid fellows, research associates or visitors. In 1973 these groups were working in 18 mixed teams at the ISR, the PS, and the SC: there were no 'pure' CERN teams active at the time^^. The teams varied in number from about 12 to 27 people (excluding major faciUties like the Q spectrometer at the PS and the Isolde collaboration at the SC), and their mean size was about 16. The CERN group in each mixed team had its own budgetary code, a research budget of 2i^ 50,000 Swiss francs/physicist/year, and dedicated technical support of :^ 0.5 technicians/physicist. (Thus each CERN group had on average two 'attached technicians'). The CERN groups had free use of the electronics equipment pool and of computer time, but had to 'pay' for some workshop services and for material drawn from the CERN stores. The outside groups worked either in mixed teams with CERN groups or in 'pure' teams of outside users. Goldschmidt Usted 32 such teams, nine at the ISR, 14 at the PS, and nine at the SC, and they comprised about 300 physicists in all. CERN provided them with certain infrastructural services free of charge - things like beams, magnets, targets, small on-line computers and big experimental faciUties, as well as engineering and technical assistance. At the same time 'It was CERN poHcy and practice that [outside] experimenters generally [had] a basic support from their home institutions which cover[ed] their detectors, electronics, their technicians, their computing, and their salaries'^^. In addition visitors were expected to pay for items drawn from the CERN stores, and for services in the mechanical, electronics, and special (plastic- and wire chamber-) workshops. Outside users were dissatisfied with these arrangements for a number of reasons. Firstly, they felt that the technical interface between the visiting groups and the host laboratory could be improved. They wanted each experiment at the PS and later at the SPS to have its own 'project engineer' allocated to it. They wanted advice on the design and commissioning of technical work (including the supervision of work orders). And they felt that they were not being given enough support during the installation of their experiments^^. The electronics pool posed a different kind of problem. Here the visitors called for an increase in the number of standard items with which it was equipped, particularly fast electronics and datahandUng units (CAMAC). This was the kind of material that visitors were supposed to provide for themselves, and so they only used the CERN electronics pool 'to a limited extent to tide them over short-term needs of apparatus, or the waiting periods due to delivery times for ordered equipment'. From one point of view the visitors did not mind this: they liked starting an experiment with brand new equipment, and were inclined to mistrust the reliability of the old. On the other hand, this attitude was 'clearly a luxury' as far as standard units were concerned, and particularly when the group was not certain to reuse material once its experiment was over. In such circumstances it was far Notes: p. 205

192

The Relationship Between CERN and its 'Visitors' in the 1970s

more logical to build up a large pool of common equipment which could be shared by all even if that raised budgetary problems, 'for which a solution should be found either within CERN or with the help of Member States' as the Working Group put it^^. The fact that visitors had to pay for services in the mechanical, electronic, and special workshops Uke the scintillator workshop posed problems at two levels. They were spelt out by Guy von Dardel, who took over as ECFA chairman in 1975, and who immediately addressed himself to the visitor question. Firstly, such payment involved an additional transfer of resources from the visiting groups/member states to CERN. As von Dardel put it, even though CERN teams were also charged for workshop faciUties '[...] in their case it [was] not real money which [was] involved but only a question of internal bookkeeping at CERN. For the visiting teams it [was] real money and', the new ECFA chairman went on, 'Swiss Francs at that, which have gone up considerably in value as we all know', von Dardel's second point was more fundamental. Should visiting teams from the member states pay for workshop services at all, he asked, considering that their governments had 'already once paid the machines and the salaries of the mechanics by their CERN contribution'^29 How did CERN react to these ideas? One of the first things that the new management did in 1976 was to abolish a 10% surcharge which had been imposed on items issued to visiting teams from the CERN stores. At the same time Van Hove drafted a set of Proceduresfor Physicists Making Experiments at CERN, reaffirming that CERN would provide, 'on request, technical support for approved experiments, including experiments in which no CERN physicist [was] involved'. This support would be available 'within the limits of [CERN's] manpower and financial resources', and bearing in mind 'the physics priorities of the overall CERN programme'. A coordinator for technical support would be appointed - a person akin to the 'project engineer' called for by WG3 , and who could handle the interface between the visitors the local services. A contactman would also be agreed between CERN and any collaboration, someone, preferably a physicist paid at least partially by CERN, who would be present on site throughout the preparation and running of an experiment. These improvements were to be made within the general framework of CERN's standing policy on visitors. They were 'expected to have a reasonable level of technical support' from their home institution, to contribute a 'fair share' of technical and financial support to any collaboration in which they worked, and to 'share their time and activity' between Geneva and their home base, 'also for data handHng and computing'. There was one important twist, though, which created some resentment among visitors because of the power it gave to the CERN management to 'interfere' (as they saw it), in the setting up of a collaboration and, in principle, to exclude a group on purely financial grounds. 'The composition of the collaboration and the sharing of support', wrote Van Hove, 'should be cleared with CERN before approval of the experiment'^^. There is one rather different point that needs to be made regarding the strains imposed on some outside users by the need to spend relatively long periods of time at CERN. This was the problem raised for university staff* of having to take their share of departmental duties, while doing research at a remote laboratory. If they made their research a top

Fifth point offriction: salary differentials between CERN staff and outside users

193

priority, asking for reduced teaching and administrative loads in their home institute, they risked alienating their colleagues and damaging their career prospects in the physics department. If they put their university life first, they were relegated to playing only a marginal role in the development of their experiment at CERN. And while these problems had always been present to some extent, they were exacerbated by the new importance of electronics experiments, their increasing size and complexity, and the concentration of resources at CERN. As one person who submitted written evidence to the working group explained, a counter physicist now had to envisage spending 'roughly equal amounts of time at the University and distant laboratory, often on a day by day basis', adding that, as far as he, a married lecturer at Manchester University who used counter techniques, was concerned, 'I see no way of continuing to make significant contributions in this branch of research after NINA closes. The personal problems', he went on, '[were] just too great under the present circumstances'^^. We have already mentioned two measures proposed by the visitors, and the working group, to improve this situation: encouraging national laboratories to build big equipment for experiments, and establishing computer networks between CERN and institutes in the member states. Both of these would reduce the time that physicists needed to spend away from their home centres. Yet these could only be palUatives. For the fact remained that outside users who maintained important links with their home institutions were fundamentally disadvantaged in that they were only temporarily at CERN. As one CERN staff member pointed out, if university staff had teaching and administrative duties to perform they 'could not accept the responsibiUty for any part of an experiment that require[d] continuous attention, so their contributions were, of necessity, limited'^^. In short the working conditions of high-energy physics, particularly from the 1970s onwards, were intrinsically biassed against the outside users of centralized facilities, and they had no choice but to accommodate themselves to that unpleasant reaUty, and to the loss of influence which it entailed.

5.7 Fifth point of friction: salary differentials between CERN staff and outside users One of the problems which particularly concerned Salvini and Harting when they alerted ECFA to the visitors problem was that outside users should be able to 'stay at Geneva without having a hard and convulsed life, and without having them feeling guilty towards their families and children'^^. This required that appropriate facilities be provided for the families of physicists who intended to spend considerable lengths of time at CERN^^. Gunn's working group found that these needs were either being conscientiously dealt with by CERN (housing, education, work permits for wives, etc.) or that they were the responsibility of the member states themselves, and so outside their brief^^. However, another of these 'national' issues, simmering beneath the surface in 1972/3, and coming clearly into the open in 1975/6, was that of the financial situation of users vis-a-vis their CERN colleagues. Notes: pp. 205 ff.

194

The Relationship Between CERN and its 'Visitors' in the 1970s

The salary question had two aspects: the differences in basic remuneration (plus Geneva allowances) between visitors from different member states, and the differences between visitors as a whole and the CERN staff. In a survey made for the working group in 1973 on the social problems of outside users it was the first aspect, the differences between the visitors themselves, that was reported as being 'a continuous source of problems'^^. However, an important revision of the CERN salary scales in December 1974 shifted attention explicitly onto the second dimension of the problem, the difference between the salaries at CERN and in the member states. At the ECFA plenary meeting in January 1975 Hogaasen (Norway) spoke of the danger of CERN becoming 'an artificial paradise with high salaries envied by everyone and losing touch with what happened on the base'. Salvini warned that 'similar criticisms were also being voiced in other countries where CERN was also regarded as an oasis, and it would help a lot if CERN showed some understanding of these criticisms'^^. The storm of protest was one reason why the CERN management decided not to apply an 8.1% cost-of-Hving adjustment at the end of 1975, instead applying 2% differentially to the salaries in the various grades^^^ ECFA, in its turn, set up a working group to look into the financial position of unpaid associates. The group's chairman, Michel Vivargent, presented its findings to the 20th plenary meeting of ECFA on 25 November 1976^^2 Vivargent's group produced two reports. The first gave data on the salaries, daily allowances, travel expenses, etc of unpaid visitors to CERN, broken down by country. The second attempted to compare the financial position of certain selected categories of unpaid associates with the CERN staff, and to assess the cost of living in the Geneva area. The matter was complicated by the lack of information for some countries, by the fact that individual circumstances varied widely, that social security systems and taxation had to be taken into account in each country, that there were constant and substantial variations in the exchange rates with some countries, and so on. All the same the working group did manage to produce useful estimates for the net disposable income of long-term visitors (and of physicists with PhDs or the equivalent, in particular). Their findings are partially summarized in Figure 5.2. It compares monthly incomes at CERN with the net incomes plus Geneva allowances for scientists in several categories of employment, and for five CERN member states^^^ Vivargent's group drew three major conclusions from their data: • that the salaries paid to physicists in the CERN member states varied widely, and were below the salaries paid to professionally equivalent CERN staff by a factor of 2 to 4; • that when the allowances paid by the member states to personnel on long-term visits to CERN were added to these salaries, their disposable income was still not high enough to allow them to have a 'reasonable' standard of living in Geneva (as defined by the working group); • that visitors' disposable incomes (salaries + allowances) were still below the salaries paid to CERN staff with equivalent responsibiUties (see Figure 5.2)^^"^.

Fifth point of friction: salary differentials between CERN staff and outside users

195

8000 7000 • • n ^ « a

6000 5000 4000

CERN UK(1) France(2) NL(3) Sweden(4) Germany(5)

3000 • 2000 0

1

2 3 Staff category

Fig. 5.2 A comparison of CERN salaries with the net incomes and allowances of visitors from five CERN member states. The numbers after each member state indicate the 'level of confidence of accuracy and completeness of figures', those for the UK being the most reliable. Data for the other countries was incomplete.

If the outside users were disturbed by these 'glaring inequaUties', as Vivargent called them, it was not simply because they wanted to ensure that they had a reasonable standard of living while working in Geneva. It was primarily because the differentials existed between physicists who rubbed shoulders daily, who worked together in the same 'mixed' teams, who were equals in all respects save in the financial compensation for what they did. And although it was obviously up to the member states to remedy the situation as best they could, Vivargent felt that CERN should not wash its hands of the problem. Appealing to all those who wanted the laboratory 'to be not only a citadel of science but also an example of human collaboration' he insisted that, 'in its own long-term interests and in the spirit of generosity for which it [was] known', CERN ought to do all it could to alert the member states to the problem which, said Vivargent, posed a serious threat to the vitality of the community as a whole^^^. In fact, of course, there was Uttle that CERN could do. The differentials between the salaries it paid to physicists and those paid to them in the member states were an inevitable consequence of the different frameworks used for calculating earnings. CERN's main references were the salary levels in other international organizations and in industry (one argument being that 'as CERN was essentially a service organization, its salary scales had been largely aUgned with those of engineers in the member states'^^^). Physicists working at home were paid on the far lower salary scales devised for the civil service or for university staff. To align these in any way was impossible. The most that could be done was to compensate for the differences by paying additional allowances to visitors at CERN. These would inevitably vary from one country to another depending on local Notes: p. 206

196

The Relationship Between CERN and its 'Visitors' in the 1970s

circumstances and custom. Thus there was nothing for it but for visitors to accept that they would be paid very different amounts of money at CERN, and that in any event they would not be as well off as their colleagues in the host laboratory - and to hope that the staff and management in Geneva would not be insensitive to the 'injustice' that that entailed.

5.8 The visitors question: a quick survey of later developments A number of initiatives concerning the needs of outside users were taken during the decade following the events we have described. For example, in 1978 an Advisory Committee of CERN Users (ACCU) was established, in 1979 the SPC sponsored an enquiry into the adequacy of decision-making procedures at CERN, and in the mid-1980s the CERN Review Committee chaired by Professor A. Abragam made an extensive survey of users' attitudes to CERN. These activities attest to the ongoing concern in the laboratory and in the member states about the CERN-user relationship. And while it is not our intention to study them in any detail - in fact we shall do little more than Hst their findings here - , they are useful for the light they throw on the tenacity of some of the points of friction which first surfaced in the early 1970s. The question of whether or not some sort of advisory committee for CERN users was desirable had already been discussed early in 1973. At that time it raised no great enthusiasm. Visitors apparently accepted that such matters could be handled by ECFA. 'The people', wrote Herwig Schopper, 'were more interested in getting integrated in the existing CERN organization'^^^. However, in 1975 a so-called Commission of Associates (or visitors) was formed spontaneously in response to changes in the Swiss income tax laws affecting short-term residents in the country. This commission was expanded in 1976 to represent unpaid associates from all countries, and to advise the CERN management on the status and working conditions of outside users^^^. ACCU was a logical extension of this body. Set up by CERN in 1978, its task was to advise the Directors General (there were two at the time) 'on the practical measures and administrative internal arrangements to be taken by the CERN Management for the utilization of the CERN facilities for research'. In particular ACCU was to watch over the 'working conditions and the arrangements for technical support of the CERN Users'^^^. The chairman and members of the committee were appointed by the Director(s) General for a period of two years, with the possibility of extension. ACCU's first chairman was E. Lillest0l, its first secretary W. Blair. ACCU achieved a good deal during the first two years of its life. It secured improvements in the accommodation for short-term visitors, it obtained satisfactory terms for medical and accident insurance of CERN users, it monitored the CERN workshop facilities and costs, it got CERN to provide support for a range of small computers used online in experiments, it arranged for the more efficient re-use of experimental equipment at CERN. Indeed reading through Lillest0rs first report, one has the impression that the only

The visitors question: a quick survey of later developments

197

major problem encountered by the committee was that of securing permits for the spouses of physicists to enable them to work in the Geneva area^^^. In particular, the technical interface between CERN and its visitors seemed to be essentially trouble-free. That granted, the opinion of one dissenting voice who had served on the committee for its first two years should be recorded, a voice which did not deny the value of ACCU, but which felt that, 'in spite of the good will of the CERN Staff, some of the main difficulties met by the visiting teams [could] not be solved' in its framework. These, the correspondent went on, lay 'in the lack of balance between CERN and the small laboratories and in the fact that the interests of CERN members and those of visiting teams [were] not similar'^^^ In short, while ACCU undoubtedly did useful work within its terms of reference, for at least one visitor those terms were too restrictive for the committee to really come to grips with the roots of the problems faced by outside users at CERN. Let us now turn to the second initiative mentioned above: the decision taken by the SPC in 1979 to set up an ad hoc committee to investigate whether the procedure for selecting experiments at CERN was still adequate. W. Paul was the chairman of this committee, and V. Telegdi and M. Vivargent, then the chairman of ECFA, were its other two members. Reporting in 1980 this committee identified two specific areas where changes could be made. Firstly, it was suggested that the procedure for refusing proposals (which happened rather less frequently at CERN (20%) than at BNL (22%), DESY (25%) and SLAC (30%)) should be improved e.g,. by allowing the spokesman to give additional information at a closed session of the experiments committee before they turned turned down a proposal. Secondly, the position of the ex officio members of committees was again questioned. While accepting that their counsel was essential, it was stressed that they 'should restrict themselves to the role of advisers'. These quibbles apart, the enquiry's overall finding was that there were 'no serious complaints by the experimental physicists, but only uneasy feelings about some aspects of the present procedure'. CERN, or rather Van Hove, had apparently expected heavier criticism than this. The Director General for Research admitted that he was 'pleasantly surprised by the outcome [...]'^^^Finally, let us say a few words about the findings of the CERN Review Committee, set up at the instigation of the British CERN delegation in the mid-1980s^^^. One of the tasks which it undertook was to consult the community of outside users to see if they were satisfied with the faciUties at their disposal for doing particle physics at CERN. A large majority of the users responded to a questionnaire which was circulated with the help of coordinators in each member state. A survey of the results, and a selection of some specific repUes to their enquiries, were published by the committee in the report it laid before the CERN Council in December 1987. The first point stressed by the Committee was that among the users 'there was uniform praise for the excellence of the experimental facilities and the scientific environment at CERN'^^^. At the same time, the scientists in the member states made a number of criticisms about CERN, many of them all-too-familiar by now. In fact the only major concern of the early 1970s which did not come up again in the mid-1980s was the need for national institutes to construct big equipment. This was doubtless because the growth in Notes: p. 206

198

The Relationship Between CERN and its 'Visitors' in the 1970s

complexity, size and cost of the big detectors being built for the SPS in both fixed target and collider modes demanded a major contribution from them and from the home universities. Apart from that, while the context was different, the complaints were the same. Taking our other four 'points of friction' in turn we find: • on the question of indefinite contracts, 'it was almost universally felt that a decrease of indefinite appointments compensated by an increase of fixed-term contracts [was] desirable [...]' (emphasis in the original suppressed)^^^. Many reasons were given for this, including the enhanced mobility in the physics community, the increased opportunity for outsiders to benefit from the stimulating environment of CERN, the attenuation of the dominant position acquired by CERN staff* inside the laboratory, and the improvement of bonds with home laboratories; • on decision-making procedures, there was again general satisfaction with the experiments committees. At the same time the report made much of the now-famiUar complaint that no mechanisms existed for outsiders to participate in decisions concerning long-term technical developments (detector developments, electronics, data acquisition and analysis software), and that CERN computing policy was not discussed widely enough by the user community^^^; • on working conditions at CERN, there was again a complaint that office space was inadequate, that the plan to charge for loaning electronics items from the pool was unacceptable, that the technical back-up for a collaboration was not being adequately coordinated, and that, in general, the technical support offered by the laboratory had deteriorated from good or even superb before LEP was built to 'poor/unacceptable now' (emphasis in the original suppressed)*^^; • finally, on the social and personal conditions of life at CERN the question of working permits for spouses came up strongly once more as did the matter of CERN salaries. Here outside users called variously for a reduction in the salaries of the top grades, a reduction in allowances and benefits for CERN staff*, the use of post-tax salaries in universities and in industry as a frame of reference for the CERN salary scales, and so on. In fact the Abragam report tells us that 'about half of the replies [to its questionnaire] contained adverse comments on the levels of salaries and allowances' at CERN**^. There are two points to be retained from this section. Firstly, there is the striking fact that many of the complaints raised by visitors to CERN have persisted for well over a decade. Secondly, and related to this, one has the clear impression that, despite all that has been done to harmonise the relationship between CERN and its outside users, there is a layer of feelings and attitudes which eludes the recommendations of the most well-intentioned and conscientious enquiry into visitor's complaints. It is a point we have remarked on before and it is worth stressing again here. Time and again the cHmate surrounding the setting up of an investigation into visitor's conditions - be it that made by ECFA in the early 1970s, or that made by the SPC in 1979/80 - was marked by tension and hostility between the users and the laboratory. And time and again the management was relieved, and many of

Concluding remarks

199

the visitors reassured, to find that the complaints were, apparently, misguided, that matters were not as bad as they had seemed, and that they could be 'resolved' by tinkering with the existing arrangements. Yet an undercurrent of discontent remained among the users, the feeling that the nettle had not really been grasped, that somehow the point of their anger and frustration had been missed. This was the kind of objection made to the Report of Working Group 3. It was also the kind of misgiving which led one ACCU member to resign after serving his statutory two years. We shall try to expose some of its roots in the final section of this paper.

5.9 Concluding remarks There is no doubt that the early 1970s heralded another turning point in the history of European high-energy physics. As everyone reaUzed the decision to build the 300 GeV machine in Geneva was to lead to an even greater concentration of resources for doing high-energy physics at CERN. CERN would no longer be the apex of a pyramid whose base comprised the national laboratories. Most of them were rendered obsolete at a stroke when the SPS was commissioned. CERN was now the locus around which European highenergy physics turned. Only DESY provided a counterweight to the forces drawing the community to Geneva. This tendency to concentration was heightened by the growing importance of electronic methods of detection and the work patterns that that entailed. As electronic detectors became bigger, more complex, and more costly, outside users played an increasingly important role in all phases of the experimental process, from building or assembUng the detector, to taking the data during a run, and to analysing the tapes produced in the experiment. It was not simply that outside users had to spend more time at the host laboratory. They also became more intimately associated with its staff and locked into its infrastructure, more closely involved in its day-to-day affairs. In short they began to see it as their laboratory. At the same time this community of the 1970s was far more experienced in the highenergy field than the pioneers who had launched CERN in the 1950s. Their predecessors had leapt from working on machines of a few MeV to working on the most powerful machine in the world and they were ill-prepared for the corresponding change in scale and sophistication in the experimental workplace. They had not yet learnt how to plan an experimental programme, they did not know what equipment to order, they could not coordinate the acquisition of the separate components required to exploit a big machine. And they were not sure what experiments to do: the appeal for proposals for work at the PS, launched by the CERN management in 1959, fell on the ears of a surprised user community which had few ideas and little or no equipment of its own^^^. This was to change dramatically during the decade of the 1960s. The staff at CERN began to learn how to run a big laboratory and to organize a competitive experimental programme. At the same time national facilities were expanded, and every major member state of CERN could boast its own 'high-energy' accelerator, and the infrastructural support needed to Notes: p. 206

200

The Relationship Between CERN and its 'Visitors' in the 1970s

exploit it. The size of the member state community grew dramatically, encouraged by the rapid expansion of the universities, and a new generation was trained who did their PhD's on one of a number of powerful machines in Europe or in the USA. Outside users, who previously may have felt (or been made to feel) that they were still 'wet behind the ears' compared to some of the CERN senior staff, began to be more confident about themselves, to regard themselves as every bit as competent as their professional homologues in the Geneva laboratory. In short they began to insist that they be treated as equals by their colleagues at CERN, and not as apprentices. These two seemingly abstract ideas - that CERN was their laboratory, and that they were every bit the professional equals of the people employed there - were twin ideals shaping the attitudes of users towards CERN. These ideals structured visitors' conception of the way things should be done, and informed the proposals they made for practical 'improvements'. The situation outside users wanted, the 'utopia' dreamt of by a von Dardel, was one in which 'the distinction between CERN and outside teams [was] abolished [...]', in which 'the allocations of CERN resources [were] decided purely on the basis of the needs of the group and the resources it [could] mobilise at home institutes', in which 'ultimately' a group 'comes to CERN with bare hands and sets up their experiment by drawing instruments such as wire chambers, counters and electronic equipment from the instrument pool, being provided with magnets and separators by the experimental support team'^^^. It was a situation in which the outside users were fully integrated into life at CERN, and accorded the dignity appropriate to first-class citizens of the laboratory, their laboratory. The CERN management and staff, for their part, saw matters rather differently. This laboratory essentially belonged to them. They were responsible for running and improving it, they were building their careers in it, they would take the blame for its failures, and the praise for its achievements, they would be the first to suffer if the member states withdrew support from it. Of course they had to provide a service to the European high-energy physics community^^^ But this was a duty imposed on them by the international character of the funding for CERN. It was a duty they discharged without resentment, but a duty nevertheless. Once fulfilled, they felt themselves free to do as they thought best for Europe, for the laboratory, and for themselves. In short, the 'conflicts' or disagreements between CERN and its user community are, at source, conflicts over ownership and control. The form taken by those conflicts will vary depending on the context. The substance will persist as long as the laboratory itself.

Notes Document on ECFA notepaper entitled 'Farewell address to professor W. Jentschke pronounced at the CERN Council Session on December 17 1975 by the Chairman of ECFA\ undated, unsigned (DGR21311). This chapter extends the study made by Dominique Pestre on the organization of the experimental work at CERN in the late 1950s and early 1960s which was pubhshed in A. Hermann, J. Krige, U. Mersits and

Notes

3. 4. 5. 6. 7.

8.

9.

10. 11.

12. 13.

14.

201

D. Pestre, History of CERN, Vol. II. Building and Running the Laboratory (Amsterdam: North Holland, 1990), chapter 8. It is based primarily on papers prepared for the Working Group set up by ECFA in 1972 to look into the relationship between CERN and its outside users. It has been supplemented by a number of formal interviews and informal discussions with CERN staff and visitors. Many of the interviews were made within the framework of a project to study multi-institutional collaborations launched by the Center for History of Physics of the American Institute of Physics in New York. My contribution to this project has been supported financially by The Andrew W. Mellon Foundation, and I wish to record my thanks to them here. The main files used for the study were two in the Director General series, DG 21220 and DG 21221, and one in Yves Goldschmidt-Clermont's papers, YGC23572, all in the CERN archives. See Pestre, op. cit., note 2, for this paragraph, in which the struggles which led to these various arrangements are described in detail. The figures for mixed teams are from CERN/SPC/272, 25/2/69. The figures quoted at the end of the paragraph are from CERN/SPC/272, 25/2/69. The quotation is from the undated memorandum by H. Schopper entitled Summary of the Discussions with Visitors on 29 and 30 January, 1973 (DG20589). See also the statement by von Dardel, note 1. The decision-making process for the 300 GeV machine is described in detail by Dominique Pestre in this volume. The first figure, and the definition of dependence, is taken from CERN/ ECFA/67/13/Rev. 2, 15/5/67 (DADM20099). The second figure is from Harting's report presented at the ECFA information meeting on 30/11/72, document CERN/ECFA/73/3, undated (DG21220). The figures for 1966 differ very slightly between these two documents. The data for 1966 are from CERN/ECFA/67/13/Rev.2, cited above. The data for 1970 are from Dick Harting's report to the 13th plenary meeting of ECFA on 25/26 May, 1972, CERN/ECFA/72/5, undated (DG21220). For more extensive discussions of the differences between the two techniques see Pestre op. cit., note 2, chapter 8, and P. Galison, How Experiments End (Chicago: Chicago University Press, 1987). See also Gambaro, in this volume, for the development of electronic detection techniques at CERN. See his report prepared for ECFA, Structure of CERN Research Groups and Support Provided, ECFA/ WG3/RLP4/73, 7/9/73 (DG21221). The lower set of points for the NP, TC, and EP divisions are taken from the CERN Annual Reports. From 1962 to 1965 these figures include visitors from the non-member states. They are counted by adding categories labelled 'visitors' and 'national teams'. From 1965 to 1979 the data do distinguish between visitors (called associates from 1973 onwards) from member and from non-member states. From 1976 onwards all experimental physicists were grouped in one division. Experimental Physics (EP) Division. Two of the upper set of three points (for 1966 and 1970) are taken from Harting's report to the ECFA information meeting on 30/11/72, CERN/ECFA/73/3, undated (DG21220) (for 1966 see also Table VII in CERN/ECFA/67/13/Rev. 2, in DG20099). The data for 1978 are from ECFA/RC/79/47, 10/10/79, a report of Working Group V under John Mulvey which was set up to study hep activities in the MS. To make them roughly comparable with the other two points on the curve we have taken the figure for the total hep community exclusive of CERN and DESY from Mulvey's Table II (1728) plus the number of 'non-particle physics users' in the members states from Mulvey's Table IX (230). See also Chapter 1.2. The minutes of the meeting are CERN/ECFA/73/3 (undated), a copy of which is in file (DG21220). Several speakers pointed out that these figures did not give a true reflection of the distribution of resources for experiments between the national laboratories and the universities. AUaby, for example, remarked that some money spent by university teams was included in the 311 MSF national laboratory expenditure. Schopper pointed out that the hep budget for a university included only expenditure on materials for an experiment, whereas the budget for a national facility also included the cost of overheads. CERN/ECFA/73/ 3, p. 12, (previous note). The minutes of this meeting, held on 1 December 1972, are CERN/ECFA/73/4, (undated). They can be found on file (DG21220). Notes: p. 206

202

The Relationship Between CERN and its 'Visitors' in the 1970s

15. The letter from Harting and Salvini, CERN/ECFA/72/10, dated 21/12/72, is attached as Appendix II to the Report of Working Group 3 of the European Committee for Future Accelerators, dated 1 August 1974 (DG21222). 16. For a summary of their contents see Replies Received to the Letter of Salvini and Harting of 21 December 1972 to Plenary ECFA Members, CERN/ECFA/RC/73/4, 29/3/73 (DG21221). 17. For the composition of the Group and its terms of reference see the minutes of the ECFA meeting on 4/5/73, CERN/ECFA/73/5, and its final report (cf. note 15). 18. The official minutes of the first meeting of Working Group 3 are paper ECFA/WG3/RLM1/73, signed by David Baugh and dated 11/7/73 (DADM20099). Mervyn's Hine record of the meeting, sent to Jentschke and Adams, and dated 28/6/73, can be found on the same file. For more information on the factual material that was sought, see the Note by the Chairman, undated, summarizing the activities of WG3, and prepared as an interim report for the ECFA meeting on 22 February 1974 (DG21221). The number of written statements received by WG3 was reported by Gunn to ECFA in January 1975 (CERN/ECFA/75/4, 16/5/ 75). 19. For the information in this paragraph see Gunn's Note referred to in the previous note, and Appendix III of the final report of the Working Group (cf. note 15). 20. The minutes of the meeting are document CERN/ECFA/74/4, 10/10/74 (DG21220) 21. The final report of Gunn's Working Group was entitled Report of Working Group 3 of the European Committee for Future Accelerators, dated 1 August 1974 (DG21222). For the minutes of the ECFA meeting see document CERN/ECFA/75/4, 16/5/75 (DG21220). 22. Letter Lipman to Gunn, 4/5/73 (YGC23572). 23. See Jentschke's 'Introduction' to Volume II, 300 GeV Working Group, Proceedings of the Second Tirrenia Study Week, Tirrenia, Italy, 20-29 September 1972, at p. 13 (CERN/ECFA/72/4 Vol. II, January 1973). 24. These remarks were made by Bruce Cork at the Spark Chamber Symposium chaired by Arthur Roberts and held on 7/2/61 at the Argonne National Laboratory. The proceedings were published in the Rev. Sci Inst., 32 (1961), 479-531. 25. The experiment was labelled WA3, 'Exclusive jqj and Kp interactions', it was an Amsterdam-CERNCracow-Munich-Oxford-Rutherford Laboratory collaboration, and the spokesman in 1976 was P. Weilhammer. See Experiments at CERN in 1976 (Geneva: CERN, 1/9/76). 26. The phrase is Mulvey's in his memo Comments on ECFA III (3) addressed to 'Director-Greneral, CERN Laboratory V, and dated 13/11/73 (DADM20099). CERN's construction of superconducting elements for low-beta sections in the ISR was cited by Mulvey as one example of what visitors called CERN's 'insularity'. Why do this at CERN, they argued, when national laboratories had groups who were just as capable of doing so? 27. For these quotations see letter Lipman to Gunn, 4/5/73 (YGC23572). Lipman had spent the previous ten months at CERN working as the leader of an experiment at the Omega spectrometer, and personally felt himself 'rather well involved in CERN'. This, and the generally objective tone of his letter, has led us to place considerable weight on the document. The type of projects the senior staff had in mind which he mentioned were muon scattering experiments, counter neutrino experiments and a large spectrometer system. 28. See the minutes of the ECFA meeting on 1 December 1972, CERN/ECFA/73/4 (undated) (DG21220). 29. WG3 Final Report, p. 14 (see note 21). 30. A. Berthelot, Elementary Particle Physics in Saclay, paper presented at the ECFA Information Meeting, CERN, 26/5/72 (YGC23572). 31. Frascati National Laboratories. A Report to ECFA. May 15,1972, Servizio Documentazione dei Laboratori Nazionali di Frascati del CNEN (YGC23572). 46-54. 32. G.H. Stafford, The Rutherford High Energy Laboratory, section 7 (YGC23572). 33. Letter Lipman to Gunn, 4/5/73 (YGC23572).

Notes

203

34. The point was made, for example, by Salmeron, at the ECFA meeting on XIMjll, minutes CERN/ECFA/ 73/4, undated (DG21220). 35. For a description of the Plumbicon see Stafford's report, note 32. In this report it is written that the proposal to build this kind of system was made in January 1971 'by a team from Birmingham University, Westfield College, London, and the Rutherford Laboratory' (p. 15). Stafford attributed the original idea to Westfield at the ECFA meeting on 1/12/72, minutes CERN/ECFA/73/4, undated (DG21220). 36. WG3 final Report..., p. 15 (see note 21). The problems faced by university physicists doing electronics experiments are discussed in greater depth below. 37. For this information see the Appendix to Mulvey's memo cited in note 26. See also the minutes of the second meeting of the Working Group, held on 17/9/73, document ECFA/WG3/RLM2/73 (DG21221), and the Report of Sub-Committee 3, dated l^jljlA (YGC23572) for more information on the national situations. 38. The quotation is from Mulvey's memo cited in note 26. In the more sober language of the final report of the working group (see note 21), we read that 'any attempt at the unnecessary duplication of similar accelerators would be damaging to the credibiHty and, hence, to the future prospects of high energy physics' (at p. 17). 39. See Point 16 in the minutes of the first meeting of the working group, document ECFA/WG3/RLM1/73, dated 11/7/73, and signed D. Baugh (DADM20099). 40. The arrangements made for the construction of these two chambers are discussed by Dominique Pestre in this volume. 41. The quotation is from the memo written by Mulvey (see note 26). As an example Mulvey added '(e.g. don't build SC elements for ISR low-jS sections at CERN if they can be built by a National laboratory)'. 42. For these figures see the unsigned memo Complementary Information on CERN Policy in Connection with the ECFA (WGS) Report, 11/4/75 (DG21222). Reporting his 1970 census figures to ECFA Harting said that there were 583 applied physicists at CERN, 351 at the national laboratories, and that the number elsewhere was negUgible — see CERN/ ECFA/73/3, undated (DG21220). 43. The figures for 31 December 1971 are taken from the report of a working group on appointment policy dated 31 August 1972, at p. 4 UUmann files (GU23800). This report describes past CERN policy in this area, and makes recommendations about how to improve it. 44. From an unsigned memo dated by hand 11.9.75, and entitled DRAFT No. 2 {final version). Complementary information on CERN Policy in Connection with the ECFA {WG3) Report (DG21222). 45. The material in this paragraph is from the working group's final report (see note 21), recommendation 7.4, and paragraph 3.8, and from the minutes of the seventeenth plenary meeting of ECFA, CERN/ECFA/75/4, 16/5/75 (DG21220). The quotation beginning 'there was a strong opinion [...]' does not give Faissner's actual words. It is a statement made in the report at paragraph 3.8 which was apparently paraphrased by Faissner at the ECFA meeting. It was Gunn himself who implied that the recommendation had been softened to 'appease' the CERN representatives on the working group - see minutes of the ECFA meeting at p. 17. 46. For these quotations see, respectively, the letter from Salvini and Harting to the members of the plenary ECFA, CERN/ECFA/72/10, 21/12/72, Appendix II to WG3's final report (see note 21), Salvini's intervention at the 17th plenary meeting of ECFA, minutes CERN/ECFA/75/4, 16/5/75 (DG21220), and letter Morpurgo to Faissner, 1/10/73 (YGC23572). The point about CERN staff being closed in on itself was also made by Mulvey. Visitors complained, he said, that 'CERN staff never spend significant periods of time working with groups in National laboratories; the traffic is all in the other direction'. See his memo cited in note 26. 47. See Hine's memo to Jentschke and Adams on the Second Meeting of ECFA Working Group ///dated 27/9/ 73 (DADM20099) and letter Goldschmidt-Clermont to Faissner, 15/11/73 (YGC23572). 48. See Hine's memo just referred to, and, for more details country by country, Baugh's minutes of the second meeting of WG3 held on 17 September 1973, document ECFA/ WG3/RLM2/73, 9/11/73 (DG21221). 49. From the Report of Sub-Committee 1 to Working Group III of ECFA, signed by H. Faissner and dated 21/12/ 73 (DG21221). See also the final report of WG3, section 3. 50. From the Report of Faissner's subcommittee referred to in the previous note.

204

The Relationship Between CERN and its 'Visitors' in the 1970s

51. From the minutes of the 16th plenary ECFA meeting held on 22/2114, document CERN/ECFA/74/4, 10/10/ 74 (DG21220). 52. All quotations from 'Dissent Blooms at AAAS Circus', Nature 229 (January 8 1971), 81-2. The AAAS is the American Association for the Advancement of Science. 53. For a general account of the left-wing critique of science in this period, see for example H. and S. Rose (eds.). The Radicalisation of Science (London: Macmillan Press, 1976), chapter 1. 54. Letter Morpurgo to Faissner, 1/10/73 (YGC23572). 55. Nature 230 (March 26 1974), 1978. 56. From the Report of the working group cited in note 43, at pp. 8, 7. See also the document DRAFT No. 2 (final version) cited in note 44. 57. See letter Goldschmidt-Clermont to Faissner, 15/11/73 (YGC23572). 58. See DRAFT No. 2 {final version) cited in note 44. See also the Memorandum from Meyer to Jentschke dated 2/2/1973 (DADM20099). J. Meyer was the head of the CERN delegation to ECFA at the time. 59. From the Report of the Working group cited in note 43, recommendation 8. 60. See for example, L. Kowarski, An Observer's Account of User Relations in the U.S. Accelerator Laboratories (Geneva: CERN 67-4, 1967) and D. Pestre, op. cit., note 2. 61. The account that follows is based on two papers prepared by Mervyn Hine for the working group, namely. Planning and Decision Making Procedures at CERN. Working Paper by M.G.N. Hine, document ECFA/ WG3/RLP6/73, 27/8/73 (DG21221) and Membership of CERN Committees, document ECFA/WG3/RLP6 Add/73, 10/10/73 (YGC23572). 62. Hine, in Membership... (see note 61). 63. In Planning... (see note 61). 64. ibid. 65. Hine, Membership... (see note 61) 66. ibid. 67. See H. Schopper's Summary of the Discussion with Visitors on 29 and 30 January, 1973 (DG20589). 68. Hine, Memorandum to Jentschke and Adams, dated 5/12/73, and reporting on the second meeting of ECFA WG3 (DG21221). 69. For this material see the undated, unsigned memorandum ECFA Working Group III, Sub-Committee 2 (DG21221). 70. See the Report of the working group cited in note 21, sections 4.5 and 7.6. It was also suggested that more theorists should be included on the committees. It was difficult to take this recommendation seriously as, in presenting WG3's report to ECFA, its chairman, Gunn, remarked that this idea had perhaps been mooted because the chairman of the sub-committee which had dealt with this matter was himself a theorist - see the minutes of ECFA's 17th plenary meeting, CERN/ECFA/75/4, 16/5/75 (DG21220). 71. See Dominique Pestre, op. cit., note 2. 72. Hine, Planning... (see note 61). This view was confirmed by scanning the minutes of these meetings, and was also confirmed in an interview with one of the secretaries of such a committee. 73. Paul at the 52nd meeting of the SPC, 25, 26/2/69, minutes CERN/SPC/74, 27/4/69. 74. For the membership in October 1963 see Hine, Membership..., note 61. The report of the working group recommended that 'A balance of external membership, both of users and of computer experts, is considered desirable for the Data Handling Policy Group, or any other committee advising the Director General on computer policy', see Report..., note 21, recommendation 7.7. 75. For material in this paragraph see Hine, Planning..., note 61, and an informal write-up of some informal notes' taken at an informal Physicists Meeting of 27 November 1972 by A.J.H. (DG20589). 76. For this information see CERN, Annual Report, 1972, 100-1, Annual Report, 1973, 98-9. 77. The figures are taken from Hine's 1972 CERN-ECFA Survey of European Computing Facilities for High Energy Physics, CERN/ECFA/74/3, 19/2/74, and an update dated 27/2/74, both in (DADM20099). As one

Notes

78. 79.

80. 81. 82. 83. 84. 85. 86. 87.

88. 89.

90. 91.

92. 93.

94.

95. 96. 97.

205

would expect, more of CERN's used capacity was taken up with analysing data from electronic experiments than from bubble chamber experiments - 52% as opposed to 36% See J. Krige in Hermann et al., op. cit., note 2, chapter 9.6. Stafford described the links established between the Rutherford Laboratory and CERN and nine work stations at UK universities to the ECFA meeting in February 1974. At this time the system could not yet transmit bulk data due to limitations in the speed of telephone lines, and there was an air shuttle service carrying tapes between CERN and RHEL - see minutes, CERN/ECFA/74/4, 10/10/74. From the draft minutes of ECFA's 19th plenary meeting held on 29/3/76, CERN/ECFA/76/12/Draft, 24/9/ 76(DGR21311). See letter Lipman to Gunn, 4/5/73 (YGC23572). For this sentence and the one before see H. Schopper's Summary of the Discussions with Visitors on 29 and 30 January, 1973, undated (DG20589). See letter Lipman to Gunn, 4/5/73 (YGC23572). See Schopper, Summary..., note 82. In presenting WG3's report to the 17th plenary ECFA meeting on 27/1/75, minutes CERN/ECFA/75/4, 16/ 5/75. Letter M.A.R. Kemp to D. Baugh, 5/9/73 (YGC23572). The following description is based on a paper prepared for WG3 by Yves Goldschmidt-Clermont entitled Structure of CERN Research Groups and Support Provided, ECFA/WG3/RLP4/73, 7/9/73 (DG21221), an unsigned paper dated 21/3/73 entitled Background information on the organization of the NP division (YGC23572), and an unsigned DRAFT No. 2 (final version) Complementary information on CERN policy in connection with the ECFA (WG3) report, dated 11/9/75 (DG21222). According to Goldschmidt-Clermont, in the NP division 'The CERN group is never strong enough to do an experiment on its own' (see his Structure..., previous note). Taken from DRAFT No. 2 (final version)..., (see note 87). CERN did provide help in these areas in exceptional cases e.g., 250 KSF in 1974 to support members of visiting teams, 500 KSF for materials, extra computer time (38% NP time in 1974), 'and the use of the NP electronics pool without charge'. From WG3 final Report..., see note 21, pp. 10-11. This paragraph is based on the WG3's Report..., note 21, 10, and a lengthy paper by Guy von Dardel entitled Working paper for the meeting of Restricted ECFA, March 20th, 1975, document CERN/ECFA/RC/ 75/4, 24/2/75, p. 11 (DG21220). Von Dardel had just taken over as ECFA chairman, and this was a wideranging discussion of the most important issues which he saw as lying before the committee. ibid. p. 9. For the information in this paragraph see the minutes of ECFA's 19th plenary meeting held on 29/3/76, CERN/ECFA/76/12/Draft, 24/9/76 (DGR21311). Van Move's Procedures for Physicists Making Experiments at CERN, 2nd Draft, dated 11/3/76, is Annex II to these minutes. Letter J. AlUson to D. Baugh, 10/9/73 (YGC23572). These problems were also of great concern in the United States - see the Report of the HEPAP Subpanel on Future Modes of Experimental Research in High Energy Physics, July 1988, US Department of Energy document DOE/ER-0380. See note 75, Physicists Meeting... . See also letter T. Sloan to D. Baugh, 7/8/73 (YGC23572). See their letter. Appendix II of the working group's Report..., note 21, In this connection see letters M.A.R. Kemp to D. Baugh, 5/9/73, letter P.J. Negus to D. Baugh, undated (YGC23572), Memorandum from G.H. Hampton to M.G.N. Hine, 31/8/72 (DADM20099) (in which Hampton states that he thinks that 'the real problem for the unpaid visitor is the financial one' and that he feels that wives cannot find work in Switzerland because they lack the necessary qualifications and linguistic fluency, rather than work permits), the report entitled ECFA Working Group III, Sub-Committee 2, unsigned and undated (DG21221), which gives very little attention to the problem, and M. Holder's paper ECFA Working Group III, Some social problems of visitors in CERN, ECFA/WG3/RLP5/73, undated (DG21221).

206

The Relationship Between CERN and its 'Visitors' in the 1970s

98. See the working group's Report..., note 21, at p. 12. 99. See his paper cited in note 97. Holder found that in a sample of 249 (out of 900) visitors who replied to a questionnaire, 130 mentioned special problems. Of these 56 mentioned housing, 52 mentioned legal status in Switzerland, 19 mentioned schooling and 15 mentioned salaries as the notable social problems which they had at CERN. 100. Minutes of 17th ECFA plenary meeting, 27/1/75, CERN/ECFA/75/4, 16/5/75. 101. See the remarks of Van Hove at the 19th plenary ECFA meeting, 29/3/76, p. 17, CERN/ECFA/76/12/Draft, 24/9/76 (DGR21311) 102. For Vivargent's statement see Annex F to the minutes of ECFA's 20th plenary meeting, CERN/ECFA/77/ 17/Draft, 27/1/77 (DGR21312). 103. The two Report[s] on ECFA Working Group on Users' Conditions, were subtitled Report by the ECFA Working Group on the Support given to CERN Unpaid Associates by their Home Countries, ECFA/76/3A, 15/ 3/76, and Financial Position of Unpaid Associates ECFA/76/3B, 19/3/76, and ECFA/76/3B/Rev, 31/8/76 (DGR21311). The figure is based on the summary table on page 10 of ECFA/76/3B. 104. See the documents cited in the two previous notes. 105. See the statement cited in note 102. 106. See the informal notes on the informal meeting held on 27/11/72 cited in note 75. 107. See H. Schopper, Summary of the Discussions with Visitors on 29 and 30 January, 1973, undated memo (DG20589). 108. See Van Hove's intervention at the 19th plenary meeting of ECFA, minutes CERN/ECFA/76/Draft, 24/12/ 76(DGR21311). 109. These formulations are taken from the 1978/79 Report by the Chairman of the Advisory Committee of CERN Users ACCU, undated (DG21313). The official terms of reference can be found, for example, in the Final Report of the CERN Review Committee, CERN/1675, 3/12/87, p. 25 (cf. note 113 below). 110. See the 1978/79 report cited in the previous note. 111. Letter Crozon to Van Hove, 25/10/79 (DG21363). 112. For the material in this paragraph see Paul's paper Methods of Selection of Experiments on CERN Accelerators, CERN/SPC/458, 1/4/80, and the minutes of the 112th meeting of the SPC at which the report of the ad hoc group was discussed, CERN/SPC/460/Draft, 30/5/80. 113. The committee comprised A. Abragam (Chairman), M. Boyer, C. De Benedetti, B.F.F. Fender, W. Paul, H. Sandvold, and J. Vodoz. Its Final Report... was presented to the CERN Council at its meeting on 17 and 18 December 1987, and is document CERN/1675, 3/12/87. Material on the users' attitudes is summarised in Chapter III and detailed in Annex II. 1. 114. Final Report..., (previous note), p. 21. 115. ibid., p. 121. See also pp. 25-6. 116. ibid. pp. 116-7. 117. ibid., pp. 118, 119. 118. ibid., pp. 121, 122. 119. For this section see J. Krige in History of CERN, Volume //, chapter 9. 120. See the document cited in note 91, at pp. 9-11. 121. For the twin concepts of CERN as their laboratory which serves the European community, see Dominique Pestre, op. cit., note 2, chapter 8.

CHAPTER 6

The ppbar Project. I. The ColHder John KRIGE

Contents 6.1 Introduction 6.2 The first steps towards defining CERN's next big machine in the mid-1970s and the management's need for an 'intermediate' project 6.3 Proposals for the quick discovery of the W and the Z - at CERN and at Fermilab 6.4 1977: ICE cools its first beams and the competition hots up 6.5 CERN launches a pp colUder at the SPS - and Fermilab drops definitively out of the race to search for the W 6.5.1 The decision to build the antiproton source 6.5.2 The choice of experiments 6.5.3 Developments at Fermilab Notes

207

208 209 213 224 232 233 237 239 243

6.1 Introduction The 1984 Nobel prize for physics was awarded jointly to two CERN scientists, Carlo Rubbia and Simon van der Meer. The citation stated that it was 'For their decisive contributions to the large project which led to the discovery of the field particles W and Z, communicators of weak interaction'. This 'large project' involved, scientifically and technically, the development of a proton-antiproton (pp) coUider and the construction of a detector to search for the W and Z particles. But it required too the strong support of a CERN management concerned about the faltering image of their laboratory, the risk that the USA would once again make a major breakthrough before CERN did, and the overcoming of stiff opposition in the nuclear physics community, in addition to the personal qualities of the Nobel laureates. In this chapter and the next we propose to study this development by looking first at the process which led to the decision in June 1978 to build a machine to collide antiprotons with protons. In the next chapter we spend a little time exploring the construction of Rubbia's team and the building of the so-called UAl detector. We have two very different kinds of account about the construction of the collider. One, written by scientists involved in the project, tends to stress the scientific and technical concerns shaping the project^ As is usual in this genre, other considerations informing the decision to proceed with the scheme are mentioned only briefly, if at all, thereby giving the impression that they were of secondary importance. Above all the alternatives to its implementation - and the associated disputes within the physics community and between the proponents of the project and the management - are mentioned only briefly, or even ignored. This does not only provide a seriously misleading account of how decisions on major new items of equipment are taken in an organization like CERN. It also gives to those decisions a spurious logic and an air of necessity and inevitabiUty which they simply did not have in the minds of the key actors at the time. Such an approach doubtless helps project an image of scientific work as a field of activity in which 'rational men' rapidly converge on the best course of action to take using solely scientific criteria to guide them. Ironically, at the same time it strips the practice of science of much of its vitality, excitement and uncertainty, just those characteristics which are typical of work at the research frontier and which attract many to the field in the first place. As we mentioned a moment ago, there are other accounts of CERN's large project which differ in kind from that written by the protagonists themselves. The most notable among these is the book by Taubes^. This is the mirror image of the 'classical approach' favoured by scientists. Taubes' aim is to turn such accounts on their head, to stress the irrational and non-rational forces at work in 'big science', the ruthless competition, the 208

CERN's next big machine in the mid-1970s

209

petty jealousy, the ceaseless rivalry. Dominating the research frontier, Taubes tells us, is not just, or even primarily, a question of scientific and technological competence, but of power, deceit, and nastiness. Consistent with this problematic he stresses and sensationalises, indeed revels in, every dispute and disagreement surrounding the development of the pp collider project, with little concern for the weight which rivalry and resentment actually played in the decision making process, and with even less respect for the historical record. Our aim in this chapter is to think about the decisions taken at CERN to embark on a pp project in a way which avoids both of these traps. Basing ourselves on the rich sources in the CERN archive we want to reconstruct the process step by step as it was lived by the actors. Those actors - scientists, engineers, managers - had at each phase of the project to balance a variety of scientific, technical, institutional, economic, political and personal considerations against each other. The scientific interest of the W and the Z was never in doubt. However, not everyone agreed that it was worth racing the Americans to discover them. The best technical system to use for the search was far from clear. Delays to the ongoing fixed target programme, and the consequent hostility of a European physics community increasingly dependent on CERN, were inevitable. And everyone realised that the member states would be unwilling to give CERN additional funds for such a project in a period of economic stringency. The story we are going to tell below explains how the management, and the two CERN Directors General in particular, along with the physicists and engineers who wanted to make a 'quick and dirty' search for the W and Z at CERN, dealt with these problems on a day to day basis. It was thanks, above all, to the combined determination of a management prepared to take a risk to raise the prestige of the laboratory, and of scientists wanting to be the first to make an important discovery, that the ground was laid for the identification of these fundamental particles in Geneva in the early 1980s.

6.2 The first steps towards defining CERN's next big machine in the mid-1970s and the management's need for an intermediate' project By the mid-1970s a number of major experimental and theoretical developments had created a ferment in the field of high-energy physics. There were the results in 1973 at CERN and later at Fermilab suggesting that one of the four fundamental forces in nature, the weak force, was propagated through neutral currents. This was followed by a number of discoveries, notably that of the J/psi particle at Brookhaven and at SLAC in 1974, which lent strong support to the idea that a fourth quark carrying the property called 'charm' might exist (see the chapter by Winter in this volume for more details). These experiments were in line with the predictions of the so-called unified gauge theory of Weinberg, Salam and Glashow, which later came to be known as the 'Standard Model' of nuclear interactions (as described in the chapter by Iliopoulos). Not only was there now a strong general interest in climbing to ever higher coUision energies where, it was said. Notes: p. 243

210

The ppbar Project. I. The Collider

'undreamed of physics' could be done. More specifically, and importantly for our purpose, the success of unified gauge theories in making sense of the mass of new experimental data lent credibility to their prediction that an intermediate vector boson existing in both charged (W"^ and W~) and neutral (Z^) states might couple the weakly and strongly interacting particles. This notion was attractive for the confirmation it gave to the Standard Model. It was also perceived to be coherent with the reductionist and aesthetic search for simplicity which, physicists argued, was an essential and historically deeprooted goal of their discipline. Not all would agree with Pierre Darriulat that 'By the mid-seventies, the search for the triplet of weak bosons W and Z had become the obvious and highest priority goal of experimental particle physics'^. Yet it must be said that any debate on the physics of the future and the machines needed for it always included the search for the W and the Z among its main objectives. The masses of the weak bosons were still only defined vaguely in the mid-1970s - the lower limit climbed gradually in 1976/7 from 20 to 40 to 50 GeV/c^, the upper limit was thought to lie at about 100 GeV/c^. And it became evident that, if they existed at all, the W and Z could only be detected by machines far more powerful than any then available or under construction. The centre-of-mass energy of the most energetic fixed target machines - Fermilab's 4—500 GeV Main Ring, commissioned in 1972, which was to be upgraded to 1 TeV (see later), or CERN's new 400 GeV Super Proton Synchrotron, which reached half its design energy in June 1976 - was far too low to ensure the production of such massive particles. So too were the energies of the available or upcoming colliders CERN's ISR (30 GeV/30 GeV) proton-proton machine, and the newest electron-positron coUiders being built at DESY (PETRA, 19 GeV/19 GeV) and at SLAC (PEP, 18 GeV/ 18 GeV). The identification of the three weak bosons would thus require an entirely new machine. The debate on just what machine was needed to do W and Z physics was inserted into already ongoing discussions on the next round of accelerators in various laboratories. New ideas for accelerators to be built at CERN had been on the agenda in the ISR division from 1972, as soon as that machine had illustrated the technical feasibility of protonproton colliding beam devices'*. While a variety of options was possible the initial choice fell on design studies of a pair of Large Storage Rings which used the SPS running at top energy as a proton injector (i.e. 400 GeV/400 GeV). In May 1975 the possibilities of building such a device using superconducting magnets was described to the SPC by Kjell Johnsen, who had led the ISR project. Johnsen also explored briefly the technical feasibihty of colliding protons in one of these rings with 14 GeV antiprotons or with 25 GeV electrons. At the same meeting the reports of two working groups (convened by L. di Leila and W. Willis) set up about a year earlier to examine the physics possibilities of such a machine and a multi-TeV fixed particle accelerator were also discussed. They concluded that both a 400 GeV/400 GeV pp collider and a 10 TeV fixed target machine could provide answers to some really fundamental questions, and could produce the weak bosons. Another alternative was also retained. On the basis of a paper from B. Wiik, then at DESY and soon to move to CERN as visitor, the possibiHty of combining the 400 GeV pp

CERN's next big machine in the mid-1970s

211

collider with a 25 GeV electron storage ring to do ep physics was not allowed to disappear from view^. About six months later, in October 1975, and with the SPS 'nearing completion — or at least first operations' J.H. Mulvey (then responsible directly to DG Jentschke for coordinating the experimental programme) addressed a note to the senior CERN management proposing that a number of concrete steps now be taken to define CERN's next big machine. He had discussed the matter with Johnsen, di Leila and Willis, as well as SLAC director Burt Richter, he said. On the basis of this he felt that it would be advisable to hold a meeting in the CERN Main Auditorium dealing with physics with a colliding beam electron-proton machine. Other potential big machines, including a proposal from Carlo Rubbia for a 60 GeV/60 GeV electron-positron coUider, could also be explored. Participation of outside physicists at the meeting was important, said Mulvey: it was essential that any new project 'be seen as European and not just 'CERN'.' To give the deUberations added weight, Mulvey added, the meeting should be preceded by a statement from one of the Directors-General to the effect that the CERN management favoured a major new project costing about 100 MSF/year and corresponding, say, to a faciUty Hke 300 GeV protons/20 GeV electrons. There was a tendency amongst physicists, said Mulvey, to think 'too small - in terms of relatively unrewarding 'ad hoc' modifications to existing machines' (e.g. rebuilding the ISR with superconducting magnets to reach 100 GeV per ring). The DG's talk should stress that this should not be the main objective^. Mulvey's proposal was positively received and a talk on ep machines was duly held on 20 November 1975. The interest aroused led him to suggest that some groups might be formed to carry forward the study of the physics possibiUties and technical problems of such a device. At the same time it now seemed that the interest of high energy e^e~ machines should also be explored. A restricted meeting to which about 20 people were invited - CERN experimentalists, theoreticians, engineers, and the Directors-General was arranged for this pupose on 29 January. Here it emerged, as Mulvey put it, that there was 'enthusiastic support for a study of the physics and technical aspects of a high-energy e"'"e~ colliding beam machine'. By contrast interest in an ep collider had waned and Mulvey thought it were best left in abeyance until Wiik arrived at CERN in the autumn^. Our available documentation does not allow us to reconstruct in detail the emergence of the electron-positron colUder as a major option. We mentioned earlier that Rubbia at least had favoured design studies of such a high-energy device. Interest in it was certainly stimulated further by Burt Richter who did not attend the meeting at the end of January but who explained his views on future e"^e~ machines in a letter written to Mulvey (and others at CERN, including the DGs) the week before. 'An e^e~ machine in the energy range of roughly 200 GeV c m . [i.e. 100 GeV/100 GeV] is a magnificent tool for studying the weak interactions and their relationship to the electromagnetic and strong interactions', the letter began. 'Both W and Z production are possible (if they exist at all)', Richter went on. In these respects at least, he said, this machine was far superior to a highenergy pp colliding beam machine - no doubt a reference to Brookhaven's proposal, then under consideration, to build Isabelle (200 GeV/200 GeV protons on protons as conceived Notes: p. 243

212

The ppbar Project. I. The Collider

in 1974, and reconfigured in 1977 to double the energy in each beam). Richter went on to mention briefly the technicalities of building an electron-positron collider, and gave a very rough estimate of its cost (2 x SPS), its energy consumption along with some industrial applications for the energy dispersed which would make it more 'socially acceptable', the constraints imposed on the interaction regions, and the site (a question of 'world poUtics' he said). The SLAC Director concluded by saying that he believed that 'the possibilities for e'^e" machines are extremely exciting', adding the hope that the subject would be intensively pursued^. Richter's letter was surely one factor which inspired the 'enthusiastic support' shown by the CERN senior staff for an electron-positron colHder at their meeting on 29 January, and their relative loss of interest in an ep device. To consolidate this support Mulvey proposed to the Directorate that a number of steps be taken. A steering group should be set up as soon as possible to discuss CERN's policy on all types of future machines. One of its first tasks would be to propose names for an e"^e~ study group. One quarter to one third of these should be non-CERN, Mulvey said. Its detailed composition should be discussed with Guy Von Dardel, the then Chairman of ECFA, which body, Mulvey insisted should be associated with the development and should arrange a 'study week', preferably outside CERN, for later that year. As for the terms of reference of the study group, Mulvey proposed that physics criteria '(e.g. 100 on 100)' should set the scale rather than considerations of site: the machine could be scaled down later to fit on the largest site available at CERN (if it was decided to build it there)^. It did not take long for Mulvey's proposals to be implemented. The steering group was established by the end of March with himself as chairman, and F. Bonaudi, an accelerator engineer, S. Fubini, from the TH division, and K. Johnsen, whom we have met, as members. Pierre Darriulat, a French experimentalist working at the ISR, had accepted their invitation to act as convener of the study group whose first meeting was scheduled for 12 April 1976. Thus were the foundations laid for what became later CERN's LEP (LargeElectron Positron Collider)*^.

It is not our intention here to discuss in detail the decisionmaking process which led to CERN, the European physics community and European governments accepting that the laboratory's next big machine would be the LEP. There are rather two points that we want to stress about the above debate by way of conclusion. Firstly, the growing consensus over the physics advantages of building a W and Z 'factory' at CERN, went hand in glove with the conviction that the project should be twinned with a 'quick and dirty' scheme to produce and detect the weak bosons. The construction of a large electron-positron collider had the advantage that the particles would be produced in collisions far 'cleaner' than those obtained with protons (or antiprotons), and that it would guarantee the long-term future of the laboratory. Intermediate projects based on existing faciUties, on the other hand, would ensure that a very important discovery was made quickly, and would provide

Proposals for the quick discovery of the W and the Z

213

precise mass values for the W and the Z which would be invaluable for the design of the LEP. Secondly, the physics interest apart - and Mulvey stressed this point - such an 'intermediate' project was important in that it would serve to maintain the levels of the annual CERN budget in the years between the commissioning of the SPS and the construction of any new big accelerator. The debates we are describing took place in a period of growing economic difficulty. It was not simply that in the early 1970s governments were being called upon to invest larger amounts of money than before in fields other than high-energy physics and space. They were also struggling to overcome an economic recession which was exaggerated by the oil crisis, and by the abolition of the gold standard by Nixon in 1973 and the ensuing shift to floating monetary exchange rates. In short the days of lavish funding for high-energy physics were over^^. CERN was feeUng the effects directly. Not only were its annual budgets scheduled to fall as the SPS moved from the period of construction into that of operation. Two governments, the UK and Germany, were insisting that it fall even faster than originally foreseen, the former because its CERN contribution, paid in Swiss Francs, was becoming an even greater domestic burden due to exchange rate fluctuations. The management was determined to oppose this situation. It was convinced that any new major project would have to be built within a constant cost envelope and, knowing the workings of state bureaucracies, also convinced that once a budget had fallen to a particular level it would be extremely difficult to persuade the funding governments to push it back up again. In particular they wanted to retain the 1980 budget level the same as that for 1979 and since the major costs of any new big machine would be borne after that period they needed a good, intermediate project to stabiHse the budget at a level which was as high as possible. It was in this context that a number of 'intermediate'-level candidates to study the W and the Z, candidates that were relatively cheap and which could be built quickly, were proposed to CERN. One of those candidates was 'Carlo Rubbia's' protonantiproton (pp) collider.

6.3 Proposals for the quick discovery of the W and the Z - at CERN and at Fermilab The possibility of reaching high centre of mass energies by colliding beams of particles rotating in opposite directions had been discussed since the late 1950s^^. They were further stimulated by the successful operation of the ISR at CERN in the early 1970s, by the physics interest of testing the underlying theory of weak interactions by identifying the W and the Z - and the kudos associated with being the first to do so -, and by important advances in the study of techniques for 'cooling' particle beams (cf below). A workshop held at Fermilab in January 1976 stimulated a number of proposals for colUding beam schemes, both at that laboratory and at CERN. All were intended to carry out the search for the weak bosons at relatively low cost, with relatively little disruption of the Notes: pp. 243 ff.

214

The ppbar Project. L The Collider

ongoing physics programmes, and before the next generation of powerful colliders, be that Isabelle at Brookhaven or Europe's next machine at CERN, was commissioned in the 1980s. To give the flavour of the debate, let us first quickly survey the three proposals that were prepared in anticipation of the June 1976 meeting of the Fermilab Program Advisory Committee, the body that advised the laboratory's director (Bob Wilson at this time) on its physics priorities. Two of them suggested the construction of proton-proton colliders, capitaHsing on FNAL's intention to extend its existing machine's power by converting it into a so-called Energy Doubler/Saver. A word first then about the Doubler. As described in a draft proposal for funding dated June 1975, the Doubler would be built by adding a ring of superconducting magnets and an acceleration system in the tunnel which contained the Main Ring of the Fermilab accelerator. The existing 400-500 GeV synchrotron would be used as an injector into this ring, and it was hoped in this way to accelerate protons to as many as 1000 GeV (1 TeV). The Energy Doubler, it was argued, could also be used as an Energy Saver: if protons from the Main Ring were injected into it at 275 GeV, and there accelerated to 400 GeV, as much as $7.5 milHon a year could be saved over running the Main Ring alone at 400 GeV. The cost of this programme was estimated to be as little as $35 milUon of new money if the improvement was completed in one year, rising to $50 milHon if the works had to be spread over several years^^. The Doubler figured in the second phase of a two-stage proposal (Proposal 478) made by FNAL scientist J.K. Walker (the spokesman) and others to detect intermediate bosons in proton-proton collisions'"^. They suggested building a high-current (1 Amp) storage ring to produce 25 GeV protons which would be collided, first with the 400 GeV protons circulating in the Main Ring, and later with the 1 TeV beam in the Doubler or Tevatron when it was ready. The former scheme would give a peak energy of 200 GeV in the centre of mass with a luminosity of 10^' cm~^ sec"' (so adequate for a good production rate of the two kinds of Ws). Once the Doubler was installed it was hoped to obtain collisions at over 300 GeV in the c.m.s. with an expected luminosity of 10^' cm~^ sec"'. An estimate of the cost of the construction of the tunnel, the storage ring and the detection apparatus amounted to about $4 million over two years, of which about $3 million was for equipment. Another experimental arrangement put forward at Fermilab in summer 1976 to discover 'the elusive W', and which was also 'versatile and sophisticated enough to react to surprises' was that described in Proposal 491, 'Clashing Gigantic Synchrotrons'. Authored by scientists from the host laboratory, Caltech and Leon Lederman, then at Columbia University, it suggested colliding counter-rotating beams from the Main Ring and the Doubler, to reach up to 1.2 TeV in the centre of mass system'^. The Main Ring energy would be 150 GeV and the Doubler would be operated in the reverse direction at 1000 GeV. A 'conservative, easy-to-design way' of achieving this reversal was described along with procedures to ensure that the scheme was compatible with normal operation of both accelerators. The expected luminosity was 2 x 10^^ cm"-^ sec"', equivalent to a production rate of about 200 W^/day.

Proposals for the quick discovery of the W and the Z

215

Both of these proposals suggested searching for the W and the Z using conventional and by then well-established technologies. The other proposal we want to describe here rehed on recent progress in beam 'cooling', i.e. techniques for reducing the momentum spread of a particle beam and so improving its luminosity or density in the collision area. Two schemes, in particular, had been under study since the late 1960s and were giving increasingly promising results. One, called stochastic cooling, was first tried out by Simon van der Meer at the ISR soon after the machine was commissioned. The other, called electron cooling, was studied by Gersh Budker and his colleagues at Novosibirsk in the Soviet Union beginning in the mid-1960s. Both of these techniques have been described in some detail by Crowley-Milling in his chapter in this volume, and will only be briefly explained here. Stochastic cooling made use of the microscopic fluctuations of a beam's centre of gravity from its equilibrium orbit to increase its luminosity. Van der Meer's idea was to damp the so-called betatron oscillations of a beam by detecting and compensating these displacements with an electronic feedback loop. By applying such damping on short beam samples over many hours it was hoped to reduce the amplitude of the transverse oscillations of the particles in the beam, and so increase its phase space density or luminosity. Van der Meer presented his first results in an internal report in 1972; they were rather discouraging and the report was never published in the open literature. Subsequent work led to more promising results which were submitted for publication in January 1975^^. Electron cooling involved having a beam of electrons travel along with a proton or antiproton beam at almost the same velocity. The heavier particles tended to lose their transverse momentum to the electrons by Coulomb scattering, and the whole system tended towards an equipartition of energies. Over a large number of turns the oscillation amplitudes and momentum spreads of the protons or antiprons were gradually reduced while the electron oscillations grew. The net effect was that the volume of phase space occupied by the beam of heavier particles was drastically reduced, making the beam denser and giving it a higher luminosity. Budker and his cofleagues pubUshed their first data on this procedure in 1967. They produced a new set of results at a National Particle Accelerator Conference held in Moscow in 1974, at a meeting held in Washingon in March 1975, and in a paper pubUshed in the open Uterature in summer 1976. The Novosibirsk group found that they could reduce the ampUtude of a 65 MeV proton beam from 1 cm initially to 0.5 mm after cooling with 35 KeV electrons. Even more exciting, the group expected the cooUng time to be about 0.5 seconds. Instead they found that it occurred in 50-60 miUiseconds^^. The possibiUty of rapidly obtaining dense beams of protons or antiprotons using electron (or stochastic) cooUng was described by one physicist as 'one of the two most important advances in beam-handUng techniques to have reached the point of practical, engineered availabiUty within the last 5 years' (the other was the development of superconducting magnets)^^. Its significance was quickly exploited by Carlo Rubbia, Peter Mclntyre (both then at the Department of Physics at Harvard University) and David Cline (Department of Physics, University of Wisconsin). The novelty of their proposal lay Notes: p. 244

216

The ppbar Project. I. The Collider

in the idea that having produced cooled antiprotons in a small stacking ring, one could inject them into the main ring, accelerate them to top energy, and collide them head-on against protons of equal energy rotating in the opposite direction in the same ring. In a paper drafted shortly after the January 1976 workshop Rubbia et al proposed a list of parameters for the Fermilab Main Ring and an antiproton source using stochastic cooling, and claimed that 'reliable estimates of production cross sections [of the massive weak boson] along with high luminosity make the scheme feasible'^^. Pushing their idea 'with typical elan', Rubbia and his coworkers submitted two related proposals based on cooHng antiprotons to Fermilab in and around May 1976^^. The first (Proposal 492) asked for about $5 million to build a small storage ring to study the dynamics of stochastic and electron cooling using both protons and antiprotons. If successful the device would be used to provide a dense beam of antiprotons for physics experiments in the Main Ring or Doubler which would become colliding pp machines with a centre of mass energy range from 300-2600 GeV. Technically, the scheme involved cooling the antiprotons in two steps. The particles were created at 3.5 GeV/c by the main beam with an iridium target. They were then transported to the accumulator ring, where their momentum spread was first reduced with stochastic cooHng. When 10^^ - 10^^ antiprotons had been accumulated, they were decelerated to 350 MeV/c, and cooled further in the same ring with electrons. That achieved, it was planned to accelerate the antiprotons back up to 9 GeV/c, to transport and to inject them back into the Main Ring, where they would be accelerated further along with the protons to 200 GeV/c. In the Doubler mode the protons and the antiprotons were both accelerated up to 400 GeV/c before injection into the superconducting ring, where they were accelerated further to 1000-1300 GeV/c and collided with each other. A tentative timetable foresaw a start of funding in August 1976 (i.e. a few months after the proposal was submitted), the testing of prototype stochastic and electron devices a year later, and the first injection of protons and antiprotons into the accumulator ring and the study of cooling phenemena another year later (i.e. Fall 1978). It was hoped to inject successfully cooled antiprotons into the Main Ring early in 1979, to complete the detector and to start experiments by the summer of that year, and to observe first W production in the Fall, i.e. three years after funding approval was given^^ Proposal 493, which was coupled with this, outUned a versatile, modest detector which could be used in conjunction with the accumulator ring to study pp collisions in the Main Ring or the Doubler, or in conjunction with the Main Ring and the Doubler to study proton-proton collisions. The 'final goal' of these coUiding beam schemes was to provide the highest centre of mass at a luminosity at least suSicient to detect the W. No cost estimates were provided, but it was suggested that the detector would take about two years to build after approval, provided adequate funds were available^^. These various ideas were discussed by the Fermilab Program Advisory Committee in June 1976. All colHding beam proposals were rejected. The PAC felt that it would be premature to settle on one design just yet. At the same time it recommended that the laboratory continue to explore the possibihties of high-energy proton-proton and/or proton-antiproton coUisions^^.

Proposals for the quick discovery of the W and the Z

217

Colliders continued to be discussed actively in the US in the following months. Their potential was investigated at a study week on cooling organized by Brookhaven in August. Fermilab organized a workshop on pp colliding beam facilities in September. And there was an ongoing debate at the laboratory on the possible uses of the Energy Doubler/Saver, including ideas for using it and the Main Ring in conjunction with antiprotons. After the Summer Study biweekly meetings on colliding beams continued to take place^"^. Three important conclusions were reached at Fermilab. Firstly, following a report by Berley and Month, it was decided that electron cooling alone was sufficient to improve beam density: additional stochastic cooHng was not needed. Secondly, it was reaUsed that the kind of scheme proposed by Cline et al in P492 was unrealistic. It was necessary first to understand better the dynamics of electron cooling before constructing a pp colliding beam facility. And finally, on the basis of these two results, in October 1976 the Laboratory Director Bob Wilson submitted a grant application to the National Science Foundation. It was for $490,000, to be available from 1 January 1977 for 'Research and Development of Particle Beam Cooling Techniques and a Feasibility Study of ProtonAntiproton ColUding Beam FaciUty'^^. Wilson's idea was to take protons from the Fermilab 200 MeV Hnac and to inject them into a specially built 200 MeV ring in which cooling and storage studies would be performed. If the results were positive, the existing facilities at the laboratory could be modified relatively easily and quickly to make possible the production, collection and acceleration of antiprotons which could then be colUded with protons rotating in the opposite direction in the Main Ring or the Doubler. This would require the later construction of a pp colliding beam facility which could then be built in three years for about $5 million, Wilson said. The grant appUcation included the results of Berley and Month's work and another proposal by Cline, Mclntyre, Mills and Rubbia (the lastmentioned now at CERN). Here they accepted the need for this kind of feasibility study, and argued that the construction of a 'realistic' cooling device at FNAL was 'Ukely to have a large impact on accelerator development in the United States for years to come'. In line with Wilson's proposal, the authors explained how 200 MeV antiprotons supplied from the booster could be cooled in a 200 MeV storage ring or 'freezer', and reinjected back into the Main Ring to lead to pp colUsions at 'several hundred GeV with luminosity in excess of 10^^ cm~^ sec~^' adequate, they said, 'to observe exciting phenomena such as W production'^^. By February 1977 work on building a cooling experiment was already in hand at Fermilab and the feasibility of converting the Main Ring and the Doubler into a pp colUding beam device was under investigation^^.

The developments across the Atlantic did not go unnoticed at CERN. The alarm was sounded in a memorandum dated 26 July 1976 by Director-General Leon Van Hove. 'The Americans', his memo began, 'appear to get very interested and active in the investigation of storage and acceleration possibilities for pp colliding beams in the Fermilab accelNotes: pp. 244 ff.

218

The ppbar Project. I. The Collider

erator'. Noting the 'great interest' shown in such schemes by the Program Advisory Committee in June, Van Hove went on to mention the workshops planned at Brookhaven and FNAL in August and September. He also remarked that new results on electron cooUng had been presented by the Novosibirsk group at a meeting in Tbilisi. The DG concluded by expressing his conviction 'that CERN must push its own efforts in this domain as fast as possible', going on to suggest that the Geneva laboratory 'could organize a small meeting next fall to review the technical outlook and to discuss the physics potentialities of a pp coUiding beam project at the SPS'^^. Following on this initiative, a study group was convened by the end of August. It held its first meeting in the Theory Division Discussion Room on 6 September 1976. Two members of the Directorate, Bonaudi and Fubini, four members of TH (Ellis, Jacob, Prentki and Veneziano) and four experimental physicists (Picasso, Pope (the convener), Rubbia and Sadoulet) formed its core. As far as we can estabUsh Van Hove also attended. This meeting defined the basic rationale, as seen by those present, for CERN's embarking on a pp project, and identified the areas where further research was needed to test its feasibility. We know this not from any oSicial minutes but from a set of extremely illuminating handwritten notes made either at or soon after the meeting, probably by Van Hove for his own records (it is reproduced in Fig. 6.1)^^. Five kinds of considerations dominated the authors' thinking. Firstly, there was the physics interest of the project. This was the 'crucial experiment par excellence', and the discovery of the W and Z intermediate bosons was the 'next major step in weak interactions'. Secondly, the project provided CERN with an opportunity to reverse the jaded image that it had accumulated, the image of a laboratory that had been working at the research frontier for over 15 years and which had seen one Nobel prize after the other elude its grasp. The difficulties were compounded by the fact that the CERN SPS had arrived five years later than its energy equivalent fixed target machine at Fermilab. Van Hove in particular feared that 'European physicists working at CERN would be limited to repeating at improved level the experiments already done or in progress at Fermilab [...]'^^. CERN needed 'more than bread and butter physics, more than [the] search for no longer new particles'. It had to 'take risks', launching an 'early, ambitious scientific project, presumably around the SPS'. Thirdly, there was the financial aspect. Any such scheme had to be 'fast and cheap' compared to what a future large project would require. The costs had to be borne within the existing budgets for machine development and the CERN experimental programme. Fourthly, there was the competition with Fermilab. The author remarked that it was preferable for CERN to concentrate on pp because it could reach a higher energy in this way than with any fast and cheap proton-proton project at Geneva. Anyway the US laboratory would soon be able to do pp collisions of 400 GeV on 1 TeV using the Main Ring and the Doubler. Furthermore, granted the better quality of the SPS magnets, CERN had a 'better chance' than Fermilab to succeed with a pp scheme.

s^

.

JfTy, A 2 '>, ^-^^c^

/*

y

4U.

0

a^^^j^p^ h^h£j<J(

r^i^..fJ

;^.///^^<

i/o6i-fo^^f^

: O-^A C^ ^ i/^tn^K

Fig. 6.1 Handwritten notes by van Hove identifying the advantages for CERN of a pp project (DGR 21298) Notes: p. 245

220

The ppbar Project. I. The Collider

Finally, the author of these notes touched on the doubts concerning the technical feasibiUty of the project. Some questions were 'simple' to resolve, like filling times, others were 'difficult', Uke cooling. All the same the note concluded on an optimistic tone: 'If it can be done, CERN should be able to do it first and better'. An open meeting to dicuss the scheme further was proposed for November. Within a couple of days of this gathering the SPC, which met on the 7 and 8 September, had been apprised of the management's interest in launching a pp project at the SPS. In a general talk surveying their plans for developing existing machines, Bonaudi mentioned the possibihty, suggesting that both stochastic and electron cooling would probably be necessary, and holding out the prospect of achieving 540 GeV in the c of m, 'a level high enough to discover the W and Z^ if they exist'. The response of at least some members of the Committee was enthusiastic. In Weisskopfs words 'all were agreed that p-p was a wonderful opportunity, even at a luminosity of 10^^ in the SPS, and theoretically extremely rich, probably even better than p-p, though he was not sure [...]'. Gregory concurred. The only concerns expressed regarded the cost - Van Hove cited a figure of $10-15 miUion based on data from Wilson, and Adams pointed out that the proposal 'would at least use the existing hardware in a very intelligent way' - and the danger that important effects would be drowned in 'garbage' i.e. the 'dirty' pp colUsion as opposed to 'clean' e+e" collisions. Lederman had expressed some doubts in this respect and his views were echoed by Veltman at the meeting. The latter was emphatic that the cross section for W production by pp was so low that the particle would never be identified against the background by this technique. Apart from this dissenting voice, however, the general tone of the short debate was very positive^ ^ CERN moved rapidly within the next few months to explore further the possibiUties of pp collisions in the SPS. Two working groups were set up early in September, one convened by Bonaudi and van der Meer to look into the technical aspects of the scheme, the other convened by Pope to study physics possibilities. Both groups gave a preliminary report on their findings at an open meeting at CERN on 24 November. A system of working papers, so-called 'pp Notes', was instituted and studies were made on topics Hke the background to be expected in W production, the use of antiprotons for strong interaction physics in the SPS, the kind of detectors needed for a pp colliding beam facihty, and the design of a pp experimental area which disrupted the normal operation of the SPS as little as possible. Early in 1977 Rubbia also wrote a report describing the feasibility of pp coUisions in the SPS^^. Theoretical work was complemented by the identification of the staff" required for developing the pp facihty. Early in November van der Meer had drawn a first tentative list of the key half-dozen people he would like for the cooHng experiment and to design the pp facility as such. A more extensive and definitive list was established by mid-January 1977 after discussion with the people involved and their division leaders, who had to be asked to release them for this purpose. Six people were to work full time on the cooling experiment, three others were to work part-time, at least initially, and additional help was promised from about another nine persons. Further assistance would be required from the PS

Proposals for the quick discovery of the W and the Z

221

Division (e.g. concerning the interfacing of the new ring with the PS), while the Site and Buildings Division was to provide various civil engineering services. About four people were available more or less full time for the design study of the pp facility and another half-dozen could be counted on for additional assistance. In sum, by January 1977 about 30 CERN scientific and technical staff were committed to one degree or another to the pp project. Carlo Rubbia was not formally included in the scheme, though van der Meer remarked that 'clearly he will remain very active, if not the main contributor of new ideas' to the study^^. The launch of the pp project at CERN was given added urgency by two bits of news from Fermilab. One was Wilson's (draft) October grant application to the NSF for funds to do a feasibility study of cooling, a copy of which was sent to CERN at the end of that month. Another, in elaboration of this, was a brief summary by Rubbia of the timetable for the Fermilab project. In his note Rubbia implied that the funds were guaranteed, that the project would get under way in January 1977, that the first physics with a simpUfied detector at low luminosity (10^^ cm~^ sec~^) would be undertaken in the course of 1978, that 1979 would be dedicated to improving the luminosity tenfold and building the final detector, and that protons and antiprotons would be injected into the Doubler in 1980, where physics at 2000 GeV with a luminosity better than 10^^ cm~^ sec~^ would be done with the new detector. While these estimates were undoubtedly optimistic, they certainly put additional pressure on CERN to move as fast as possible with its own project^^. By mid-January 1977 the reports of the two working groups set up a few months before were ready. Pope's group described the various physics possibiUties of a pp project at the SPS which gave energies of 540 GeV in the centre of mass with a luminosity of 10^^ cm~^ sec"^. It would open up the 'possibility of an early exploration of several crucial issues such as the existence of weak intermediate bosons, the study of high px particles, and the search for spectacular new hadronic phenomena such as suggested by new cosmic ray data'. Arguing that the CERN scheme was comparable in energy, luminosity, and interest with pp physics with the Fermilab Doubler, they urged that 'a complete design study and exploratory cooling tests begin as soon as possible'. A possible design for the pp source was presented by the group led by van der Meer. Their aim was to reach luminosities of around 3 x 10^^ cm~^ sec~^ in pp coUisions with a centre-of-mass total energy of 540 GeV. Their first worked out design study proposed that the antiprotons be produced at 3.5 GeV/c from a small tungsten target using 26 GeV protons from the CERN PS. These particles would then be injected into a 'shuttle ring' with a radius of about 25 m, where they would first be cooled stochastically and decelerated to a kinetic energy of about 100 MeV in order to reach the electron cooling region. At this low energy the antiprotons would be transferred to a second ring of the same average radius and housed in the same tunnel. This ring would operate at a fixed energy of 100 MeV and would be used to further improve the density of the antiproton beam using electron cooling. Four electron cooling sections would be needed if stochastic cooling did not work particularly well in the previous stage; a less demanding system Notes: p. 245

222

The ppbar Project. I. The Collider

would be used if the beams arrived already cooled from the shuttle ring. Once the antiprotons had been cooled further and stacked up to the desired number (hopefully some 10^^ ps per day) they would be transferred back to the shuttle ring, accelerated up to 5 GeV/c or more, and injected anticlockwise into the SPS, where they would be accelerated with protons up to 270 GeV^^ The feasibility of cooling was to be explored by a sub-group of van der Meer's group, led by G. Petrucci. A request to the CERN DGs to authorize a capital project to make these tests - the so-called Initial Cooling Experiment (ICE) - was submitted on 31 January 1977 and the project was adopted by the Executive Board on 17 February. To move as quickly as possible, and to reduce costs, it made extensive use of equipment already available on the CERN site. The ring, about 25 m across, was composed of four magnetic sectors (on the 'corners') separated by four straight sections. The magnets for the ring were to be those used previously for the g-2 experiment (to measure the magnetic moment of the muon) at CERN, suitably modified. A new vacuum chamber to reach 10~^ torr at the start of the experiment would be built 'using as far as possible existing design and spare parts from ISR and SPS'. Electron cooUng would be tried in one straight section and the equipment to test it had to be built from scratch. In the other straight sections as well as along the magnetic sectors a number of pick-up stations and accelerating and decelerating structures and kickers would be mounted to test stochastic cooling. Appropriate beam diagnostic detectors would be installed along the ring to measure cooling. The project was estimated to take two years, starting immediately, with the first year being taken up with the construction of the ring and its equipment, while cooling tests were foreseen for 1978. Its overall cost was calculated to be 6 million Swiss Francs, 3.2 million for materials, the remainder for 36 man-years of staff costs. The race with Fermilab to test the feasibility of cooling was on^^.

Within less than five months after the subject had first been seriously discussed at a small meeting in the TH division, CERN had embarked on an experiment to test the feasibility of cooHng antiprotons, with a view to using them to create the W in the SPS, which was still in the commissioning phase (200 GeV had been reached on 4 June 1976). The project was driven almost entirely by CERN staff and the senior management, including both Directors-General, who knew that in Carlo Rubbia they had a 'product champion', a person with the intelligence, ambition and determination to take overall charge of the project and to push it through to completion. If the management backed this scheme so quickly and unambiguously it was because, the physics interest apart, they came to identify it with the future expansion and even survival of CERN itself. At a mundane level, it was just the kind of exciting project which would encourage member states to maintain the level of the CERN budgets at a time when many were calling for deep cuts, so facilitating the acceptance and construction of CERN's next big machine. More fundamentally, if CERN beat Fermilab to the discovery of the W the years of 'coming second to

Proposals for the quick discovery of the W and the Z

223

the US' would be over, and the past disappointments at the laboratory - the refined study of 'no longer new particles' - could be reinterpreted as necessary phases of a learning process rather than as symptomatic of a structural 'failure' to dominate the research frontier. As our account has made clear, in backing at least a feasibility study on cooUng, the ICE experiment, the CERN staff and management sought neither external support nor official sanction for their actions. The SPC was informed, as we have seen, and an open meeting was held at the laboratory in November 1976 to discuss physics possibiUties and technical aspects. However, at this stage anyway, the user community and the member states were barely involved. At best they were informed indirectly and in a piecemeal way: they were not asked for their blessing. Scepticism not to say downright hostiHty from some theoreticians, John Ellis in the TH division, and M. Veltman (from the Netherlands) in the SPC in particular, was brushed aside. This was possible because, at least at this stage, costs were relatively low - though everyone knew that they would rise rapidly if cooling was proven feasible. It should also be added that Van Hove was given immediate encouragement to proceed with a pp project by a very senior member of the French physics establishment, P. Lehmann^^. Indeed it is significant that French scientists both at CERN (notably Sadoulet) and without (e.g. Repellin) were quick to become associated with the pp project, and to make an important contribution to its very earliest definition phase in the last quarter of 1976. Above all, though, if Fermilab was immediately starting an R and D project on cooUng in anticipation of launching a pp project, CERN had no time to waste. While the pp project got oif to a flying start at CERN with httle or no opposition, this did not mean that its implementation was guaranteed even if cooling proved feasible. After all the ultimate aim of the scheme was to detect the weak bosons as quickly as possible and some people had other ideas about how to do that which did not involve taking the risks associated with an entirely new technique. In particular there was the possibility of upgrading the ISR in various ways and of using it as a proton source to do pp collisions with the SPS. These possibilities were energetically discussed at a workshop called by CERN to review the ISR physics programme for the period starting around 1980. Almost 60 people attended this two-week meeting which began in Geneva on 4 October 1976. Its major overall conclusion was that proton-proton colliding beam machines could make a valuable contribution to understanding the structure of hadrons and investigating the weak, electromagnetic and strong forces. It emphasized that proton-proton colliding beams were particularly suited to studying particles produced with high transverse momentum and suggested that the ISR continue its current programme in this direction with improved luminosity and more powerful detection equipment. For the period after 1980 the workshop considered a number of major modifications to the machine to gain energy, the aim being mainly to discover the W and the Z. One (the ISR/SPS Bypass) involved simply making provision to coUide protons from one ISR ring with the circulating beam in the SPS. Another (the SCISR) involved replacing the existing ISR magnets with superconducting magnets and either keeping the same ring geometry (energy in each ring inNotes: p. 246

224

The ppbar Project. I. The Collider

creased from 30 to about 100 GeV) or rebuilding the machine in the same tunnel to give a top energy of 120 GeV per beam. A third (the MISR) required moving the ISR magnets to a new tunnel and combining them to give one 60 GeV ring which could either be put into the SPS tunnel or into a specially constructed 60 GeV tunnel tangential to the SPS. In either case the coUision of a 60 GeV beam from the 'ISR' with a 270 GeV SPS beam would give a centre of mass energy of about 255 GeV. The workshop 'strongly urged that these schemes be given serious consideration'. And indeed by the end of January 1977 Design Study Leaders for both the SCISR and the MISR had been chosen^^. Thus even as the first phase of CERN's pp project was undertaken it was clear that it would have to face competition both inhouse at the ISR, whose users were determined to protect the longterm future of 'their' machine, and at Fermilab, where the Doubler threatened to render it redundant.

6.4 1977: ICE cools its first beams and the competition hots up With feasibility studies of cooling agreed at Fermilab and at CERN, and with the construction of the test rings underway at both laboratories, Rubbia felt that it was essential to start thinking about the detector to be used to discover the W and the Z. Time was short, he insisted. If ICE gave the desired results - and he was pretty sure that cooling would be proven feasible 'as early as the beginning of 1978' - one might well be able to observe pp collisions around 1980. It would take as long - two to three years - to construct the experimental equipment as it would to build the antiproton source. Then there was the question of money: the detector was likely to cost as much as the p facility, and its costs had to be included in the estimates of laboratory expenditure on the pp project from 1978 onwards. Finally, there were the changes to be made to the SPS tunnel to accommodate the experiment. On 1 March 1977 Rubbia circulated a letter to about 30 physicists from CERN and its member states, as well as Dave Cline in Wisconsin, inviting them to attend a study week on the detector to be used in conjunction with a pp facility. It was scheduled from 28 March to 2 April. Rubbia explained why he thought it was important to proceed with due haste, and he insisted that those who came should be prepared to 'participate actively' in the work, and make a 'full-time commitment for the duration of the indicated week'. About three dozen people duly attended the gathering, which alternated days on which prepared talks were given (e.g. 'New electronics for p-p detectors', and 'hadron calorimetry') with more informal working days. At the end of the week a short document was prepared for the attention of the CERN management summarising quickly the technical options for a An large solid angle detector for W and Z searches, and discussing how best to do pp physics with a minimum of disruption to the ongoing SPS physics programme. Conveners were identified to continue work in six different areas ('Event simulation', 'Muon identification', etc.), and it was agreed to meet again in July^^.

1977: ICE cools its first beams and the competition hots up

225

In parallel with these developments on the scientific front the CERN management set about 'selling' the pp project to the SPC, the Council and to physicist-users in the member states. And while the majority were in favour of CERN proceeding with the scheme, it should also be said that the management's task was not always an easy one. Indeed, as Adams was to put it, his co-Director-General Leon Van Hove, responsible for research, 'had to battle with the formidable forces of the nuclear particle physics community who were by no means 100% behind the pp project"^^. The criticism and opposition was based on several considerations. Firstly, there was the argument that there was no point in CERN building a pp facility if Fermilab was going to do so anyway. Two members of the SPC, Jentschke (the previous CERN DG) and Veltman (whom we met earlier) felt that such 'dupUcation' was undesirable in a period of economic stringency^^. This argument was given added weight by speculations such as those made by Dave Cline at Rubbia's study week. Cline, who was invited to describe progress at the FNAL, implied that they might be doing useful pp physics very quickly with some device. A test ring for cooling protons was already under construction, and Cline suggested that antiprotons might also be injected into the ring rather quickly. If they were collected for just a few hours a pp luminosity of 10^^ cm"-^ sec"^ in the Main Ring (i.e. at 450 GeV) might be obtainable. This, he said, might be sufiicient for a first scan for the intermediate bosons'*^. In short there was always the danger that a 'quick and dirty' scheme in the US might - again - do the breakthrough physics before CERN did. The main argument used to deflect this objection, as used by Adams, was that the vacuum in the Fermilab Main Ring was far poorer than that in the SPS, and that genuine 'dupUcation' would only arise once the Doubler, with its better vacuum, was built. Rubbia, basing himself on Cline's paper, confirmed the point. The pressure in the Main Ring was then some 7 x 10~^ Torr, while the average pressure in the SPS was already better than 10~^ Torr. The luminosity Ufetimes of the beams at CERN would be correspondingly far greater (about 18 hours for a proton energy of 250 GeV compared to some 150 seconds at Fermilab). Rubbia concluded that 'a dramatic improvement of vacuum [was] needed before FNAL could envisage reaHstic coUiding beam experiments', while 'conditions of the SPS vacuum appear[ed] to be acceptable'^^. Jentschke, unlike Veltman (see later) was not opposed to the construction of the pp facility as such. Rather he was concerned that the German delegation which, along with the British, was trying to push down the levels of the CERN budget, would refuse to fund the project on the grounds that it was already being built elsewhere. To meet the economic objection the CERN management argued that the project could be fitted into existing CERN budgets. 120 MSF had been set aside for SPS improvements from 1977-80. Adams and Van Hove set three priorities for this expenditure. 28 MSF was needed immediately to increase the machine's intensity, which was currently 5 x 10^^ protons/pulse compared to 2 X 10^^ at Fermilab. 18 MSF was required to extend the North experimental area. Finally, 'it was very desirable for CERN to aim rapidly at energies well above the SPS and ISR ranges'. If technically feasible, the use of the SPS as a pp collider was the fastest and Notes: p. 246

226

The ppbar Project. I. The Collider

most cost-effective way of achieving this, opening up a new field of physics at a fraction of the original investment cost of the SPS. 'Rough estimates', said Adams, indicated that the remaining 74 MSF in the SPS improvement budget 'might be sufficient to cover its costs, though the real sum would only be known towards the end of this year when the design study was completed'. The CERN management, in short, were not to be stopped by economic considerations. Determined to compete with Fermilab, they would take as much money as possible from the existing SPS budget, finding the balance needed elsewhere in the programme once the feasibiUty of cooling had been demonstrated^. The SPC may have been willing to accept this argument, but there was still the Council to contend with. The tactic adopted by the management here was to insist that the pp project was not a major new facility which required Council approval. Rather it was to be treated as an 'experiment' like any other in the CERN programme. The decision on whether to proceed with it or not was thus purely an 'internal' affair, a question to be settled by the management in consultation with the SPC and the physicist users in the light of the funds available. The Council was to be informed of the choice of priorities, and could set the annual level of resources for CERN bearing the project in mind. But the adoption of the pp option was not dependent on the Council voting in favour of it^^. As we mentioned earlier, in defending the pp 'experiment' the CERN management also had to contend with various sections of the physics community who felt that it was not the only, or necessarily the most desirable installation for CERN to build. At one extreme there was the line of argument adopted by Veltman in the SPC. The Dutch theoretician was an ardent supporter of a 100/100 GeV e"^e~ machine and was opposed to any other major expense, be it the pp facility, an ep collider or even full exploitation of the ISR into the early 1980s. Veltman was convinced that an energy shortage of dramatic proportions was about to strike western society, that an economic crisis loomed in the 1980s and that, in the Hght of this 'impending disaster' it was essential 'that absolutely no project that may postpone the e"'"e~ machine must be alio wed "^^. Few people went this far. However there was a strong body of opinion which was emphatic that options other than the pp facility in the short term and a large electron-positron collider in the long term should be kept open. Two such options were actively promoted in 1977. Firstly, there was an electron-proton coUider. As we said above, the interest in this alternative had waned in 1976, when it was displaced by the enthusiasm shown for building a large e"^e~ collider. All the same B. Wiik, who was visiting CERN at the time, proposed in December 1976 that design studies continue for a 25-30 GeV electron ring to be installed in the SPS tunnel. Electrons from this ring would be colHded with protons in the main ring. A preliminary investigation was sufficiently encouraging for CERN to set up an interdivisional group to explore the project, significantly labelled CHEEP, in greater detail. Its progress was reported to the SPC in April 1977. The group was convinced that it would be possible to build rather quickly a conventional electron ring to do ep physics with the SPS for less than 200 MSF. An ep luminosity of 10^^ to 10^^ cm"^ sec~^ could be expected with an initial centre-of-mass energy of 200 GeV. Apart from the physics potential of such a device, stressed by Fubini in his contribution to the meeting, ('I believe

7977; ICE cools its first beams and the competition hots up

227

that [...] every effort should be made to provide CERN with such a faciUty'), the ep option had the added advantage that the electron ring could be used as an injector for LEP, to which, said Fubini, it would be complementary 'both from the point of view physics and of engineering'^^. This interest in ep was reinforced by some influential members of the UK physics community. An ECFA study week on a possible CERN ep colUder was organized by the Rutherford laboratory from the 10-14 October 1977. Its aim was to present to a wider audience the conclusions of an ECFA study group which, 'with strong support from the CERN staff, has studied the technical feasibility of the scheme proposed, the detectors needed to exploit the physics and the physics interest of such a facility'^^. Bonaudi, accompanied by Fubini, presented CERN's plans for future machines to the gathering on the first day. The discussion afterwards, as reported by Bonaudi, was 'lively', the tone being set by 'A. Donnachie [who] opened with a strong statement, saying that pp is a gamble and disrupts SPS physics; e+e" is far away in time, expensive, and 'ehtist'; ep is good as a stop-gap and disrupts only mildly the SPS programme'. Not everyone shared this point of view of course but at the end of the day Bonaudi was struck by the 'lack of popularity of pp [...]', primarily because of its interference with the SPS fixed-target programme"^^. The ep machine was not the only alternative canvassed by some British at this meeting. Mike Albrow, who was an active experimentalist at the ISR, insisted that CERN should also consider financing the superconducting version of the machine (the SCISR), which would be suitable, inter alia, for W and Z studies. Two weeks later he addressed a memo to the Directors-General signed along with other ISR physicists Banner (Saclay), Camilleri, Darriulat and Di Leila (all CERN-EP) and Jacob (CERN-TH). Here it was argued that recent research with superconducting magnets in the ISR division had indicated that magnetic fields of 5 Tesla could be achieved, giving an energy of at least 120 GeV per beam with a luminosity of at least several xlO^^ cm"-^ sec~^ in a potential SCISR. This machine, it seemed, could be built in 3.5 to 4 years (from approval to first injection). These conclusions, the memo insisted, 'were nothing short of spectacular. As a result, SCISR should join CHEEP and PbarPSPS as an option for an intermediate project at CERN'. It could be treated as an ISR improvement programme and could be built at a low price (preliminary estimates suggested about 160 MSF). It would have negUgible effects on other CERN programmes, above all that at the SPS which would not be affected at all. And it offered, in the authors' view, the best chance in Europe for actually discovering the Z^. To firm up their estimates Albrow and his colleagues ended by inviting the DGs to convene a study group to explore further the parameters of an SCISR and to authorize without delay the design, development and construction of an SCISR dipole magnet prototype^^. The opposition from an important section of the British users to the pp project caused some embarassment for the management. This was not a user group that they could afford to aUenate. It was large, gifted and advised a government which was doing all it could to push down the level of the CERN budget. It was also a user group which had just been Notes: pp. 246 ff.

228

The ppbar Project. I. The Collider

forced into a more or less total dependence on CERN and was determined that the laboratory should respond to its needs. Britain's CERN contribution was by far the largest item in the overall UK nuclear physics budget, and had been sharply increased by the weakening of sterling againt the Swiss franc. To meet the situation the government had decided to close down the Rutherford accelerator Nimrod in May 1978 and to reduce activities at Daresbury's Nina. As Bonaudi noted, there was consequently 'an extreme concern for, and dependence on CERN by the U.K. users', with a 'particular sensitivity to anything touching the SPS programme, on which they depend[ed] almost entirely'. This boded ill for the pp project, which would require major and ultimately disruptive excavation works in the SPS tunnel^ ^ The Directors-General refused to see either of these proposals as a genuine option to the pp project. They were totally dismissive of the suggestion made by Albrow and his colleagues, being against any scheme which might prolong p - p physics at CERN beyond 1982-3, when Isabelle was scheduled to come onstream at Brookhaven. They told the authors of the memo that they were free to update the CERN report on pp colUding beams 'if you so wish' so as to incorporate the new SCISR parameters. But Adams and Van Hove refused to authorize the construction of a prototype SCISR dipole magnet 'for the moment' 'in view of the clear priority given to the LEP project'^^. The position adopted on the ep collider was more flexible. Both the SPC and the management felt in 1977 that studies on an ep machine should continue for the time being. It was one of a number of useful 'intermediate' projects (cf above) which could be undertaken before the large electron-positron collider was built (or was a possible alternative to a LEP in the case that funding for the bigger collider was not forthcoming). An ep machine might even speed up acceptance of the latter if governments decided to site the new big machine at CERN (since the electron ring could then be used as an injector). Once again though the ep option, like the SCISR, was not seen in these quarters as a rival to pp: that was to be built anyway. Indeed the SPC consistently argued that the pp project 'could be regarded as a large experimental facility manageable within the CERN budget, whereas the ep project would be of the dimensions of a new programme for CERN (about 200 million Swiss francs and about 200 staff)'. A decision on it was thus subject to an entirely different logic. It was to be taken in the Hght of the evolution of the project to build a LEP, recommended to the SPC by ECFA in May 1977 as 'the prime candidate for a major European project for the 1980s'^^. With the pp scheme thus shielded both from the Council and from bids by physicists for a rival 'intermediate' project, it still remained to cushion concerns that it was highly risky and disruptive of the fixed target physics programme. These objections were widespread: they were raised by users at CERN and at Fermilab. The feasibility studies on cooling were, of course, a first step intended to meet the objection that a pp collider was a gamble. The management's hand was further strengthened in this regard by the emergence of an interest in antiprotons as such. Indeed no sooner had it been decided that CERN should seriously consider building a low-energy antiproton ring, than physicists began to think of the research possibilities opened up by their having at their disposal a relatively intense,

1977: ICE cools its first beams and the competition hots up

229

pure (i.e. pion-free), low momentum (1 GeV/c) and low momentum spread (Ap/p « 10~^) beam of antiprotons as provided by the p cooling project. A study group reported its findings in June 1977, the management immediately discussed ways of meeting the technical requirements without disrupting the pp collider project, and a general discussion was held at a workshop on 'Intermediate Energy Physics' held in September 1977 at CERN^^. Physicists at the ISR were also quick to consider the use to which they might put an antiproton beam. A study group set up at the second session of the workshop on 'Future ISR Physics' held at CERN in September 1977 concluded that 'a rich domain of physics could result from the assumed p option added to the ISR and that a rapid realization should be strongly encouraged'^^. In short, even if the attempt to use an antiproton faciUty in conjunction with the SPS to search for the weak bosons backfired, the management could rest assured that other important physics could be done with a successfully cooled low-energy antiproton beam. The risks inherent in the pp collider project were thus sharply reduced and the physics constituency in favour of building a p source was considerably enlarged. The thorny question remained of the disruption of the SPS physics programme caused by the installation of the pp facility. This was not tackled in depth by the management in 1977. There were still too many unknowns - the feasibiUty of cooling, the detailed design of the antiproton source, the kind of detector needed - for meaningful estimates to be made^^. All the same it was essential that Rubbia and his colleagues never lost sight of the issue, designing their detector so as to delay the shutdown of the SPS for as long as possible and to reduce the downtime to a minimum. One way of doing this, as suggested by Adams early in the year, was to proceed stepwise. As he put it to the SPC in February 1977, one could first build the antiproton storage and cooKng rings and have them produce a suitable antiproton beam. Only once that was proven feasible would one undertake the required and disruptive modifications to the SPS tunnel. This approach, the D G continued, had the added advantage that it helped minimise the inherent risks of the project^^. Adams' concern about this issue can be gauged from a skirmish which immeditaely ensued between he and Rubbia over the latter's plans for the pp project at CERN. As we mentioned earlier, on 1 March 1977 Rubbia sent a letter to about 30 scientists asking them to participate with 'full commitment' in a study week starting at the end of the month. Its main aim was to define a general purpose detector 'as soon as possible, since its geometry is determinant in defining the required modification of the SPS tunnel', and since it would take at least three years to build. Adams, who did not receive the letter directly from Rubbia, was incensed. In a sharply worded reply dated 23 March he asked that the study week consider not only equipment which would require major excavations in the SPS tunnel, but also the possibiUties of doing experiments in the long straight sections of the accelerator. The reason for this, he went on, was that the SPS would have a heavy commitment to 400 GeV physics in 1980, 'and to stop that for however many months it will take to excavate an experiment area underground, may prove more difficult than you presently seem to think'. It may be necessary, the D G concluded, to start pp experiments 'in a more modest way and only construct monster equipment later on'^^. Notes: p. 247

230

The ppbar Project. I. The Collider

Adams' request was not unheeded. Certainly the document prepared immediately after the study week 'for the attention of the CERN management' was emphatic that, even if some small angle scattering experiments could be done using the straight sections of the SPS, the bulk of the new discoveries were to be expected at large soUd angles. On the other hand it did seem possible to approach full potential in several phases and so restrict the disruption to the fixed-target programme. To start with one might simply install the heart of the detector - a central chamber, a y-detector, the magnetic core and a hadron calorimeter - in a straight section without making appreciable modifications to the structure. Further stages, beginning with an external muon identifier, could then be successively added, the construction of the final enlarged area requiring a shutdown of 90 days at most. Still unresolved was the problem of how to move equipment into the tunnel in the earlier phases. In any event it seemed that significant physics, including searches for the intermediate bosons, would already be possible at phase (1) and that 'major modifications to the tunnel could be delayed until an appropriate time when the feasibility and the success of the p - p will be conclusively demonstrated'^^. The last phrase could have been Ufted directly from Adams' intervention at the SPC a few weeks before. We should not be misled by this conciliatory tone in a document prepared specifically 'for the CERN management': it was surely intended less as a serious physics proposal than as a means to assuage Adams. As such it should be seen in conjunction with another bitter remark made by the DG in the same letter to Rubbia. Remarking ironically that he appreciated the 'enthusiastic tone' with which Rubbia had invited participants to the study week, the DG immediately went on to say that he had just learnt that the physicist was showing similar enthusiasm for a pp project at Fermilab. 'Riding two horses in the same race demands acrobatic skill', the DG added, 'especially if the horses start comparing notes'. In short there was considerable tension between Adams and Rubbia over the pp project, a tension that burst out into the open on more than one occasion. It was indicative of the pressure on the management to have this project succeed, a pressure heightened by Rubbia's determination to get his way, and by his skilful exploitation of the real or presumed threat of a rival project across the Atlantic. Carlo Rubbia's main aim was to discover the weak intermediate bosons before anyone else using a pp collider. His relationship to the two institutions that could fund the project was essentially instrumental: he would do his physics at the centre which offered him the resources he needed to make the discovery first. In 1976 he had proposed a project to Fermilab and, when CERN decided that it too should embark on a pp scheme, he gladly began to exploit that avenue too. Certainly, it seemed increasingly likely that it would be preferable to do the work at CERN, particularly as 1977 wore on. The management was fully committed to the project, the vacuum in the SPS was far better than in the Fermilab Main Ring, there was a resident expert on cooHng in the person of van der Meer, and resources at Fermilab were stretched by the demands on money and manpower being made by the Doubler. On the other hand, Cline had suggested that, with a suitable detector, one could see the W and Z even at a luminosity of some 10^^ cm~^ sec~\ and there were efforts under way to improve the vacuum in the Main Ring^^. Rubbia ac-

1977: ICE cools its first beams and the competition hots up

231

cordingly kept in close contact with the Fermilab project, notably through Cline, and gladly gave them his invaluable advice. It was understood that if CERN demonstrated the reliabiUty of stochastic cooHng Fermilab would incorporate it into their scheme. Rubbia's right-hand man on the detector side, Bernard Sadoulet, simultaneously explored the design requirements of a charged particle detector to be used with a large solid angle detector at the SPS (or at Fermilab of course). He also explored the possibiUty of assembling and testing large detectors in halls adjacent to the interaction region, before rolling them quickly into place, so as to disrupt the fixed-target programme as little as possible at the Doubler (or at CERN of course)^^ A quick and dirty experiment at Fermilab was not to be totally excluded then. And even if it proved to be impossible - as was increasingly Ukely - there was considerable mileage to be gained by still playing the competitive card, by insinuating to the CERN management, the European physics community and the member states that it was just possible that useful pp physics could be done at Fermilab earlier than at CERN62 Adams of course did not like this. He too wanted Rubbia and his team to discover the W and the Z before anyone else - and as Director General he wanted that discovery to be made at 'his' laboratory. The prestige, indeed the very future of CERN, depended on it. To this end he and Van Hove were prepared to fight to the last ditch wherever it was needed - be that the Council, the SPC or the users community - to push the pp coUider through. And they expected Rubbia and his team to stand by them, to have confidence in them, to respect, when necessary, the constraints under which they were working. The competitive card could surely be played, but the management wanted to control the context and the timing of its use. 'Riding two horses in the same race' - if there really was a race - was a tactic to be used collectively and in consultation, and not to further one's own individual ambitions within the laboratory and against a D G already doing everything he could to protect one's interests.

In parallel with these developments, and consistent with the urgency and priority which CERN attached to the pp project, Petrucci and his team went ahead rapidly with the installation of the ICE. By May 1977 it was hoped to inject protons into the ring in the autumn^^. Ongoing theoretical work and studies at the ISR of momentum cooling using the so-called filter method made stochastic cooUng look more and more promising, and so it was decided to test this technique first and before the January-February 1978 shutdown^^. This programme was held to. A status report by Bonaudi on 1 November indicated that Petrucci's team were 'working hard to inject the first protons in December 1977'. Three weeks later Petrucci himself stated that 'should no major accident occur, proton injection in ICE could start by 5 December'^^. In the event the first systematic ICE run took place from 17 to 22 December 1977. Bonaudi immediately reported 'some very good news on ICE' in a personal memo to Adams handwritten at 18.00 hours on Sunday 18 December. The diagnostic system, based on measuring the so-called Schottky noise. Notes: pp. 247 ff.

232

The ppbar Project. I. The Collider

was working 'beautifully', and one could 'see the Ap distribution of the beam drifting slowly towards low momenta [...]'. Indeed by the end of this first round of restricted tests one had clear evidence for a sharp and rapid (within three minutes) decrease in the momentum spread of a beam in the longitudinal direction using stochastic cooling^^. Thus encouraged, and under pressure to explore quickly and thoroughly the potential of stochastic cooling, the group decided to concentrate its efforts on this technique, though electron cooHng was not ignored altogether. By mid-May 1978 the ICE experiment was effectively completed. It had been designed, built and assembled in ten months, and protons had been injected into the ring before Christmas 1977. It had cost 4.3 MSF - about 30% more than the 3.2 MSF originally authorized due particularly to an underestimation of the costs of diagnostic equipment and the electron cooling system. It had taken 32 man years of staff time and 48 man months of temporary labour^^. It had successfully tested many aspects of the theory and practice of stochastic cooling, including the development of new techniques like the socalled 'filter method' for reducing the momentum spread along the length of the beam. It had proved conclusively that cooling could work in all three beam degrees of freedom, and that the overall Ap could be sharply and quickly reduced using van der Meer's technique^^. Correlatively it illustrated the possibility of a spectacular increase in beam lifetime, as stochastic cooling of beam size and momentum spread, in conjunction with high vacuum (5 X 10"^ torr) in the beam pipe, could practically eliminate beam decay due to Coulomb scattering on the residual gas. Indeed in a paper pubHshed in September 1978 the ICE team reported that antiprotons had been stored in their ring and held there for 85 hours^^. The CERN management's faith in the feasibihty of cooHng, and in the ability of their engineers to demonstrate it quickly and effectively, had been justified. Their relief and excitement, indeed the relief and excitement of all those involved in the pp programme, were manifest. And as the management grappled with a Council increasingly determined to force down the laboratory's operating budget - and a Fermilab whose own cooHng ring seemed to be advancing rapidly - the success of ICE boded well not simply for the technical, but also for the political future of the collider project in 1978^^.

6.5 CERN launches a pp collider at the SPS and Fermilab drops definitively out of the race to search for the W As we have mentioned before, while ICE was being constructed, steps were being taken at CERN to design an appropriate detector and the antiproton source itself. The technical assessment of both was completed during the first six months of 1978. At the end of May the SPS experiments committee, the body formally empowered to advise on physics priorities at that machine, recommended Rubbia's experiment for approval. Two weeks later, on 8 June 1978, the CERN Executive Board officially decided to proceed with a pp project. Confronted with the progress at CERN, the technical limitations of using the Fermilab Main Ring for pp coUisions, and the determination to make the completion of

CERN launches a pp collider at the SPS

233

the Doubler his top priority, in November the FNAL's new director, Leon Lederman decided to withdraw definitively from the 'race' to beat Europe to the discovery of the W and the Z. 6.5.1 THE DECISION TO BUILD THE ANTIPROTON SOURCE In June 1977, not wanting to lose a moment if cooling proved feasible, the CERN management began to think how best to organize the pp project. Two alternatives were discussed. One was to set up a new division for the project, recruiting staff from the rest of the laboratory. The other was simply to divide the project into parts, make use of people in existing divisions, appoint a group leader from each, and have the project managed by a board comprising an overall project leader and the several group leaders. The later option was adopted on the grounds that it was less heavy and because much of the work demanded technical changes to existing machines. The details of the arrangement were firmed up in January 1978, with ICE already a success. Simon van der Meer was appointed project leader, and the PS division was identified as the host division for the project. Other major contributing divisions were the ISR and the SPS. A socalled 'pp steering committee' was established 'to ensure that decisions and work on all p activities [were] consistent and in line with the priorities of CERN'. Chaired by Franco Bonaudi its initial members were S. van der Meer, R. Billinge, B. de Raad, G. Brianti, F. Ferger, C. RubbiaandP. Falk-Vairant. They were soon joined by Executive DG Adams, M. Crowley-Milling and G. Munday^^ Two main modifications to the design of the antiproton source were adopted in the first few months of 1978. First, it was decided to use only stochastic cooUng with a single d.c. ring. As we saw above the preliminary design of the facility, as proposed in June 1977, was based on electron cooling and used two rings. Electron cooling only worked rapidly at very low antiproton energies, energies far below that at which a useful initial antiproton beam could be obtained. An additional ring was thus needed to decelerate the 'highenergy', wide momentum spread antiprotons (3.5 GeV/c) to an energy appropriate for electron cooHng (0.45 GeV/c). Further studies of stochastic cooling at the ISR and on ICE, however, led to the conclusion that this technique would work satisfactorily on 3.5 GeV/c protons, so eliminating the supplementary 'shuttle ring' originally foreseen^^. The second, far more controversial decision, concerned the injection energy of the antiprotons into the SPS. One scheme had the cooled antiprotons of momentum 3.5 GeV/c extracted from the p source and transferred directly to the SPS, where after a number of complex manoeuvres they would be accelerated along with protons to 270 GeV. The other had the cooled antiprotons transferred back to the PS, where they would be accelerated to 26 GeV before injection into the SPS. The former scheme avoided synchronization problems between the PS and the SPS, and was cheaper by 4-8 milUon Swiss francs, mostly required for longer beam transfer Unes. Its great disadvantage was that as many as 600 hours of machine development time would be required on the SPS between June 1978 and June 1980, when the antiproton source was due to be commissioned. This would seriously disrupt the SPS fixed-target programme and hamper the foreseen inNotes: p. 248

234

The ppbar Project. I. The Collider

tensity improvement studies planned before the long shutdown demanded by the conversion of the new accelerator to the colliding beam mode. The 26 GeV option shifted much of this machine development onto the PS, and would not interfere with normal SPS operation. Moreover some of the work could be done while the SPS was undergoing modifications, thereby possibly shortening the timescale of the pp project. The debate on these alternatives, colloquially known as 'the Dutch war', pitted two senior engineers on the pp Steering Committee, de Raad and van der Meer against each other, de Raad favoured injection at 26 GeV. Van der Meer had 'strong reservations about the operational risks of p acceleration in PS', and preferred transferring the antiprotons to the SPS at 3.5 GeV. The deadlock was broken by Adams who, after weighing the pros and cons of both schemes, decided in May 1978 that it was worth spending the extra money on 26 GeV injection^^. The other main preoccupation of the management in 1978 was the cost of the pp project, which was clearly going to be far higher than the original 75 MSF proposed the year before for the 'experiment'. The figure to be publicized descended steadily as the time approached for a formal decision to be taken and a budget allocated. At a meeting of the directorate held on 12 May it was decided to proceed with the scheme on the basis of the ICE results, and that the 'Announced cost of pp should be reasonably low: 124 MSF [...]'^^. Two weeks later the pp Steering Committee resolved that 'the total project cost as presented would be 114.5 MSF [...]'^^. This figure was preserved by the Executive Board when it formally adopted the project on 8 June 1978. It formed the backbone of Adams' estimates laid before the SPC about ten days later. Here the total material cost of the pp facihty was given as 114.5 MSF plus 15.5 MSF (so 130 MSF), the additional expense being for 'experimental infrastructure' and CERN's contribution to the detector. Savings to CERN, said Adams (e.g. on electricity during the long shutdown of the SPS) could reduce this to 110 MSF. On the other hand if a second experimental area was added this would require a further 20-30 MSF^^. It seemed then that the overall cost of the pp facility with two detection regions would be around 150 MSF - a far cry from the 75 MSF put forward before cooling was tested and the final design parameters fixed (see Fig. 6.2). Two factors were built into this revised cost estimate. Firstly, there was the genuine effort to make savings wherever possible. For example at the meeting of the pp Steering Committee on 12 May it was remarked that 'everybody was busy trying to cut costs, simpHfy equipment or borrow existing apparatus' like power suppHes and bending magnets. At the same time there can be little doubt - and the language used in the quotes in the previous paragraph confirms the point - that the CERN managment felt obliged to conceal, to some extent, the real costs of the scheme so as to make them more palatable. To give just one example, the estimate of the cost of commissioning the first experimental area at Long Straight Section 5 (LSS5) decreased from about 34 MSF to some 27 MSF to 23 MSF between April and June^^. It is impossible to say precisely how much of this was due to genuine savings and how much was done for public relations purposes. Suffice it to say that the CERN management did literally everything they could to bring down the figures for the pp project which they presented to the SPC, FC and Council.

CERN launches a pp collider at the SPS

235

6p cCsc.

U '^^^ o /uA-v.//. .,/

Tiwa^

//

rV /n.:T^^;./

?r.Z PC

€-<^

r^^^

11

I:H /V Fig. 6.2 Handwritten notes by Van Hove of the discussion in the Directorate of 12/5/78 (DGR 21298) Notes: pp. 248 ff.

236

The ppbar Project. I. The Collider

Everybody knows that in a complex project of this kind some 'packaging' of cost estimates is quite normal; surely none of those presented with the data took them Uterally. What is more no one was going to challenge them seriously at this stage. There may have still been some scepticism about the chances of the pp project actually succeeding; there was Httle if any opposition^^. An important group of UK physicists had joined Rubbia's team. The proponents of SCISR had accepted defeat and some of them were preparing their own proposal for the pp facility. Finally, a second experimental area was being opened up specifically to widen representation from the member states, so wooing an even broader spectrum of physicists and their governments to the scheme. Granted this favourable climate one may ask why so much time and effort was put into cutting back the costs of the venture. The reason is that, unfortunately for the CERN management, the decision to go-ahead was taken in a very complex financial context. As we mentioned earlier, two governments, Britain and Germany, were trying to force CERN budgets down from 600 MSF in 1978 to 580 MSF in 1979, 570 MSF in 1980 and 560 MSF in 1981. To oppose this the management argued that the only way that this profile could be sustained was by making cuts to the SPS programme and by reducing support to outside users. But the same management was arguing for an ever-expanding and ever-more costly pp facility. By reducing the costs of the latter as much as possible they surely hoped to persuade the Council that the laboratory was facing a genuine crisis. It only remains to say that the tactic failed. At the Council meeting in June 1978, just a couple of weeks after the Executive Board had decided to press ahead with the pp project, the German delegate took the lead in saying that he could not accept that CERN was short of money. It was managing to build the pp facility from funds left over from the 300 GeV programme. And it had deliberately chosen to make cuts in those areas most unpalatable to the member states, a procedure he felt to be biassed. That said, with France having come around to the German view, several other delegates said that they could no longer justify a figure of 590 MSF for CERN in 1979. And Council voted the budget for the next year at 580 MSF^^.

Earlier in this chapter we referred to the tension which existed between Adams and Rubbia. This persisted in 1978. Indeed on the day the Executive Board decided to proceed with the project, 8 June 1978, the Executive DG addressed an offensive poem to the physicist, a poem which Taubes has reproduced and which, he claims, Rubbia kept on the wall in his office. It ran as follows: Clever Simon met a Bagman, Leader of a Team. Said Clever Simon to the Bagman I can cool a beam.

CERN launches a pp collider at the SPS

231

Bagman said to Clever Simon I can use this scheme. By being first and talking faster Bigman I will be^^.

To add insult to injury at one of his regular talks to the CERN staff a month later Adams, having described the pp project, remarked that its 'entrepreneur' was Carlo Rubbia, a 'CERN staff member and well known transatlantic commuter'. This was deemed so offensive that Adams was forced to apologize publicly at the end of August. The word 'entrepreneur', he said, in 'current English industrial jargon means the person who first sees the benefits and possibilities of a scheme and then drives it through to successful conclusion'. Unfortunately, the DG went on, and contrary to his intention, it had been interpreted by some as derogatory. He concluded by stressing Rubbia's key role in the development and implementation of the pp facility^ ^. We have already explored some of the considerations which, in our view, informed this conflict between Adams and Rubbia. If we raise this matter again it is not to sensationaUse conflict but because such exchanges have surely contributed to the popular image of Adams as someone who was never particularly keen on the pp scheme. More precisely it is frequently said that, as constructor of the new and powerful SPS, he was very loath to see anyone tamper with it so soon after it was commissioned. The evidence we have seen demands that this view be nuanced. Certainly the Executive DG wanted to restrict the shutdown of the SPS as much as possible, as indicated, for example, by his preference for 26 GeV injection of the antiprotons against the judgment of van der Meer. Here as always his argument was that one should try to disturb the fixed-target programme as little as possible. Perhaps he was rationaUzing, and simply wanted to protect his machine. But perhaps he was genuinely concerned to protect the users, all the more so as he had to deal with a current of opposition to the project from the UK physics community. Perhaps it was both. All the same it must be said that nowhere in our documents have we seen him hostile to the pp project as such, on the contrary. He may have disUked Rubbia (and he was not alone in that!) and have been threatened by the physicist's ongoing collaboration with CERN's archrival Fermilab. But as far as we can judge Adams never let his personal feelings distract him from the importance which he, as DG, attached to the pp project for CERN and for European high-energy physics in general. 6.5.2 THE CHOICE OF EXPERIMENTS It will be remembered that the first major brainstorming session on the design of the detector to be used at the pp collider was organized by Rubbia as soon as the CERN management agreed to go ahead and test the feasibiUty of cooling. During the remainder of 1977 the future collaboration was gradually put in place and the basic features of the detector were worked out^^. Progress was reported by Rubbia to the SPS experiments committee at an open session on 1 November 1977. As he explained to the SPSC, the Notes: p. 249

238

The ppbar Project. I. The Collider

envisaged huge An detector was 'multipurpose'. It was suited not only to the search for the weak bosons, but also to studies of high transverse momentum (high px) jets, as indicated by results at the ISR (and QCD), and also possibly to the production of free quarks. In discussion the committee thought it might be advisable to equip a second straight section of the SPS with a 'simpler' detector than that proposed by Rubbia and his team, and one specifically dedicated to the search for the W and Z. The chairman called for proposals to this effect, saying that all letters of intent should be submitted by the end of January 1978, i.e. within three months^^. Two proposals had been laid before the SPSC before the deadUne. One, P92, spokesman Rubbia, was over 150 pages in length. It was signed by over 50 scientists from nine institutions (Technische Hochschule Aachen, Annecy LAPP, University of Birmingham, CERN, College de France, Queen Mary College London, University of CaHfornia at Riverside, Rutherford Laboratory, and Saclay), and some visitors, including David CHne from the University of Wisconsin. The other, P93, spokesman Pierre Darriulat, was far shorter, and was signed by 21 scientists from just three institutions (CERN, Saclay and Orsay). It proposed an experiment 'the main purpose of which [was] to detect the production and decay of the W and Z^ bosons at the SPS pp facility'^'^. The SPSC had a first discussion on these proposals at its meeting in February 1978 and, three months later, at the end of May, it recommended Rubbia's proposal P92 for approval by the CERN Research Board. It did not yet commit itself to Darriulat's proposal. In the SPSC's view, P93 was a 'good experiment which should be considered for approval if budgetary conditions were to pemit it'. At the same meeting Van Hove confirmed that the management would welcome new proposals for an experiment in a second area, calling for submission within the next six months^^. When, towards the end of the year, the SPSC had to decide on the experiment which would supplement Rubbia's they had in fact two candidates before them. One was P93. The other was PI 19, 'Proposal to Search for New Particles'. It was signed by over 40 physicists from eight institutions and was masterminded by Sam Ting, who had won the Nobel prize for his discovery of the J/psi particle in 1974 (independently identified by Burt Richter at SLAC). At its meeting on the 13 December 1978 the SPSC opted for P93 bearing in mind 'the relative complexity of the two experiments [Ting's was said to be 'stretching technology to the limit'], the mass resolution likely to be achieved [it would be seriously reduced by electromagnetic forces on the wires in Ting's detector], sensitivity to foreseable background in the W search and ability to deal with unforeseen backgrounds'. Darriulat and his team were thus finally given the green light to proceed with construction, six months after Rubbia's group had got under way^^. Two other important experiments were also duly agreed on. One, proposal PI05, later UA4, was intended to measure the antiproton-proton cross section over a wide energy range up to 540 GeV in the centre of mass. The other, proposal P108, later UA5, used a streamer chamber to observe visually the complex events occurring in the collider, so highlighting particularly interesting new phenomena which could be investigated further with the dedicated detectors^^. In short, not one, but a complex of detectors com-

CERN launches a pp collider at the SPS

239

plementing and supporting each other were to be installed in the SPS tunnel to ensure that the 'elusive' bosons did not sHp through CERN's fingers.

There were a number of reasons why the CERN management favoured a second experiment to search for the W and the Z. For one thing, there was pressure from inside the physics community itself for an additional opportunity to enter this exciting domain. Indeed four of the physicists who signed P93 (Banner, Camilleri, Darriulat and Di Leila) were the very same men whom, just a few months before, had failed to convince Adams and Van Hove of the merits of upgrading the ISR with superconducting magnets - an alternative intermediate project to CHEEP and pp at the SPS, they had said, which 'offers the best chance in Europe for actually discovering the Z^ via its decay to iii^fi~\ Rebuffed by the DGs, they were determined not to be left on the sidelines^^. There was also a strong scientific case to be made for a second experiment. Rubbia's detector was a complex and sophisticated piece of equipment which would be searching for elusive particles in a dense background of 'garbage'. It was a high-risk experiment. An independent check on what his group thought they had seen in a simpler detector would provide invaluable confirmation for their results. To this it should be added that Rubbia had a reputation for rushing into print when others would have waited for more and better statistics^^. The last thing the CERN management wanted was for his team to announce a result claiming a major discovery, only to have to revise their interpretation: the damage to the laboratory's prestige and reputation would be incalculable. Then there was the economic argument, used on more than one occasion by Van Hove: by opening up a second experimental area for 20-30 MSF CERN could make better use of the capital invested in the pp collider project for relatively little extra expenditure. Finally, 'poUtical' considerations also played a role. Van Hove was emphatic that physicists from as many member states as possible should be involved in experimental work at the colUder^^. It was one way to blunt criticisms of the project inside the physics community and, as we explained earUer, to sell it more easily to governments in the member states who were increasingly reluctant to sustain the level of CERN's budgets. 6.5.3 DEVELOPMENTS AT FERMILAB For much of 1978 the debates and decisions at CERN took place against the background of an ever-present fear that Fermilab might beat the laboratory to the discovery of the weak bosons. Of course everyone knew that the low vacuum in the Main Ring would make it very difficult to obtain a clear and unambiguous signal. A luminosity of little more than 10^^ cm"-^ sec~^ and a beam Ufetime of about an hour seemed just too low to do useful pp physics: that would only be guaranteed when the Doubler was operational. Yet, the difficulties notwithstanding, the nagging doubt remained that CERN might be pipped Notes: p. 249

240

The ppbar Project. L The Collider

at the post. It was amplified by a number of new calculations and new developments in the first few months of the year. Firstly, Rubbia was repeatedly reassessing the conditions needed to observe the Ws and steadily reducing the maximum luminosity required for reliable identification. In February 1978 he calculated the conditions needed to observe 20 candidate events with the p source planned by CERN, with the detector described in P92 and with 25% of the running time on the SPS available for pp physics. He concluded that a luminosity of 5.5 X 10^^ cm"^ sec"^ twenty times less than the design luminosity in the CERN source, would probably be sufficient. This was 'well within the expectations for the first running-in year of the project' - but also 'quite close to reaHstic expectations for Fermilab' with the cooling ring then under construction and with lifetimes in the Main Ring of one hour. Rubbia concluded that it was 'very likely' that the US laboratory 'might have some pp colHsions at L = 10^^ at least one year before CERN'. Fermilab's weakness lay on the detector side, but even here it was conceivable that they could design and build something relatively simple rather quickly. CERN clearly had no time to waste, he concluded: the laboratory's 'critical path to the W goes through a rapid realization of machine and the right detector'^ ^ It would, we think, be too simple to dismiss these estimates merely as 'scare tactics' intended to pressure the management, which had still not formally agreed to build the antiproton source, and the SPSC, which had just had a first discussion on proposals P92 and P93 for pp experiments. For Rubbia's arguments were soon confirmed by Roy Billinge, who visited Fermilab at the end of March along with Simon van der Meer. Both engineers saw the progress made with the cooling ring and attended one of the working meetings of the groups building it. The building for housing the ring was complete, all the magnets were made and measured and the first of them installed, and the electron gun, provided by SLAC, was ready for operation. The first runs were scheduled for July. In an internal report written after his visit Billinge remarked that the group was 'clearly pressing ahead very quickly,' and that laboratory director Bob Wilson had confirmed that 'they were utterly committed to cool antiprotons'. Though reassured by Lee Teng at FNAL and Burt Richter at SLAC that useful pp physics waited on the Doubler, Billinge feared that Fermilab would probably have antiprotons in the Main Ring well before CERN, and that they could do a quick and dirty experiment to discover the W. Even if that was unfeasible, he concluded that CERN might only 'have a slight lead, since it is not inconceivable that if funds are available from October, they could complete the energy doubler (at least as a storage ring) by the end of 1980'^^. Billinge's impression that FNAL was moving fast is confirmed by an 'Optimistic Colliding Beam Schedule' produced by Huson, one of those responsible for the project, at the end of April 1978. This schedule foresaw the start of proton cooling in October 1978, the improvement of the vacuum in the Main Ring to better than 5 x 10~^ torr and the injection of cooled antiprotons into that ring by March 1979, and the first test of 250 GeV proton-antiproton coUisions about six months later. If this schedule was even roughly kept to it would give Fermilab a lead of a year or more over CERN^^.

CERN launches a pp collider at the SPS

241

Fermilab's scientists, it should be said, also made no effort to conceal their wish to pick the brains of their colleagues in Geneva. Just before Christmas 1977 David Cline (FNAL) and Hermann Grunder (LBL) invited CERN to send over a dozen scientists and engineers to a workshop to be held in Berkeley at the end of March. The topic was 'Producing High Luminosity High Energy Proton-Antiproton ColUsions', one possible application of which was in the energy doubler^^. Seven experts went from Geneva, including Roy Billinge, Carlo Rubbia and Simon van der Meer. In his opening address Bob Wilson joked that, as regards cooling, 'our colleagues at CERN, whom I regard as working for us, are helping to solve the problems and we'll apply the solutions at Fermilab to their dismay'^^. Those present duly obliged, describing the CERN antiproton source and giving various talks on the theory and practice of cooling. Indeed the conference proceedings pubHshed as an appendix the entire, 135 page CERN 'Design Study of a Proton-Antiproton Colliding Beam Facility', which had only just been completed and circulated as an internal report^^. Rubbia went further than simply sharing everything that CERN knew about cooUng with his scientific colleagues and potential rivals in the US. During the course of the workshop he came up with yet another revolutionary idea for cooling, this time with electrons. Up until then electron cooling had always been thought of as a technique to be used only at very low energies. What Rubbia argued was that in the range of 50 GeV and above the appropriate electron energy for cooling was sufficiently high for an electron beam to self-cool by synchrotron radiation. He suggested that one could capitaUse on this by building a small electron storage ring to produce a very cold electron beam. This could then be synchronized with passing proton or antiproton beams in a straight section coincident with their orbits. Theory suggested that remarkable cooling times, of the order of a few minutes, were achievable. In his written contribution to the proceedings Rubbia considered the application of the scheme to the SPS. The concept was immediately taken up by Fermilab engineer Alessandro Ruggiero, who calculated that fast high-energy cooling using electrons from a small storage ring also seemed feasible in the Main Ring^^. That granted it is hardly surprising that Fermilab hoped to hold a longer workshop in the summer 'to go into more detail' - or that BilUnge 'expressed the view that it was rather doubtful that CERN would agree to send a large contingent a second time'^^. The threat that Fermilab might discover the W before CERN was only really laid to rest when the laboratory's director was changed in the autumn of 1978. Bob Wilson's relationship with the AEC which funded the facility had degenerated steadily since 1976. At that time some of his construction budget remained unused after building the Main Ring and getting it to work reliably. He hoped to funnel this money into the Doubler, but to his dismay the AEC 'preemptively' withdrew the surplus. At the same time, in October 1977, the US Congress authorized $10.5 milUon to begin the construction of Isabelle at Brookhaven. This was followed by an announcement by President Carter early in 1978 that $275 million would be put aside for building the proton-proton coUider at the east coast laboratory. Wilson tendered his resignation as a sign of protest against the lack of support for the development of the Doubler - and to his chagrin it was accepted. In October 1978 Leon Lederman took over the directorship of FNAL^^. One of his first tasks was to call a Notes: p. 250

242

The ppbar Project. I. The Collider

review of collider options at FNAL in which 'the efforts, money, time scales must be reaUstically appraised in the Ught of our heavy commitments in the 400 GeV and doubler construction programs'^^^. The meeting was duly held on 11 November 1978. We have a few notes of its proceedings taken by participants, a few published comments made by Lederman himself 13 years later, and a highly dramatized account of what he calls the 'Armistice Day shootout' by Taubes. Three points emerge clearly from the formal documents. Firstly, that Lederman aimed to have a beam circulating in the Tevatron by July 1981 and a good beam six months later. Secondly, that he wanted the laboratory to keep open a colliding beam option, and wanted to build in what was needed for that purpose. More specifically, it was envisioned to do pp collisions in the Doubler ring at 1 TeV for each beam, and/or pp coUisions in the Main Ring at 150 to 250 GeV against the Doubler at 1 TeV. Finally, it was decided to abandon the antiproton option in the Main Ring 'because the energy makes it less interesting than the doubler pp option and because of poor vacuum and field quality in the main ring'. In short the priority as seen by Lederman was to get the Tevatron up and running before starting coUiding beam physics^^^ Taubes, in his characteristic style, sees this meeting as the turning point in the competition between Fermilab and CERN. Quoting Lederman years after the event, he has the new director say that after the meeting it was clear to him that 'We were going to let CERN win'^^^. Independent evidence suggests that the 'race' such as it was was already over at least the month before. Telegdi, who was desperately trying to convince Van Hove to let him do fixed-target experiments with antiprotons at the SPS wrote on 22 October 1978 that 'FNAL does not constitute a serious competition in this field'. This was fully confirmed, he went on, at a recent meeting of the ICFA (International Committee for Future Accelerators) held at the American laboratory. To give further weight to his argument Telegdi added that he had just seen Rubbia, who agreed fully with his opinion on this matter, and was not unduly perturbed by the possibility that the arrangements for fixed target work might cause an additional six month delay in the commissioning of the antiproton source^^^. In short by the autumn of 1978 it was clear that the CERN pp collider had the field more or less to itself, at least until 1982/3 when first the Tevatron and later (1986) Isabelle was supposed to come on stream across the Atlantic. The absence of direct competition did not mean that CERN slackened its eff'orts to build the pp collider. Indeed the antiproton source was ready almost exactly two years after the project was approved, and it was run in during the long shut down of the SPS which took ten months instead of the anticipated five. At 5 am on 10 July 1981 collisions between protons and antiprotons at a centre of mass energy of 540 GeV were observed for the first time in Rubbia's UAl (Underground Area 1) detector. Excitement ran high as, after ironing out a number of diSiculties 'pp collision events relayed on-line from the streamer chambers into the accelerator control room [were] exploding every second or so on a TV screen like fireworks'. For the month before Christmas 1981 the SPS was devoted entirely to machine development and pp physics. The period ended 'with a beautiful run where beams were kept in coUision for 36 hours, with a luminosity Hfetime near the design

Notes

243

value of 24 hours'. Hundreds and thousands of events were gathered by the experimentaHsts before the machine was shutdown^^"*. CERN was on its way to the Nobel prize, though it would take another year before a sufficient number of candidate events had been accumulated for the W to be announced.

I am grateful to physicists Pierre Darriulat and Maurice Jacob, and historian Lillian Hoddeson for helpful comments on an earlier draft of this chapter.

Notes 1. Typically P. Darriulat, The W and Z Bosons: Chronicle of an Announced Discovery, paper presented at Erice, 1994, and L. Van Hove, The pp Collider: a New Idea and its Itinerary at CERN, one of a number of so-called 'potted histories' by key CERN personalities available in the CERN archive (published in Italian in A. Bertin and A. Vitale, La Luce Pesante - Carlo Rubbia, Cronaca di un Nobel (Bologna: PoUgrafico Editoriale, 1984), pp. 239^6). See also P. Watkins, The Story of the Wand the Z (Cambridge University Press, 1986), chapter 5. 2. G. Taubes, Nobel Dreams. Power, Deceit and the Ultimate Experiment (New York: Random House, 1986). 3. The quote is from the paper cited in note 1. 4. The role which accelerator engineers coming free from one machine had in the early 1960s on shaping the debate at CERN over the next generation of accelerators has been described by Pestre in A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN, Volume //(Amsterdam: North Holland, 1990), chapter 9. 5. For this paragraph see K. Johnsen's paper prepared for the SPC, Long-Term Storage Rings Developments, Annex I to the minutes of the meeting held on 12-13/5/76, document CERN/SPC/376, 19/6/75, and the minutes themselves, CERN/SPC/376/Draft A, 16/6/75. A report specifically dealing with the use of antiprotons in a 400 GeV ISR is K. Htibner, K. Johnsen and G. Kantardijan, The Feasibility of Antiprotons in the ISR, CERN/ISR-LTD/75^5, September 1975 (DGR21298). For a wideranging report see L. Camilleri (ed). The Physics Interest of a 10 TeV PS, 400 GeV x 400 GeV Proton Storage Rings, ande-p Storage Rings, CERN Yellow Report 76-12. 6. Memo J.H. Mulvey to W. Jentschke, L. Van Hove, J.B. Adams, Long-Range Plans for Future Major Facilities at CERN, 13/10/75 (DGE21576). 7. For this paragraph see memos by Mulvey to Johnsen et al (5/1/76), entitled Studies of Future Machines (20/ 1/76), and entitled Study of Future Machines (6/2/76), both in (DGE21576). In fact the physics interests of an e-p facility were described in a report authored by Wiik and others in the summer of 1976, cf. Part C of Camilleri (ed), op. cit. note 5. A design study was produced six months later: R. Billinge et al.. An e-p Facility in the SPS, internal report CERN ISR-ES-GE-GS/76-50, December 1976. 8. Memo Burton Richter to J.H. Mulvey (and others). Future e^e' Machines, 23/1116 (DGE21576). 9. Memo J.H. Mulvey, Study of Future Machines, 6/2/76 (DGE21576). 10. Memo J.H. Mulvey, High Energy e^e~ Study, 7/4/76 (DGE21576). Darriulat's group's report, entitled Physics with Very High Energy e^e~ Colliding Beams, was ready within about six months and pubHshed as CERN Yellow Report 76-18 in November 1976. A design study for a 100 GeV electron-positron storage ring, authored by R, BiUinge and others, was ready by March 1977, and another followed in August (CERN Yellow Report 77-14). In May 1977 the ECFA recommended that an e+e" storage ring of 140-200 GeV c m . energy (LEP) be considered as the prime candidate for a major European project for the 1990s. Notes: p. 250

244

The ppbar

Project.

I. The

Collider

11. In a context of rising costs and, above all, decreased US-USSR tension as exemplified by the ratification of the Salt II Nuclear Disarmament Agreement in 1973, the physics community once again began to suggest that there should be a coordination of machine building on the world scale. Indeed the so-called Helsinki Agreement on Security and Cooperation in Europe stated that 'scientific and technical cooperation constitute[d] an important contribution to the strengthening of security and cooperation [...]', and identified high-energy physics as one possible field for joint ventures. Following on this an International Study Group on Future Accelerators in High-Energy Physics, composed of members from the US, Europe, Japan and the USSR met at Serpukhov from 17-25 May 1976 to draft recommendations for collaborations between two or more regions. In the medium term it was agreed that such regions confer with one another and agree to avoid duplicating facihties. In the longer term, i.e. beyond 10 years, it was suggested that a Very Big Accelerator (10 TeV, fixed target) might be envisioned in which all regions share the cost. In the wake of this meeting the lUPAP set up, in June 1976, an Interregional Committee for Future Accelerators (ICFA) to carry the deliberations further. These debates occurred in parallel to those we are discussing here, but barely impinged on them. For details see, for example. Report of the International Study Group on Future Accelerators and High Energy Physics, Serpukhov, May 17-25, 1976 (circulated as document ECFA/RC/76/6), in file (DGE21576), and statements by Guy Von Dardel to the SPC at its meeting on 15/6/76 (CERN/SPC/393/ Draft, 5/8/76) and on 2 November 1976 (CERN/SPC/399, 26/1/77), brief comments by Ronald R. Rau, Report of Foreign Travel, l/U/l^, attached to a letter from Rau to Adams, 3/11/76 (DGE21561), and Van Hove's Draft Lecture on Future Accelerators for Erice School, 25/8/76 (DGE21576). 12. Dominique Pestre has described these debates in detail in chapter 9 of A. Hermann et al. History ofCERN, Volume II (Amsterdam North Holland, 1990), cf. note 4. 13. See the (tentative) Energy Doubter/Saver Proposal, Fermi National Accelerator Laboratory, June, 1975, in file (DGE21576). For an introduction to the Fermilab machine and his plans for the Doubler see R.R. Wilson, 'The Batavia Accelerator', Scientific American 230 (February 1974), 72-83. For an historical account of the Doubler see L. Hoddeson, 'The First Large-Scale Application of Superconductivity: The Fermilab Energy Doubler 1972-1983', Historical Studies in the Physical and Biological Sciences 18/1 (1987), 25-54. See also L.M. Lederman, 'The Tevatron', Scientific American (March 1991), 48-55. 14. Fermilab Proposal 478, R. Huson, P. Livdahl, R. Stiening, L. Teng, F. Turkot, and J.K. Walker (FNAL), Proposal to Search for Intermediate Boson Production in Proton Proton Collisions at 200 GeV in the Center of Mass, undated (Fermilab archives). This document and all others from this source were kindly provided by the Fermilab history project. 15. Fermilab Proposal 491, C M . Ankenbrandt, T.L. Collins, H.E. Fisk, R.P. Johnson, P. Limon and J. Peoples (FNAL), A.V. Tollestrup and R.L. Walker (California Institute of Technology) and L. Lederman (Columbia University), Clashing Gigantic Synchrotrons, May 1976 (Fermilab archives). 16. For the initial report see S. yan der Meer, CERN Internal report, CERN/ISR-PO 72-31 (1972). The first published paper is by P. Bramham, G. Carron, H.G. Hereward, K. Hiibner, W. Schnell and L. Thorndahl, 'Stochastic Cooling of a Stored Proton Beam', Nuclear Instrum. Methods 125 (1975) 201-2. 17. The key paper summarising the work of the Soviet group is G.I. Budker, N.S. Dikansky, V.I. Kudelainen, I.N. Meshkov, V.V. Parchomchuk, D.V. Pestrikov, A.N. Skrinsky and B.N. Sukhina, 'Experimental Studies of Electron Cooling', Particle Accelerators 1 (1976), 197-211. For a summary see the unsigned article 'Electron Cooling Offers High Luminosity Antiproton Beams', Physics Today, (April 1977), 17, 19 and the CERN Courier, 'Proton-Antiproton Workshop' 18, April 1978, 111-4. 18. The remark was made by Andrew Sessler (LBL) in welcoming participants to the workshop cited in the following note. 19. The paper by Rubbia, Mclntyre and Cline, 'Producing Massive Neutral Intermediate Vector Bosons with Existing Accelerators', which was submitted to Phys. Rev. Letters in March 1976 was never published there. According to Taubes {pp. cit. p. 22) it was rejected because one referee regarded it as 'entirely inappropriate' for the journal - and because it threatened Isabelle. It was later published in H. Faissner, H. Reithler and P. Zerwas (eds.), Proceedings of the International Neutrino Conference Aachen 1976, (Vieweg, 1976), pp. 683-

Notes

20. 21.

22.

23.

24. 25.

26.

27.

28. 29.

30.

31. 32.

33. 34.

245

7. It is also reproduced as Appendix A in Proceedings of the Workshop on Producing High Luminosity High Energy Proton-Antiproton Collisions, March 27-31,1978, Berkeley, CA, which was jointly organized by LBL and Feraiilab, and published as Report LBL-7574, UC-34c, CONF-780345 (1978). It is referred to hereafter as LBL-FNAL Workshop, March 1978. The remark was made by Bob Wilson in his talk 'CoUiding Beams at Fermilab', LBL-FNAL Workshop, March 1978, p. 8. FNAL Proposal 492, D. Cline, P. Mclntyre, D.D. Reeder, C. Rubbia, L. Sulak, M.A. Green, E.M. Rowe, W.S. Tryeciah, and W. Winter (Universities of Harvard and Wisconsin), Proposal to Construct an Antiproton Source for the Fermilab Accelerators, May 1976 (as stated in Proposal 493). FNAL Proposal 493, D. Cline, P. Mclntyre, D.D. Reeder, C. Rubbia and L. Sulak (Universities of Harvard and Wisconsin), Search for New Phenomena Using Very High Energy pp andpp Colliding Beam Devices at Fermilab, (undated, but probably May 1976). The results of the PAC were described by Wilson in his talk 'CoUiding Beams at Fermilab', LBL-FNAL Workshop, March 1978, p. 8.1 would Hke to thank LiUian Hoddeson for additional information on this PAC meeting. Some of this information is from memorandum L. Van Hove to J.B. Adams and others. Developments Concerning pp Colliding Beams, 26/7/76 (DGE 21576). See also document cited in the following note. Research Proposal Submitted to the National Science Foundation, Proposed Amount: $490,000, Proposed Effective Date: January 1, 1977, Proposed Duration: 12 months. Research and Development of Particle Beam Cooling Techniques and a Feasibility Study of Proton-Antiproton Colliding Beam Facility, Principal Investigator R.R. Wilson, dated October 1976 (GP22539). D. Cline, P. Mclntyre, F. Mills and C. Rubbia, Collecting Antiprotons in the Fermilab Booster and Very High Energy Proton-Antiproton Interactions, Report TM-689, 2000.000, appendix II to grant proposal cited in previous note. Progress at Fermilab was described by Bonaudi to the SPC at its meeting on 22-3/2/77, minutes CERN/SPC/403/Draft, and by David CHne in his pp Note 08, 1 May 1977, Possibilities for AntiprotonProton Colliding Beams at Fermilab, a talk given at the CERN pp workshop organized by Rubbia at the end of March 1977 (JBA22633). See also the unsigned article 'Electron CooUng Offers High-Luminosity Antiproton Beams', Physics Today (April 1977), 17, 19. Memorandum L. Van Hove to J.B. Adams and others. Developments Concerning pp Colliding Beams, 26/7/ 76 (DGE21576). The handwritten memo is headed 6/9/76, pp physics discussion in TH Disc. room. Van Hove was informed of this meeting by Fubini, who had been invited by Pope to attend this, the first meeting of a study group on physics possibihties of antiprotons in the SPS, in a memo dated 31/8/76 (DGR21298). This is from his 'potted history' cited in note 1. The fear that CERN would just repeat at its new machine what the US had already done was, he wrote, 'a dilemma which I felt very strongly in 1976 when I took up my functions as research director-general'. The minutes of the SPC meeting on 7 and 8 September 1976 are document CERN/SPC/397 Draft, 14/10/76. The various studies are taken from the reference list in the report authored by Bonaudi and van der Meer and by Pope on Antiprotons in the SPS, CERN/DG-2, 11/1/77 (JBA22684). An example of one of the earliest pp notes (#15) by Rubbia and Sadoulet on an antiproton-proton experimental area, and dated 27/9/ 76, is in (JBA22633). An extensive collection is available in the private papers of David Dallman, who was a physicist in experiment UAl (see next chapter). van der Meer's staff complements are given in his handwritten note. Staff for pp Project Study, 2/11/76 (DGE21576) and his memo Manpower for p-p Study, U/l/ll (JBA22684). Van Hove sent the (draft) Fermilab grant proposal to Adams on 2/11/76, after receiving a copy from a physicist in Chicago (DGR21298). Rubbia's explanatory note, marked 'Confidential' was written three days later. In it he claimed that the $5 million for the feasibiUty study would be contributed equally by the NSF

246

35.

36.

37. 38.

39.

40.

41. 42. 43.

44. 45.

The ppbar

Project.

I. The

Collider

and ERDA, and that R. Huson was the project leader, see memo C. Rubbia, Summary and Timetable of FNAL p Option, 5/11/76 (DGR21298). Antiprotons in the SPS. Part I. Report of the Working Group on the Technical Aspects, by F. Bonaudi and S. van der Meer, Part 11. Report of the Working Group on Physics Possibilities, by B. Pope, CERN/DG-2, 11/ 1/77 (JBA22684). See also Bonaudi's report to the SPC, meeting on 22-3/2/77, CERN/SPC/403,/Draft, 15/4/ 77. This two step scheme, involving both stochastic and electron cooling, was similar to that proposed by Rubbia and his colleagues to Fermilab in May 1976 (Proposal 492), though in the CERN case two rings were envisioned and not just one. And of course Rubbia also played an active part in this preliminary design study for the CERN facility. For this information see document Authorization of Capital Project, and its appendices, dated 31/1/11, attached to the Agenda for the 3rd meeting of the so-called 'Accelerator Club', dated 1/2/77 (Brianti files: Accelerator Club), and the SPC minutes cited in the previous note. The Accelerator Club was an informal forum set up at Adams' suggestion in which the senior staff of accelerator divisions and the Directorate met regularly to discuss possible future developments of the CERN machines. It first met on 8/11/76 and thereafter about once monthly - see memo by J.B. Adams to F. Ferger and others. Accelerator Club, 20/10/ 76 (Brianti files: Accelerator Club). His support is mentioned expHcitly in the memorandum L. Van Hove to J.B. Adams and others. Developments Concerning pp Colliding Beams, 26/7/76 (DGE21576). These projects are described in a summary report on the workshop, CERN/ISRC/76-32 dated 2/11/76 and prepared immediately after the meeting by B.C. Pope, and in a trip report which Rau, a visitor from BNL at the workshop, sent to Adams under a covering letter dated 3/11/76 (both in file DGE21561). The allocation of the MISR and the SCISR to Design Study Leaders is described in a memo from Ferger to Adams dated 24/1/77 (DGE21576). In his report Rau expressed doubts about the interest among physicists in upgrading the ISR. His views should perhaps be treated with some caution though, as he was keen to have Isabelle funded and in an official report might play down the interest in rival pp collider projects which could render it obsolete before it was commissioned. Such lukewarmness, if it existed, was unlikely to discourage the design engineers at this stage anyway, particularly given the positive recommendation from the workshop. More information on the various schemes for upgrading the ISR is provided in Crowley-Milling's chapter in this volume. For this and the preceding paragraph see circular letter from Rubbia dated 1/3/77 (DGE21576), undated information circular from Rubbia to all participants p-p Study Week, CERN, March 28th-April 2nd, 1977 (DGR21298), and undated, unsigned report on the results of the study week. Conclusions of the Study on Detectors (DGE21576). These 'conclusions' will be discussed again later. Handwritten, draft letter Adams to 'Brian' (Southworth), commenting an article on the pp project for the special edition of CERN Courier devoted to the discovery of the W and the Z (Vol. 23, No. 9, November 1983) (JBA22684). See minutes of the SPC meeting held on 22-3/2/77, CERN/SPC/403 Draft, 15/4/77, and a Discussion Note on Future High Energy Machines, by M. Veltman, undated but probably around spring 1977. D. Cline, Possibilities for Antiproton-Proton Colliding Beams at Fermilab, CERN pp Note 08, 1/5/77 (talk given at Rubbia's pp workshop held at the end of March 1977). Adams' reply to Jentschke is in the minutes of the SPC held on 22-3/2/77 (cf note 35). See also his exchange with Salvini at the meeting of the SPC on 26-7/4/77, minutes CERN/SPC/405/Draft, 9/6/77. Rubbia's calculations are in a note marked confidential and entitled Comparing the CERN and FNAL Designs for pp Colliders, 15/6/77 (DGE21576). This information is from the minutes of the SPC cited in the previous note. 'One of the most important steps' in the evolution of the project, wrote Adams to Southworth, 'was to convince the Council that the pp project was only an experiment and therefore did not need Council approval', undated draft letter, written in response to an article for the CERN Courier of November 1983 (JBA22684).

Notes

lAl

46. See his memo Discussion Note on Future High Energy Machines, undated, but around spring 1977 (DGE21576). 47. This paragraph is based on the minutes of the SPC held on 26-7/4/77, CERN/SPC/405/Draft, 9/6/77. 48. For a report on the ECFA study week see Wiik's report to the SPC at its meeting on 26/10/77, CERN/SPC/ 415/Draft, 13/2/77. 49. Memorandum from F. Bonaudi to the Directors-General and the members of the directorate. Report on Meeting of U.K. Users at RHEL, 10 October 1977, lS/lO/11 (DGE21576). 50. Memorandum to Adams and Van Hove from M. Albrow and others. The SCISR Project: Construction of a Dipole Prototype and Setting up of a Study Group, lAllOjll (DGE21576). The design studies are reported in J.P. Gourber, Superconducting Conversion ofthelSR (SCISR), ISR WORKSHOP/2-4,19/9/77 (DGE21561), memo Gourber to Bonaudi, SCISR Study, ECFA/Secr./77/56, 18/10/77 (DGE21576), and Bonaudi's report to the ISR workshop held at CERN from 14-21 September, Special Session on New Machine Developments and Cooling, ISR WORKSHOP/2-12, November 1977 (JBA22635). In summarising this workshop in verse Maurice Jacob made much of the advantages of the SCISR (colloquially referred to as Caesar) as not interfering with the SPS programme: 'C'est certes au SPS que Ton confie la tache de lutter de vitesse avec le Tevatron/L'avantage de SCISR, etudie sans relache est d'eviter I'arret du supersyncrotron'. In a private communication Jacob insists that the proponents of the SCISR 'did not push anything against pp in the SPS' and that, obviously, at an ISR workshop 'some lip service to SCISR had to be paid'. The enthusiastic tone of the memorandum of 24/10, which seems to have been taken rather seriously by Adams and Van Hove, suggests that others saw the matter differently. 51. See Bonaudi's report on the meeting with UK users just cited. 52. Memorandum J.B. Adams and L. Van Hove to Albrow and others, Your memorandum of 24 October, 1977 concerning SCISR, lllUIll (DGE21576). 53. The first quotation is from the minutes of the SPC held on 26-7/4/11, CERN/SPC/405/Draft, 9/6/77. Adams' idea that an ep collider may actually facihtate the acceptance of LEP if that was built at CERN, and his general interest in an ep machine, is clear from these minutes as well as his memo to Bonaudi, Accelerator Studies, 21/1/11 (DGE21576), and his report to the SPC, Design Studies at CERN on New Particle Accelerators and Intersecting Beam Machines, CERN/SPC/410, 25/8/77, in draft as a memo to Van Hove and others. Studies at CERN on e+e" Machines ande-p Machines - 1st Draft. Paper for the next SPC meeting, 13/ 7/77 (DGE21576). The ECFA recommendation is document ECFA/77/21, attached as Annex I to CERN/ SPC/407/Draft, 12/8/77. 54. For this development, which eventually became the highly productive LEAR project, see e.g. contributions by Astbury and Soergel at the SPC meetings of the 22-3/2/77 and the 26-7/4/77 respectively (minutes CERN/SPC/403/Draft, 15/4/77 and CERN/SPC/405/Draft, 9/6/77), U. Gastaldi, A Possible New Experimental Approach to the Study ofthepp System at Low Energies, CERN pp Note 13, 10/10/77, which is the text of a lecture he had given at Erice in April that year, memo E. Lohrmann to F. Bonaudi, Possible Experiments with Antiprotons, 13/6/77, and Bonaudi's Notes on a Meeting on Low-energy Antiproton Experiments, 18 August 1977, 24/8/77, both in (JBA22684). 55. The report of the antiproton study group is in Maurice Jacob's summary of the findings at the workshop on future ISR physics which was held from 14-21 September at CERN. They are in report CERN/ISRC/77-20, ISR WORKSHOP/2-5, 26/9/77, in file (DGE21561). 56. It was raised by Adams at the SPC in February (CERN/SPC/403/Draft, 15/4/77) and handled more extensively at the SPC on 26/10/77, minutes CERN/SPC/415/Draft, 13/2/78, where Adams said that 'a firm estimate of the SPS downtime needed to install the pp facility would not be available before next year [i.e. 1978]'. 57. Adams' argument is in the minutes of the meeting, CERN/SPC/403/Draft, 15/4/77. 58. Letter Adams to Rubbia, 23/3/77 (DGE21576). 59. For this paragraph see the report Conclusions... cited in note 39.

248

The ppbar Project. I. The Collider

60. For a progress report on the situation at Fermilab towards the end of 1977 see the minutes of the SPC held on 26/10/77, CERN/SPC/415/Draft, 13/2/78. 61. B. Sadoulet, Comments on Charged Particle Detectors for thepp Large Solid Angle Detector, pp Note 16,15/ 6/77, and Radiation Problems with Assembly Halls Adjacent to Experimental Areas {Doubter Collider case), pp Note 28, 15/8/77, both in (JBA22633). 62. Taubes claims that when the Fermilab PAC, in June 1976, put all collider projects temporarily on the backbumer, Rubbia decided to concentrate 'almost exclusively on CERN. He was motivated by revenge as much as anything: the desire to prove to the American physics community, specifically to Wilson, that they had missed a chance of a Hfetime' (Taubes, op. cit., p. 24.) If this is so, it suggests that Rubbia's subsequent arguments that Fermilab might proceed with a collider were purely tactical, and intended only to put maximum pressure on the CERN management. We doubt this interpretation, as many other reliable sources (e.g. Billinge) remained convinced until well into 1978 that Fermilab might do useful pp physics before CERN. In any event, it is most unlikely that, with the technology still unsettled and the physics communities on both sides of the Atlantic not at all convinced of the idea, Rubbia would have decided already in summer 1976 to concentrate 'almost exclusively' on CERN. 63. See ICE Progress Report, 1/6/77, in (GP [= Gunther Plass] 22539). 64. A report on progress and a graph showing the results of stochastic cooling tests on the ISR, are to found in Bonaudi's presentation to the second session of the workshop on future ISR physics, made in the special session on new machine developments and cooling. Report ISR WORKSHOP/2-12, November 1977 (JBA22635). 65. For these quotations see, respectively, Bonaudi's memo to the DGs and the Directorate, Progress on ICE Experiment, 1/11/77, and Petrucci's memo to Picasso, 23/11/77, both in (JBA22635). 66. The handwritten memo, to 'John' and dated 'Sunday. 18.00 hours' is in (JBA22635). The report on the First ICE Run (from 17 to 22 December, 1977), dated 13/1/78, is in (DGE21585). 67. Data from memo, Petrucci to Gabathuler, Material Cost, Staff and Labour of the ICE project, 18/5/78 in (DGE21585). 68. For a survey of the results of ICE see van der Meer's report to the SPC meeting on 20/6/78, in CERN/SPC/ 423/Draft, 25/8/78. 69. M. Bregman et al., 'Measurement of Antiproton Lifetime using the ICE Storage Ring', Physics Letters 78B (No. 1), 11 September 1978, 174^5. 70. For congratulatory messages to Petrucci and the ICE team see memos to them from Bonaudi (21/12/77) in (DGR21298) and from Van Hove and Adams (23/12/77), in (DGE21576). See also memo Bonaudi to Wikberg, 15/12/77 (DGR21298). 71. The relevant documents are memo Adams to Bonaudi et al.. Organization ofthepp Project, 29/6/77, memo Ferger to Adams in reply, S/7/71, memo Ferger to Adams concerning the contribution of the ISR division to the pp project and to ICE, 28/9/77, memo van der Meer to Bonaudi, Manpower Estimates for pp Group, 27/ 9/7, all in (DGE21576), and memo Munday to Barbalat et al.. Organization of the Project for the Cooled Anti-proton Source, DIR/PS-Memo 78-7, 12/1/78 (DGE21585). The initial composition of the pp project steering committee is described in a memo from Bonaudi to the DGs and the members of the Directorate dated 12/1/78 (DG21585). 72. The details are in Preliminary Description ofthep-p Facility, report SPS/DI/PP/Int. Note/77/9, l>(iieill, and Design Study of a Proton-Antiproton Colliding Beam Facility, report CERN/PS/AA 78-3, 211 \ 11%, both in (JBA22633). 73. See the minutes of the 3rd and 4th meetings of the p Project Steering Committee, held on the 14/4/78 and the 12/5/78, documents PS/AA/Min 78-4, 24/4/78 and PS/AA/Min 78-6, 17/5/78. Adams' paper weighing the alternatives is Choice of Injection Energy for pp in SPS, 25/5/78. All three are in (DGE21585). He announced and defended his decision to the p^ Steering Committee at its 6th meeting held on 26 May, minutes PS/AA/ Min 78-9, 1/6/78 (DGE21585). The Executive DG was heavily influenced by Crowley-Milling's estimates of

Notes

74. 75. 76.

77.

78. 79. 80. 81. 82. 83. 84.

85. 86.

87. 88. 89.

90.

249

the time needed for machine development on the SPS, as described to the SPSC: The Impact of the pp Proposal on the SPS Experimental Programme, CERN/SPSC/78-67, 19/5/78. See the handwritten (by van Hove) notes taken during the directorate meeting held on 12/5/78), in file (DGR21298), and reproduced in Fig. 6.2. See minutes of the 6th meeting held on 26/5/78, PS/AA/Min 78-9, 1/6/78 (DG21585). These figures are from Bonaudi's memo Project 'Antiprotonsfor the SPS\ 31/5/78 (JBA22633), which were taken over by Adams in his report to the SPC on 20/6/78, minutes CERN/SPC/423/Draft, 25/8/78. Van Move's tinkering with the costs is clear in his memo to Adams and others First Draft for Oral presentation of pp Project at the Meetings of SPC, FC and Council, 30/5/78 (DGR21298). The first two figures are from handwritten tables (probably by Billinge) dated 10/4/78 and then 27/4/78, with the costs of Experimental Area Equipment removed for ease of comparison. The final figure was that given by Adams to the SPC. For an idea of the reduction in the cost estimate of the antiproton accumulator see memo PS/AA/RB/78-6, 1/6/76 in the files deposited by Plass (GP22539). The formulation is Van Move's who writes in his 'potted history' (cf note 1): '...there was practically no opposition, although still much scepticism, when we took the go-ahead decision in mid-1978'. See the minutes of the 61st Council session held on 22-23/6/78, CERN/1301/ Draft, 26/10/78. See also the meeting of the SPC just before (20/6/78), CERN/SPC/423/Draft, 25/8/78. Memo Adams to Rubbia and van der Meer, Approval of pp Facility, 8/6/78 (DGE21585). Adams' talk to the CERN staff was on 6/7/78 and was published along with the CERN Bulletin on 7/8/78 (see DGE21525). Mis apology or 'Corrigendum' dated 24/8/78 is in the same file. This is described in more detail in the following chapter. See the minutes of the SPSC of the 1-2/11/77, CERN/SPSC/77-106, 3/11/77. A. Astbury et al., A 4n Solid Angle Detector for the SPS Used as a Proton-Antiproton Collider at Centre of Mass Energy of 540 GeV, CERN/SPSC78-06, SPSC/P92, 30/1/78; M. Banner et al.. Proposal to Study Antiproton-Proton Interactions at 540 GeV CM Energy, CERN/SPSC78-8, SPSC/P93, 31/1/78. The minutes are respectively CERN/SPSC/78-27, SPSC 52, 22/2/78 and CERN/ SPSC78-75, SPSC 55, 6/6/ 78. The proposals are M. Battiston et al.. The Measurement of Elastic Scattering and of the Total Cross Section at the CERN pp Collider, SPSC/P114, 6/10/78 (later UA4) and M.G. Albrow et al.. An Investigation of Proton-Antiproton Events at 540 GeV CM Energy with a Streamer Chamber Detection System, SPSC/P108/S, 29/5/78 (later UA5). See minutes of the SPSC held on 13/12/78, CERN/SPSC/78-154, SPSC 60, 13/12/78. The material in square brackets is from Taubes, op. cit., p. 58. The quotation is from the memo cited in note 50 from Albrow, Banner, Camilleri, Darriulat, Di Leila and Jacob to Adams and Van Move, The SCISR Project..., 24/10/11 (DGE21576). Taubes quotes Van Move as saying: 'Rubbia had done good experiments. None were very good. And he left them very quickly when they were not giving the beautiful things that he had expected when he started. It was, of course, a very important fact for us to remember, that you could not rely totally on Rubbia's critical judgement, nor on his own sense of continuity' (op. cit., p. 41). Sadoulet was sceptical to the point of cynicism: speaking about Rubbia he reportedly said 'Mis numbers are what they are. They are usually wrong — but if they suit his purpose nothing is wrong', quoted in Taubes, op. cit. p. 6. As the Research DG put it to the SPSC in May 1978, 'The selection of experiments will take into account the desirability to have one or more relatively simple experiments able to provide physics results rapidly, as well as the requirement that as many Member-State Institutions as possible should be given a chance to participate in pp colliding beam physics at the SPS', minutes of the SPSC held on 30-31/5/78, CERN/SPSC7875, SPSC 55, 6/6/78. See also his personal notes taken at the meeting of directorate a few weeks before on 12/ 5/78 (DGR21298). Taubes (o/?. cit. p. 59) quotes Ting as insisting that these considerations, and not scientific and technical arguments, were probably decisive in the rejection of PI 19. None of the physicists I have spoken to about this choice agree with him.

250

The ppbar Project.

I. The

Collider

91. Letter Rubbia to Van Hove, 28/3/78 (DGR21298). 92. This information is from the 'personal notes' BiUinge made after his visit to the USA from the 21/3 to 1/4/78. He sent a copy to Adams, Bonaudi, Munday and van der Meer suggesting that they were not suitable for distribution. A copy is in (JBA22684). See also the article by Brian Southworth for the CERN Courier entitled Troton-Antiproton Workshop', (Vol. 4, April 1978, pp. 111-4) which clearly owes much to BiUinge. A draft of this report dated 9/4/78 is in (DGE21585). 93. Memo F.R. Huson, Optimistic Colliding Beam Schedule, 4/26/78 (Fermilab archives). 94. The letter of invitation on LBL notepaper is dated ll/n/ll (DGE21585). 95. The remark is from Billinge's trip report cited in note 92. It was repeated in the article in the CERN Courier devoted to the workshop (cf. note 92). The proceedings of the conference were cited earlier but will be repeated here for convenience: Proceedings of the Workshop on Producing High Luminosity High Energy Proton-Antiproton Collisions, March 27-31, 1978, Berkeley, CA, jointly organized by LBL and Fermilab, and published as Report LBL-7574, UC-34c, CONF-780345 (1978). It is referred to in this text as LBLFNAL Workshop, March 1978. 96. We refer to report CERN/PS/AA 78-3, dated 27/1/78. 97. The relevant articles are C. Rubbia, 'Relativistic Electron CooUng for High Luminosity Proton-Antiproton Colliding Beams at Very High Energies', LBL-FNAL Workshop, March 1978, pp. 98-101, and A. Ruggiero, 'High-Energy Electron Cooling', ibid., pp. 166-70. Ruggiero's paper was based on Rubbia's contribution, was written after the workshop, and was included by Cline for completeness. The technique is also described in the CERN Courier's account of the workshop published in April 1978. 98. From Billinge's trip report cited in note 92. 99. This material from Taubes, op. cit., pp. 35-6 and Wilson's opening speech at the FNAL-BNL Workshop, March 1978. 100. The aims and programme for the meeting are in letter Lederman to 'Ryuji', 26/10/78 (Fermilab archives). 101. The documents are B.C. Brown's notes. Discussion on Colliding Beam Options, C. Ankenbrandt's Colliding Beam Facility Meeting Notes, and R.P. Johnson's Notes from November 11th Colliding Beam Discussions. Particularly useful is a paper drafted five days later by S. Ecklund, Summary of Colliding Beam Plans, 16/11/ 78, which specifically states that pp in the Main Ring had been abandoned (Fermilab archives) and describes the envisioned options. 102. Taubes, op. cit., p. 37. 103. Letter Telegdi to Van Hove, 22/10/IS. See also memorandum Telegdi and Strolin to Van Hove, Parasitic Exploitation of the pp facility for Fixed Target Experiments, 12/9/78, both in (DGR21298). 104. See report by L. Evans, J. Gareyte, W. Scandale and L. Vos, Commissioning of the CERN SPS ProtonAntiproton Collider, report CERN/SPS/82-9 (DI-MST), June 1982 (JBA22636).

CHAPTER 7

The ppbar Project. 11. The Organization of Experimental Work John KRIGE

Contents 7.1 Introduction 7.2 How are collaborations formed and how international are they? 7.3 How are collaborations organized internally? 7.4 How is credit allocated in large teams? 7.5 Is teamwork antithetical to individual autonomy and creativity? Notes

251

252 255 260 265 267 272

*What will never happen again is what happened to me once when I was a graduate student. [...] My thesis supervisor rang me up one day and said, 'Hey I have just had a great idea and we could do it by slightly modifying our experiment. We just have to sneak in a few extra hours beamtime*. And we did an experiment. And the next week we repeated it. [...] I have never done an experiment Uke that in high-energy physics, where you just on the spur of the moment did something, a Httle bit of bricolage, a little bit of playing around, got a significant measurement, went away, analyzed it for two days, published it. We're a long way from that'. UAl physicist who did his PhD on a small synchrotron in the mid-1960s.

7.1 Introduction In the previous chapter we described the steps taken at CERN to launch a pp colUder project. As we intimated there, this project had two dimensions. There was the research and development required to build an antiproton source to be used in conjunction with SPS protons. And there was the design and construction of detectors appropriate for studying collision processes at 540 GeV in the 'dirty' proton-antiproton environment. These detectors had to satisfy a number of constraints. They had to be able to identify the W and the Z in the first instance, and at least one of them had to be 'multipurpose'. While the Standard Model predicted the existence and the upper limits of the masses of the bosons, who could be sure it was right? And how could one justify such a major investment of human and material resources for a single, risky experiment? There was 'undreamt of physics to be done with the coUider, and a detector had to be built to do it. These detectors also had to be built fast. They had to be ready as soon as protonantiproton collisions of a useful luminosity could be obtained in the beam tubes, i.e. in about three years. The proponents of the project were determined to be the first to identify these new particles; in particular they were determined to beat their arch rivals at Fermilab, across the Atlantic, to the discovery. Thirdly, the construction, installation and use of the detectors had to disturb the fixed target programme at the SPS as Httle as possible. Many physicists were already disappointed and frustrated by the late arrival (compared to Fermilab) of a fixed target machine in the 300 GeV range at CERN (see Chapter 3 by Pestre). They would bitterly resent it if their plans were immediately disrupted by a handful of their colleagues, and a CERN management, who were determined to convert the SPS into a collider, and some of them would not hesitate to do what they could through the SPC and the Council to block such a project if they felt that its protagonists were riding roughshod over their needs. 252

Introduction

253

Finally and related to this, the structure of any collaboration set up to design, build and operate these detectors would have to be sensitive to the 'political' constraints imposed in a supranational organization like CERN. To retain the support of a European user community increasingly determined to be integrated into CERN (see chapter 5) and member states' governments determinated to hold down expenditure (see chapter 6), the team had to include representatives of institutions from 'as many member states as possible' (Van Hove), subject of course to technical need and scientific competence. In this chapter we shall discuss the building and internal organization of the multiinstitutional, multinational teams that were set up to search for the W and Z. Our approach is not simply descriptive - a classical and quite adequate account at that level has already been written ^ Rather it is organized around a set of questions of interest to historians and sociologists who study institutional aspects of large scientific projects. In line with the quotation at the head of this chapter, it takes off from the position that experimental work in high-energy physics has undergone a major transformation since the 1960s, particularly with the expansion and the domination of the workplace by the electronic mode of detection. If before the individual physicist could perform an experiment on the spur of the moment with only a minimum of infrastructural support, now it demands the collaboration of a large number of people with a variety of skills (experimental physicists, applied physicists, electronics engineers, computer scientists, etc.) who can spend years rather than weeks or months building and testing a detector, itself able to be adapted to a whole variety of experiments. The individual scientist working alone to test a new idea with equipment he or she knows thoroughly (and may have helped build in the local workshop) has been replaced by a multidiscipUnary team with an agreed division of labour, which plans its work using classical managerial techniques, which negotiates important contracts with industry, and which builds a piece of equipment of which each person is specialized in only a part, and which no one understands in detail in its entirety. MultidiscipUnary teamwork in 'basic' research is of course not peculiar in time or place to high-energy physics during the last two or three decades. It was central to the Manhattan and radar projects during the last war. It was also commonplace in industrial laboratories (the development of the transistor, research into petrochemicals, etc.) long before it became entrenched in national or international centres Uke Brookhaven or CERN. What is unusual about high-energy physics is the way this transformation of the workplace in the laboratory has been lived and conceptualized by the participants themselves and some of those who have studied them - Swatez in the early 1960s, GaUson some two decades later, and the American hep community itself which, in 1988, expressed anxiety, through a HEPAP subpanel, about the emerging 'modes of experimental research' in the field^. While it is difficult to generalize from this scant material, one image that emerges, and which is tenacious partly because it reinforces a number of deeply-entrenched distinctions among physicists (basic/applied research, university/industrial laboratory), is of the steady industrialization of the experimental workplace in high-energy physics. It is suggested that multilayered managerial structures have been imposed, that hierarchical relationships have Notes: p. 272

254

The ppbar Project. II. The Organization of Experimental Work

replaced free exchanges between equals, that bureaucracy is rampant, and that decisionmaking processes have become increasingly formalised. From the point of view of the individual physicist, work has become boring and repetitive, with little scope for creativity and autonomy. In short, 'basic' research in experimental high-energy physics has allegedly now adopted the work patterns of applied research. The free-wheeling, creative atmosphere of the university laboratory has been supplanted by the constricting procedures and regimentation of the large corporation. This picture is undoubtedly symptomatic of important changes in the nature of experimental work. Yet it must be handled with care. For one thing, it is partly the result of studies which have focussed on the work done in Luis Alvarez's group in Berkeley in the early 1960s^. Here an assembly-line approach was indeed adopted to facilitate the processing of hundreds of thousands of photographs taken on the 1.8 m hydrogen bubble chamber. As such the studies are, to some extent, specific to a certain type of detector work with electronic detectors left far more scope for individual initiative - , specific to a certain laboratory - there is no evidence that European bubble chamber physicists went to the extremes adopted at the LBL in the early 1960s, if only because they lacked the technology to do so - , and specific to a certain period of time - in the late 1960s new technologies were invented which considerably reduced the drudgery in the analysis of bubble chamber film. Generalizing the Berkeley situation to the field as a whole is thus particularly hazardous in this case. A second reason for caution is that the image is laden with nostalgia, with a yearning for a romanticised past, for a golden age^. It emerges particularly forcibly in the sayings and writings of people like Don Glaser, who won the Nobel prize for inventing the bubble chamber, of Luis Alvarez, who won the prize for developing and exploiting the technique, and of Robert Wilson, the founder and first director of Fermilab. Glaser left the field rather than work in what he called (in an interview made in 1983) 'the factory environment of big machines'^. Alvarez, speaking in 1967, 'began to despair at an industrialized nuclear physics that had become, in his words, 'just a little dull"^. Wilson has described, with masterful ambiguity, his 'fight against team research'^. These people, however, are hardly representative: all three were highly individualistic and creative people. Their remarks and attitudes, while certainly reflecting and sustaining a certain ethos in the physics community, are not necessarily a reliable guide to the actual state of affairs. Nor should they be taken as indicative of what the average competent physicist feels about his or her work situation. My main aim in this chapter is to lay the foundations for a better understanding of multi-institutional, multinational collaborations in high-energy physics^. To this end I shall present the findings deriving from archival research and interviews with physicists who worked in two such collaborations set up to exploit the pp collider which we described in the previous chapter^: U A l , whose spokesman was Carlo Rubbia, and, to a lesser extent, UA2, the 'backup' experiment whose spokesman was Pierre Darriulat^^. These collaborations comprised respectively about 100 and 50 scientists around the time when they began taking data (1981). These are analyzed with reference to a number of

How are collaborations formed and how international are they? 'classical' sociological questions - how are such collaborations formed and how international are they? how are they organized? how is credit attributed to individual researchers? is there scope for individual autonomy and creativity within them? My central finding is that the experimental workplace in high-energy physics is far less structured, the atmosphere far more informal, and personal satisfaction far more widespread, than the prevailing views would lead one to believe. This does not mean that the structure of such collaborations is not similar, in some respects, to that which one can find in some industrial laboratories. But only that it differs strongly from some deeply-entrenched preconceptions about the organization of teamwork which have tended to dominate the reflections of physicists and of those who have studied them up until now. 7.2 How are collaborations formed and how international are they? Table 7.1 gives a breakdown by country of the membership of the two main collaborations we are studying here. It has two striking features. Firstly, that about 25% of the participating physicists are CERN staff" or CERN-paid. Secondly, that the bulk of the remaining participating scientists are from one or more of four European countries (France, (Federal Republic of) Germany, Italy and the United Kingdom). Smaller European states, and states which are not members of CERN, are not heavily represented. One obviously cannot generalise from the data in Table 7.1. But they cohere with our previous conclusion, based on a more copious sample, that institutions in the 'big four' European countries, along with scientists based at CERN itself, are the major users of CERN's high-energy faciUties^^ CERN may be a European, even an international laboratory. But the collaborations that it hosts 'mirror the uneveness in the distribution of wealth, power, and resources among nations - they do not, and doubtless cannot redress it'^^. To understand why this should be so, it is illuminating to describe how a major collaboration like UAl was set up in the first place. As we pointed out in the previous chapter, in September 1976 CERN Director-General Leon Van Hove, in consultation with Carlo Rubbia and other physicists and engineers, became convinced that the laboratory should launch a pp project. By January 1977 he and his co-DG, John Adams, had given the go-ahead to build a ring to test the feasibility of both stochastic and electron cooling of antiproton beams (the ICE experiment). Soon thereafter Rubbia invited about 30 physicists from CERN and its member states, as well as Cline from Wisconsin, to a study week to be held at CERN at the end of March. Its aim was to define the characteristics of a multipurpose detector which could detect W and Z candidate events in 'dirty' high-energy proton-antiproton coUisions. Full commitment was demanded from the three dozen or so people who attended the meeting. At the end of the week which lasted from 28 March to 2 April, a short document was prepared for Adams and Van Hove outlining the various technical options for a large An solid angle detector for weak boson searches. Ways of building and installing it without disrupting the ongoing fixed target programme at the SPS were also mentioned. Conveners were selected to Notes: pp. 272 ff.

255

256

The ppbar Project. II. The Organization of Experimental

Work

Table 7.1 The distribution by country, in 1979/80, of the institutes and scientists who participated in experiments UAl and UA2 at CERN

Country

UAl Institutes'^

Scientists^

France Italy Germany UKingdom USA Austria

CERN^ 3 1 1 3 1 1

26 27 8 8 22 3 6

Totals

11

100

Country

UAl Institutes*

Scientists^

France Italy Denmark Switzerland

CERN'^ 2 1 1 1

12 15 7 5 5

6

44

''The institutes involved at the time were Rhein. Westf. Tech. Hochscule, Aachen, (FRG), Lab. de Phys. des Particules, Annecy (F), Birmingham University (UK), CERN, Lab. de Phys. Corpulaire, College de France, Paris (F), Queen Mary College, University of London (UK), University of CaHfornia at Riverside (USA), University of Rome (I), Rutherford High-Energy Laboratory (UK), Centre d'Etudes Nucl. de Saclay (F), Inst, fur Hochenergiephysik, Vienna (A). *The institutes involved at the time were University of Bern (CH), CERN, University of Copenhagen (D), Lab. de TAccel. Lineaire, Orsay (F), University of Pavia (I), Centre d'Etudes Nucl. de Saclay (F). ^The scientists attached to an institute are mostly, but not necessarily, nationals of the country in which the institute is based. These figures must be read with that Hmitation in mind. '^Thesefiguresinclude CERN staff and visitors paid by CERN. Source: Experiments at CERN 1980 (CERN: Geneva, August 1980)

guarantee a continuing activity of the work in six different areas (event simulation, muon identification, etc.), and it was agreed to meet again in July^^. During the next six months about 30 so-called ppbar notes were written. These were technical memoranda most of which discussed the features of the detector needed to do colliding beam physics at very high energies. They were written by scientists based at several different institutes (Annecy LAPP, CERN, Rome University, Saclay, University of California at Riverside...) and circulated among all those interested^"^. On 8 November this core set of people (about 25) met formally and held a 'general discussion on how to get organized from now on'. Six institutions were represented. They set themselves an extremely tight schedule. 1 December was the deadline for the final sketch of the detector. The final drawing of the detector with optimal parameters was to be ready by Christmas. By mid-January the proposal to be submitted to the SPSC (the experiments committee responsible for making recommendations about what proposals should be accepted) was to be typed. And on 31 January 1978, we are told, there was to be 'Propaganda made - Proposal submitted'^^.

How are collaborations formed and how international are they?

257

The 'collaboration' met formally (in the sense that minutes were written and circulated among those present) at least once a week from then on until mid-January. The numbers present stayed constant at about 25. However there were important changes in the institutions represented. Aachen, Annecy LAPP, CERN, College de France, Saclay and Riverside were the initial core. There was a representative from Harvard University at one or two meetings, and from the Inter-University Institute in Brussels at another: neither institution remained formally part of the group. More significantly, a number of British groups joined during this time. At the meeting on 15 November it was reported that there was an 'Interest from Rutherford Lab. (where C.R. [Carlo Rubbia] and B.S. [Bernard Sadoulet] are going to make some propaganda on Monday) [...]'. The trip was made, and the following week, on 22 November, Rubbia reported that 'One result of the seminar held at RHEL [was] the interest of Birmingham for our project' - indeed two Birmingham University representatives attended this meeting. By mid-December Rubbia had been informed in writing of Rutherford's interest in the collaboration: they would like to join 'our group together with 4/5 other physicists and adhoc technical support'. (The physicists were doubtless the representatives from the third interested UK group. Queen Mary College). At this point (13 December 1977) Rubbia felt that the collaboration was approaching its optimal size, and that 'from now on it [would] be harder to join our group'. In particular it was agreed 'that any other large institution who would like to join [would] give serious problems'. The proposal for experiment P92 (subsequently called UAl or Underground Area 1) was submitted to the SPSC on deadline - 30 January 1978. It ran to over 150 pages including references, and was signed by 52 scientists'^. 48 of these were from the nine main institutes we have mentioned - Aachen (5 representatives), Annecy LAPP (6), University of Birmingham (10), CERN (8), College de France (4), Queen Mary College (4), University of California, Riverside (3), Rutherford Laboratory (4), and Saclay (4). The other four signatories of the proposal were visitors from Wisconsin, Harvard and Rome Universities. At the collaboration meeting on 7 February 1978 Rubbia reported that two proposals and two letters of intent to do colUding beam physics had been submitted to the SPSC and that each group would have to defend its proposal at open presentations as early as 21 February. He felt that his collaboration would need 60-90 minutes to describe first the experimental set up and then the physics programme. Regarding the latter, it was suggested that although 'one speaker only for the physics programme would be better for the continuity of the talk', on the other hand 'four speakers from different labs [would] show that we are already a working collaboration'. It was decided that Sadoulet (CERN) should describe the detector and that the physics be split into three topics to be dealt with by Dowell (Birmingham), Linglin or Delia Negra (Annecy) and Rubbia. Rubbia would speak on the W and the Z particles, the major discoveries that were anticipated by the collaboration. Early in April Rubbia reported on the progress with the SPSC. Collaboration meetings were now being held every two to three weeks, and were being regularly attended by about 40 people from the nine collaborating institutions. Rubbia reported that two out of five proposals (those that became UAl and UA2) had been considered and refereed. Notes: p. 273

258

The ppbar Project. 11. The Organization of Experimental Work

and that 'Nothing appeared in the minutes but ours went through without any major objection'. At the end of May 1978 the so-called Coordination Committee for experiment P92 met for the first time. A member of the CERN Directorate who was responsible for the experiments to be done at the pp collider (P. Falk-Vairant) was in the chair. He explained that this committee would meet roughly bimonthly, and that its task would be to 'follow and supervise closely the progress of the proposed experiment'. Each collaborating institution was to be represented on it. (This committee subsequently came to be called the UAl Executive Committee). One of its first tasks was to draft an agreement setting out the responsibility of each institute in the collaboration. It would include a time table, cost estimates, a list of physicists with at least a three-year commitment to the proposed experiment, detailed information on manpower needs, and so on. About this time too the collaboration was informed that two further institutes, Rome University and the Institute for High-Energy Physics in Vienna would like to join the collaboration. Both were ultimately accepted, though not without some difficulty, a point to which we shall return below. Indeed when the CERN Research Board, on the recommendation of the SPSC, accepted the UAl proposal on 29 June 1978 the number of participating institutes was still just nine and the document distributing responsibilities between the laboratories had not yet been drawn up. This was finally settled by 31 October 1978. A mere three years later the huge detector, which weighed around 2000 tons and which included some highly sophisticated, state-of-the-art technology, began taking data for the first time.

The most important point we want to stress about this 18-month process of formation and growth is that it occurred because of the combined effect of a number of very different considerations. Certainly the scientific interest of the experiment and the technical design of the detector were the cornerstones underpinning the setting up and consolidation of this collaboration, and its successful implantation at CERN. However, on their own these cannot account for the process we have just described: a number of other social, institutional and political considerations have to be taken into account if we want to understand how and why the UAl collaboration 'gelled'. Three were particularly important. Firstly, there was the mutual trust and respect between the scientists themselves, the conviction that each group in the collaboration was capable of pulhng its weight and deHvering its part of the detector on time and in good working order. This trust was built up over time, and on the basis of first-hand experience. In fact one often finds that there is strong continuity in the core membership of collaborations. Having worked successfully together before, the same people tend to think of what they might do together next as one experiment draws to an end. Correlatively, it was precisely because this trust was lacking, because it was feared that it was not a 'strong group', that the collaboration initially reacted so negatively when it learnt that a team from Vienna was interested in joining^^. The addition of the Rome group, on the other hand, was unproblematic. One of their

How are collaborations formed and how international are they?

259

representatives (Salvini) had been actively working with the collaboration as a CERN visitor since early 1977 and his name was included on the original proposal. The second major consideration affecting the entry of groups into the collaboration was the knowledge that they had the infrastructural and financial support at their home institutions which was needed to take on a major construction project. This, for example, was one reason why Rubbia solicited support at the Rutherford laboratory even though he had not worked with some of the British groups before. 'We are fairly weak, hardware wise', he told the embryonic collaboration at CERN, 'and we are eager to accept hdw people like RHEL'^^ Political considerations, though never explicit, were also not far beneath the surface. The pp project at the CERN SPS only received the Council's backing in June 1978, i.e. several months after the core of the collaboration that planned to use the colUder had been formed. Its acceptance was not a foregone conclusion. As we pointed out in the previous chapter, many physicists and engineers doubted the technical feasibility of the scheme. Others, notably in Britain, were also not keen on it for fear that converting the SPS into a collider would seriously impede fixed-target physics at the machine. What is more the UK government was taking the lead in trying to force down the level of the CERN budget, and could hardly be expected to favour another new scheme, particularly if its physics community was lukewarm about it. One way of swinging this delegation behind the project was to draw physicists from several institutions in Britain into the collaboration. Thus it was no coincidence that Rubbia and Sadoulet went to Rutherford 'to make some propaganda' for P92 only six weeks after two members of the CERN Directorate had discussed CERN's plans with UK users at the RHEL and had found a 'lack of popularity of ppbar, which we must try to correct', as they put it^^. While 'political' and policy considerations probably played some role in encouraging a UK team to join, they seem to have been the dominant reason for initially accepting the Vienna group into the UAl collaboration. This is related to the fact that CERN, as a European laboratory, must serve, and must be seen to be serving the physics communities in all its member states. There is a constant pressure on those in the laboratory to incorporate scientists from a wide range of institutions, and particularly those from smaller countries, in the Ufe of the laboratory^^. Thus in March 1978 we find Walter Thirring, a senior Austrian theoretical physicist, writing to fellow theorist Van Hove expressing both enthusiasm for the pp project and concern that 'as the size and complexities of large experiments go up it will become increasingly difficult for smaller laboratories to compete with the large laboratories of the bigger member states of CERN'-^^. Behind these more general sentiments was the obvious wish that a group from Austria be included in the UAl collaboration. Indeed one of those interviewed remembers 'Van Hove and Carlo [Rubbia] arguing that small countries should find their places in UAl for Council to support the project'. Indeed, it was shortly after Thirring's contacts with senior management that the group from Vienna joined the collaboration, and that the CERN Council accepted the pp venture. The Vienna physicists, it should be said, rapidly showed themselves up to the technical and managerial tasks they were called upon to do inside the collaboration. Notes: p. 273

260

The ppbar Project. II. The Organization of Experimental Work

One should not generalise too quickly from this case. There is no evidence, for example, of similar 'poUtical' pressure being applied on UA2. Yet the grounds for Thirring's concern are clear. It is obviously desirable to include in a collaboration groups from big countries like Britain and France. Both had large national facilities and the associated infrastructural resources, including money to pay for the parts of the detector they built, workshop facihties to construct them, and computing power sufficient to handle the data taken in the experiment. Small institutes, particularly those in small countries, simply could not match this (see Table 7.3 later), and so risked being squeezed out as collaborations grew bigger and the need to share the burdens more pressing. We have now touched one of the main reasons for the uneven distribution of institutes shown in Table 7.1. What our discussion has shown is that the internationalism of collaborations at a laboratory Hke CERN is born more of pragmatic needs than of an idealistic commitment to 'universaUsm'. These 'needs' can be for scientific, technical, financial and even political support. The spirit of universaUsm may move scientists to collaborate, but only insofar as it coheres with their own particular interests^^. As Morrison, himself a CERN physicist, has put it, 'The simplest and possibly the best reason why groups collaborate is that collaboration is to their advantage'^^.

7.3 How are collaborations organized internally? Work in a large collaboration has to be organized. The size of the detector (it can weigh thousands of tons), the nature of its construction (particularly if it is modular, with different units being built by different groups), the time constraints (the need to meet deadlines and to compete with rivals), the mass and variety of data to be analysed (there are many physics topics to be studied), the sheer number of people involved (tens or hundreds working together) - all of these demand that some sort of organizational structure is set up inside a collaboration. And when one contrasts this situation with the picture of the individual scientist following freely where Nature leads, it is but a short step to identifying work inside a large collaboration with work inside a large corporation. In this section we want explore the plausibility of this analogy. We shall see that, while superficially there are some parallels (planning and coordination of project, division of tasks, hierarchy of responsibilities...), any simple identification of an experimental collaboration with a tightly controlled industrial laboratory fails. And it fails because the qualified physicists and engineers who work in large teams tend to regard and to treat each other as professional equals and peers, people who are working alongside them to achieve a common objective. There is one important distinction to bear in mind before we get under way. The 'industrial' model, in so far as it has any plausibiHty at all, can only apply to the period during which the detector was being constructed. In the case of UAl and UA2 this lasted for three to four years (from design to commissioning), which was remarkably fast for devices of this type. During this phase the work was carefully organized and planned as we

How are collaborations organized internally?

261

shall see. Once the detector started taking data, however, and the analysis of physics results began, a far looser organizational structure was put in place. Physics analysis, the HEPAP tells us, is 'intrinsically next to impossible to 'manage"-^^. This is not to say that physicists are free to explore whatever topics they like, but simply to indicate that the constraints on what they do are not those identified in the simplistic model we are attacking - and to insist that whatever merits that model may have, its value is restricted to the construction phase of the detector. The detectors for UAl and UA2 were not built exclusively at CERN. Both consisted primarily of a number of interlocking modules with a An geometry (rather Uke the layers of a cylindrical onion) along with triggers which selected interesting events and a data acquisition system^^. These various components were shared between the collaborating institutes which generally built them at home, bringing their various subdetectors or components to the host laboratory for final testing and assembly. The division of labour between the various centres was defined in a formal 'Agreement on the Sharing of Responsibilities [...]' part of which is shown in Table 7.2^^. How were these responsibilities distributed? To begin with it was clear that the central detector of UAl, the heaviest and most techically advanced part of the device, should be built at CERN. This component, as envisaged in the UAl agreement, consisted of 'a volume filled with about 11000 drift chamber wires in order to record an image of the many tracks produced in the coUisions. The electronics for the detector capable of continuous recording between [proton-antiproton] bunch crossings is entirely new', the document went on, 'and must be developed', adding that CERN 'accepts entire responsibility for the device including the electronics and readout'. The fact that CERN had the Table 7.2 The distribution of responsibilities for the construction of U A l . For more information on the components see Watkins (note 1). For the full names of the institutes see the notes to Table 7.1 Responsibility

Institute

Magnet Central Detector Data Acquisition Gondolas Bouchons Hadron Calorimeter Trigger Electronics Muon Detector Forward Calorimeter Luminosity Detector

CERN CERN CERN Saclay + Vienna Annecy LAPP Rutherford HEL^ Rutherford HEL'^ Aachen College de France - Rome Riverside

a) Rutherford HEL is a collective name for all the UK groups. Source: Annex 2 to the draft Agreement on Sharing Responsibilities.. (note 26) Notes: pp. 273 ff.

262

The ppbar Project. II. The Organization of Experimental

Work

money, the personnel, and a considerable amount of inhouse knowhow in this technique (see the chapter by Gambaro in this volume) meant that the host laboratory was a natural 'choice' for building this module. As for the remaining components, they were distributed on the basis of the interests, past experience, and resources of each participating institute, though of course there was also a certain amount of horse-trading between the various collaborating laboratories. The UK groups in UAl, for example, would have liked to build the rather challenging electromagnetic calorimeter. Instead this job went to Saclay, while the British groups were given the less demanding hadron calorimeter. At the same time the latter secured the trigger processors for both calorimeters, an item which played a crucial role in the data taking. In agreeing to build a part of a detector an institution was also committing personnel, money and computing time to the collaboration. Table 7.3 shows the extent of these commitments as envisaged at the end of 1978. It confirms the heavy involvement at every level by the major institutions in two big member states, Britain and France. Indeed, along with CERN, the three institutes in each of these countries were together responsible for about two-thirds of the physicists, programmers, and engineers involved in the construction of the detector, were expected to bear over 85% of its cost in terms of material, and anticipated providing 90% of the required computing time for data anlaysis. The coordination of the building, assembly and installation of the UAl detector was entrusted to a Technical Committee chaired by Hans Hoffmann. This committee met every Table 7.3 The commitments made by the collaborating institutes in UAl in terms of various categories of personnel, of money, and of computing time Institute

Physicists, Programmers'*

Aachen Annecy Birmingham CERN C. de France Q. Mary Coll. Riverside Rome RHEL^ Saclay Vienna

6 9 10 + 2 students 11 + 7 6 + 2 students 3 7 4 + 3RAs 8 + 3 phys 3

Engineers"

2 see RHEL 5 2 see RHEL 1 4 + supp. staff 3 2

Technicians Draftsmen'*

Money (MSF)*

Computing time''

2 3-5 1 or 2 5 + supp. staff 7 1

2.0 2.5 w CdF.'' see RHEL 14.5 2.5 w. Ann.'' see RHEL 0.4 0.5 3.8 2.5 0.4

11% see RHEL 33% 11% see RHEL 5% 5% 24% 11%

2 2 3

a) Figures from Annex 1 to the Agreement... cited in note 26. b) Figures from letter Falk-Vairant to Yoccoz, 14/12/78 (DGR21298). They are in millions of Swiss francs. c) Figures from paragraph 9 in the Agreement... cited in note 26. The computing time was for data analysis and it was assumed that the collaboration would need 1000 hours a year on a CDC 7600 computer or equivalent. d) The combined contribution of groups from Annecy LAPP and the College de France was 2.5 MSF. e) The Rutherford Laboratory had overall administrative responsibility for the British participation in UAl.

How are collaborations organized internally?

263

week throughout the construction period. About 25 people regularly attended these meetings. In addition many other formal meetings (in the sense of meetings for which minutes were kept and circulated within the collaboration) were held at CERN during this phase of UAl's Hfe, each intended to deal with specific tasks. Thus we find central detector meetings, muon detector meetings, calorimeter meetings, trigger meetings, gas system meetings, on/off*-Hne software meetings, database meetings, graphics meetings etc. In addition there were regular meetings of the whole collaboration and of the executive committee, these being the only two formally constituted bodies which met regularly throughout the entire Hfe of the collaboration, from construction through data taking and analysis^^ The most striking feature which emerges from an analysis of the attendance at these committee meetings at CERN is the key role played by a small core of people. We find that perhaps 20 scientists were responsible for writing the minutes of the various meetings and that they were mostly senior people: about 15 of them 'represented' their institutes on the executive committee. We find that although as many as 85 different people might have attended meetings of the technical committee during a year, there was again a small number, maybe five or six, who attended regularly, week after week, people like Sergio Cittolin who was repsonsible for the data acquisition system, Bernard Sadoulet who was reponsible for the central detector, and Guy Maurin who was responsible for the overall administration of the group. Finally we find that the spokesman and head of the collaboration. Carlo Rubbia, while taking the chair at collaboration meetings, and not missing an executive committee meeting, was far less often present at lower level meetings. This was even the case with the all-important technical committee, where he apparently attended about 60 % of the time in 1978, about 40% in 1979, and seldom if ever in 1980^^ The picture then seems to be clear, and coherent with the classic pattern of business organization. We have a pyramidal structure, with the spokesman at the apex, the 'boss', a layer of middle management, say 25 people in the centre who were responsible for the dayto-day organization of the construction of the detector at CERN, and a broad base of scientists below that (remember that there were about 100 physicists and engineers in the UAl collaboration in 1980), a mass of people who were more or less excluded from the loci of power and of decision-making. There are two criticisms that can be levelled at this model. Firstly, it is wrong to assume that because there is a hierarchy of responsibiHty inside a large collaboration, then necessarily the bulk of the scientists are excluded from the decision-making processes. As a general rule this is simply not so. The main purpose of the meetings that were held was not to pass on instructions but to share information, to communicate and to consult, and to decide collectively. Correlatively attendance at meetings was not an obUgation imposed from above, but a response to a perceived need to be informed about things that directly concerned one's work. In fact many meetings were arranged on an ad hoc basis to discuss a particular problem, and were dissolved after two are three sessions when the problem had been resolved. There is planning and there is coordination inside a collaboration, and there is a core of people who have more responsibiHty than others, and who have to ensure Notes: p. 274

264

The ppbar Project. II. The Organization of Experimental Work

that certain things get done. But as a general rule there is not top-down management, there is shared decision-making. The second weakness of an overly formal picture of how a collaboration is organized is that it misses the ongoing, informal relationships between the members. The scientists and engineers in a collaboration, from the senior physicists down to the junior graduate students, were in constant working contact with one another and with the technicians, rubbing shoulders together, discussing what had to be done and how best to do it, taking myriads of mini-decisions throughout their long, often very long, working days. Those with special responsibiUties were never far from the workplace, their offices arranged to ensure accessibility and to facilitate communication^^. Meetings punctuated this ongoing exchange of information. They were pauses intended to iron out specific problems or to discuss new ideas, after which everyone plunged back onto the 'shop floor'. There are two other qualifications to be made before we leave this point. We have suggested above that the picture of a collaboration as having a pyramidal structure is misleading, that the managerial structures are more fluid, hierarchical relationships are more blurred, bureaucracy is less important, than any unsophisticated industrial model and much literature has not yet moved beyond that level of analysis - would lead one to believe. Indeed, one might add that when interviewing physicists in UAl and UA2 many of them were puzzled by the notion of there being a middle management in the collaboration and felt that it was somehow inappropriate. At the same time it has to be said that, at least as far as UAl was concerned, the picture painted above is somewhat idealistic. For here there was undoubtedly a boss. Carlo Rubbia, who by his genius, his determination, his charisma, and by his notorious inability to tolerate opposition, in fact imposed his will on the collaboration, to the extent that no important decision could be taken without his first giving the green light. At the same time it is instructive to note how many of those interviewed resented this, revolted against a structure in which there was Rubbia and the rest, as one of them said. In short, some collaborations might indeed be organized like large corporations with a top-down management structure - but it goes against the grain of scientists who believe that authority and power should derive from experience and expertise, that compliance should be the result of consultation and persuasion not coercion, and that decisions should be made collectively not imposed from above. The second point to note is that the work organisation we have described has, in fact, much in common with what is found in some business corporations, notably those in the high-technology sector. Here, as in a major collaboration in physics, managerial practices have had to be developed to maintain the motivation and commitment of creative people. The catch phrases are 'flat structures, the absence of hierarchy, decentralisation and devolution of responsibilities'. We should be careful then when rejecting the 'industrial model' as a suitable guide to understanding how collaborations are organised. It is rather a particular version of that model that probably needs to be jettisoned once and for alP^.

How is credit allocated in large teams?

265

7.4 How is credit allocated in large teams? There are three ways whereby scientists doing basic research conventionally gain credit for what they do: by publishing in the refereed literature, by speaking at conferences, and by impressing their colleagues and peers by their diligence and professional competence. Traditionally the first of these, pubhcations, has been the most important means of assessing output and abiUty. However, with the growth in the size of collaborations, and their current policies for drawing up authors' lists, other more 'subjective' criteria are coming to the fore, to the consternation of a physics community which finds itself trapped between past values and present reaUties. Publication in the refereed literature is still the single most important goal of the researcher in basic science. The pubUcation serves two main sociological purposes. Firstly, it is an indicator that the authors have, in the eyes of their peers, made a novel contribution to knowledge. As such, and particularly in an activity like basic science which is driven by competition, a publication serves to attribute priority to its authors for the results they have obtained. Secondly, publications are widely regarded as an 'objective' criterion of achievement in the field. As such, publishing articles is central to the functioning of a community which aspires to giving rewards primarily on the basis of scientific merit. Having one's name on a paper is thus of considerable importance to physicists. How are authors' Usts drawn up inside big collaborations? First, the usual basic distinction is drawn between constructing the detector and doing physics with it. The pubhcations deriving from the former, which deal with technical innovations, are submitted to journals Uke Nuclear Instruments and Methods. Their authors' Usts are relatively short and include only people who have been directly involved in the work described in the paper. There is apparently no great difficulty in settling authors' Usts for this kind of publication, as most physicists see such work as essential but relatively unimportant as a means of gaining credit amongst their peers - it is 'considered by physicists to be a sort of second hand publication [...]' one of them said. The situation is more delicate when it comes to publishing physics results. On the one hand, granted the work that they have done on it for many years, physicists want to have their names on papers deriving from 'their' detector. On the other hand, given the variety of results achieved with some of the 'multipurpose' facilities, they cannot possibly hope to be actively involved in all aspects of analysis. To satisfy these potentially conflicting considerations, collaborations tend to adopt a poUcy of generosity. They include the name of everyone involved in the collaboration for any length of time, who has made a significant contribution to its work, and who has a global understanding of the physics results reported, on every analysis paper. There are local variations within this scheme of course. Visitors or graduate students who were not involved in building the detector have to dedicate a minimum period - typically a year - to doing analysis along with the rest of the group before qualifying for authors' Usts. Some physicists who are highly specialized in one aspect of the work might only sign a subset of the papers. The very early papers might include the names of one or two people which will later disappear Notes: p. 274

266

The ppbar Project. II. The Organization of Experimental Work

- the accelerator engineer Simon Van de Meer who shared the Nobel with Rubbia was given credit on the UAl paper announcing the discovery of the W, and was then removed from the author's list. But the general rule remains unchanged. Any physicist who is seen to have made a significant contribution to any aspect of the collaboration's work signs every paper^^ By being generous in drawing up author's lists collaborations reduce to a minimum the potential for conflict which arises when people feel their names have been been unjustifiably left off a paper^^. In fact it appears that only about 5 % of the names ultimately included are ever contested in a collaboration. The main source of difficulty concerns engineers and technicians. On the one hand many physicists recognize that some engineers and technicians have made important contributions to the development of the detector, and feel that they should duly be given credit for this on papers reporting results even if they are not really au fait with the physics. Against this it is felt that the proper place for engineers and technicians to publish is in journals like NIM which are dedicated to detector R & D , and that anyway a publication list is not as important professionally for them as it is for physicists - rewards are distributed differently in the different fields. As a result the consequences of putting engineers', and particularly technicians', names forward for authors lists can be so divisive that it takes a very determined group leader to push the idea through. As one interviewee explained, a pubHcation bestows a very high status on a technician in his or her institute, and can lead to enormous friction not only inside the home institute itself, but with other institutes in the collaboration who are not putting forward technician's names. Two last comments before we leave this point. Firstly, the ambiguity about including the names of engineers and technicians on physics papers is a consequence of the fundamental changes in experimental work that we are looking at in this paper. On the one hand it arises from the mix of professional groups in the collaboration (see Table 7.3), from the fact that physicists, programmers, engineers and technicians work together over long periods of time around the same piece of equipment, all of them contributing in important ways to the final result. On the other hand, it is symptomatic of the changed role of the physicists themselves, of the blurring of the boundaries between the physicists and other professional categories'^. To be a physicist in a collaboration of this kind is to master a number of very different techniques, techniques shared by computer scientists, by electronics engineers, by high-level technicians, and so on. The main criterion for having one's name on a paper reporting physics results may be that one is a physicist. The difficulties that we have just described arise partly because the notion of who is a physicist is itself contestable. The second point worth noting is the confusion in physicists minds about the value of publications. On the one hand, they are extremely concerned to get the credit that comes from having one's name on a paper, and determined that justice be seen to be done in authors' lists. This is partly because they cHng to the traditional view of the value of papers. More importantly perhaps, it is because external assessors - fundgivers, faculty boards - still regard publication Hsts as an 'objective' measure of performance. At the same time there is a tendency for physicists to place less weight on the publication as a

Is teamwork antithetical to individual autonomy and creativity?

267

means of gaining reward. All those interviewed would agree that 'publications count for very little' now, the credit one has being diluted by the fact that an individual is 'merely' one of tens or hundreds. The policy of generosity may avert conflict. But it imposes anonymity ('I don't even read the authors' Usts' anymore, one interviewee said), and the obligation actively to seek rewards in other ways as well. Conferences are the second main way for gaining credit in the physics community. They serve two important functions. Firstly, even though results are tentative and unrefereed, contributions to conferences serve to establish priority. They are particularly important in a field that is at once highly competitive and in which experimental data are thick with interpretation. Physicists want to report their results quickly - indeed the week or two before an important conference are a time of feverish activity in a collaboration. But they know that it can take a long time to converge on an agreed interpretation of their data, and for the community to accept them as reliable. Conferences are a way of resolving the dilemma, a way of presenting data fast without over-commiting oneself to them. The second important function of conferences is as a forum for gaining visibility in the outside community of peers for both the individual and the group. Conferences are loci for making, or breaking, credit and credibility. One person is plucked from 'anonymity' in the collaboration and propelled into the limelight. At the same time the entire collaboration is given prominence and pubUcity. Physicists thus attribute considerable importance to speaking at conferences, even vigorously contesting the order of presentation of papers if they feel that it does not give their work the prominence which they think it deserves^^. The third and last way of gaining credit inside a collaboration is by making an individual contribution to an aspect of the collaboration's work. This could be anything from designing and commissioning an important piece of detector hardware to tackling a particular physics topic in an interesting and unususal way. The key thing is to do something which individuates you from the other members of the collaboration - and to ensure that other people in the group know what your contribution is. As one interviewee put it, there is no point having bright ideas if you do not tell others about them, and there is no point either in burrowing away on your own if no one else is aware of what of you are doing. In short, it is increasingly difficult inside large collaborations to gain recognition simply because one is a good physicist. As the traditional 'objective' criteria of assessment, like the publication, become less important inside the community, so physicists are finding that they have to 'sell' themselves, to make sure that their eff*orts are visible to the rest of the collaboration. What you know matters. Who you know - and who knows you - also matters, and increasingly so.

7.5 Is teamwork antithetical to individual autonomy and creativity? The conventional industrial model of large collaborations reflects and reinforces another pervasive view about work in large teams: that it leaves no space for individual autonomy and creativity. Individual researchers, as Robert Wilson puts it, are typically Notes: p. 274

268

The ppbar Project. II. The Organization of Experimental Work

seen as 'doing creative, poetic, and enduring work [...]' while team research is regarded as 'superficial, uncreative, and dull; [...]'^^. Mertonian sociologists would go further. Since 'basic science is an individualistic enterprise', team research cannot be compatible with basic research^^. As we shall see in this section, all of those interviewed confirmed Wilson's feeUng that these attitudes are Uttle more than 'preconditioned responses' and 'cliches'. They persist because they are part of a constantly regenerated ideology which pivots around images of the scientist as an individual creative genius. They are increasingly irrelevant, not simply because they do not square with the realities of an individual's life in a large collaboration. More fundamentally, I shall argue, they are inappropriate because physicists working in such teams have a very different idea to their predecessors of only 20 to 30 years ago of what doing physics actually means. They draw - they have had to draw - the boundary between their activity as physicists and the activities of technicians and engineers in ways which are new, at least for Europe. But more of that later. First, let us try to capture what individuals working in the collaborations we studied felt about team research. While there were obviously differences in emphasis between the respondents, one of them summed up the situation in terms which would probably be acceptable to all. 'I feel sorry', he said, 'that teams have become so big. On the other hand, we have to live with it. And [I would] say that we [have] managed a lot better than I could have [foreseen]'. This attitude is confirmed by the findings of the American HEPAP subpanel cited earlier who were also surprised to find that even young investigators were not disenchanted with teamwork. 'We happily transmit the view from within large collaborations', the panel reported in 1988, 'that - at least for many - life is far more challenging and far less anonymous than it sometimes seems to be from without, despite all the frustrations'^^. Teamwork then, is not fundamentally incompatible with individual fulfilment and job satisfaction, an observation which would surely be utterly banal and unsurprising but for the pervasive grip of the myth of the lone scientist. The most basic reason why individuals do not feel crushed inside large collaborations is that there is a high degree of fragmentation and distribution of tasks (see Table 7.2). As a result physicists find themselves actually working in small groups, sometimes of only five or six people, groups that will be responsible for a particular part of the detector or for the analysis of a particular set of data. Within these groups there is considerable scope for individual autonomy and creativity^^. In fact the detectors are so complex, and the data so profuse, that there is an enormous variety of work to be done: hardware R & D , electronics, computing, analysis... Ironically, then, and quite contrary to what conventional wisdom would have us beHeve, there can be more scope for individual autonomy in a large collaboration than in a small one. That autonomy, of course, is not a priori guaranteed. On the contrary - and this is another reason why the reality of group research does not square with the myth - , individual physicists and institutions take deliberate steps to try to ensure that they are not dominated in a collaboration. They are careful about whom they team up with. As one university physicist in UA2 put it, he preferred to work in collaborations with five or six

Is teamwork antithetical to individual autonomy and creativity?

269

other groups rather than in a very large collaboration like UAl because in that way 'a rather smallish group as we were could have a major role'. In similar vein the three British teams went into UAl as 'one strong group because we felt that we had to put up a united front and because we felt we would work better that way'. Participating institutes also try to take responsibility for a crucial part of the detector as this will give them more power inside the collaboration. For example, by building the trigger processors for the calorimeters in UAl the British groups were guaranteed a central role in the collaboration. Finally when it comes to data anlaysis, physicists do their best to ensure that they can work in an area which interests them. As one group leader put it, he had 'always been very careful about the behaviour of my group inside the collaboration', making sure that 'we are doing interesting things', not just building detectors for other people, but 'doing our physics'. In short, if physicists find that they have space for individual satisfaction inside collaborations it is also because they adopt deliberate strategies to protect their autonomy and that of their group. So far I have concentrated on structural and strategic explanations of why work in collaborations - or least UAl and UA2 - was compatible with individual autonomy and creativity. There are also more personal considerations. Above all there was the pleasure of being involved in a collective effort directed towards a shared objective. This might have meant working night and day with 50 or 100 people down in a humid and cold pit to assemble a detector as quickly as possible. Or it might have involved spending hours with one's colleagues discussing the significance of the data coming off the device. These are aspects of group life which are simply not accessible to the individual worker or, indeed, to the worker in a small team. This brings me to the last advantage of team research that I want to mention: that there are a large number of people available to discuss results during the analysis phase^^. This is invaluable given that novel data off a detector are open to a wide range of diverse interpretations, and that convergence on a shared meaning requires an intensive exchange of ideas. By meeting frequently with their colleagues - every day if they are working on a hot topic (cf. above) - the members of the collaboration slowly build a coherent and justifiable version of the phenomena which they believe in, and which they can present to their peers as a 'result'. Seen in this fight, group discussions surrounding data are not only satisfying to the individuals who participate in them. They are epistemologically essential. What of the disadvantages of research in very large teams, what do the participants feel they have 'lost'. The feature most often mentioned by those who have worked in smaller groups is that they can no longer contribute to, and master, all aspects of the experiment. They are forced to speciaUse, and increasingly so as the collaborations get bigger. As a result they do not feel that they are 'in touch' overall with the equipment they are using, that somehow the detector and its data are out of their control. We have argued above that doing experimental physics in a big collaboration can indeed be satisfying to individual participants. And as we have remarked, at one level this finding is banal, little more than a useful antidote against a number of cliches and 'preconditioned Notes: p. 274

270

The ppbar Project. II. The Organization of Experimental Work

responses' about the nature of team research. At the same time, from another, more interesting point of view, this result is of considerable significance. For it indicates that experimentalists in large collaborations have a conception of their role, of what it is to be a physicist, which allows that it can be creative and satisfying to spend four or five years perhaps more - of one's life designing and building a piece of complex, heavy equipment, that that too is 'doing physics'. This has not always been so, at least not in Europe. Certainly physicists have always understood that equipment was needed to do an experiment, and have often designed and built it themselves, perhaps with the help of one or two technicians. But this kind of work was done quickly, exceptionally in a few weeks (see the quotation at the head of this paper), more hkely in a few months, at most perhaps in a year. After that they would get down to taking and analysing data, doing physics with a big P as the practitioners usually call it. However as the timescales for detector building have extended, and as physicists have become involved in all aspects of construction, so they have come to redefine what physics is (to the extent of being willing to give a PhD in physics to a graduate who works entirely on developing a piece of detector hardware). And to redefine their identity as physicists. Of course these attitudes were not uniformally shared among those we interviewed. There was some nostalgia for the past. There was also the usual conservatism about the future: while it was 'reasonable' to spend three to five years building a detector (as the interviewee had done), doing so for eight years, the time needed for the new generation of devices, was 'another thing'. But the central image was clear: Interviewer: Did you yourself play a role in building equipment? Physicist: Yes. Interviewer: You stopped doing physics? Physicist: No. That's doing experimental physics. The contemporary experimentahst's concept of 'doing physics' is not simply different, it is also obviously far broader and richer than that of his or her predecessors of only a generation ago. The following sequence of quotations give one an idea of what is involved. The physicist just cited was asked if he would not have liked to be taking data on another experiment while building the detector for UA2 (which took over three years of fulltime effort). He repHed: *'No, I can't do that. I mean I really want to be, when I have an experiment to do, [involved] from the beginning. I can't do other things. [...] That's my problem. I mean in fact, when you design and build a calorimeter [...] you don't actually go blind into a certain design. You build a prototype and then you take this prototype to a beam and then you play with the beam and you change the components [...]. You design a system offlashlightswhich sends artificial signals to the photomultipliers to keep the stability under control, and this requires writing a program that manages all this pulsing by computer, and writes files of calibration constants. Then you know you change the thickness of the lead and the scintillators to see how much you can influence the linearity [...]."

This takes about a year, whereupon the design is frozen, and discussions with industry begin in earnest. Since the photomultipUers have to be very stable

Is teamwork antithetical to individual autonomy and creativity?

Ill

"you have to do a lot of searching among the various photomultipliers on the market to find out which one is the most stable. You have to discuss with industry. That's all physics. And then eventually you write technical notes and you publish in technical journals. Its not only screwing screws. Its development, its R & D."

Once the order is placed, "it takes a few months before you have thefirstpieces coming back for the assembly, and during that time you start thinking about physics again. You develop simulation programs, you write special physics routines which will eventually be used in the final analysis. And then when the things come back from industry, and they're assembled, then our calorimeters have to go back on test beams for caHbration. [...] We spent a year [...] at the PS, caHbrating everything in the calorimeter cell".

Building detectors, in short, involves a variety of activities and mobilizes a number of very different skills and techniques, all of which are now seen to be an integral part of doing physics, not a distraction from its main purpose, all of which are included in what it means to be an experimental physicist. Included too, as these quotations show, is a relationship with industry which was more or less foreign to European physicists working at CERN in the late 1950s and early 1960s. At that time it was the engineers, the accelerator builders, who were actively engaged with industry, who designed and built protypes, who exchanged knowledge and experience with their counterparts in firms, who pushed suppliers to the technological limit. For physicists, on the contrary, the relationship to industry was essentially passive. It was seen as a suppUer of sophisticated though standard equipment, which was bought off the shelf and treated more or less as a 'black box'. This is no longer so. The relationship with industry is far more dynamic, interactive. Physicists now see it as a source of new ideas and techniques to be exploited and adapted to their novel purposes. CCDs, or Charge Coupled Devices, are a good case in point. Developed in the early 1970s , the technology was originally limited 'to expensive and complex miUtary systems'. By the mid-1970s it appeared that the technology 'may be on the verge of making a 'big splash into low-cost high-volume applications". And an informal note was circulated inside the embryonic UAl collaboration explaining their potential for 'use with charged particle detectors'^^. Put differently, the concept of being a good experimental physicist now includes being aware of what new products industry, and especially high-tech industry has to offer, and of being able, as Pestre put it, 'to use industrially available material in new and interesting ways"^^. This new identity, these new attitudes among European physicists, are in fact indicative of a generalization of the role of the physicist which emerged in the United States between the 1930s and the 1960s. Basic science was transformed in this period, above all by its integration into the military-industrial complex. A new way of doing physics emerged, a new kind of researcher was moulded, a researcher who, to quote Pestre again, 'can be described at once as physicist i.e. in touch with the evolution of the discipline [...], as conceiver of apparatus and engineer, i.e. knowledgeable and innovative in the most adNotes: p. 274

272

The ppbar Project. II. The Organization of Experimental Work

vanced techniques [...], and entreprenuer [...]', i.e. capable of mobilizing and managing important human and material resources^^. Until the early 1960s this transformation in the role of physicist was restricted to the United States, where it was embodied in the activities of men like Luis Alvarez: European physcists were largely excluded from it. But then a new generation came on the scene, the men and women of whom we are speaking here. They completed their PhDs in the early 1960s. Most of them spent at least two or three years working in the States. And - competition oblige - they internalised the role of a physicist which working in large collaborations around big detectors demands of them. I would particularly like to thank Pierre Darriulat and Eric Eisenhandler for valuable comments on an earher draft of this paper. This work was done with additional financial support from the Andrew W. Mellon Foundation.

Notes 1. We refer to P. Watkins, The Story of the W and the Z (Cambridge University Press, 1986), for example. 2. The locus classicus of the eariy research is G.M. Swatez, 'The Social Organization of a University Laboratory', Minerva, 8 (1970), 36-58, which was based on work done at the Radiation Laboratory of the University of California from 1963 to 1965. See also, for example, W.O. Hagstrom, Traditional and Modern Forms of Scientific Teamwork', Administrative Science Quarterly, 9 (1964): 241-63, L. Kowarski, Team Work and Individual Work in Research', in N. Kaplan (ed). Science and Society (Chicago: Rand McNally, 1965), 247-255, and A. Weinberg, 'Scientific Teams and Scientific Laboratories', in G. Holton (ed.) The Twentieth-Century Sciences. Studies in the Biography of Ideas (New York: W.W. Norton, 1972), 423-42. For the 1970s see, for example, D.R.O. Morrison, 'The Sociology of International Scientific Collaborations', in R. Armenteros, A. Burger, Y. Goldschmidt-Clermont, and J. Prentki (eds). Physics from Friends. Fetschrift for Ch. Peyrou (Geneva: Multi-Office, 1978), 351-365, R.R. Wilson, 'My Fight Against Team Research', in G. Holton (ed.) op. cit., 468-79 and J. Peoples Jr., 'How Detector Collaborations Evolved; A Personal Recollection', in J. Nonte (ed). Supercollider 3 (New York: Plenum Press, 1991), 727 et seq. These are accounts by physicists. For accounts by historians, see P. Galison, 'Bubble Chambers and the Experimental Workplace', in P. Achinstein and O. Hannaway (eds) Observation, Experiment, and Hypothesis in Modern Physical Science (Cambridge: The MIT Press, 1985), 309-73, P. Galison, 'The Evolution of Large Scale Research in Physics', in Report of the HEPAP Subpanel on Future Modes of Experimental Research in High Energy Physics, July 1988, US Department of Energy Washington, D.C., Report DOE/ER-0380, 79-93, P. GaHson, 'Bubbles, Sparks and the Postwar Laboratory', in L.M. Brown, M. Dresden, and L. Hoddeson, Pions to Quarks. Particle Physics in the 1950s (Cambridge: Cambridge University Press, 1990), S. Traweek, Beamtimes and Lifetimes. The World of High-Energy Physicists (CambhdgQ: Harvard University Press, 1988), especially chapters 4 and 5, and D. Pestre, 'The Organization of the Experimental Work Around the Proton Synchrotron, 1960-1965: The Learning Phase', in A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN. Volume H. Building and Running the Laboratory, 1954-1965 (Amsterdam: North Holland, 1990), chapter 8. For a recent general survey of big collaborations in the USA see J. Genuth, Historical Analysis of the Selected Experiments at U.S. Sites, Report produced for Center for History of Physics, American Institute of Physics, New York, November 1991. 3. For example, Galison 'Bubble Chambers' and 'Bubbles, Sparks', and Swatez 'Social Organization', see note 2.

Notes

273

4. On nostalgia see, for example, S. Blume's contribution to R. Bud and S. Cozzens (eds), Instruments and Institutions. Making History Today (Washington: SPIE Volume IS09, 1992). 5. Quoted in Galison, 'Bubble Chambers', note 2 on p. 316. 6. From Galison 'Evolution', note 2 on pp. 86-7. 7. See Wilson, op. cit. note 2. For Wilson's role in the founding of Fermilab, see C. Westfall, 'Fermilab: Founding the First US Truly National Laboratory', in F.A.J.L. James (ed.). The Development of the Laboratory. Essays on the Place of Experiment in Industrial Civilization (London: Macmillan, 1989), pp. 184-217. 8. A previous version of this paper was pubUshed as J. Krige, 'Some Socio-Historical Aspects of Multinational Collaborations in High-Energy Physics at CERN Between 1975 and 1985', in E. Crawford, T. Shinn and S. Sorlin (eds). Denationalizing Science. The Contexts of International Scientific Practice. Yearbook of the Sociology of the Sciences, Vol. 16 (Dordrecht: Kluwer Academic PubUshers, 1993), 233-62. 9. The interviews were conducted within the framework of a project to study multi-institutional collaborations in hep which was initiated by the Center for History of Physics of the American Institute of Physics. My part of the work was devoted to interviewing some 40 physicists on 5 experiments at CERN, and to identifying important collections of relevant documents. The tapes and rough transcripts of these interviews are lodged in the Center for History of Physics archive at the AIP in New York and in the CERN archive in Geneva. 10. Many of the documents used for UAl were from the private collections kept by CERN physicists David Dallman (which is very extensive) and Alan Norton. Both are at CERN. The author would Uke to thank Kyoung Paik for help with sorting through the documents, and for making rough transcripts of the interviews. 11. See J. Krige, 'The International Organization of Scientific Work', in S.E. Cozzens, P. Healey, A. Rip and J. Ziman, The Research System in Transition, NATO ASI Series D: Behavioural and Social Sciences - Vol. 57 (Dordrecht: Kluwer Academic Publishers, 1990), 179-97. see also Fig. 1.4. 12. ibid, p. 190. 13. For the announcement of the study week see the circular by Rubbia in (DGR21298). The note prepared afterwards for the management and entitled Conclusions of the study on the detectors is in (DGE21576). 14. There is a selection of these ppbar notes in (JBA22633), for example. 15. The minutes of this meeting are in the Dallman papers (see note 10). Unless otherwise stated all of the following material dealing with the setting up of UAl is from this collection. The documents are headed SPS ppbar Project. Summary of the meeting... or Minutes of the meeting held on... From about 8 March 1978 they were headed SPS ppbar P92 collaboration. 16. A collection of the papers of the SPSC (Super Proton Synchrotron Committee) is in the CERN archive. 17. The early negative reactions to the Vienna group joining were mentioned in several interviews. I have also seen this in a document which I cannot now retrieve. 18. Minutes of the meeting of the SPS ppbar project held on 13 December 1977 (Dallman papers). We described some of the faciUties available at Rutherford in chapter 5. 19. For the visit to the RHEL as also being a propaganda exercise, see the Minutes of the SPS ppbar project meeting held on 15 November 1977 (Dallman papers). For the report by the CERN management on the attitude of UK physicists see the memo by F. Bonaudi dated 18 October 1977 (DGE21576). 20. For the general problem of the relationship between a host laboratory and its outside users see e.g. Kowarski and Pestre, op. cit., note 2, and chapter 5 of this volume. 21. Letter Thirring to Van Hove, 10/3/78 (DGR21298). For the extent of the contribution made by larger member states to UAl see also Table 3 below. 22. Crawford has stressed that universalism and internationalism are not 'immutable' parts of science, but bound to time and place - see E. Crawford, 'The Universe of International Science, 1880-1939', in T. Frangmyr (ed), Solomon's House Revisited. The Organization and Institutionalization of Science (Canton MA: Science History Publications, U.S.A., 1990), 251-69, on p. 252. 23. Morrison, op. cit., note 2, on p. 353. 24. Report of the HEPAP Subpanel, cited in note 2, on p. 31. Notes: p. 274

274

The ppbar Project. II. The Organization of Experimental Work

25. For a useful technical description of the UAl detector see Watkins , note 1, chapter 9. 26. The Agreement on the Sharing of Responsibilities Amongst the Participants in the Experimental Programme based on a 4pi-Solid Angle Detector for the SPS used as a Proton-Antiproton Collider at the Centre of Mass Energy of 540 GeV, dated 31/10/78, is in (DGR21298). 27. The list of meetings was collected together in the UAl List of Publications prepared annually by Denis Linglin (Dallman and Norton papers). Of course we are only speaking of the meetings held at CERN here. There were similar ongoing formal and informal contacts taking place around the building of the separate detector components in the collaborating institutes. 28. We do not have a copy of the minutes of every Technical Committee meeting, and so we need to be cautious in our formulations. For the three years mentioned here we have the minutes of about 25 meetings, so around 50% of those that were held. 29. On the importance of how offices were arranged in UAl - a point mentioned frequently in interviews - see also Traweek, op. cit., note 2, chapter 1. 30. For information on the so-called New Organisation see R. Scase, 'Dinosaurs in the New Organisation', Financial Times, 25 November 1991, from which the quotation is taken, and e.g. R. Scase and R. Goffee, Reluctant Managers (2nd ed) (London: Routledge, 1991). 31. One interviewee mentioned that at one of the LEP detectors at which he now works there were 13 different physics topics distributed between some 400 physicists. All of them sign every paper produced even if they are working on a different topic. 32. Morrison, op. cit., note 2, on p. 359 writes that 'authorship is one of the few areas where there can be serious friction and real unhappiness' in a collaboration. 33. This point is developed more extensively in the following section. 34. G. Taubes, Nobel Dreams. Power, Deceit and the Ultimate Experiment (New York: Random House, 1986), on p. 220 attributes these words to Rubbia, after the UAl spokeman had been told that UAl would present its results the day after UA2 at an important physics meeting: 'If this is not changed', Rubbia allegedly told one of the organisers, 'I do not think we go. This program makes us look like a spare wheel on a car. [...] Either we get basic symmetry of UAl and UA2 in these subjects or we boycott the program. I don't see any other choice'. 35. Wilson, op. cit., note 2, on p. 468. 36. See Hagstrom, op. cit., note 2, on p. 241. 37. See Report of the HEPAP Subpanel, cited in note 2, on p. viii. 38. In fact one of the key managerial tasks in a collaboration is to give each group responsibility for building a piece of equipment which requires a certain amount of ingenuity and yet is not so challenging that it takes on a Ufe of its own. 39. For the importance of constantly discussing one's results see Taubes, op. cit., note 34, Book II, and Traweek op. cit., note 2, p. 117 et seq. 40. The remarks about CCD devices are from P. Davies, B. Hallgren and H. Verweij, Short Study of the Charge Coupled device CCD 321, ppbar Note 31, 5/9/77 (JBA22633). 41. D. Pestre, 'Some characteristic features of CERN in the 1950s and 1960s', in A. Hermann, J. Krige, U. Mersits and D. Pestre, op. cit., note 2, on p. 800. 42. ibid., on p. 799.

PART II

Physics Results

This Page Intentionally Left Blank

CHAPTER 8

Physics in the CERN Theory Division John ILIOPOULOS

Contents 8.1 Introduction 8.2 Birth of the Group 8.3 The Copenhagen years 8.4 Moving to Geneva 8.5 CERN, the Centre of Europe 8.6 The rise of the Standard Model 8.7 Beyond the Standard Model 8.8 Conclusions References

278 279 279 289 295 307 312 323 324

277

8.1 Introduction This chapter has not been written by an historian. In fact, my respect and my sympathy for historians have considerably increased in the course of this work; so has also my determination never to become one. I fully enjoyed the long hours I spent in the CERN archives reading old documents and manuscript notes, as well as the discussions I had with some of my senior colleagues, but even now, I cannot say that I really know what happened. I know several stories but I cannot reconstruct history. I think that, for the first time, I understood the wisdom of the old movie by Kurosawa 'Rashomon' which I fuUheartedly recommend to anybody who wishes to study history. I discovered experimentally that human memory, including my own, is partial and selective and the more certain one feels about his recollection of a particular event, the more one should doubt it. On the other hand, having taken part in many committees, I know too well that the entire story rarely appears in the proceedings. Many a time, during my search, I decided, out of frustration, to drop the whole enterprise and it is only because I was reluctant not to honour my promise that I continued. However, I had to compromise. When I started, I intended to write a well-documented historical chapter, solidly supported by archives and witnesses. Yes, I was that naive! I thought that the matter would have been relatively easy since the facts are recent, I have taken part personally in many of them and for the others, I could rely on my contacts with the protagonists, most of whom are still active. This turned out to be an impossible task. An experienced historian may have been able to find his way through, and solve, the various puzzles of conflicting evidence, but I could not. So this chapter, rather than being the truth, is just my version of the facts. I apologize to those who will find that my story does not correspond to the one they told me. It is not that I was not Hstening to one of them, but that I was listening to them all. Finally, I found that I could not answer some of the more 'historical' questions I had asked myself. This chapter will not tell the story of the CERN Theory Division; it will give instead my idea of the physics that was done there. Sailing close to the shore of impersonal scientific facts has been my way to avoid being lost in endless speculations. It was an easy solution and, in fact, a rewarding one. For, during these years, we have witnessed one of the greatest triumphs of abstract theoretical thought. One often says that progress in physics occurs when an unexpected experimental result contradicts the current theoretical beliefs. This forces physicists to look for new ideas and eventually it gives rise to a new theory. Such has been the case most of the time in the past, but the revolution that brought geometry under the form of gauge theories into physics had a theoretical, better an aesthetic, motivation. It is not possible to tell the story of the 278

Birth of the Group

279

CERN Theory Division without, at the same time, telUng the story of this exciting achievement. This is the rewarding part. 8.2 Birth of the Group The estabUshment of CERN, its origins as well as the motivations that lay behind it, have been presented more expertly and more thoroughly in the first volume of this series. There we find that the first fully operating research group that was created was the Theory Group. (There were no divisions yet). It may sound curious that one of the first acts of the founding fathers towards an experimental high-energy centre was to hire some theorists and indeed, in this respect, Europe departed from the American model. Brookhaven, the analogue and rival to CERN in these early years, never developed a large theoretical group. What was even more important was that the special role of the theorists in an experimental centre was clearly recognized. Although they were actively encouraged to act as consultants to the experimentaUsts and to participate in the establishment of the experimental programme, this has never been made a necessary condition. Excellence in research was supposed to be the first criterion. In fact we can find among the early fellows, as well as among the staff* members later, several theorists whose interests were abstract and mathematical. I do not know for sure who first suggested the establishment of a group of theoretical studies, but I suspect that its spiritual father was no lesser man than Niels Bohr, an already legendary figure in theoretical physics. Since the early days of quantum theory, Niels Bohr had run in Copenhagen the most famous and the most successful Institute of Theoretical Physics of all time. Copenhagen became intimately connected with quantum mechanics. The Niels Bohr Institute was the Mecca (or Jerusalem), the place where, for generations, every young theorist aspired to go. But times had changed. The Old Master was more and more absorbed in his activities for disarmament and the prevention of nuclear war. Europe, divided between East and West, had not yet healed the wounds of the war. Supremacy in scientific research had crossed the Atlantic and found new homes in the flourishing American universities. The newly created European Organization for Nuclear Research offered Bohr an opportunity to revive his Institute. In an historical decision the Interim Council of CERN, in its first session in May 1952 in Paris, decided to create a Group of Theoretical Studies and to appoint Niels Bohr at its head. The group would be provisionally hosted by the Institute in Copenhagen. 8.3 The Copenhagen years What this decision meant in practice was that CERN funds were available to hire theorists from the member states to work in Copenhagen. Indeed, for the year 1952-53 we find the first fellows:

280

Physics in the CERN Theory Division THEORY

1952-1953

L. Michel J.E. Hooper T. Sigurgeirsson E.R. Caianiello V. Roglic St. Fallieros A. Gamba R. Haag Z. Jankovic

(France) (United Kingdom) (Iceland) (Italy) (Jugoslavia) (Greece) (Italy) (Germany) (Jugoslavia)

I assume that all of them were paid by CERN but I am not sure that at the beginning there was any clear distinction between visitors paid by CERN and those paid by the Institute. However, things soon became more formal. An agreement was signed between the CERN Council and the Danish government specifying the privileges and immunities of CERN employees in Copenhagen. Furthermore, the fellows were appointed by the Council following a proposal by Bohr. I have not found any case in which the Council acted contrary to Bohr's proposal, either by refusing to hire somebody or by imposing another choice, although occasionally they postponed a decision, often for financial reasons. In fact, in these early years, the Theory Group represented the only scientific activity of CERN and it was only normal that the Council followed closely its performance. In the minutes of the first sessions we find many references to discussions about the work of the Group, contrary to what happens today where the activity of the Theory Division, being a higher order correction to the CERN budget, is rarely discussed by the Council. For example, in papers presented in 1992 by the Director General to the Scientific Policy Committee and the Finance Committee (The scientific activities of CERN and budget estimates for the years 1993-1996', CERN/SPC/646/Rev., CERN/FC/3543, 19 May 1992) the chapter concerning the Theory Division covers less than two pages out of a total of 84 pages. In the early days everybody seemed concerned about attracting the most promising young theorists to work in Copenhagen. In a letter to R.W. Penney dated 20 July 1954 S. Rozental, then Deputy-Director of the group, noted: '... In fact, I doubt whether we shall get the right people by applications; probably we shall have to try to find them ourselves ...'. The principle of roughly one fellow per member state seems to have been agreed upon already at that time. Visitors from non-member states were also occasionally admitted. In June 1956, the Ford Foundation offered CERN a $400 000 grant for a period of five years which was used to finance such visits. As years passed the group increased in size and, in September 1954, we find 24 theorists and two secretaries working in Copenhagen. Also from this date, C. Moller succeeded Niels Bohr as head of the group. There was also a slight dispersion. A few theorists were dispatched to Liverpool, Glasgow and Uppsala. These centres opened their experimental facilities to European collaboration.

The Copenhagen years

281

THEORETICAL GROUP STAFF (COPENHAGEN) AS AT SEPTEMBER 1954 Names

Functions

Nationality

Date

N. Bohr A.O.G. Kallen

Sen. Phys. Dir. TH Phys. TH (fellow and later on member of personnel 1954 (?)) Seer. TH

DK S

5.1952 1952

DK F UK Iceland I Y Gr I D Y D

18.8.1952

1952

D F CH DK DK

1.3.1953 10.1953 1.9.1954 1.8.1954 1.9.1954

USA DK

1.9.1954 1.9.1954

DK NL N S NL I UK

1954 4.1954 1.1954 1.1954 1.1954 9.1954

E. Abrahamsen L. Michel J.E. Hooper T. Sigurgeirsson E.R. Caianiello V. Roglic St. Fallieros A. Gamba R. Haag Z. Jankovic G. Liiders G.O.J von Gierke B. d'Espagnat K. Adler A. Bohr C. M0ller B.R. Mottelson S. Rozental E. Jacobsen N.M. Hugenhohz E. Eriksen P.O. Froman D. Harting G. Fidecaro G.R. Bishop

Phys. TH fellow (1.11.1953: Engineer PS Group) Phys. TH fellow Phys. TH Phys. TH Sen. Phys. TH Sen. Phys. Dir. TH (Copenhagen) Sen. Phys. TH Sen. Phys. Dep.-Dir. TH (Copenhagen) Seer. TH Copenhagen

Phys. TH Phys. TH Proposed by N. Bohr in Oct. 1953 to be engaged in Sept. 1954. Decision postponed by Council, its session Oct. 1953. Was never engaged: accepted research fellowship at Oxford (Ref. Weekly Report No 59, Jan. 54)

282

Physics in the CERN Theory Division

I believe that in Bohr's mind the Copenhagen arrangement was meant'to be a long term one, but other delegates thought otherwise. For example, the British delegation submitted a note to the Council meeting of 20 June 1953 in Rome in which we read: The United Kingdom point of view on this question is that a theoretical physics centre should be maintained at Copenhagen, as part of the European Organization, for a period of five years, the position then to be reviewed. The centre should not, in this period, build a permanent institute, but should if possible use existing premises. The period of five years is suggested to secure reasonable staffing stability. It would be desirable to have some estimate of the cost to the European Organization unless details are already available. It is observed that according to CERN/GEN/5, the present budget estimates allow for an average total of about 900 000 Swiss Francs per annum to be spent on theoretical work and other forms of cooperation. The French delegation responded with a similar note in which the proposed period was reduced to three years. A theoretical study Group should be at work at Geneva when the construction of the Synchro-cyclotron is achieved, i.e. following the present evaluation, at the latest 4 years after the entry into force of the Convention. It will be therefore desirable to establish this Group during the year preceding the putting into operation of this accelerator. Consequently, the contracts to be eventually concluded with theoreticians in Copenhagen, should be limited to a period of 3 years. The amount of S.F. 900 000 mentioned in chapter D of the programme proposed by the Council at its fifth session, as shown by the table on page 11 of document CERN/GEN/5, must be divided between the activities of the Copenhagen Institute and the cost of other forms of cooperation. Furthermore, the sums needed for the establishment and the gradual development of a theoretical Group within the Geneva Laboratory, ought to be reserved at an appropriate time. It is also amusing to note that the cost of the Theory Group represented at that time the main item in the CERN budget! As things finally worked out, the agreement with Copenhagen lasted five years. With an official letter dated 16 January 1957, C.J. Bakker, then Director General, informed the Danish Government of the Council's decision to terminate the agreement with Copenhagen on 1st October 1957. As of this date, the Theory Division joined the laboratory in Geneva. What was the scientific activity of the group during the Copenhagen period? We have ample information on this question because Rozental was submitting detailed scientific reports to the Council every three months with full lists of publications, seminars, coUoquia, etc. The first thing we notice is that, to a large extent, the Group acted as a training centre for young theorists. This is not surprising. In postwar years, physics education in most European universities left a lot to be desired. Chairs were few and often held by old professors who had not kept up with the latest scientific developments. Organized graduate studies were almost absent. It was not exceptional to see research centres playing the role of graduate schools. For example, in France, A. Messiah taught the course, which gave rise to his textbook on quantum mechanics, not in a university but in Saclay. Gen-

The Copenhagen years

283

erations of French physicists had to learn modern physics in the Summer School at Les Houches. In the Rozental reports we repeatedly see courses on rather elementary subjects, such as the classic 'Angular Momentum in Quantum Mechanics', taught in the Centre. Presumably, for many young visitors, their position in Copenhagen was that of a graduate student rather than of a postdoctoral fellow. Nevertheless, the group was active in research. A substantial part was devoted to theoretical nuclear physics, a choice which reflects both the scientific interests of many senior physicists in Copenhagen, as well as the only experimental activity in Europe outside cosmic ray physics. Strictly speaking, it is in this field that the most significant scientific work was done. A. Bohr and B.R. Mottelson had just completed their work on nuclear levels which, later, gave them the Nobel prize. In the early fifties the subject was in full expansion with many experimental groups producing new results. A large part of this theory was elaborated and applied to particular nuclei by the Copenhagen Group. However, I do not know whether we can consider it as a CERN activity in view of the fact that the principal investigators belonged to the Copenhagen permanent staff and the subject was essentially dropped once the group moved to Geneva. Quantum field theory and elementary particle physics, the subjects that would become the main scientific activity of the CERN Theory Division, were also present during the Copenhagen years. Partly in order to appreciate correctly the significance of their contributions and partly for future reference, we shall briefly present the international scene during the same period. The fifties must have been extremely exciting years for elementary particle physics. It was during this period that the subject became an independent, fully grown discipline. This was mainly due to the systematic use of accelerators which marked the separation from cosmic ray research and set the era of big science. The decade witnessed the growth of pion physics, the study of the first pion-nucleon resonances and the discovery of antinucleons. The first heavy flavours were introduced and understanding their deep significance still makes heavy demands upon us. The triumph of renormalization theory created enthusiasm followed by depression. Parity was found to be violated and the V-A theory was established. The fundamental role of symmetry was recognized and the first non-Abelian gauge theories were constructed. A detailed account of all these wonderful adventures goes far beyond the scope of this essay, so we shall only say a few words about them. Since this chapter is about theory, I shall follow the development of theoretical ideas. The so-called 'modern era' of quantum field theory has a precise starting date: 2 June 1947, the date of the Shelter Island conference. The most important contribution that was presented at this conference was not a theoretical breakthrough but an experimental result: Willis Lamb, of Columbia University, reported the measurement of an energy difference of about 1000 MHz between the 2^1/2 and 2P\/2 levels of the hydrogen atom, in contradiction with the Dirac theory. The 'Lamb shift' shows the real nature of the effects of vacuum polarization. Its importance is not that it was unexpected. As Steven Weinberg puts it: '... It was not so much that it forced us to change our physical theories, as that it

284

Physics in the CERN Theory Division

forced us to take them seriously.' In the months which followed, Richard Feynman and Julian Schwinger set the foundations of the theory of renormalization, a well-defined prescription to compute the higher order terms in the perturbation series of quantum electrodynamics. As it turned out, similar ideas had been developed independently in Japan by Sin-Itiro Tomonaga, who was the first to give the complete computation of the Lamb shift. The entire programme was formally described by Freeman Dyson in 1949. Quantum electrodynamics, the theory of interacting photons and electrons, supplemented with the programme of renormalization, is one of the most successful theories in physics. Its agreement with experiment is spectacular. But it was also the first successful quantum field theory, the quantum mechanics of a relativistic system with an infinite number of degrees of freedom. Although the essential ideas were already developed in the late forties, a large amount of work was still necessary for the theory to be completed. The more technical part of the renormalization programme was elaborated by Bogoliubov and Parasiuk in the Soviet Union around 1955 and by Klaus Hepp in Zurich in the sixties. The appHcation of the programme to meson theories was done by Matthews and Abdus Salam in Great Britain in 1949-1951. Some of the ground work, including, in particular, the correct form of the propagator in quantum field theory, was laid down by E. Stiickelberg at the University of Geneva, who must also be credited, together with A. Peterman, with the introduction of the concept of the renormalization group in 1954. The contribution of the Copenhagen Group to this effort was rather modest. I have singled out an article by A. Peterman who was a fellow from Switzerland. In 1957, he published one of the first two-loop calculations of the electron anomalous magnetic moment [1] (the classical one-loop calculation was done by Schwinger). In particular, he was the first to exhibit the difference between the anomalous magnetic moments of the electron and the muon. Although with modern techniques, such computation sounds rather simple (for comparison, the four-loop calculation was completed a few years ago), it represents a milestone in our understanding of quantum electrodynamics. First of all, it required a mastery of the intricacies of the renormalization program which few theorists possessed at the time and, second, the actual calculations, both analytic and numerical, were quite involved. The result confirmed the agreement with experiment. As already said, the success of quantum electrodynamics is that of renormahzed perturbation theory. It is the same approach which, to our great surprise, led to the revolution of gauge theories and the construction of the Standard Model. Even today we do not understand why this approach works so well, neither do we know whether reaUstic quantum field theories exist outside perturbation. It was precisely during the fifties that the axiomatic formulation was initiated. In this line of thought the Copenhagen contribution is very significant. In 1955 Rudolf Haag published a classic paper [2], the first in a series, in which he set the mathematical foundations of scattering in the framework of quantum field theory. He showed the impossibihty of accommodating, in the same Hilbert space, the bare and the renormalized vacuum states, thus showing that the so-called 'interaction representation' was a very ill-defined concept. For the first time he used sophisticated

The Copenhagen years

285

mathematical techniques borrowed from the theory of topological vector spaces at a time when topology was terra incognita to most theoretical physicists. The second 'exact theorem' concerning quantum field theory that was published by the Copenhagen Group is due to Gerhart Liiders. Starting from the pioneering works of Eugene Wigner, theorists had studied the invariance properties of quantum field theories under the discrete transformations of space inversion or parity (P), time reversal (T) and particle-anti-particle conjugation (C). These transformations present a special interest in the framework of a quantum theory as compared to that of the classical case. A profound theorem was proven, called the 'CPT theorem', which states that, under very general assumptions such as relativistic invariance, locality and positivity, the product of these three operations is an invariance of the world. It implies, in particular, the exact equality of masses and life-times between particles and anti-particles. There exist several proofs of this theorem and one of them is due to Liiders who was in Copenhagen in 1954 [3]. The problem was suggested to him by Bruno Zumino and it is amusing to notice that the title of the paper is 'The equivalence of invariance under time reversal and under particle-antiparticle conjugation for relativistic field theories'. Invariance under parity was taken for granted! It is not mentioned as a specific assumption in the abstract and it is only at the end of the second page that we learn, without any particular emphasis, that for the validity of the proof, the theory must be invariant under space reflexions. Apparently, parity violating theories were not considered worth studying. And this happened in 1954, just two years before the earthquake. The enthusiasm raised by the successes of quantum electrodynamics did not last long. It was natural for theorists to try to apply the same techniques of renormalized perturbation theory to the other elementary particle interactions, namely the strong and the weak ones. In fact, a large amount of work was done concerning meson-nucleon theories which were supposed to describe nuclear forces. The results were disappointing. At the formal level the renormaUzation programme was shown to be applicable to a particular form of the coupUng (the so-called pseudo-scalar theory) but the results were useless for practical computations. The reason is a profound difference in the strength of strong interactions as compared to the electromagnetic ones. The perturbation expansion is a formal power series in a dimensionless parameter, the renormalized coupUng constant. Its numerical value is determined by experiment. For quantum electrodynamics, this value turns out to be roughly equal to 1/137, the celebrated fine structure constant. The smallness of this number is responsible for the success of the theory since higher order terms soon become negligible and a good estimate of the result can be obtained by keeping only the first few terms. The corresponding number for pion-nucleon interactions is instead of the order of 10 and the very idea of a power series expansion becomes meaningless. This is, of course, the reason why strong interactions are strong! The dynamics is often dominated by resonance production, a phenomenon completely outside the scope of perturbation theory. For a few years this caused considerable confusion among theorists which was soon resolved by abandoning field theory techniques in strong interactions. Few theoretical

286

Physics in the CERN Theory Division

contributions to this subject can be considered as being significant and I have not found any of these coming from Copenhagen. What about the weak interactions? Since they were supposed to be much weaker than the electromagnetic ones, this objection did not apply. However, a new theoretical problem appeared there: since 1934, Enrico Fermi had proposed a remarkably simple and elegant field theory model which seemed to describe all known phenomena of weak interactions perfectly well. It became known as 'the four-fermion theory'. The trouble is that, as was immediately realized, the renormalization programme did not apply. One could not resolve all the ambiguities, to any given order of perturbation theory, by redefining only a finite number of constants. The theory in fact lacked any predictive power. This double failure soon tarnished the glory of quantum electrodynamics. The general disappointment was such that renormalization theory became an essentially esoteric topic in particle physics. When I was studying in graduate school, in the early sixties, the subject was not even taught in most universities. New approaches were developed, all of which were initiated in the United States. In fact, as years passed, Europe, if anything, seemed to be losing ground! For strong interactions these new approaches involved two concepts: internal symmetries on the one hand and analytic properties of the S-matrix on the other. It is amusing to notice that Werner Heisenberg can be considered as the father of both, because he was the first to introduce a sort of isospin symmetry for nuclear forces in the thirties as well as to use S-matrix ideas in a remarkable paper written during the war. However, it is fair to say that, in their modern form, they were both developed in the United States. I believe that the milestone of the symmetry approach is a little-known work of Fermi. In 1952 he used a simple isospin symmetry argument in order to deduce the / = | dominance in 140 MeV pion-nucleon scattering. He had been studying pion interactions at the 450 MeV Chicago synchro-cyclotron. The cross sections for n^p -^ n^p{a^^), n~p -^ n°n{(7~°) and n~p -^ n~p{a ) at their highest pion energies (140 MeV) were measured to obey approximately c"*"^ : (7~° : a = 9 : 2 : 1 which follows from isospin only i f / = I dominates. In the same year, K.M. Watson proved that the average numbers of pions produced in nucleon-nucleon collisions satisfy the relation n^ -\-n~ = 2if. Simple ratios of Clebsh-Gordan coefficients! It was the first time that results of this kind were obtained in particle physics from symmetry principles alone, independently of any detailed dynamical model! From this time symmetry became the name of the game! It entered the world of particle physics and proved to be the most profound and most powerful concept. At the beginning, its role appeared to be limited because most symmetries were assumed to be global. As such they had Httle influence on the underlying dynamics. They could only provide relations among masses or amplitudes. It took many years for physicists to realize that in the framework of gauge theories, it is symmetry which determines the dynamics. But more about this later. In the symmetry approach I want to mention one contribution coming from Copenhagen. In 1953, Louis Michel, a French theorist, already well known from his analysis of the electron spectrum in muon decay, introduced the ingenious concept of what became

The Copenhagen years

287

later known as G-parity, a combination of charge conjugation and a 180° rotation in isospin space [4]. This simple idea had a considerable impact on pion physics because now all pions, neutral as well as charged, were eigenstates of G-parity. Furthermore, as it turned out, it was straightforward to generalize this concept to higher symmetries. The analyticity approach was from the start more ambitious. I believe that its origin should be traced back to the realization that the analyticity properties necessary to derive the Kramers-Kronig dispersion relation for the scattering of light by matter, can be obtained from causaUty without the use of detailed dynamical assumptions. I do not know who is the father of this important observation which may go back as far as the twenties. The earliest reference I found is due to van Kampen, who was a student of Kramers'. In strong interactions, the first dispersion relations were written down by M. Goldberger in 1955 for the pion-nucleon forward scattering amplitude. The importance of this work can hardly be overestimated. Few papers in particle physics have had comparable influence and in a few years this approach had become the main school of thought in strong interactions. Its domination was such that it reached occasionally almost religious dimensions. Europe in general and the CERN Theory Division in particular, played an important role in its development, but not during the Copenhagen years. So I shall leave this story here and pick it up again later. Maybe the most spectacular progress that was made in theoretical particle physics during the fifties was in the physics of strange particles and the properties of weak interactions. It was one of these fortunate circumstances in which cooperation among theorists and experimentalists proved to be most fruitful. Unexpected experimental results gave rise to novel theoretical ideas which in turn suggested new experimental research. Much to my regret, I shall not tell this wonderful story in any detail because I must admit that the role of Europe in it was not very briUiant. The first evidence of 'heavy flavours' goes back to 1936 with the discovery of the muon. In retrospect it marked a new era in physics. It was the first 'elementary particle' whose role in the structure of the world was, and still is, mysterious. Just after the war the first hadrons with 'strange' properties appeared also in cosmic rays. Quite surprisingly, their behaviour seemed to depend on whether one looked at their production or their decays. They were copiously produced, which meant that they had strong interactions, but they were long-lived with life-times characteristic of weak interactions. The puzzle was eventually solved between 1953 and 1956 with the introduction by Murray Gell-Mann and K. Nishijima of a new quantum number, called 'strangeness', which was assumed to be conserved by the strong and electromagnetic interactions but violated by the weak ones. The physics of strange particles soon became an invaluable source of information for experimentaUsts and a choice field for theorists. The highlights of this story are the following: (i) Murray Gell-Mann and Abraham Pais noticed that the two neutral A^-mesons with well-defined strangeness quantum numbers, X° and IC, are not eigenstates of the total hamiltonian since weak interactions do not conserve strangeness and allow for virtual A;°-^=>X° transitions as well as A^ decays. The states with well-defined Ufe-times are instead Kl and J^L which are two linear superpositions of K° and K". (ii) A. Pais and O. Piccioni

288

Physics in the CERN Theory Division

predicted the phenomenon of regeneration, the fact that a K^ beam passing through a sUce of matter regenerates a K^ component. Beautiful examples of simple quantum mechanics! (iii) On the experimental side, a new puzzle soon came up: it is known as the 'T - 0 puzzle' from the names of two decay modes of what seemed to be one and the same particle. The 0 decay was a two-pion mode of a charged, strange meson. The r-mode was a three pion one. All studies (mass, Ufe-time, scattering properties) indicated that the same A^-meson was responsible for both. Using a novel method to analyze three-body decays (the 'DaUtzplot') one could show that the A^-meson had zero spin. The three pion mode implied that it had negative parity. But then parity conservation forbids the two-pion mode. That was the puzzle! (iv) All attempts to resolve the puzzle by 'conventional' means failed. The answer turned out to be simple, unbelievable and profound. In 1956 two Chinese bom American theorists, T.D. Lee and C.N. Yang, went through the Uterature on j8-decay. To their astonishment they found that, up to that moment, there was absolutely no evidence that parity was conserved in weak interactions. They made the bold proposal that it was not! Next year, it was proven beyond any doubt that they were right! Specifically designed experiments, involving polarized initial states, showed that the violation was maximal in j8 as well as /^-decays. A most astonishing result! A physical state is not equivalent to its mirror image! (v) The last point I want to mention here is the search for an understanding of the nature of weak interactions. It has been one of the most exciting and most rewarding enterprises in the history of elementary particle physics. The road was long and circuitous and many a time it seemed that it was leading to a dead end. Out of the struggle for such an understanding grew many ideas, the importance of which transcends the domain of weak interactions and covers most of modern physics. A detailed history of this adventure has not yet been written. When it is written, it will appear as a play in several acts. I shall only give here the titles. The first act culminates in 1934 with Fermi's fourfermion theory, a most extraordinary paper, written just after the discovery of the neutron and the conjecture about the neutrino. The second is called 'twenty years later' and it describes the struggle to determine the form of the interaction. It ends around 1957 with the introduction of V-A by R.E. Marshak and E.C. Sudarshan. Some of the experiments necessary to that end will remain as monuments in the history of physics (example: Goldhaber's measurement of neutrino's helicity). The third act is a very short one: it has a prologue by S.S. Gershtein and Y.B. Zel'dovich in the Soviet Union and a main part by M. Gell-Mann and R.P. Feynman in the United States. It solves exactly one half of the problem of determining the weak interaction hamiltonian. The punch line is C.V.C. (Conserved Vector Current) and it identifies the vector part of the strangeness conserving weak current with the isospin current of strong interactions. This is obviously not the end of the play but it is time for an intermezzo. We are in 1957, i.e. time to move to Geneva. Until now, Copenhagen has not been part of the scenery in this weak interaction play. Let me attempt to summarize: within the five years the CERN Theory Group stayed in Copenhagen, I have singled out four papers in field theory and particle physics: Peterman's calculation of g — 2, Haag's rigorous formulation of scattering theory, Liiders'

Moving to Geneva

289

CPT theorem and Michel's G-parity. To those who may think that four papers in five years sound Hke a poor harvest, let me remind them that their contents can be found in today's textbooks. A very severe selection criterion! I do not know how many papers from our present prolific literature will be parts of the textbooks within twenty-five to thirty years from now. My judgement is that, as far as the level of scientific output is concerned, the Centre was a success. My criticism is that, only in nuclear physics, did it succeed in creating a school. With the obvious danger of exaggeration, I would say that all the important work in particle physics was done by individuals who happened to visit Copenhagen. None stayed long enough to attract other young fellows and create a group. I suspect that this is also due to the fact that the nuclear physics attractor was locally too strong, and in any case the situation changed when the group moved to Geneva. 8.4 Moving to Geneva In 1954 Felix Bloch was appointed as the first Director General of CERN. He was supposed to go to Geneva because construction was planned to start soon. He was not very enthusiastic with the idea of being alone with only construction engineers to talk to, so he asked the Council permission to bring two theorists with him. He first invited Anatole Abragam from France. Abragam was not a high energy physicist. Like Felix Bloch, he was a very well-known speciaUst of nuclear magnetism. He was head of a group at Saclay and promised to come to Geneva only part-time. In fact he never stayed for long and, in any case, Bloch resigned his post and returned to Stanford the year after. As a result, Abragam had even less motivation to visit CERN and he rarely did. Let me only mention that his work has influenced the experiments in the laboratory in later times, because he developed novel methods to build polarized targets. But this chapter is about theory. The first theorist to join CERN in Geneva was Bernard d'Espagnat. He had been in Copenhagen as fellow and was highly recommended to Bloch by M0ller. With a letter dated 10 July 1954, Bloch offered him the position starting October of the same year. A few months later, in January 1955, d'Espagnat was joined by a second theorist, Jacques Prentki. D'Espagnat and Prentki both came from Leprince-Ringuet's laboratory at the Ecole Poly technique in Paris. They had been working on the physics of strange particles and on the theory of weak interactions, the 'hottest' subjects of the time, and they continued their collaboration in Geneva. In fact the work they did together during the next years is probably CERN's most significant theoretical contribution of the early times. I shall present here two main ideas: the first is an attempt to find a geometrical meaning to the conservation of strangeness in strong interactions and the second is a search for the symmetries of weak interactions. Strong interactions were known to conserve electric charge and baryon number. Electric charge conservation was generalized quite early to a full invariance under three-dimensional rotations in isospin space, a non-Abelian synunetry. Isospin, electric charge and baryon number were not, however, independent symmetries, they were related by

290

Physics in the CERN Theory Division

Q = h-\- B/2, where Q, I2 and B denote the electric charge, the third component of isospin and the baryon number, respectively. Although I do not know who first wrote down this simple relation explicitly, it was generally assumed to be correct. The electric charge of a particle determined the isospin multiplet to which it belonged. This connection was broken with the introduction of strangeness. Already in his 1953 paper, Gell-Mann proposed to assign half-integer isospin to X-mesons and integer isospin to E and A hyperons, although they were all integrally charged. The relation was eventually modified to 2 = ^3 + f + f where S denotes strangeness, a new quantum number. Thus the conservation of strangeness can be seen as a decoupUng between the conservations of the other three quantities which now become independent. The quest for higher internal symmetries dates from this observation. It was one of the major theoretical problems of this period and d'Espagnat and Prentki made some very important contributions. (The problem was eventually solved by M. Gell-Mann and Y. Ne'eman in the early sixties with the introduction of unitary symmetry). Two directions were explored: in a 'conservative' approach, d'Espagnat and Prentki attempted to enlarge the symmetries of strong interactions by considering reflexions, together with rotations, in the three dimensional isospin space [5]. The idea was based on the ingenious observation that the phase transformations responsible for electric charge conservation were in fact equivalent to reflexions in isospin space, provided one used spinors of the second kind to describe ^-mesons and cascade baryons. They wrote down the most general interaction Lagrangian invariant under isospin rotations and reflexions and showed that it automatically conserved strangeness. They even used their formalism in order to predict the possible existence of an isoscalar 0~ meson several years before the discovery of rj and rj\ As far as I know, they were the first to make such a prediction. This 'minimal' scheme was not a very powerful one. In particular, it made no prediction concerning the masses of particles belonging to different isospin multiplets. In 1957, d'Espagnat and Prentki, in collaboration with A. Salam, considered a more 'radical' approach in which the symmetry group of the strong interactions was increased from SU{2) to 0(4) [6] (I believe that the idea of an internal symmetry higher than isospin is due to A. Pais who, already in 1954, proposed a first version of 0(4)). The algebra of 0{4) is that of SU{2) x SU{2) i.e. that of two isospin groups. Therefore, one has two 'third isospin components' to connect with electric charge and strangeness. Several versions of 0{4) have been published by many authors differing in the representation assignment of the various particles and/or the compact or non-compact form of the group. However, as far as I know, d'Espagnat and Prentki, following their work with Salam, were the first to address in detail the question of the symmetries of weak interactions. This brings me to their second major contribution which is beautifully summarized in their 1958 Nuclear Physics paper [7], 'A tentative general scheme for weak interactions'. This paper contains a comprehensive picture of the symmetries of all interactions. For the first time the whole hierarchy of symmetries and interactions is clearly presented. Four levels are considered:

Moving to Geneva

291

(1) The very strong interactions are invariant under 0(4). (2) The medium strong ones break 0{4) and leave one SU(2) (isospin) and the third component of the other (strangeness) invariant. (3) The electromagnetic interactions conserve only the third components of the two SU(2ys (electric charge and strangeness). (4) Finally, the weak interactions were supposed to be invariant under a different SU(2) subgroup of 0(4). Thus strangeness violation was the result of a mismatch between the medium strong and the weak interactions. Let me add here that the idea of introducing medium strong interactions was already known, but in its early versions it was supposed to describe the interactions of ^-mesons as opposed to those of pions which were the very strong ones. The correct scheme, as we know it today, appeared for the first time in d'Espagnat and Prentki's paper. Incidentally, I never quite understood why these authors, after having written this extremely lucid and beautiful paper, failed to discover the Cabibbo theory immediately after the introduction of SU(3). In fact, they almost did so! Let me anticipate in time and describe a 1962 paper [8], pubUshed in // Nuovo Cimento, in which they reconsider their theory in the language of SU(3). This is the most amazing part of the story! In section 3 of this paper one finds explicitly the correct form of the Cabibbo current with an arbitrary angle called a. Then they proceed to show that in a current x current theory the two empirical selection rules |A 51 < 1 and |A / | < | for non-leptonic processes are related. And they stop there! They do not mention that this form of the current allows for an unambiguous definition of the concept of universality, a very important element of the Cabibbo theory, and that one can actually determine the weak angle by looking at semi-leptonic decays. In their paper leptons are only mentioned in the last paragraph. It seems that they were misled by an erroneous experiment claiming a large AS = —AQ admixture in strangeness changing semi-leptonic processes. Since I have gone this far, let me also give the end of the story. The following year a short paper appeared, again as a CERN preprint [9]. The author was a young visitor from Italy, Nicola Cabibbo. He took over the idea of a current which forms an angle with respect to medium strong interactions, but he carried it to its logical conclusion. This form allows for the only consistent definition of universality. The concept of universality had been introduced several years before and it was often expressed by the vague assumption that all possible weak processes had the same strength. Cabibbo noticed that this assumption did not make sense. Using modern quark language, his remark can be translated into the statement that, with one quark of charge | and two quarks of charge — \, one could always construct one hadronic current which is coupled to leptons and one which is not. He chose to define universaUty by the assumption that the coupled current involves the same coupUng constant as the purely leptonic processes. He then proceeded to compare strangeness conserving and strangeness changing semi-leptonic decays and he deduced the value of what became known as the 'Cabibbo angle'. I do not know whether he

292

Physics in the CERN Theory Division

was unaware of the wrong experimental result or whether he showed the good physical judgement to ignore it, but he clearly understood that the semi-leptonic processes were the important ones. There are very few articles in the scientific Uterature in which one does not feel the need to change a single word and Cabibbo's is definitely one of them. With this work he estabhshed himself as one of the leading theorists in the domain of weak interactions. After this short excursion, let me come back to history. In 1957, the relative isolation of d'Espagnat and Prentki ended. CERN's headquarters were now ofiicially in Geneva, and all its employees came there. They included the theorists from Copenhagen as well as new appointments. The group expanded rapidly, left the provisional barracks it occupied near the airport and moved to more permanent premises in Meyrin. The evolution of the Division is shown in the following two Tables. The first gives the composition in June 1959 under the direction of Markus Fierz. The second contains all physicists who have had permanent appointments. Some remarks: the arrival dates shown are supposed to represent their first affiliation with CERN. Indefinite contracts were not granted until later. (CERN's policy for inStaff", TH Division as on 12 June 1959 M. FIERZ

Director

B. d'ESPAGNAT S. FUBINI J. PRENTKI

Senior Staff Members

D. AMATI R. ASCOLI J.E. BOWCOCK F. CERULUS D. FELDMAN V. GLASER C. FRONSDAL D. GEFFEN R. HAGEDORN E.M. HENLEY B. JAKSIC R. JOHNSTON J.M. JAUCH T. KANELLOPOULOS W. KLEIN S. KOHLER D. LURIE

A. MARTIN Ph. MEYER G. MOLIERE A. PETERMANN Mrs. SALZMAN G. SALZMAN R.F. SAWYER D. SPEISER R. SHERR F.L. SCARF W. THIRRING HA. TOLHOEK B. YITALE J.D. WALECKA J. WESS K. WILDERMUTH Y. YAMAGUCHI

293

Moving to Geneva NAME HAGEDORN PRENTKI PETERMANN GLASER AMATI MARTIN BELL VAN HOVE ERICSON JACOB ZUMINO FUBINI ELLIS VENEZIANO DE RUJULA FERRARA ALVAREZ-GAUME ALTARELLI

Rolf Jacques Andre Vladimir Daniele Andre John Leon Torleif Maurice Bruno Sergio John Gabriele Alvaro Sergio Luis Guido

ARRIVAL

NAT

1/04/54 1/01/55 1/09/55 1/10/57 1/02/59 1/01/60 11/01/60 4/09/60 5/09/60 1/06/67 29/05/69 1/06/73 1/09/74 1/07/77 6/09/77 1/03/81 23/06/86 1/03/87

DE F CH I I F UK B S F USA I UK I E I E I

definite appointments was not specific to the Theory Group and has been reviewed elsewhere). I do not know exactly what the date 1st June 1973 represents for Sergio Fubini, but his connection with CERN is much older. He joined the Theory Group in November 1957 and stayed as a full-time member until February 1960. Between 1960 and 1964, he was partly at CERN and partly in Padua, he left for Italy and the United States in 1964 and came back to CERN in 1971. Rolf Hagedorn's first appointment at CERN was in the PS Division where he was in charge of computing the multiparticle cross-sections and distributions. Since this work gave rise to some important concepts in high energy physics, I shall have the opportunity to mention it again later. His indefinite appointment in the Theory Division dates from January 1961. Bernard d'Espagnat is not mentioned among the permanent members. With a letter dated 25 May 1959 he resigned his position at CERN in order to accept a 'Maitrise de conferences' at the newly founded campus of the University of Paris at Orsay. I consider this move as unfortunate. First, because it broke a very successful and fruitful collaboration. Although d'Espagnat continued to visit CERN, his collaboration with Prentki slowly faded away. Their last joint paper that I remember dates from 1963. Neither of them singly did subsequently as interesting and important work as that which they had done together. Secondly, because they represented a line of research, that of weak interactions and symmetries, which came out considerably weakened. Leaving aside the question of relative personalities, a simple counting shows that the majority of new appointments at CERN was not in this direction.

294

Physics in the CERN Theory Division

One of the most influential members of the Theory Division does not appear in the tables. It is Tatiana Faberge, who joined the Group as Secretary in March 1957. Few contributed to the shaping of the Division as much as she did and, in fact, her influence has extended far beyond the CERN boundaries to the international community of theoretical high energy physics. She organized all the administrative work, which turned out to be absolutely essential for the rapidly expanding Division, she introduced the preprint numbering system which is still in use today and which has been since copied by many other institutions, but, above all, she succeeded in creating around the Theory Division Secretariat an atmosphere of friendship cherished by a whole generation of physicists. The present preprint numbering system started in 1958. The paper with the number ThOl has a date of Oct. 30, 1958 and contains some lecture notes to P.S. on strange particle physics with an introduction by J.M. Jauch. The expansion of the Division can be inferred by following the Th preprint numbers. By the end of 1959, we are still at Thl2, in 1960 we reach Th79, in 1961, Th 155 and at present the number approaches ThTOOO. An important turning point in the history of the Division was the appointment of its first Director. Until 1960, it functioned under interim directors, first Niels Bohr and C. Moller in Copenhagen and then Bruno Ferretti and Markus Fierz in Geneva. None of these appointments was meant to be a long term one. The subject appears in the minutes of practically every session of the Scientific Policy Committee (SPC) since 1956 as well as in those of many Council meetings. Many European and American physicists were consulted and were asked to nominate possible candidates. The position was offered to several leading theorists. We shall have an opportunity later to comment on the difficulties encountered in this process but I want to emphasize at this point that the long-term vacancy of the position was not the result of negligence or lack of coordination of the CERN authorities. The chairman of the SPC at the time was W. Heisenberg and one sees through the documents that he spared no effort to find a high level particle theorist who would be willing to take the job. After many unsuccessful attempts the offer was made to Leon Van Hove, a Belgian physicist who was at that time at the University of Utrecht. Van Hove was not a high-energy physicist. Although quite young, he was already well-known, mainly for his work in Statistical Mechanics. His name is still associated with the thermodynamic limit in an interacting system. The problem is a very fundamental one because it raises the question of the very applicability of statistical mechanics to the description of phase transitions, given the fact that the partition function for a finite system is an analytic function of the parameters of the theory. In the forties it was not yet fully realized that discontinuities can emerge when one takes the limit of an infinite system. Whether and how this can be done was answered by Van Hove in a pioneering 1949 paper. Apparently, several members of the SPC were worried that his lack of expertise in CERN's field of research would prevent him from fulfilHng the task assigned to the Director of the Theory Division, which consisted in conducting high level research, attracting new theorists, directing the research of the young fellows and taking an active part in the establishment of the laboratory's experimental programme. Van Hove was finally contacted in 1959 and came to CERN in September 1960. His appointment was initially for one year and became

CERN, the Centre of Europe

295

indefinite the year after. It is plausible that Heisenberg, or somebody else, transmitted to Van Hove the reservations that were formulated in the SPC on his account; in any case this appointment marked a turning point in the scientific orientation of the young Division leader. Not only did he stop working in statistical mechanics and embrace particle physics, but also his very style of work changed. From abstract and mathematical it became phenomenological following closely the experimental results. I shall describe in the next section some of his work on multiparticle dynamics which, however, is not at the same level as his earlier rigorous results in statistical mechanics. Let me only remark here that he exercised a great influence on the development of the Theory Division, both through his position as Director, as well as through his strong personahty.

8.5 CERN, the Centre of Europe This section will cover the decade from 1960 to 1970. The first thing that should be explained is the title. To a large extent, it appUes to the entire Laboratory, but, obviously, I shall only refer here to the Theory Division. It is impossible to assign a precise date at which an institution reaches the age of maturity, but for the CERN Theory Division, this date can be placed around 1960. The nineteen fifties were the years of preparation and, to some extent, the years of uncertainty. CERN was the first example of international scientific cooperation and for many physicists its future was not guaranteed. Being a new venture it did not have the prestige of a university chair. If experimentaUsts were often attracted by the facilities the laboratory could provide, many theorists preferred even a junior faculty position to a CERN staff* membership. Under these conditions, it is no wonder that the Council had such great trouble in finding a Director for the Theory Group. Well-estabUshed theorists were not wilUng to give up their prestigious chairs. This situation changed radically around 1960. There are several reasons for this. First, the experimental facilities were completed and the first results were obtained. Although few great discoveries were made (I can only think of the decay mode n ^^ e\ which was found at the SC and was missed in the United States), the work of the laboratory had gained international recognition. The Theory Division had expanded and developed a very active and very rich visitors' programme. This should be contrasted with what happened in most European universities where visiting positions were extremely few if not totally unavailable. By the mid-sixties, CERN had most probably the largest theoretical highenergy physics department in the world. The fellowships reserved to post-docs from the member states made Geneva the meeting place of the best young theorists of Europe. Practically all leading European and American physicists would visit CERN regularly. Especially during the summer months, all available desk space was used. There were even occasional angry letters by American theorists whose applications for unpaid visits were turned down. As a fellow theorist has put it, everybody who was somebody had to visit CERN. An invitation to give a seminar at CERN was considered as a great achievement.

296

Physics in the CERN Theory Division

Furthermore, at least as far as theory was concerned, the entire enterprise was left to the young generation. I remember my first visit to CERN while I still was a graduate student. I was sitting in the back row of the seminar room and remarked that I could not see a single white hair. Coming from a country in which a university professor was never below fifty, I was very impressed. All this made the Theory Division a very exciting and stimulating place. Gone were the days when one '... could not get the right people by applications'. A CERN staff membership was an offer one could not refuse. I know of many physicists who turned down a CERN offer in the fifties. I also know quite a few who did so in the seventies and eighties. There is hardly any in the sixties. Let me also emphasize that, contrary to a wide-spread belief, CERN salaries at that time were not significantly higher than those in the rest of Europe. When I moved to CERN as a post-doc in 1966, I received a very small raise as compared to my French beginner's salary. CERN salaries were driven up by the spectacular rise of the Swiss franc which only occurred in the very late sixties and the seventies. In 1966, however, the French and the Swiss francs were approximately equal. As a result, during the sixties, CERN in general and the Theory Division in particular, were the undisputable scientific centres for high-energy physics in Europe. This domination was such that it gave rise occasionally to personal conflicts and tensions. Some theorists resented the fact that CERN had made no offer to them. This was accentuated by the very rapid initial expansion which created an essentially frozen situation during the sixties. I do not know whether a different policy, namely a more gradual expansion, would have been preferable. It would have certainly left room for a more equilibrated spectrum, both with regard to age and scientific interests, but on the other hand, an initial critical mass was necessary for the success of the enterprise. Quite apart from this question, one should also acknowledge the very essential role that CERN played as a training centre for European theorists. If after 1970 it ceased to occupy the unique position it had during the sixties, this is, to some extent, the ransom of success. So much for the title. It is obvious that I cannot cover in any detail the numerous scientific contributions of this period, not even all those which were judged significant at the time. They are too many. After all, for the main scientific centre of Europe, the opposite would have been catastrophic! There is hardly any subject of theoretical high energy physics which was not touched upon by some member or long-term visitor of the Division. As I shall show presently, several contributions were of fundamental importance, although, of course, the selection which follows is entirely my own. I have distinguished two rather vast areas, weak interactions and symmetries on the one hand and dynamical models for hadronic reactions on the other. Most of the work was done on these two subjects, but I shall also mention some very significant out-of-the-main-stream contributions. I have already presented in the last section the important work that was done in the Division in the domain of weak interactions by d'Espagnat, Prentki and Cabibbo. Maybe this is the right place to complete the story I left unfinished in Section III. The object of the game was to determine the weak current. Here to determine means to

CERN, the Centre of Europe

297

identify it with a known operator of the strong interactions. As we saw, CVC solves the first half of the problem. The weak vector current is identified with the current of isospin symmetry. The identification of the axial part was more subtle: Naively, one would expect an extension of the symmetry of strong interactions from 5(7(2) to chiral SU{2) X SU{2). The trouble is that there is no obvious trace of such a symmetry in the hadron spectrum. Nucleons do not appear to have degenerate, or almost degenerate, partners with opposite parity. The answer is called PCAC (Partially Conserved Axial Current) and it involves the concept of spontaneous symmetry breaking. Several names can be associated with it, including M. Goldberger, S. Treiman, Y. Nambu and J. Goldstone. The conclusion is that strong interactions do obey an approximate chiral SU{2) X SU(2) symmetry but the axial part is spontaneously broken with the pions being the corresponding Nambu-Goldstone bosons. The final act in the classical weak interaction play marks simultaneously the beginning of a new era. It refers to the building of the first neutrino beams in the early sixties. Until then, decays of unstable particles and nuclei provided the only available tools for the study of weak interactions. All these are low energy and low momentum transfer processes. The construction of high energy neutrino beams, which turned out to be a technological wonder, opened new, in principle unlimited, horizons. It gave rise to the first full-scale CERN-Brookhaven competition, which is a very interesting story by itself. CERN developed a superior engineering project but lost the physics part and this failure had a bad influence on the morale of the organization. On the scientific side, the first neutrino experiments proved the separate identity of the second neutrino and established the individual electron and muon quantum numbers. Cabibbo's 1963 paper put the final stone in the classical construction of weak interactions. Nothing important happened in this direction during the following years either at CERN or abroad. However, two years later, a totally unexpected experimental result opened a new chapter which is not yet closed. A measurement of K^ decays revealed the existence of the In mode, in contradiction with the invariance under CP. This result, less than ten years after the discovery of parity violation, came as a shock to the international physics community. The reluctance to admit CP violation was such that all early theoretical work on the subject aimed at reestabUshing CP conservation by inventing various schemes to explain the KP results. Although CERN theorists played an important role in these investigations, I shall not describe them because they all have been disproved experimentally. Among the names I would have mentioned, had I done a more extensive study, are those of John Bell, Jacques Prentki and Martinus Veltman. Incidentally, I want to point out that even some important contributions by American physicists, like T.D. Lee or L. Wolfenstein, appeared as CERN publications because their authors were visiting CERN. This is but one example of the very active visitor's program of the organization. The only paper from the Theory Division on the subject of CP violation which has passed the test of time, is a very clear analysis by John Bell which has been presented in a joint report with Jack Steinberger [10]. Bell does not propose a model but gives the most general framework to analyze the data. The essential new result is a set of relations which

298

Physics in the CERN Theory Division

unitarity imposes among the elements of the mass and decay matrices of the I^ — K° system. The report, written in Bell's classic style, is considered to be one of the best articles in the subject. Today, almost thirty years after the discovery of CP violation, the chapter is still open. We do not know whether it is a property of the weak interactions or whether it provides the only manifestation of a new, super-weak interaction. As I said earlier, the search for an understanding of the nature of the weak current had let theorists to uncover a hidden symmetry of the strong interactions. The study of chiral symmetry soon became a central problem in theoretical particle physics. It coincided with the establishment of the eightfold way and was thus extended to SU{3) x SU{3). The extension o{ SU{2) (isospin) to SU{3) as the symmetry group of strong interactions was not a straightforward one. SU{2) is realized in a simple way with the nucleons belonging to the fundamental two-dimensional representation. The direct generalization would yield a triplet (/?,«, A). In fact, this model was proposed in the fifties by Sakata but it was soon disproved by the data. The correct solution, found independently by M. GellMann and Y. Ne'eman, assigns the eight baryons p,n, A^l^"^,lP,E~,E^ in the eight-dimensional adjoint representation of SU{3) and leaves the fundamental triplet empty. This was probably the reason why it took so long to discover. Physicists were conditioned by isospin into beUeving that the lowest-lying states should belong to the fundamental representation. On the other hand, hadron spectroscopy, which was a very rapidly expanding subject, showed that mesons formed SU{3) octets and baryons formed octets and decouplets. This pattern, together with the absence of triplets and the proliferation of 'elementary particles', led some theorists to wonder whether we were not simply uncovering another layer of the onion, i.e. whether all hadrons were not bound states of a few 'elementary' constituents which would form triplets. The 'quark model' was proposed independently by Gell-Mann and George Zweig, an American physicist who was visiting CERN in 1964. He called his constituents 'aces' while Gell-Mann called them 'quarks'. Incidentally, I want to point out that Zweig's papers [11] have never been published. Apparently, this was due to his insisting on submitting them to the Physical Review, contrary to CERN's policy to publish only in European journals. One of the early calculations using quarks as constituents of hadronic matter is due to Victor Weisskopf, then Director General, and Roger Van Royen [12]. Although the quark model soon became quite popular, the status of quarks themselves varied considerably in the course of time. Through the results from deep inelastic lepton-nucleon scattering, as well as those from large angle hadron collisions, they evolved, from purely mathematical objects, into the realm of 'elementary' particles. Incidentally, one of the main motivations behind Weisskopfs decision to build the ISR, was the smashing of the nucleon and the discovery of physical quarks. This programme was realized, but in an unexpected way. The ISR did support the evidence, first found at SLAC, for the existence of quarks, although it did not produce them as physical particles. Immediately after discovering SU{3), Gell-Mann proposed the chiral SU{3) x 517(3) algebra of currents. In fact it was this paper that was published in the Physical Review,

CERN, the Centre of Europe

299

while the previous one on the eightfold way remained as a preprint. It was immediately realized that current algebra was a very powerful scheme and, for several years, it provided one of the dominant research themes in theoretical high-energy physics. Its first, and most important, success was obtained, independently, by Stephen Adler and WiUiam Weisberger in 1965. They expressed the weak axial vector coupling in terms of the pion-nucleon scattering amplitude. A masterful appUcation of PCAC and a direct way to fix the relative scale between axial and vector currents, thus giving experimental support to the idea of chiral symmetry. One of the most significant papers in the early period of current algebra came from the CERN Theory Division. It is signed by Sergio Fubini and Giuseppe Furlan in 1964 [13]. They proposed a general method to derive sum-rules out of the equal time commutators of the algebra. They considered a particular matrix element, they saturated the product of current operators with intermediate states and used spectral integral representations to transform it into a sum-rule. The method is very powerful and it was used extensively. The following year, together with G. Rossetti, they proposed an improved version [14], which made use of dispersion relations and was manifestly covariant. In fact, two methods had been developed to extract physical information out of current commutators: the first was this one and the second, proposed by Steven Weinberg in 1966, consisted in writing the Ward identities of chiral symmetry in the form of low-energy theorems. During the late sixties, current algebra became one of the main research subjects of the CERN Theory Division. Numerically the production was quite substantial (I contributed personally to that). But among the few results of some importance that I can think of, one is a theorem due to David Sutherland, a fellow from Scotland, and also to M. Veltman and John Bell [15]. Sutherland was the first to look at the consequences of chiral symmetry in the presence of electromagnetic interactions and he derived a very simple, although unexpected, result: at the limit of exact PCAC, i.e. no explicit breaking of chiral symmetry, the electromagnetic decays of pseudoscalar mesons, such as n^ or Y\, are forbidden. The argument is very simple and depends only on the canonical commutation relations among neutral components of vector and axial currents. This result was embarrassing for two reasons: first, it was in obvious contradiction with experiment. Second, it seemed to be against all naive expectations coming from simple field-theory models. This second difficulty was not immediately recognized and brings me to an important contribution of the Division, the celebrated Bell-Jackiw paper on anomalies. As far as I know, the first person to worry about the compatibility of Sutherland's theorem with field-theory and current algebra was Roman Jackiw, an American post-doctoral fellow who was spending a year at CERN on leave from the Society of Fellows at Harvard. I remember Jackiw discussing this problem with me and we both asked the advice of Henri Epstein, a French mathematical physicist and expert on field theory. Epstein explained to us, using a very sophisticated language, that naive consequences of classical equations of motion and symmetries in field theory are not necessarily correct at the quantum level. I was satisfied with this explanation which involved singular products of distributions and all the associated mathematical artillery, but Jackiw was not. Especially when he became aware of an

300

Physics in the CERN Theory Division

old calculation by Jack Steinberger who, in 1948, had computed the n^ —> 2y decay width in the one-loop approximation and had obtained the correct answer. Steinberger had used a model in which the pion was a nucleon-antinucleon bound state and had assumed a pseudoscalar pion-nucleon coupUng. It turns out that the one-loop diagramme, although linearly divergent by power-counting, is in fact convergent once gauge invariance is imposed and the trace over y-matrices is performed. Jackiw, discussing with Bell, realized that Steinberger's model was essentially identical with the a-model, which was considered as a field-theory example of current algebra. Now the contradiction was clear: on the one hand we had a model which was supposed to reproduce all the results of chiral symmetry, including Sutherland's theorem; on the other we could compute explicitly in perturbation theory and find a non-zero answer. Bell and Jackiw wrote a remarkable paper [16] which contains two parts: in the first they set the problem in a clear and unambiguous way. They compute the one-loop diagram using PauH-Villars regulators, the only gauge invariant scheme known at that time, and they correctly identify the origin of the problem with the auxiliary Pauli-Villars regulator fields whose masses break the conservation of the axial current. The second part, although incorrect, is also very interesting. They attempt to construct a modified Pauli-Villars regularization which would guarantee the simultaneous conservation of both gauge and chiral symmetries. They were the first in a long series of unsuccessful attempts to regularize the anomaly away. This paper, which was soon followed by a similar but more complete one by Adler, established the concept of anomalies in gauge theories, which proved to have deep and far-reaching consequences in theoretical high energy physics. A few years later, in 1971, Bruno Zumino, who had already joined CERN, and Julius Wess from Karlsruhe, found a set of consistency conditions which determine the form of the possible anomalous terms in any gauge theory [17]. The importance of this paper grew considerably over the years. It was originally recognized as a very useful method to discriminate among various anomaly calculations. However, with the introduction of powerful mathematical techniques to the study of the anomaly structure of gauge theories, the Wess-Zumino consistency conditions became the starting point of a new field of research, that of topological field theories. The last paper I want to mention in the domain of weak interactions and symmetries is a 1969 Nuclear Physics article by David Gross and Christopher Llewellyn Smith [18]. They generalized, to the case of neutrino-nucleon deep inelastic scattering, a sum-rule previously obtained by Curtis Callan and David Gross for electroproduction. In particular, they discussed the structure function which corresponds to the vector-axial-vector interference term which is absent for electron scaterring. These sum-rules played an important role in the development of the parton-model ideas and the eventual emergence of quantum chromodynamics. There have been a couple of additional seminal papers using current algebra ideas from the TH Division, but they belong to the pre-history of the Standard Model and I shall review them in the next section. In a more complete study, one should have mentioned some of the attempts at constructing a relativistic generalization of SU(6), i.e. at finding a symmetry group containing, in a non-trivial way, Poincare and internal symmetry.

CERN, the Centre of Europe

301

However, today we know of the futility of all these attempts, so I shall not pursue this subject any further. Let me now come to the second major subject, that of the study of dynamical models for strong interactions. As I said earlier, a very general approach was developed during the fifties which was based on the analyticity properties of the scattering amplitude continued analytically in the complex energy plane. The first dispersion relations were written in the United States between 1955 and 1957. Soon after, there appeared two very fundamental contributions. They gave the subject a tremendous impulse and made it the most promising approach for the understanding of hadronic reactions. The first is due to Stanley Mandelstam who had just joined the University of California at Berkeley (in fact his first paper was written while he was visiting Columbia). Mandelstam extracted from the square diagram in qr" field theory the analyticity properties of the two-particle elastic scattering ampUtude as a function of two complex variables, energy and momentum transfer. He made two important assumptions: first, one of 'maximum analyticity' which means that the only singularities of the amplitude are those imposed by unitarity and crossing symmetry and second, an assumption about a polynomial boundedness of the ampHtude in any complex direction in energy and/or momentum transfer. These two assumptions allowed him to write a double dispersion relation, the so-called 'Mandelstam representation', which became the bible for hadronic physics. Partly motivated by this work, TulUo Regge, a mathematical physicist from Italy, pubUshed in 1959 and 1960 two papers in which he introduced the fundamental concept of complex angular momentum. If the continuation in the complex plane seems natural for a continuous variable, such as energy or momentum transfer, the same idea applied to angular momemtum, which can take only discrete values, was a quite revolutionary one. In fact, in such a case the uniqueness of the continued analytic function is not guaranteed by the standard theorems. Regge studied the non-relativistic model of potential scattering where he could construct the resulting analytic function in the complex /-plane explicitly. As far as I know, the argument for the general case, which is based on an assumption about the asymptotic behaviour of the amplitude for large / and uses a mathematical theorem by Carlson, was first pointed out by Andre Martin. One of the important practical results of Regge theory was the idea that the asymptotic behaviour of the scattering amplitude for large values of the energy could exhibit a non-trivial dependence on the momentum transfer. The Mandelstam representation on the one hand and the Regge behaviour on the other, soon became the cornerstones of a very ambitious proposal, known as the analytic •S-matrix theory. Its main advocate was Geoff'rey Chew from Berkeley who, together with Steven Frautschi, expressed the set of rules which were supposed to determine directly the elements of the S-matrix for any hadronic reaction without appealing to an underlying dynamical model such as field theory. This approach, which from exaggerated heights of faith has fallen into totally unjustified depths of oblivion, gave rise to many fundamental concepts in high energy physics in the development of which the CERN Theory Division played an important role. The work done was in two parallel directions. The first was mathematical and aimed at a rigorous derivation of the somehow vague postulates of

302

Physics in the CERN Theory Division

analyticity and asymptotic behaviour, starting from the axioms of quantum field theory. The second was directed towards phenomenology and comparison with experimental data. In the first direction I want to present the work of Jacques Bros, Henri Epstein and Vladimir Glaser on the one hand and Andre Martin on the other. Glaser was the central figure of mathematical physics at CERN. As a young visitor in Gottingen he had participated in the elaboration of the LSZ (Lehmann, Symanzik, Zimmermann) programme. (In fact, the third paper in the series appeared as GLZ, where G stands for Glaser). Already around 1960, Glaser had started thinking about the problem of analytic completion in quantum field theory. In 1961, he lectured on this subject in Paris. Jacques Bros and Henri Epstein were interested in the same problem and Glaser invited them to CERN. This initiated a long lasting and very fruitful collaboration. Their first joint paper, published in 1963, is considered a classic [19]. In the framework of the LSZ axioms, they derived an analyticity domain for the four-point function, considered as a function of six complex variables (energy, momentum transfer and four mass variables), which contains a vicinity of the physical region. In the LSZ formalism the ^S-matrix elements are obtained by Fourier transforming certain vacuum expectation values of products of field operators. Several such functions can be constructed, such as retarded, advanced, time-ordered etc. Causahty impHes well-defined support properties for these functions in position space, which in turn translate into a primitive analyticity domain in momentum space. Moreover, these Fourier transforms coincide in certain real regions. Therefore, by the edge-of-thewedge theorem, they are all boundary values of a unique analytic function. Bros, Epstein and Glaser in their 1963 paper proved that the analyticity domain for the four-point function is larger than the primitive one and contains the physical region. For the first time in physics they used very sophisticated geometrical techniques of analytic completion borrowed from the theory of functions of several complex variables. In 1965, they completed this result by proving the crossing property always for the four-point function [20]. They showed that any couple of physical regions in the {s, t, u) space corresponding to scattering amplitudes involving two incoming and two outgoing stable particles with arbitrary masses, are connected by a certain domain of analyticity. Bros, Epstein and Glaser studied the so-called 'linear' problem, in which the unitarity condition, a non-linear relation, is not used. Originally unitarity was used in order to control the magnitude of the scattering ampHtude. The oldest pubHshed example I have found is an article by T.D. Lee in a CERN report of 1961. He argued that the lowest order Fermi theory of the weak interactions must break down at some energies because the cross section for ev -^ ev grows too fast, like k~^, although the only contributing partial wave is J =\. The best known example is a brillant article by Marcel Froissart, who derived his famous bound also in 1961. However, the most systematic use and the most thorough exploitation of the unitarity relation is due to Andre Martin. Through the sixties and the early seventies he created at CERN the best school for this problem, he introduced several other theorists into it and established himself as the undisputed expert in the field [21]. He obtained two sorts of results: rigorous bounds, a la Froissart, for the growth of hadronic total cross-sections, as well as limits on the pion-pion scattering ampHtude on the one

CERN, the Centre of Europe

303

hand, and an enlargement of the analyticity domain of scattering ampUtudes on the other. In both fields, his results are among the most powerful known today. His initial programme on the analyticity domain aimed at proving the entire Mandelstam representation from the axioms of field theory. Already in 1959 he gave, in collaboration with John Bowcock, a first derivation in the framework of a potential model [22]. In 1966 he obtained the first results in relativistic field theory. In the linear programme, Bros, Epstein and Glaser had proved dispersion relations for negative momentum transfer — ^ < r < 0. Martin, using the unitarity relation, obtained dispersion relations for t < \R\ which includes real positive t. For the special case of pion-pion scattering, crossing symmetry allowed him to obtain the same result for t inside a domain D containing the real segment t = —2%I? to t = Ai?. For not too high energy the domain contains part of the Mandelstam cuts. In a subsequent paper Martin extended this result and established the largest rigorous analyticity domain. It is essentially through his work that we are convinced today that Mandelstam representation is not derivable from field theory. I shall leave the domain of mathematical physics at this point and move to some interesting phenomenological models for strong interactions, which have been developed at CERN. I shall present three of them: Amati, Fubini and StangheUini's multiperipheral model. Van Hove's work on diffraction scattering and his method on the longitudinal phase space analysis and Hagedorn's thermodynamic model. All three aimed at a description of multiparticle production hadronic collisions which represent the bulk of experimental data. None is entirely successful, hardly a surprising result if one takes into account the simultaneous presence of several competing mechanisms, none of them being clearly dominant except for some reactions and some regions of the phase space. The so-called 'peripheral' model was introduced in 1960 by Sidney Drell and F. Salzman and G. Salzman. The name comes from the fact that this model assigns a dominant role to the exchange of the Ughtest strongly interacting particle, the pion, between the incident particles. In a series of papers in 1961 and 1962, Daniele Amati, Sergio Fubini and Antonio StanghelUni, partly in collaboration with Mario Tonin and Luciano Bertocchi, generalized the concept of peripherism to a multi-peripheral model [23]. They gave a theoretical justification to the peripheral model by showing that it corresponds to keeping only the nearest singularities in the Mandelstam representation, the so-called 'strip approximation', an approximation which is justified if the energy is not too high. At higher energies the same analysis yields the multiperipheral model for inelastic reactions which consists in taking a chain of lower energy amplitudes Unked together by virtual pions. As a next step, they considered the corrections to the model induced by unitarity. They showed that these correction terms could not be interpreted as coming from the exchange of simple poles in the angular momentum plane and they were thus led to postulate the existence of Regge cuts. This was considered as an unorthodox suggestion and they had trouble with the referee who did not want to accept this idea. Van Hove's main scientific interest at CERN was on high-energy hadronic collisions. He concentrated in the small-angle diffraction region and in an early 1964 paper he developed the ideas of diffraction scattering as the shadow of inelastic coUisions [24]. In 1969 he

304

Physics in the CERN Theory Division

proposed the so-called 'longitudinal phase space analysis' [25], which is not a detailed dynamical model, but rather a general method to study multiparticle reactions. It is based on the phenomenological input that the largest part of the total cross-section is made out of small transverse momemtum secondaries. Van Hove proposed to separate phase space into a longitudinal and a transverse part and to keep only the longitudinal projection. He explained that this physically amounts to generalizing to many-body processes the distinction of two-body coUisions into forward elastic, backward elastic and exchange processes. Although this method involves no fundamentally new concepts of any kind, it has been extensively used by experimentalists and even by many theorists. Surprising as it may sound. Van Hove turned out to be one of the most phenomenologically oriented senior theorists of the Division. Under his influence CERN developed a very strong group for the study of diff'ractive scattering phenomena. Unfortunately this was not a very good choice. We know to-day that the 'soft' scattering events are not very interesting but, in the sixties the accelerator energies available were not sufficient to produce many large transverse momentum events and so the fundamental significance of the latter was not clearly recognized. Hagedorn's thermodynamic model grew out of his early association with the PS division. As I said earlier, he was in charge of computing the multiparticle cross-sections and distributions. In the absence of any detailed dynamical model, he made the simplest possible assumption, namely that a very complicated interaction may take place in a certain volume F, but the probabilities for the different final states are determined by the available phase space. This gave rise to the CERN version of the statistical model which he formulated already in 1959 [26]. Later, when he moved to TH, he continued to work in the same direction. He also used the experimental information of limited transverse momentum for final particles and had the idea of associating it with an upper bound for possible values of temperature [27]. He thus postulated a new form of thermodynamics with a maximum value of temperature of the order of 160 MeV, or 10^^A^. Apart from its obvious astrophysical consequences, the model also made the novel prediction of an exponentially growing hadronic mass spectrum. Both these features, finite limiting temperature and exponential mass spectrum, were met with some scepticism when they were first proposed in 1965. However, they later found their place in the framework of dual models. This brings me to one of the most influential papers in the entire CERN pubHcation list, the celebrated 1968 article by Gabriele Veneziano [28]. The reason I shall not go into much detail is that, as far as I remember, Veneziano arrived at CERN from the Weizmann Institute with the manuscript essentially ready. So although the paper appeared as a CERN article, the entire credit should not go to the Division. In fact, in 1968 Veneziano was at CERN only as a summer visitor. Nevertheless, it is true that CERN theorists did play an important role in the subsequent development of these ideas. Veneziano's paper has the title: 'Construction of a crossing-symmetric, Regge-behaved amplitude for linearly rising trajectories'. In the traditional approach one starts from a dynamical model, for example field theory, and tries to compute the scattering amplitude.

CERN, the Centre of Europe

305

Veneziano did the opposite. He guessed a very special form and postulated it directly at the level of the amplitude. He never asked the question of the existence of an underlying theory which would give rise to such an ampHtude. His main example was Hector Rubinstein's toy reaction mt -^ nco. This process is not physically measurable, and its only merit is simplicity. The separate conservations of angular momentum and isospin imply the description by a single invariant amplitude. Veneziano postulated that this amplitude, considered as a function of the Mandelstam variables s, t and w, is given by a ratio of Ffunctions. This extremely simple form has almost magic properties. It is crossing symmetric by construction, the singularities of the F-functions reproduce a spectrum of particles lying on linearly rising Regge trajectories and it has the correct Regge asymptotic behaviour. Most important, it exhibits the property of duaUty, i.e. the sum of Regge exchanges in the cross channels gives rise to the resonances in the direct channel. This model, which was subsequently generalized to multiparticle ampUtudes as well as to particles with spin and isospin, became the base of an entire branch of theoretical physics, that of dual models and string theories. Out of these studies emerged new fundamental concepts, such as supersymmetry, infinite dimensional algebras or two-dimensional conformal field theories, whose importance trancends the domain of high-energy physics. I shall come back to them in a later section. This concludes my brief account of the work done in the Division in the two principal subjects, that of weak interactions and symmetries and that of strong interaction dynamics. Before closing this section I want to mention some out-of-the-mainstream contributions. I have chosen three subjects: mathematical physics, nuclear physics and foundations of quantum mechanics. Mathematical physics has always been well represented in the CERN Theory Division. In the sixties the permanent staff members in this field were Vladimir Glaser and Andre Martin. I have already had the occasion to present an important part of their work. Here I shall give some additional information. In 1958, Walther Thirring proposed a field theoretic model involving a massless Dirac field, interacting through a four-fermion contact term, in one space and one time dimensions. The purpose of the model was to represent, in a simpUfied two-dimensional world, a theory which was strongly advocated by Heisenberg. However, as had already been pointed out by Thirring, the model, although very simple, had many interesting properties and, over the years, it became a very useful tool in quantum field theory. The main reason is that the model turned out to be exactly solvable and the first operator solution was given the same year by Glaser [29]. It was completed in 1961 by K. Johnson. Glaser gave an explicit expression for the operator ^{x) as a function of the incoming field. He showed that the ^-matrix is unitary, but it is given by a pure phase, so all nontrivial scattering amplitudes in the model vanish. Thirring's model was the first exactly solvable relativistically invariant quantum field theory and its subsequent study exemplified many interesting phenomena such as two-dimensional bosonization (the model turned out to be equivalent to the Sine-Gordon bosonic model) or the appearance of anomalous dimensions for the operators of a quantum field theory.

306

Physics in the CERN Theory Division

The second contribution in mathematical physics that I want to mention comes from H. Epstein and V. Glaser. In a series of papers around 1970 they presented a novel method for the study of the renormalization programme in perturbation theory [30]. They showed by an inductive construction order by order in perturbation series that the only ambiguities in the definition of the «-point Green functions are concentrated on the origin in position space and, therefore, they can be absorbed by local counterterms in the Lagrangian. The resulting series satisfies, at each order, the requirements of locahty. Let me now come to nuclear physics. As I have said earlier, this was the most important research subject of the Theory Group during the Copenhagen years where the emphasis was on nuclear structure. After 1957 many fellows came to Geneva, so this activity persisted. However, practically no new appointments were made in this field which soon disappeared from the publication list of the Division. The only contribution from this period that I want to mention is the so-called 'cluster model' for nuclear structure [31] proposed in 1958 by Th. Kanellopoulos and K. Wildermuth. The model describes nuclei as aggregates of smaller nuclei and has been quite successful, especially for certain low-lying states. After 1960, a new period begun. With the construction of the PS, the main experimental activity for high-energy physics moved there. The SC became principally a nuclear physics machine. In fact for many years this machine provided the main information about the pion-nucleus interaction, well before the construction of meson factories. I understand that it was Victor Weisskopf, then Director General, who decided to create a corresponding small group in the Theory Division. Torleif Ericson, a nuclear physicist from Sweden, was put in charge of it. Just before joining CERN, while he was visiting Berkeley on leave from the University of Lund, Ericson had published a short article in the Physical Review Letters [32], where he predicted what became known later as 'Ericson fluctuations', i.e. the phenomenon of chaotic continuum fluctuations in nuclear reactions. He developed this idea further while at CERN [33] and, with the recent explosion in the study of chaotic dynamics, this work has been recognized as very important. At CERN Ericson did not pursue the Copenhagen tradition of the study of nuclear structure. In collaboration with Magda Ericson, a nuclear theorist from France, they were among the first to study the interaction of pions with nuclei and to explore a regime which was intermediate between the low energies of traditional nuclear physics and the new high energies of elementary particles. This decision was a fortunate one. The subject turned out to be quite interesting and allowed them to respond to the expectations of the experimental groups working on the SC without losing contact with the rest of the Theory Division. In 1966 M. and T. Ericson published a long article in Annals of Physics [34] which, apart from summarizing their earlier work, contained many novel ideas whose significance has grown in time. Starting from the data on TC-N scattering and n production in A'^ — A^ collisions they derived a non-local potential for the interaction of pions with finite-size nuclei which takes absorption effects into account and correctly describes multiple scattering phenomena. It is this last point, which is based on a novel development in multiple scattering theory, which

The rise of the Standard Model

307

has had many repercussions in many other areas, such as many-body physics, nuclear matter theory, etc. This article constitutes one of the basic references in this field. In the late sixties, following the developments of current algebra and PCAC in elementary particle physics, the Ericsons applied these techniques to the pion-nucleus interaction [35], where the finite size of the nucleus presented a new conceptual difficulty. They derived the soft-pion theorems and studied the effects of the extrapolation off-mass-shell. I think it is fair to say that over the years the CERN team, enriched periodically with a few fellows and visitors, became one of the strongest in this field worldwide. I have left to the end the subject of the foundations of quantum mechanics. It was certainly out of the mainstream, not only at CERN, but everywhere. In the Division it was the work of a single man, John Bell, who first succeeded in taking it out of the hands of philosophers and bringing it into the world of physics. I believe that everybody who has ever taught quantum mechanics has felt a certain degree of uneasiness concerning its basic axioms. One way to express this feeling is to say that quantum mechanics predicts two possible evolutions for a physical system: The first is the usual Cauchy-type evolution described by Schrodinger's equation. The second, more obscure, is the reduction of the wave function when a measurement is performed. The most popular example of this problem is the famous EPR (Einstein, Podolsky, Rosen) experiment. Bell's fundamental contribution to this question was two-fold. First he showed that von Neumann's theorem on the mathematical impossibility of introducing hidden variables in quantum theory was wrong [36]. All the existing proofs, starting from that by von Neumann, had made some additional, and in fact unjustifiable, assumptions concerning the states characterized by such hidden variables. Second, and most important, he showed that the question was in fact a physical one, i.e. it could be answered by experiment. In his famous 1964 paper he derived the so-called 'Bell inequahties' [37]. He showed that no local hidden variable theory could reproduce the quantum mechanical prediction for an EPR-type experiment. I think that these two papers, in addition to stimulating exciting experimental work, have completely changed our perception of the profound nature of quantum mechanics.

8.6 The rise of the Standard Model This section breaks the story. It does not cover any particular period in time, let alone one of the CERN Theory Division. Although it relates the most extraordinary achievement in modern theoretical physics, it is going to be rather short, because the role of CERN in it was only marginal. However, it would have been a mistake to omit it altogether. First because gauge theories changed completely our way of thinking. After 1971, nothing was the same as before. But also because in science, pleasure and excitement do not come solely by watching the success of one's own ideas. They come mostly from following closely the whole enterprise, from sharing the disappointments and taking part in the expectations.

308

Physics in the CERN Theory Division

The road to the Standard Model was a series of misunderstandings. Never in history have so many missed so much for so long. Essentially all the important milestones went unnoticed when they were first proposed. Many important ideas had to be rediscovered again and again. The protagonists did not seem to be aware of each other's, and occasionally even of their own, work. Among the numerous conclusions a historian of science can draw from the study of this period, a very astonishing one is the ultraspecialization of the high-energy theoretical physics community. In most universities worldwide, young researchers were inadequately trained in quantum field theory, let alone statistical mechanics. I remember a remark I made when I passed my thesis: I told the committee that the only things I was really required to know, were how to compute tree-level Feynman diagrams and how to read the Rosenfeld tables. I was only sHghtly exaggerating! The first milestone was the construction of non-abelian gauge theories by C.N. Yang and R.L. Mills in 1954. They explicitly wrote the covariant derivative and the curvature tensor for SU{2). They wanted to apply these ideas to isospin, although their detailed motivation is not clear. In the paper they have some remarks concerning global symmetries and locality which I do not understand, but I believe that they were attracted by the aesthetic value and the high degree of symmetry of the theory. To say that this is one of the most important papers in particle physics, sounds today like a trivial statement, but it was certainly not recognized as such at the time. Although it did stimulate a certain amount of interest, it appeared to be plagued by massless vector bosons and nobody knew what to do with them. In this connection, there is a very interesting correspondence between Yang and Wolfgang Pauli who feared that the infrared behaviour of these theories would be untractable. This question of the infrared singularities continued to confuse people even after the proof of renormalizability. It was finally settled by T. Kinoshita and A. Ukawa who proved in 1976 that Yang-Mills theories give a perfectly well-defined field theory at the Green function level. Singularities arise only when one attempts to go on mass-shell. I cannot resist mentioning at this point an intriguing and essentially unknown paper by Oscar Klein who, in 1938, wrote something which looks close to a Yang-Mills theory for the interactions between nucleons. The trouble is that he has made some crucial although trivial mistakes in elementary group theory and, even today, it is very hard to judge its real significance. During the late fifties and the early sixties, there appeared a series of papers which, following the intermediate vector boson hypothesis, attempted to use massive Yang-Mills theories for weak interactions. Julian Schwinger considered an electroweak theory based on the group SU{2) with the photon being the neutral boson. Sidney Bludman wrote an SU{2)^^^^ X ^(l)e.m. n^odel in which all weak currents, charged as well as neutral, were left-handed. The most interesting contribution of this period comes from Sheldon Glashow who first understood that, in an SU{2) x U{1) theory, the photon is not necessarily the vector boson of U{1). It is in general a superposition of U{1) and the neutral component of SU{2). In this way he introduced a mixing angle, the celebrated 0w It is amusing to notice that, at the same time, he made all sorts of wrong claims concerning the renormalizability of massive Yang-Mills theories. They were due to mistakes in field theory.

The rise of the Standard Model

309

which is surprising from a student of Schwinger's and shows the extent of unfamiUarity of particle physicists with the intricacies of quantum field theory. I leave the story of Yang-Mills theories at this point in order to start another one. To the best of my knowledge, so far CERN theorists had not worked in this field. The new story is that of spontaneous symmetry breaking. It entered the world of particle physics through the works of Y. Nambu and J. Goldstone. By the mid-sixties everybody had accepted the idea that chiral symmetry was spontaneously broken with the pions being the nearGoldstone bosons. Completely unnoticed went a work of PhiHp Anderson who, in 1962, studied the phenomenon of spontaneous symmetry breaking in the presence of long-range forces. But at that time nobody in high-energy physics was reading papers in statistical mechanics. Two years later Robert Brout and Fran9ois Englert fully developed this idea in the framework of a relativistic field theory. They showed that in a spontaneously broken gauge symmetry the vector gauge bosons acquire a mass and the Goldstone bosons decouple and disappear. The resulting theory has massive vector bosons and at least one physical scalar field. The same conclusion was reached independently by Peter Higgs and also by T.W.B. Kibble. Again, there was no immediate reaction. I remember Brout giving a seminar at CERN in 1966 or 1967.1 did not understand much of it, but I discovered that I was in good company. One of the reasons is that we were all focussed on strong interactions. If I remember correctly, Brout was trying to apply this idea to the breaking of SU{2>).

In 1967 Weinberg's paper appeared in Physical Review Letters. He took over Glashow's model of SU{2) x U{1) and appUed the idea of spontaneous symmetry breaking. The result was revolutionary; for the first time weak and electromagnetic interactions were treated on equal footing. The breaking of the symmetry was responsible for their apparent different strengths as well as for their mixing. The Glashow angle was not an assumption any longer, but a natural consequence of the model. The paper was clear and beautifully written, still it passed unnoticed. It was presented in our study group at CERN, I believe by Bruno Renner. We unanimously decided that it was uninteresting. I promptly forgot everything about it. There were two reasons for this. First, Weinberg did not have any proof for the renormalizabiUty of his model. Second, as was already mentioned in the title, it was a model for leptons only. Its extension to hadrons seemed impossible. We were all much too attached to the universality of weak interactions and we considered the mere suggestion to abandon it as sacrilegious. Let me interrupt here in order to present some of the early CERN contributions. I have chosen two of them. Around 1966 Veltman was trying to understand the deeper origin of the conservation, or near conservation, of the weak currents. In particular, he tried to throw some light on the general confusion which prevailed at that time concerning the so-called 'Schwinger terms' in the commutators of two current components. While he was on a visit from CERN to Brookhaven, he wrote a paper in which he suggested a set of divergence equations which generalized the notion of the covariant derivative of quantum electrodynamics [38]. This fundamental idea was taken up the next year and developed further by

310

Physics in the CERN Theory Division

Bell [39]. He rederived the divergence equations starting from a formal gauge invariance. Although the emphasis was still on Schwinger terms, the underlying gauge principle was explicitly stated. For Veltman this was a clear signal that weak interactions were described by a Yang-Mills theory. Unfortunately for CERN he left that year for Utrecht. His opposition to Van Hove, his former teacher, was legendary and an endless source of jokes in the CERN corridors. Senior staff appointments in the CERN Theory Division have often been criticized and Veltman's case is among the most striking ones. He was already at CERN, he probably wished to stay, but Van Hove wouldn't allow it and nobody in the Division was willing to oppose him. The second contribution of the Theory Division had a totally different motivation. In the late sixties, through the successes of current algebra, a few people started realizing that strong interactions could not provide a cut-off for the weak ones. I believe that the first to make this remark were B.L. loffe and E.P. Shabahn from the Soviet Union. To lowest non-trivial order the weak interactions would give quadratically divergent contributions of the form GA^, where G is the Fermi coupling constant and A the cut-off. This raises the spectre of strangeness and parity violations in strong interactions unless A is chosen to be very small. From the absence of such violations loffe and Shabalin obtained a very low value of A, of the order of a few GeV. This was quite disturbing because the cut-off is supposed to give the energy scale up to which the theory can be trusted. The cure to this disease was found at CERN by Claude Bouchiat, Jacques Prentki and myself in 1968 [40]. We proved that, under the assumption that the chiral SUi}) x SU(}) symmetry breaking term in the hamiltonian transforms like the quark mass term, the operator which multipHes the leading divergences is diagonal, i.e. it does not connect states with different quantum numbers, strangeness and/or parity. This settled the question of the leading divergences. However, the next-to-leading ones turned out to be equally troublesome. To «-th order they are of the form G ( G A ^ ) " and they can contribute to the A^ - A^ mass difference or to processes like A^ -^ f^^f^'- From the experimental point of view, it is as unacceptable to have these processes as ordinary first order weak transitions as to have parity and strangeness violations in strong interactions. Trying to cure this second disease, Sheldon Glashow, Luciano Maiani and myself were led to the introduction of the charmed quark, but again it was after we had left CERN. We proved that weak interactions can be formulated as a Yang-Mills theory even in the hadronic sector. Unfortunately nobody, not even Weinberg, brought Weinberg's 1967 paper to our attention. In the meantime several people were studying Yang-Mills theories from a field-theoretic point of view. The correct Feynman rules were obtained for the massless case by R.P. Feynman, B.S. De Witt, L.D. Faddeev and V.N. Popov and S. Mandelstam. But the most important work was done by Veltman who studied the divergence structure of the massive theory. He was the first to realize the vital significance of the Ward identities and the importance of working on-shell. In 1971, the world learnt of a student of his, Gerard 't Hooft, who proved the renormalizabihty of the spontaneously broken theory and the unitarity of the resulting 5-matrix. This was the turning point. From this moment gauge theories stormed particle physics.

The rise of the Standard Model

311

The final touch to the electroweak theory was made the following year. Strictly speaking Weinberg's model for leptons is non-renormalizable because the Adler-Bell-Jackiw anomalies spoil the Ward identities for the axial current. Claude Bouchiat, Philippe Meyer and myself realized that adding the quarks resulted in a cancellation of the anomalies thus removing this final obstacle. A consistent, renormalizable theory of the electroweak interactions was, finally, at hand. Let me here pause again in order to present the post-1971 CERN contributions. I shall only mention two which refer to the construction of the model. The first is a variation, published by Jacques Prentki and Bruno Zumino in 1972, which did not have neutrino induced neutral currents [41]. Since it was disproved by the Gargamelle experiment the following year, I shall not comment on it any further. The second is a very interesting analysis by Christopher Llewellyn Smith in 1973 [42] who asked himself the following question: in the spontaneously broken phase, when everything is said and done, the theory only has massive particles. By naive power counting it is hopelessly non-renormalizable. However, we know that its tS-matrix is calculable. How can one see this property without knowing anything about the underlying gauge symmetry? And, second, are there any other theories with a similar hidden renormalizability. In order to answer these questions he used the concept of 'tree-unitarity', which says that the S-matrix elements of a renormalizable theory in the tree approximation, considered as functions of the incident energy, cannot grow faster than a certain power of the energy. If this condition is not fulfilled the theory is non-renormalizable already at the one-loop level. The important result, which was generalized later by J.M. Cornwall, D.N. Levin and G. Tiktopoulos, is that any Lagrangian of dimensions less than or equal to four, involving scalar, spinor and vector fields, satisfies tree-unitarity, only if it is equivalent to a spontaneously broken gauge theory, with the possibiUty of adding arbitrary mass terms to vector fields associated with invariant abelian subgroups. I come now to the second branch of the Standard Model, i.e. quantum chromodynamics, the gauge theory of strong interactions. Contrary to the electroweak model, it had a very precise experimental motivation. SLAC's famous results on deep inelastic electronnucleon scattering, followed by similar ones at CERN and elsewhere, prompted theorists to formulate the concepts of the parton model, which is based on two assumptions. Nucleons are bound states of elementary constituants, called partons. At very short distances partons interact with the virtual photon as free, point-Uke particles. In 1970, H. Leutwyler and J. Stern from CERN showed that the parton model results concerning the structure functions for deep inelastic scattering, can be obtained if one assumes that the free-field singularities dominate the commutator of two current operators in the vicinity of the light-cone [43]. It was one of the first attempts to introduce field-theoretic ideas to the parton model and played an important role in the final development of quantum chromodynamics. The first person to discover the property of asymptotic freedom was Gerard 't Hooft who announced it at a meeting in Marseille in 1972. It was presented as a property of Yang-Mills theories with unbroken gauge symmetry. The physical theory of quantum

312

Physics in the CERN Theory Division

chromodynamics was proposed the following year by H.D. Politzer as well as D.J. Gross and F. Wilczek 8.7 Beyond the standard model This is the last section. It is supposed to cover the period after 1971. In fact, I shall be extremely brief and general for the last ten or twelve years. This should not be interpreted as a value judgement. I have a very high respect for the work done at present in the Division. However, my rule, up to now, has been to give the general trends and single out only the individual contributions which have become part of our scientific heritage. I am unable to make such a selection among the papers published in the eighties. There are two reasons for that: the obvious one is that the lapse of time is too short and I am getting too old and out of touch. But there is a more profound one. For reasons upon which I shall comment later, theoretical high-energy physics has become increasingly abstract and mathematical and further removed from experimental data. I believe that it is impossible to tell right now which, if any, of our present speculations, which are very interesting in their own right, will be incorporated into the physics curriculum of the twentieth first century. However, if I had to, I would bet on the mathematical techniques, not so much on the detailed physical models. I believe that geometry and topology, the natural languages of gauge theories, have come to stay. If the sixties forced the average physicist to learn elementary group theory, the seventies and the eighties did the same for differential geometry and topology. As I said earlier, gauge theories radically changed our way of thinking. A historian going through the literature of the early seventies, may get the mistaken idea that nothing had happened. The scientific journals are not saturated with papers on gauge theories. However, this conclusion is wrong for several reasons. First it ignores the obvious fact that the papers published at a given moment usually represent projects which had started several years earlier. Second, and most important, gauge theories represented a real break with respect to our old ideas and prejudices. There were so many new things to learn, so many new techniques to master. If I remember correctly, most people were aware of the revolution that was taking place, although few had the courage to join the fun immediately. Before going into the work of the Theory Division, let me again present the main theoretical ideas which dominated high-energy physics after the Standard Model. The first direction was, naturally, the study of the physical consequences of the model and their comparison with experiment. It was a long programme which went through several stages. In the early seventies the aim was to discriminate among the various possible models. The emphasis was on yes-or-no experiments, like the existence of neutral currents, that of charmed particles, heavy leptons, parity violation in atomic physics, etc. As the experiments progressed, more quantitative questions could be asked, but it was only quite recently that the entire model could be tested at the level of radiative correc-

Beyond the standard model

313

tions. A parallel approach has been followed concerning quantum chromodynamics. The first evidence for a Q^-dependence of the structure functions was found in the early seventies, but it took almost twenty years of strenuous efforts in deep inelastic lepton scattering, jet production experiments, studies of charmonium and T-systems and, finally, the hadronic decays of Z^, before the full two-loop calculations could be meaningfully compared with the data. The amount of theoretical work that has been invested in these studies has been quite impressive, second only to the unprecedented experimental eff*ort. The second direction of theoretical studies is commonly described by the title 'beyond the standard model'. The motivation is very clear. Gauge theories have opened new horizons in the theory of the fundamental interactions. Many old problems were solved, only to make room for new and more profound ones. Questions which could not be meaningfully addressed before, now became liable to scientific investigation. This extraordinary theoretical drive can be summarized by two words: more symmetry. Every time a new problem appeared physicists reacted by searching for a model with higher symmetry. According to one's taste or prejudice, this process can be viewed either as a search for a truly unified theory of all interactions, or as an endless series of'fuites en avant'. I shall try to give the main steps: The standard model is not a unified theory. It is based on the group U{\)y. SU{2) X SU{3) and each factor brings a new coupling constant. What is worse is the presence of the abehan factor U{1) because (7(1) admits any number of coupUng constants. In a non-abelian group the coupling constant is fixed by the gauge boson selfcoupling and it must be the same, apart form Clebsh-Gordan coefficients, for every matter multiplet. For t/(l), however, this is not so, in other words, the standard model does not explain the observed quantization of electric charge. Faced with this problem, physicists took the first step towards higher symmetry. The hypothesis of grand unification states that U{\) X SU{2) X SU{3) is the remnant of a larger, simple group G, which is spontaneously broken at very high energies. This idea was first proposed in 1974 by Howard Georgi and Sheldon Glashow who considered the group SU{5). Other groups, such as SO{10), Ee, etc., have also been studied. Using the renormalization group equations, one can estimate the order of magnitude of the unification energy which turns out to be larger than 10^^ GeV. A very important consequence of grand unified theories is the non-conservation of baryon number, and this has triggered a very intense experimental eff'ort to detect a possible proton decay. Grand unified theories are aesthetically attractive and solve the problem of electric charge quantization. However they raise a new one: they involve two widely separated energy scales, the super-heavy breaking occurs at energies above 10^^ GeV, while the standard model one at 10^ GeV. The only way to implement a spontaneous symmetry breaking using the available field-theory technology, is to introduce appropriate scalar fields. However, scalar fields have a tendency to acquire, through higher order corrections, masses equal to the largest available mass scale. This means that grand unified theories cannot sustain, in a natural way, the two energy scales. The light breaking tends to join the heavy one. This is known as the 'gauge hierarchy problem'. Once more theorists tried to

314

Physics in the CERN Theory Division

increase the symmetry of the model. It was easy to see that going to higher gauge groups did not help. All grand-unification groups suffer from this disease. What was needed was a symmetry which would keep scalar fields naturally light, in other words a symmetry which would make scalar fields behave like fermion fields were known to behave. This led to the idea of a fermi-bose symmetry, or supersymmetry. Such a scheme was found in twodimensional models by Jean-Loup Gervais and Bundji Sakita and was introduced in fourdimensional field theories by Julius Wess and Bruno Zumino in 1973 [44]. Supersymmetric grand unified theories have been constructed and their properties have been extensively studied. It turns out that supersymmetry must survive at sufficiently low energies and its consequences should be detectable in the near future. A rich spectroscopy of new particles is predicted. The new problem arises now at the high-energy front. The presence of new particles makes the unification energy higher, of the order of 10^^ GeV. This is too close to the so-called 'Planck scale' of 10^^ GeV, which means that we can no longer neglect gravitational interactions. This opens a completely new chapter. Particle physicists had ignored gravitation which had resisted all attempts at quantization. Supersymmetry offered a new line of approach. The anti-commutator of two global supersymmetry transformations is a space-time translation. Therefore, gauging supersymmetry implied the gauging of translations, in other words local supersymmetry would include general relativity. It was hoped that the remarkable convergence properties of supersymmetric quantum field theories would finally win and yield a consistent quantum gravity. The dream of a truly unified gauge theory of all fundamental interactions would have been realized. The simplest supergravity theory was constructed in 1976 by Sergio Ferrara, Daniel Friedman and Peter Van Nieuwenhuizen. It was a toy model containing only the graviton and its superpartner, the gravitino. The candidate for a real theory, the supergravity with eight supersymmetry generators, was constructed and studied in 1978 by Eugene Cremmer and Bernard Julia. The N =% supergravity was the end of a road, the road to symmetry. No field theory with higher symmetry is known to exist. Therefore it was either the sought for solution, or the entire approach would have failed. Its perturbation theory was studied in detail. For several years people hoped for a miracle to happen. It did not. By the early eighties all were forced to admit that TV = 8 supergravity remained a hopelessly non-renormalizable theory. The road to symmetry appeared to lead to a dead end. This failure was interpreted as a failure of local quantum field theory. The very notion of a local field, which was inherited from the notion of a point particle in classical mechanics, had to be abandoned. This concept had been challenged several times in the past and people had often tried to construct theories of extended objects. However, it was only recently that the motivation for such a radical step appeared to be compelling. Strings are the simplest extended objects. Although theories of higher dimensional objects have been studied (membranes, etc.), only strings seem to yield consistent theories. They use the concepts and techniques developed for the dual models, but the physical meaning has changed. The fundamental length is no more of hadronic scale but of Planck scale: not 10"^^ but 10"^^ cm. Joel Scherk has played an important role in this conversion. In 1974,

Beyond the standard model

315

in collaboration with John Schwarz, he proposed to interpret the spin-two zero-mass state which appeared in the spectrum of the dual models as the graviton, and in 1976 together with Eugene Cremmer, he used the Kaluza-Klein mechanism of dimensional compactification in order to arrive at four-dimensional theories. The connection with the theory of two dimensional gravity, a central theme in many recent developments, can be traced to the work of A. Polyakov in the early eighties and the recent revival of the theory is due to Michael Green and John Schwarz who, in 1984, constructed the first anomaly-free superstring theories. For somebody who is used to local quantum field theory, the obvious generaUzation to a theory of quantized strings would be to consider a theory in which the fields, instead of being operator-valued functions (in fact, distributions) of the space-time point x, they would be operator-valued functionals of the string function. We could call such a theory 'quantum field theory of strings'. Nobody has succeeded in writing such a theory and we believe today that it can not be written using the available mathematical technology. Let me note in passing that one of the most attractive features of string theory in the eyes of many theoretical physicists, is precisely the fact that it makes contact with the most advanced research in modern mathematics. The approach which has been followed in string theory corresponds to a first quantized theory and it is the generalization of particle mechanics. The classical mechanics of a freely moving relativistic string can be obtained by extremizing the invariant area of its trajectory which is a two-dimensional world-surface. Let its points be parametrized by X^{a^ T). The index // runs form 0 to J — 1, where d is the dimensionality of the embedding space in which the string is moving. On the other hand, X^ can be viewed as an ordinary field in a two-dimensional space. It is this equivalence between string theory and quantum field theory in 1 + 1 dimensions that helped to make progress in the theory of quantized strings and established a connection with the statistical mechanics of two-dimensional critical phenomena. A most remarkable result is that d can not take arbitrary values. Assuming that the ambiant space is flat, one can construct a consistent theory of superstrings only if d= 10. Hence the need to consider the possibiUty of compactifying the six additional dimensions and to study the properties of the resulting theory. The problems one encounters in this programme, both mathematical and physical, are formidable and at present it is too early to accurately evaluate the significance of these ideas. However, I want to emphasize that superstring theory is today the only candidate for a consistent theory of quantum gravity. Furthermore, at least one of its ingredients, namely supersymmetry, can be tested experimentally in the near future. Let me now come to the contributions of the CERN Theory Division to this world effort. I shall start with the first direction, the physics of the Standard Model. For reasons of presentation I shall distinguish two periods, before and after 1976. The separation date has not been chosen randomly. BeUeving in gauge theories in 1972 required an act of faith. Above all, faith in field theory, and most theorists had learnt to mistrust field theory. By 1976, on the other hand, gauge theories had passed many experimental tests. The study of their physical consequences became the dominant research theme everywhere. The CERN Theory Division was no exception.

316

Physics in the CERN Theory Division

In the early seventies, the CERN papers on gauge theories are very rare. I have already mentioned the Prentki-Zumino model and Llewellyn Smith's work on the high-energy behaviour of weak interaction ampUtudes. In fact, in 1972, the Division had seventeen staff members (nine permanent and eight fixed term). The only one among them who studied the phenomenological consequences of the Standard Model was Llewellyn Smith. His 1974 article on the properties of neutral currents [45], written in collaboration with Dimitri Nanopoulos, was the first complete study in this new and exciting field. This lack of interest, coming from the theorists of a laboratory whose first claim to fame was precisely the discovery of weak neutral currents, is hard to understand. I shall come back to this question in the Conclusion because I believe that it reflects quite accurately the Division's weakest point, namely its slow response to this revolution. During the same period Fermilab had developed a very active group of gauge theory phenomenology. Let me notice, however, that some interesting contributions came from visitors and fellows. I shall present briefly a few of them. One of the first complete one-loop calculations in the new renormalizable electroweak theory is due to W.A. Bardeen, R. Gastmans and B. Lautrup and appeared in 1972 [46]. They computed several static quantities of the vector bosons and the fermions in the model and discussed the gauge invariance of the S'-matrix elements. There was also a series of papers by C.H. Albright, often in collaboration with C. Jarlskog, on charmed particle production, properties of heavy leptons etc. [47]. Between 1972 and 1974, Gerard 't Hooft was a visitor at CERN. During the same period, Veltman also spent some time there. They pubUshed several very important papers on the properties of gauge theories, some of which have opened new fields of research. Together they wrote two papers. The first, presented in the 1972 Marseille meeting, completes the renormalization programme for spontaneously broken Yang-Mills theories [48]. The second studies the one loop divergences in the theory of gravitation [49]. In a series of two papers published in Nuclear Physics in 1973, 't Hooft developed the renormalization group algorithm in the scheme of dimensional regularization [50]. The following year he published, again in Nuclear Physics, three fundamental papers. In the first he showed that an SU{N) gauge theory in the limit iV^^ oo is described by planar diagrammes only [51]. Numerous studies have been performed since using this idea. In the second he solved such a theory in the special case of a two-dimensional space-time [52]. Finally in the third he constructed his famous magnetic monopole classical solution [53]. He studied an 0(3) gauge theory with a triplet of Higgs fields. He showed that there exists a classical solution, which is regular everywhere and corresponds to a unit magnetic charge. After 1976, the situation changed radically. It was obvious that gauge theories had come to stay. The electroweak model was already taught in all graduate schools and quantum chromodynamics was admitted as the fundamental theory of strong interactions. At CERN several research teams were formed, mainly by the younger members. The one by John ElHs, Mary-K. Gaillard and Dimitri Nanopoulos soon became one of the most active world-wide. Their first paper I want to mention is a 1976 article on the phenomenological profile of the Higgs boson [54] which, for several years, was the guide to experimental

Beyond the standard model

317

research. Between 1977 and 1978, E.G. Floratos, D.A. Ross and C.T. Sachrajda performed a two-loop calculation for the deep-inelastic scattering in quantum chromodynamics [55]. A similar calculation including the time-like region, was completed in 1980 by W. Furmanski and R. Petronzio [56]. Andre Martin used his expertise in potential models to derive many rigorous results in charmonium spectroscopy. The discovery in 1977 of the upsilon provided a new system for a more accurate appUcation of these ideas. His review article in Physics Reports, written in collaboration with H. Grosse, summarizes all the results on heavy quark-antiquark bound states [57]. As we shall see presently, this intense phenomenological activity was developed in parallel with other, more abstract, subjects. Together, they made the CERN Theory Division during the late seventies a very exciting and stimulating place. Let me now come to the second direction, the one I had called 'beyond the Standard Model'. Here I shall not follow any chronological order, but I shall present the CERN contributions according to the sequence grand unified theories - supersymmetry - supergravity - strings. The 'standard' grand unified model is SU{5). We know today that it does not fit the data, but it still exemplifies all the essential theoretical ideas. The two fundamental papers on SU{5) are the 1974 Georgi-Glashow one, where the model was proposed, and a second one in the same year by Howard Georgi, Helen Quinn and Steven Weinberg, where the renormalization group evolution of the three physical coupling constants was computed and they were found to meet roughly at the grand unification scale. In 1977, this idea was taken again at CERN by A.J. Buras, J. EUis, M.K. Gaillard and D.V. Nanopoulos [58]. They made a more complete calculation of the renormalization group functions and, most important, they were the first to examine the evolution of the fermion masses. SU{5) predicts the mass ratios of the down quarks and the charged leptons of a given family, but these predictions are valid at the grand unification scale. The CERN team computed the evolution of these ratios at low energies. Their best known result is that the mb/m^ ratio agrees with experiment only if the model contains just three fermion famihes. As I said earUer, an essential prediction of grand unified theories is the non-conservation of baryon number. In 1978 M. Yoshimura remarked that this property could be used to explain the observed dominance of matter over anti-matter in the Universe. He was, apparently, unaware of a similar proposal formulated more than ten years before by A.D. Sakharov. In fact, Yoshimura's paper contains some technical mistakes which are absent from the early Sakharov's paper. During 1978 and 1979 several groups corrected and expanded this idea and one of the first to do so was the trio ElHs-Gaillard-Nanopoulos from CERN [59]. These works were quite significant because they contributed to the development of a new field, the apphcation of particle physics to astrophysics and cosmology. The concept of a symmetry between fermions and bosons was first introduced in two space-time dimensions, in the framework of dual models. Jean-Loup Gervais and Bundji Sakita discovered such a symmetry, which was called 'supergauge symmetry' in the dual model formulations of A. Neveu and J.H. Schwarz and P. Ramond. In four dimensions related ideas had also been studied in the Soviet Union by Yu. A. Gol'fand and E.P.

318

Physics in the CERN Theory Division

Likhtman as well as D.V. Volkov and V.P. Akulov. However, I think it is fair to say that the enormous impact of supersymmetry on theoretical high energy physics is due to the work of Julius Wess and Bruno Zumino. In fact, supersymmetry occupies a very special place among our fundamental concepts; up till now it has received absolutely no experimental support, still it has excercised a tremendous influence in practically every recent development in particle physics. Wess and Zumino in their 1973 paper introduced the four-dimensional supersymmetry algebra [44]. (In fact, they were still calling it supergauge algebra: the word 'supersymmetry' was introduced by A. Salam and J. Strathdee in 1974). They showed that the algebra closes with the use of commutators and anti-commutators and that it contains the algebra of the Poincare group. They also built, by trial and error, the first irreducible representations in terms of field operators, a 'scalar' multiplet containing a Majorana spinor and four scalar fields, as well as a 'vector' multiplet with one vector, two spinors and four scalars. They also found the first rule for a tensor calculus, because they showed how one could multiply two scalar multiplets in order to obtain a third one. Finally they constructed free invariant actions with the scalar and the vector multiplets and showed that, in both cases, some of the components were non-propagating auxiliary fields. It is a most remarkable paper combining technical skills with exceptional intuition. In a second paper [60], they studied a Lagrangian field theory model with a self-interacting scalar multiplet. The model consists of Yukawa, 4^^ and ^^ coupHngs and it is renormalizable by power counting. Supersymmetry manifests itself in the form of relations among masses and coupling constants. Wess and Zumino showed that, at the classical level, the Majorana spinor and the two physical scalars have the same mass and all couplings can be expressed in terms of a single coupling constant. They computed explicitly the radiative corrections at one loop order and found that these special relations imposed by supersymmetry were maintained. This led them to discover a most peculiar feature of the model: at the order of one loop, there was no mass or coupHng constant counterterm. Only a common wave function renormalization was required. I remember Zumino explaining these puzzling results to me during one of my visits to CERN. I could not see any deep reason for these divergence cancellations and I concluded that they ought to be one loop accidents and they should disappaer at higher orders. Nevertheless, we decided to check the two-loop counterterms. To our surprise we found that the cancellation persisted. It took us several weeks to find the general proof to all orders [61]. These non-renormalization theorems made supersymmetry a possible candidate for the solution of the gauge hierarchy problem in grand unified theories. An important step in the development of supersymmetry theory was the introduction of the superspace formalism by A. Salam and J. Strathdee in 1974. It was completed the same year by Sergio Ferrara, Zumino and Wess [62]. The formalism consists in writting the supersymmetry transformations as generalized translations in an eight-dimensional superspace. A point in superspace is parametrized by an ordinary four-vector x^ and an anticommuting complex two-component Weyl spinor 9^- Because of the anticommuting character of the 0's, a field in superspace (a superfield) is equivalent to a finite number of

Beyond the standard model

319

fields in ordinary space, in other words, this method provides an algorithm for finding field representations of supersymmetry. Furthermore, since the product of two superfields is again a superfield, we have the basis of a complete tensor calculus. One can construct Lagrangians directly in superspace and derive Feynman rules for superfields. These rules have considerably simplified supersymmetry calculations and have uncovered the origin of the non-renormalization theorems. The final ingredient which was needed before applying supersymmetry to particle physics was the construction of the supersymmetric extension of gauge models. This problem was solved at CERN in two fundamental papers of 1974, the first by Wess and Zumino and the second by Ferrara and Zumino. The first derived the supersymmetric extension of quantum electrodynamics [63]. It used the component formaHsm and showed that in order to supersymmetrize quantum electrodynamics one should extend the electron field to a full complex scalar multiplet and the photon field to a full vector multiplet. Furthermore, the scalar function of the gauge transformation should also be extended to a scalar multiplet. The resulting theory describes the electromagnetic interactions of the electron and its scalar partners but also Yukawa-type coupHngs between the electron, its scalar partners and the spinor partner of the photon. In the same paper, the concept of the so-called 'Wess-Zumino gauge' was introduced. In fact, in a general gauge the theory is non-polynomial. Wess and Zumino showed that there exists a partial gauge fixing which puts to zero many auxiliary fields of the vector multiplet and makes the theory polynomial. There is still the freedom to perform ordinary gauge transformations, but they should be compensated by a supersymmetry transformation. The Ferrara-Zumino paper addressed the question of the supersymmetrization of Yang-Mills theories [64]. It used the superfield formalism and derived a very simple and interesting result: in the analogue of the WessZumino gauge, a Yang-Mills theory describing the interaction of the gauge bosons with a multiplet of Majorana fermions in the adjoint representation of the group, is automatically supersymmetric. These two papers opened the way for an application of supersymmetry to particle physics. Pierre Fayet from the Ecole Normale Superieure in Paris wrote the supersymmetric extension of the standard electroweak model and derived all the phenomenological consequences. His results have been extensively used for the experimental searches of the supersymmetric particles. He often visited CERN and a couple of his papers appeared as CERN preprints. It is too early today to say whether supersymmetry will enter the future editions of the Rosenfeld tables. If it does, it will certainly be CERN's most important theoretical contribution. However, even today we can assert that it has been one of the most influential ideas of the last twenty years. The two most important supergravity models, the first N =\ supergravity and the largest N =S one, were discovered at the Ecole Normale Superieure in Paris, where many of their properties have also been investigated. Nevertheless, many significant contributions came from the CERN Theory Division regarding both the mathematical structure and the phenomenological appUcations. Stanley Deser and Bruno Zumino presented in 1976 their formulation ofN=l supergravity [65]. They used the first order formaHsm for

320

Physics in the CERN Theory Division

gravitation in which the vierbein and the connection are treated as independent fields. It turned out that this simpUfied considerably the calculations and they were able to show in a simple and elegant way that the sum of the Einstein term and that of a massless minimally coupled Majorana spin 3/2 field described by a Rarita-Schwinger action, is invariant under local supersymmetry transformations. Furthermore the resulting equations of motion were free of the pathologies associated with higher spin fields. All early formulations of supergravity were written in terms of physical fields. Only the graviton and the gravitino were present. The physical interpretation was unambiguous but the closure of the supersymmetry algebra required the use of the equations of motion. This was not quite satisfactory from the field theory point of view, especially for the implementation of the renormalization programme. The minimum set of auxiliary fields, which guarantees the invariance of the action off-shell, was first found by Ferrara and van Nieuwenhuisen at CERN in 1978 [66]. The same authors presented the set of rules for a tensor calculus of supergravity [67]. These rules turned out to be very useful for the construction of invariant actions satisfying local supersymmetry. One of the outstanding problems in every attempt to build a quantum theory of gravitation is the observed vanishingly small value of the cosmological constant. In perturbation theory this parameter is divergent and one has to fine tune it to zero. Between 1983 and 1984 a particular class of supergravity theories was found in which the cosmological constant naturally vanished without any fine-tuning of parameters. In these theories the minimum of the super-Higgs potential was equal to zero but it had flat directions which made the vacuum expectation value of the scalar field undetermined, at least in the tree approximation. These models were called 'no-scale models' [68]. They were developed in collaborations mainly between the CERN Theory Division and the Ecole Normale Superieure in Paris. The main contributors were J. Ellis, S. Ferrara and D.V. Nanopoulos from CERN and E. Cremmer and C. Kounnas from ENS. In a series of papers the most general no-scale models were constructed and the possibility of determining the minimum of the potential by radiative corrections was examined. The interest for these models has been revived more recently because, as Edward Witten has shown, they may appear naturally in the framework of some superstring theories. They represent the most promising candidates for a reaUstic effective theory of supergravity. This brings me to the last development in the road beyond the Standard Model, the theory of quantized superstrings. It grew out of the dual models which were developed in the late sixties and seventies. As I said earlier, one can distinguish two periods in their history: the early one in which the motivation was the description of hadron physics and the late one which aimed at a quantum theory of gravitation. The transition was gradual extending over almost a decade, but the most active periods were before 1975 for the first and after 1984 for the second. The CERN contributions to the development of the dual models were very important. Let me comment here briefly on the main steps. The original Veneziano formula described the four-particle amplitude in an approximation which we would call today tree-order. Obviously, two generalizations were re-

Beyond the standard model

321

quired before one could talk about a complete theory: the construction of a tree-level Appoint amplitude and the extention to an arbitrary number of loops. Both problems attracted immediately the attention of many theorists worldwide, and the CERN contributions were among the most significant. The problem of the A^-point ampHtude was practically solved already in 1968. The first paper on the subject is a Physics Letters article by K. Bardakci and H. Ruegg [69] who were both visiting CERN. As far as I know they were the first to write the A^-point function as a multiperipheral diagramme with the exchange lines represented by Regge families. In their first paper they applied this idea to the five-point amplitude (two incoming and three out-going particles). This technique was subsequently generalized to the six- and seven-point functions and finally to the entire A^-point amplitude by Chan HongMo and Bardakci and Ruegg [70]. Similar results were obtained independently by C.J. Goebel and B. Sakita. It took longer to derive the correct form of the multi-loop amplitude. As far as I know, the first to reaUze that unitarity impUed the multi-loop generalization was Holger Nielsen from Copenhagen who made a conjecture about the form of the amplitude. The formal solution was developed mainly at CERN by Claude Lovelace [71] on the one hand and Victor Alessandrini and Daniele Amati on the other [72]. These papers are very important because, for the first time, the M-loop function was written as an integral over a surface with Af-holes. This expansion in the genus of the surface became the standard perturbation series in string theories. A second fundamental question in dual models was the problem of unitarity and the absence of ghosts from the spectrum of states. The problem is similar in principle, although much more complicated in practice, with the corresponding one in gauge theories. Let me consider the simplest example of quantum electrodynamics. Gauge invariance, which is associated with the vanishing photon mass, implies the presence of only two heUcity states. When quantizing the theory, one has a choice between two strategies: Stick to the physical degrees of freedom, to the expense of manifest Lorentz covariance, or introduce unphysical states in order to ensure covariance at every step. In either case a more or less complicated proof is needed before one could claim that the resulting theory is physically relevant. It was soon reahzed that string theories had a very large gauge invariance, which can be viewed as the invariance under reparametrizations of the twodimensional multi-hole surface. Therefore, the crucial problem emerged, whether states of negative norm (ghost states), are present in the spectrum of physical states. The complete answer to this question turned out to be lengthy and rather complex with CERN theorists contributing many important steps. The first unitarity proof in a covariant quantization approach for the open string model is due to P. Goddard and C.B. Thorn in 1972 [73]. They showed the absence of ghosts for the Pomeron sector, i.e. unit intercept at / = 0 for the corresponding Regge trajectory, provided the dimensionaUty of the embedding space was d=26 for the bosonic string or J = 10 for the Neveu-Schwarz one. This result was extended the following year to the closed string by David Olive and Joel Scherk [74]. The second approach, namely the

322

Physics in the CERN Theory Division

quantization in a transverse, non-covariant gauge, was followed, also in 1972, by P. Goddard, C. Rebbi and C.B. Thorn who showed the Lorenz covariance of the resulting theory [75]. In this connection, let me mention another important issue, namely the nature of the Pomeron singularity. In constructing higher order dual amplitudes, one obtains, in general, cuts rather than poles. C. Lovelace conjectured that, at Z) = 26, the Pomeron cut was reduced to a pole. In 1972, Eugene Cremmer and Joel Scherk established the existence of the Pomeron poles and showed that they had the correct factorization properties [76]. Between 1968 and 1973 the study of dual models was the main research subject in the CERN Theory Division. Around two hundred articles were written but I have chosen only the ones which I consider more important from today's perspective. Another criterion was the strength of the authors' connections with CERN. Before leaving this subject I want to mention one more article which satisfies this criterion only marginally: two out of four authors were at CERN. It is an article by P. Goddard, J. Goldstone, C. Rebbi and C.B. Thorn. Although the relation between dual models and string theories was established quite early, (it goes back to the classic works of Y. Nambu, H.B. Nielsen, L. Susskind, etc. in 1969-1970) most results were initially obtained using the old dual model language. One of the first systematic studies of these models as string theories is due to these authors and it was pubUshed in Nuclear Physics in 1973 [77]. With the emergence of quantum chromodynamics the initial enthusiasm for dual models as the theory of strong interactions gradually disappeared. As I said above, some theorists started suspecting that the correct domain of applicability of string theories should be quantum gravity rather than hadronic physics. In this connection, I want to mention a 1977 Nuclear Physics paper by F. Gliozzi, J. Scherk and D. OUve, which appeared as a CERN preprint, although only the third author was at CERN [78]. They studied the Neveu-Schwarz-Ramond superstring model in the low-energy region and showed that it gives rise to a supergravity theory. The new era of superstring theories started officially in 1984. For several years it dominated theoretical high-energy physics research and contributed to the development of many fundamental concepts mainly at the frontiers with mathematical physics and statistical mechanics. Important progress has been made through the cross-fertilization of these fields. Physicists and mathematicians, having seemingly different motivations, have found their work intimately related. Progress towards a covariant formulation of string theories has profited from advances in the theory of two dimensional critical phenomena and, conversely, many string-motivated works on conformal field theory in two dimensions opened new paths in statistical mechanics. In the phenomenology of elementary particles the situation is less clear. String theories seem to restrict the various choices of grand-unified models but the precise connection is still obscure. I believe that the field faces an important challenge. Its future depends upon our ability to make progress towards non-perturbative solutions. As happened with local field theory, all questions which admit a perturbation expansion have, to a large extent, been understood. We are now facing the hard, strong-coupHng problems. Their solution requires, most probably, the elaboration of new mathematical tools and, almost certainly, the introduction of new

Conclusions

323

physical ideas. Whether and how this will happen will determine the real significance of much of the work already done. This is the reason why, as I already explained above, I shall not single out any of the recent work done in the Division. Nevertheless, I want to emphasize that it has often been at the frontier of current research. 8.8 Conclusions CERN spans forty years of history. Forty years that have shaped our understanding of the physical world. To this understanding the laboratory has contributed its fair share. We can look at its record from two points of view. The first is the wish of the founding fathers, namely the development of high-energy physics in Western Europe. Here, the emphasis is on the role of the laboratory as training centre for European physicists. The second is CERN's own research record, its contribution to the creation of new knowledge. Let me examine each point separately for the Theory Division. I have had already the opportunity to emphasize CERN's contribution to the renaissance of European high-energy physics. I believe that, for the Theory Division, the most important element has been its extremely rich visitor's programme. No other place in the world has had such a high ratio of kinetic energy to rest mass. This programme not only offered post-doctoral positions to generations of young theorists, but also gave them the opportunity to meet many of the most influential physicists from Europe and the United States. It is this extremely high concentration which made CERN such a unique place. I do not know who, if anyone, should be credited for this open-door policy, but it played a key role in the fulfilment of CERN's pedagogical mission. Let me give some crude statistics. I asked three of my colleagues, independently, to name 30 leading European high-energy theorists between 40 and 60 years of age. As it turned out, the lists were, to a large extent, identical. Out of the 36 physicists in the combined Hst, 32 had been at CERN for at least one year. And for most, this visit corresponded to their formative years. The scientific record of the CERN Theory Division was the subject of this chapter. As I have already said, it has pubUshed around 7000 papers. I have tried to mention the ones I considered to be most significant. What is the overall picture? It will not come as a surprise to the historian to discover that the performance of European theorists went, by and large, in parallel with that of their experimental colleagues. During the fifties and the sixties the United States exercised a clear dominance over the entire subject. Europe's role followed the rise of the Standard Model. The CERN theorists have often been blamed for their lack of participation in the construction of the Standard Model. I consider such a reproach as meaningless. I tried to show that the Standard Model was discovered mainly by individuals often working in relative isolation. Most of them could not have been hired by CERN anyway. Furthermore, the same reproach could be addressed equally well to most other institutions in the world. What I find more disturbing is the Division's failure to respond promptly after the discovery. Revolutions are always made by very few. Most CERN theorists were slow to realize that one was taking place. The first failure can be

324

Physics in the CERN Theory Division

attributed to bad luck. The second shows a certain bias in the hiring decisions. The obvious reason is that the overwhelming majority of the senior members were not interested in weak interactions and they did not hire younger members who were. This unbalance was later corrected. After the early seventies, the entire laboratory, experimentalists as well as theorists, often took a leading role. For the theorists this leading role was expressed both through work on the phenomenology of the Standard Model and through the introduction of new fundamental concepts. The main milestones on the road beyond the standard model have been grand unified theories, supersymmetry, supergravity and superstrings. CERN played the key role in the development of supersymmetry and very important ones in that of the other three. Although they still remain in the domain of theoretical speculations, they represent thirty years of world eff'ort, thirty years of striving for unity in Nature. I do not believe that they will turn out to be entirely on the wrong track! This chapter relates the history of the CERN Theory Division. It is not a review article. Only CERN publications are presented. Occasionally, when a comprehensive report exists on a given subject, I refer to it rather than to the original pubUcations.

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]

A. Peterman, Helv. Phys. Acta 30 (1957) 407. R. Haag, Dan. Mat. Fys. Medd. 29 (1955) Nr 12. G. Liiders, Dan. Mat. Fys. Medd. 28 (1954) Nr 5. L. Michel, Nuovo Cim. 10 (1953) 319. B. d'Espagnat and J. Prentki, Phys. Rev. 99 (1955) 328. B. d'Espagnat, J. Prentki and A. Salam, Nucl. Phys. 3 (1957) 446; ibid. 5 (1958) 447. B. d'Espagnat and J. Prentki, Nucl. Phys. 6 (1958) 596. B. d'Espagnat and J. Prentki, Nuovo Cim. 24 (1962) 497. N. Cabibbo, Phys. Lett. 10 (1963) 531. J.S. Bell and J. Steinberger, Th605, Oxford International Conference on Elementary Particles, Sept. 1965. G. Zweig, Th401 and Th 412, unpublished. R. Van Royen and V.F. Weisskopf, Nuovo Cim. 50 (1967) 617; E51 (1967) 583. S. Fubini and G. Furlan, Physics 1 (1965) 229. S. Fubini, G. Furlan and C. Rossetti, Nuovo Cim. 40 (1965) 1171. D. Sutherland, Phys. Lett. 23 (1966) 384; J.S. Bell and D. Sutherland, Nucl. Phys. B4 (1968) 315; M. Veltman, Proc. Roy. Soc. A301 (1967) 107. J.S. Bell and R. Jackiw, Nuovo Cim. A60 (1969) 47. J. Wess and B. Zumino, Phys. Lett. 37B (1971) 95. D.J. Gross and Ch. Llewellyn Smith, Nucl. Phys. B14 (1969) 337. J. Bros, H. Epstein and V. Glaser, Nuovo Cim. 31 (1964) 1265. J. Bros, H. Epstein and V. Glaser, Commun. Math. Phys 1 (1965) 240. A. Martin, ^Scattering Theory: Unitarity, Analyticity and Crossing'. Lecture notes in Physics, Vol. 3, Springer-Verlag, 1969. J. Bowcock and A. Martin, Nuovo Cim. 14 (1959) 516.

References

325

[23] D. Amati, S. Fubini, A. Stanghellini and M. Tonin, Nuovo Cim. 22 (1961) 569; L. Bertocchi, S. Fubini and M. Tonin, Nuovo Cim 25 (1962) 626; D. Amati, A. Stanghellini and S. Fubini, Nuovo Cim 26 (1962) 896. [24] L. Van Hove, Rev. Mod. Phys. 36 (1964) 655. [25] L. Van Hove, Phys. Lett. 28B (1969) 429; Nucl. Phys. B9 (1969) 331. For a review see Phys. Rep. 1 (1971) 347. [26] R. Hagedorn, Nuovo Cim. 15 (1960) 434; Proceedings of the International Conference of Theoretical Aspects of very high Energy Phenomenon, CERN 1961, CERN 61-22, p. 183. [27] R. Hagedorn, Suppl. Nuovo Cim. 3 (1965) 147; R. Hagedorn and J. Ranft, Suppl. Nuovo Cim. 6 (1968) 169; R. Hagedorn, Astron. and Astroph. 5 (1970) 184. [28] G. Veneziano, Nuovo Cim. 57A (1968) 190. [29] V. Glaser, Nuovo Cim. 9 (1958) 990. [30] H. Epstein and V. Glaser, Lectures at the Les Houches Summer School (1970); Ann. Inst. H. Poincare 29 (1973)211. [31] Th. Kanellopoulos and K. Wildermuth, Nucl. Phys. 7 (1958) 150; see also CERN 59-23. [32] T.E.O. Ericson, Phys. Rev. Lett. 5 (1960) 430. [33] T.E.O. Ericson, Ann. Phys. (NY) 23 (1963) 390 and Phys. Lett. 4 (1963) 258; T.E.O. Ericson and T. MayerKuckuk, Ann. Rev. Nucl. Sci. 16 (1966) 183. [34] T.E.O. Ericson and M. Ericson, Ann. Phys. (N.Y.) 36 (1966) 383; for a most recent presentation, see T.E.O. Ericson and W. Weise, 'Pions and Nuclei', International series of Monographs in Physics, 74, Clarendon Press, Oxford 1988. [35] T.E.O. Ericson, Progr. Part. Nucl. Phys. 1 (1978) 173; M. Ericson and M. Rho, Phys. Rep. 5 (1972) 57; T.E.O. Ericson and W. Weise, Ref. [32], chapter 9. [36] J.S. Bell, Rev. Mod. Phys. 38 (1966) 447. [37] J.S. Bell, Physics 1 (1964) 195; this article, as well as the one of Ref. [34], have been reprinted, together with other articles on the Foundations of Quantum Mechanics, in J.S. Bell, 'Speakable and unspeakable in quantum mechanics' Cambridge University Press, 1987. [38] M. Veltman, Phys. Rev. Lett. 17 (1966) 553. [39] J.S. Bell, Nuovo Cim. 50A (1967) 129. [40] C. Bouchiat, J. Ihopoulos and J. Prentki, Nuovo Cim. 56A (1968) 1150; J. Ihopoulos, Nuovo Cim. 62A (1969) 209. [41] J. Prentki and B. Zumino, Nucl. Phys. B47 (1972) 99. [42] Ch. Llewellyn Smith, Phys. Lett. B46 (1973) 233. [43] H. Leutwyler and J. Stem, Nucl. Phys. B20 (1970) 77. [44] J. Wess and B. Zumino, Nucl. Phys. B70 (1974) 39. [45] Ch. Llewellyn Smith and D.V. Nanopoulos, Nucl. Phys. B78 (1974) 205. [46] W.A. Bardeen, R. Gastmans and B. Lautrup, Nucl. Phys. B46 (1972) 319. [47] C H . Albright, Nucl. Phys. B70 (1974) 486; ibid. B75 (1974) 539; C H . Albright and J. Cleymans, Nucl. Phys. B76 (1974) 48; C H . Albright and C Jarlskog, Nucl. Phys. B84 (1975) 467; C H . Albright, C Jarlskog and L. Wolfenstein, Nucl. Phys. B84 (1975) 493. [48] G. 't Hooft and M. Veltman, Thl571, unpublished. [49] G. 't Hooft and M. Veltman, Ann. Inst. H. Poincare 20 (1974) 69. [50] G. 't Hooft, Nucl. Phys. B61 (1973) 455; ibid. B62 (1973) 444. [51] G. 't Hooft, Nucl. Phys. B72 (1974) 461. [52] G. 't Hooft, Nucl. Phys. B75 (1974) 461. [53] G. 't Hooft, Nucl. Phys. B79 (1974) 276. [54] J. Ellis, M.K. Gaillard and D.V. Nanopoulos, Nucl. Phys. B106 (1976) 292. [55] E.G. Floratos, D.A. Ross and C T . Sachrajda, Nucl. Phys. B129 (1977) 66; ibid. B152 (1979) 493. [56] G. Curci, W. Furmanski and R. Petronzio, Nucl. Phys. B175 (1980) 27; W. Furmanski and R. Petronzio, Phys. Lett. 97B (1980) 437. [57] H. Grosse and A. Martin, Phys. Rep. 60 (1980) 341.

326 [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68]

[69] [70] [71] [72] [73] [74] [75] [76] [77] [78]

Physics in the CERN Theory Division A.J. Buras, J. Ellis, M.K. Gaillard and D.V. Nanopoulos, Nucl. Phys. 135 (1978) 66. J. Ellis, M.K. Gaillard and D.V. Nanopoulos, Phys. Lett. SOB (1979) 360. J. Wess and B. Zumino, Phys. Lett. 49B (1974) 52. J. Iliopoulos and B. Zumino, Nucl. Phys. 76 (1974) 310. S. Ferrara, B. Zumino and J. Wess, Phys. Lett. 51B (1974) 239. J. Wess and B. Zumino, Nucl. Phys. B78 (1974) 1. S. Ferrara and B. Zumino, Nucl. Phys. B79 (1974) 413. S. Deser and B. Zumino, Phys. Lett. 62B (1976) 335. S. Ferrara and P. van Nieuwenhuizen, Phys. Lett. 74B (1978) 333. S. Ferrara and P. van Nieuwenhuizen, Phys. Lett. 76B (1978) 404. E. Cremmer, S. Ferrara, C. Kounnas and D.V. Nanopoulos, Phys. Lett. 133B (1983) 61; J. EUis, A.B. Lahanas, D.V. Nanopoulos and K. Tamvakis, Phys. Lett. 134B (1984) 429; J. Ellis, C. Kounnas and D.V. Nanopoulos, Nucl. Phys. B247 (1984) 373; R. Barbieri, E. Cremmer and S. Ferrara, Phys. Lett. 163B (1985) 143. K. Bardakci and H. Ruegg, Phys. Lett. 28B (1968) 342. H.M. Chan, Phys. Lett. 28B (1968) 425; K. Bardakci and H. Ruegg, Phys. Rev. 182 (1969) 1884. C. Lovelace, Phys. Lett. 32B (1970) 703. V. Alessandrini, Nuovo Cim. 2A (1971) 321; V. Alessandrini and D. Amati, Nuovo Cim. 4A (1971) 793; V. Alessandrini, D. Amati, M. Le Bellac and D. Olive, Phys. Rep. 1 (1971) 269. P. Goddard and C.B. Thorn, Phys. Lett. 40B (1972) 235. D. Olive and J. Scherk, Phys. Lett. 44B (1973) 296. P. Goddard, C. Rebbi and C.B. Thorn, Nuovo Cim. 12A (1972) 425. E. Cremmer and J. Scherk, Nucl. Phys. B50 (1972) 222. P. Goddard, J. Goldstone, C. Rebbi and C.B. Thorn, Nucl. Phys. B56 (1973) 109. F. Ghozzi, J. Scherk and D. Olive, Nucl. Phys. B122 (1977) 253.

CHAPTER 9

The SC: ISOLDE and Nuclear Structure p. Gregers HANSEN

Contents 9.1 Introduction 9.2 The early interest in nuclear physics at CERN 9.2.1 The conferences on high energy physics and nuclear structure and nuclei far from stability 9.2.2 CERN's nuclear structure committee (NSC) and other scientific committees 9.2.3 Studies of complex nuclear reactions by radiochemical methods 9.2.4 Some open problems in nuclear physics in the sixties and seventies 9.3 Experiments with muons and pions 9.3.1 Muonic x-rays 9.3.2 Pions and nuclei 9.3.3 Test of quantum electrodynamics and the masses of the pion and the muon 9.3.4 Scattering and production of pions on nuclei 9.3.5 Other experiments with muons 9.3.6 Looking back 9.4 The early ISOLDE 9.4.1 On-line mass separation, Copenhagen 1950-51 9.4.2 The ISOLDE collaboration is formed 9.4.3 The ISOLDE facility 9.4.4 The heart of the matter: targets and ion sources 9.4.5 The first experiments 9.4.6 Radiation-detected optical pumping (RADOP) comes to ISOLDE 9.4.7 Why at CERN? 9.5 The SC improvement programme (SCIP) 9.5.1 The plans for upgrading the SC 9.5.2 SCIP is delayed: poUtical, commercial and technical difficulties 9.5.3 Conflicting views: should the SC be shut down or upgraded? 9.5.4 The users are heard: Physics III and the SCIP advisory panel 9.5.5 Post-SCIP developments: the acceleration of ^He and heavy ions 9.6 The evolution of the scientific programme at ISOLDE 9.6.1 The isotope separator and its beams

327

329 330 331 333 334 336 340 340 343 344 347 349 350 351 352 353 358 360 362 366 369 370 370 373 375 377 379 380 381

9.6.2 Nuclear masses, spins, moments and radii 9.6.3 Nuclear spectroscopy 9.6.4 Exotic decays, strength-function phenomena and statistical aspects 9.6.5 Applications to atomic and solid-state physics 9.7 The last defence of the Cyclotron: 1979-81 9.7.1 The plans for SIN-ISOLDE 9.7.2 The discussions in CERN's committees 9.7.3 A decision on the future of ISOLDE 9.7.4 Epilogue 9.8 Concluding remarks Notes References

328

386 389 390 392 393 393 396 398 400 401 403 405

A force de frapper a coups redoubles sur la meme porte, elle finit toujours par s'ouvrir. Ou alors c'est une porte voisine, qu'on n'avait pas vue qui s'entrebdille, et c'est encore plus beau.

Michel Tournier Le roi des aulnes (1970)

9.1 Introduction The 600 MeV synchro-cyclotron (SC) commissioned in 1957 was originally foreseen as a tool for training physicists in high-energy experimentation and as a stopgap measure until the 28 GeV proton synchrotron (PS) was ready. The story of its construction and glamourous early contributions to particle physics has been told by Ulrike Mersits [1, 2]. Based on rather conventional techniques, and being a modest scale-up of similar accelerators elsewhere, the SC was not, and certainly never became, the master machinebuilder's darUng. However, it had, and continued to have, an extraordinary grip on physicists from the time of its first operation until the final shutdown in 1990. It is characteristic that when the proton synchrotron was about to be commissioned in 1960, most of the leading particle physicists were reluctant to leave the SC. Pestre [3] relates that very few teams were prepared for doing real experiments at the PS (as opposed to apparatus tests) and there even seemed to be machine time to spare. The reasons he gives for this are certainly all vaUd, such as lack of experience with high energies, lack of knowledge about the beams, and fear of difficulties with the running-in of a very advanced accelerator. But it was equally important that the experimenters had splendid possibiUties for front-line research with the secondary muon and pion beams of the SC, especially in the field of weak-interaction physics, which had become a central topic with the discovery of the non-conservation of parity in 1957. At the beginning of the period covered in the present chapter, the SC had to a large extent changed cUentele. It was to an increasing degree serving nuclear physicists, who were attracted by the possibiUty of using muons and pions as tools for nuclear-structure physics. By 1965 the nuclear research at the machine was already prominent enough to have contributed some of the most important scientific results obtained at CERN during the period 1960-65, as can be seen from a selective listing [4] prepared by the outgoing Director General, Victor F. Weisskopf. This included the use of muonic x-rays for measuring quadrupole moments, studies of excited states in helium from pion interactions with lithium, and measurements of pion double charge exchange. The next development at the 329

330

The SC: ISOLDE and Nuclear Structure Table 9.1 Physics activities at the SC Particle Physics Electron decay of the pion g-2 Beta decay of the pion /i channel Nuclear Physics Muonic and pionic x-rays Nuclear muon capture Pion Scattering Nucleon Scattering Reactions of ^He and heavy ions up to 87 MeV/nucleon Applications Muon-spin resonance (/^SR) for soHd-state work: Metals, semiconductors, polymers Radioisotopes for medicine

ISOLDE Programme Spins, moments, radii by methods from atomic physics Nuclear spectroscopy and structure Far unstable nuclei and rare decaymodes Strength functions and statistical aspects of beta decay Atomic physics: x-rays, optical spectra of francium Implantation for sohd-state physics Applications

SC, the on-line isotope separator ISOLDE, was at that moment being prepared and over the whole period 1957-90 new applications of the SC kept appearing, as can be seen from Table 9.1. An interesting review of some of the scientific activities at the SC were presented [5] at a closing ceremony called 'SC 33'. The present chapter concentrates on the story of the machine in its middle life, roughly 1965-81, but I have rather freely cited events and scientific results from earlier as well as from more recent times if they helped to put the activities described here in perspective. The purely scientific accomplishments in all of the fields cultivated at the SC can be found in numerous books and review articles, and for this reason I restrict myself to a condensed summary (sects. 9.3 and 9.6) of this aspect. I have, on the other hand, given a rather broad and detailed coverage of human and organizational matters, which are less often discussed in the scientific literature, where only the results count, and I give many details about the interactions of the users with CERN and the associated technical and scientific metamorphoses of the SC. Four of the six main sections are dedicated to this aspect, to science policy and scientific politics. I describe first in some detail the birth of a nuclear physics programme at CERN (sect. 9.2) and that of ISOLDE (sect. 9.4). This is followed by an account of the fight 1971-74 for the cyclotron improvement programme (sect. 9.5) and of the last successful defence of the cyclotron 1979-81 (sect. 9.7).

9.2 The early interest in nuclear physics at CERN The two sections (9.3 and 9.4) following this one describe some of the early activities in nuclear physics around the SC during a period of ten years, from the first initiatives taken

The early interest in nuclear physics at CERN

331

by CERN in 1963 up to the shut-down of the cyclotron for a major upgrade during 197374. The present section consists of four, between them quite unrelated, sub-sections, and serves to set the stage for the events to follow and to provide some necessary background information. First, in sect. 9.2.1, some of the mechanisms that brought the nuclear programmes at CERN into being are examined, namely (i) initiatives from CERN, the traditional CERN method, (ii) the interaction of the users with CERN and with each other directly and (iii) through scientific conferences. Once a recognized user community began to exist, it was important to create more formalized Hnks to CERN in the form of scientific committees that could communicate with the users and give proper advice to the CERN Management. Section 9.2.2 describes how the committees responsible for the research at the SC were organized and functioned. The last two sections provide scientific background information. In view of the important role that was played by nuclear chemists in the creation and development of the on-line mass separator ISOLDE, it seemed useful to give (sect. 9.2.3) a brief account of some of their early activities at CERN and in their home laboratories. Finally, the last section (9.2.4) mentions some of the important themes in nuclear-physics research in the sixties and seventies. 9.2.1 THE CONFERENCES ON HIGH ENERGY PHYSICS AND NUCLEAR STRUCTURE AND NUCLEI FAR FROM STABILITY A conference held at CERN during the last week of February 1963 was instrumental in launching a programme of nuclear physics at CERN. The initiative came from Victor F. Weisskopf, CERN's Director General from 1961-65, who charged Torleif Ericson, responsible for nuclear theory in CERN's Theory Division, with arranging a conference in order 'to bring the diverging fields of high energy and nuclear physics together once more'. Co-organizer and third member of the Organizing Committee was Amos de-ShaUt from the Weizmann Institute in Rehovoth. The meeting was built up around nine invited onehour lectures, each followed by several hours of discussion. It was decided to make the lectures - or what in some cases seem to be brief summaries of them - available in the form of a CERN report [6], which gives a fascinating and often very accurate preview of the research that was to come in this field in the next years. Of special relevance to the topics covered in this chapter are the papers by J.C. Sens on 'Muons and Nuclear Structure' and by Ericson on 'Interactions of Pions With Complex Nuclei'. Torleif Ericson's own recent research at that time had been concerned mainly with statistical aspects of nuclear reactions, and, in particular, the discovery of what today is referred to as the 'Ericson fluctuations' [7, 8], an early gift from CERN to nuclear physics. He has later said [9] that, not being able to find a suitable speaker on pions and nuclei, he decided to take on this task himself. During the preparations he became so interested in this field that it became his main occupation during the next decades. It seems, however, that not many others were swayed by the meeting, at least not directly.

332

The SC: ISOLDE and Nuclear Structure

The list of participants in the conference contains relatively few of those people who were to be active in experimental research of this kind at CERN during the following years. The attendance was largely by senior Europeans and by a surprisingly large number of Americans. It is tempting to conclude that the role of the conference was to win recognition rather than proselytes. Another conference series played a role in the development of research in the field of nuclei far from stabiUty, which is the subject of sects. 9.4 and 9.6. Around 1963 the time seemed ripe for an attack on this problem, which was known to require a major experimental effort. As will be discussed in sect. 9.4.2 the first ideas for an experiment at CERN were put forward that year, and the following year Ingmar Bergstrom (Stockholm) gave lectures on the subject that were widely appreciated and later published [10]. Subsequently, he organized a conference in 1966 in Lysekil (Sweden), his home town, with the participation of most of those who in the coming years were to contribute to the field. Among the new results were the discovery of extreme nuclear systems such as ^He (consisting of two protons and six neutrons) and new theoretical ideas due to W.S. Swiatecki and V.M. Strutinskii on the interplay between nuclear masses and shell structure [11] (see sect. 9.2.4). At that time the preparation of CERN's ISOLDE Programme (to be discussed in sect. 9.4) was already far advanced. Nevertheless the Lysekil conference and its sequels were essential in creating a strong and enthusiastic European community interested in the CERN experiments. Contrary to what was the case for the muon-pion experiments mentioned above, the ISOLDE-type physics tended to be regarded with some reserve by CERN and recognition came only stepwise and over a long period. For the whole of the time period discussed in this chapter it is characteristic that the main initiatives in the fields covered by ISOLDE have come from collaborations in the member countries. The 'International Conference on High Energy Physics and Nuclear Structure' has developed into an institution, and has been held subsequently in Israel and then in many other places, the twelfth being at M.I.T. in 1990. 'The International Conference on Nuclei Far From Stability' has fared similarly; the sixth in the series was held in Bernkastel (Mosel) in 1992. The ideas for experiments involving on-line experiments on short-lived nuclei had not been sufficiently far advanced to be presented at the 1963 conference but there were informal contacts via CERN's Nuclear Chemistry Group (see sect. 9.2.3). Alexis C. Pappas (Oslo) and Gosta Rudstam (CERN) had reported to Weisskopf and Ericson about the possibilities for studying far-unstable nuclei. The latter summarized the situation in a note [12] which, as far as SC research was concerned, identified as main areas (i) scattering of nucleons, (ii) muonic x-rays and nuclear capture, (iii) scattering of pions, (iv) pionic x-rays, and (v) production 'by special techniques' of radioisotopes far from the stability line and with very short half-lives. The main ingredients for the CERN nuclear-structure programme were now in place and Weisskopf, in a letter dated 13 February [13] invited a number of physicists from inside and outside CERN to a meeting. It took place at CERN immediately, on 24 February. The participants^ expressed their support for nuclear-

333

The early interest in nuclear physics at CERN

structure research at CERN and Weisskopf closed the meeting by encouraging proposals for experiments at the SC. 9.2.2 CERN'S NUCLEAR STRUCTURE COMMITTEE (NSC) AND OTHER SCIENTIFIC COMMITTEES The activities described above had established the interest at CERN and in the member countries in a nuclear programme at the Geneva laboratory, and the next necessary step from CERN's side was to set up a structure that could make recommendations on the new research. This meant fitting nuclear research into CERN's system of scientific committees, which, as discussed in some detail in the chapter by Pestre [3], had come into existence during the years 1959-62. The scientific committees at CERN serve as advisers to the Director General, who according to the statutes is solely responsible for the scientific programme of the laboratory. The committee structure existing in 1964 had been accepted by Council at its meeting on 8-9 December 1960. Under the new organization, the body advising the Director General directly, the Nuclear Physics Research Committee (NPRC), would receive input from the three scientific committees: the Emulsion Experiments Committee (EmC), the Track Chamber Experiments Committee, and the Electronics Experiments Committee (EEC). Since the three committees had jurisdiction at both the PS and the SC, it was necessary to introduce also two scheduUng committees, which took care of allocations of machine time, and which reported directly to the NPRC. The EmC in its meeting on 15 December, 1960 also decided to create an executive sub-committee, the 'Working Party' [14]. At the start the EmC Committee had 20 members in addition to the two machine coordinators and ex officio members from the CERN Directorate and accelerators. The meetings were held as closed meetings, but it was announced that one representative per group should be invited to one of the three annual meetings of the Committee. Together with the head of CERN's NP Division^, Peter Preiswerk, Torleif Ericson now proposed [15] that the Director General create a Nuclear Structure Committee (NSC). This was set up soon after with Ericson as chairman. Among the first members were Neil W. Tanner (Oxford) and Ole Bent Nielsen (Copenhagen). The complete Ust of members is not known; we have not found the minutes [16] of the first and fourth meetings. The importance of the emulsion technique was, however, decreasing rapidly and following a proposal by Gregory, Ekspong and van Hove [17] in the spring of 1966 it was decided to merge the EmC with the NSC. The proposal was presented by Wolfgang Paul, the Physics I Director, in the EmC Meeting [18] on 24 May and in the NSC Meeting^ on 12 June. The new body, which was named the Physics III Committee, had Gosta Ekspong as chairman and Torleif Ericson as vice-chairman. The structure was parallel to that of the (re-organized) Track Chamber Committee; it consisted of a 'Parliament' (the expression used by Paul) with one official representative of each interested group and a small Preparatory Committee'. It was decided that the latter should be composed of Ekspong, Notes: p. 403

334

The SC: ISOLDE and Nuclear Structure

Ericson, Paul, and two representatives of each of the two communities thus united: emulsions and nuclear structure. This two-chamber structure relatively quickly developed into the system that has prevailed up to now (1993) for all CERN committees, that of an open meeting with free access followed by the 'closed committee meeting'. As the name 'Preparatory Committee' indicates, the mode of operation was different in the late sixties. The closed meeting, which usually was held in the morning, preceded the open meeting with public presentations and discussions [20] after which the Chairman pronounced the Committee's verdict. This sometimes left the impression that the decisions had been made before the case had been heard, and the preparatory meeting was occasionally jokingly referred to as the 'troisieme bureau', the most secret of the French secret services. In 1976 the PH III Committee was re-named the SC Committee (SCC), which existed until 1978. In the years 1966-78 the chairmanship was held successively by G. Ekspong, O. Kofoed-Hansen, D.H. Wilkinson and V. Soergel. A new committee (PSCC) was formed in 1978 to advise on research both at the SC and at the PS, where the nuclear and medium-energy programme at LEAR was beginning to play a prominent role. This committee, which existed until the shut-down of the SC in 1990, was successively chaired by R. Klapisch, P.G. Hansen, H.J. Specht and M.J. Albrow.

9.2.3 STUDIES OF COMPLEX NUCLEAR REACTIONS BY RADIOCHEMICAL METHODS Chemical techniques have from the very first beginning played a central role in the development of nuclear physics. The experimental discovery of fission by Otto Hahn and Fritz Strassmann in 1938 and the subsequent discoveries of the transuranic elements and of a host of new radioactivities from fission were all due to chemists working in the borderline field between physics and chemistry, a discipline usually referred to as 'nuclear chemistry'. The history, achievements and status of this field up to the fifties can be found in an interesting and informative book by J. Hai'ssinsky [21]. Nuclear Chemistry had been provided with a foothold at CERN when the laboratory was set up, and has been encountered briefly in the previous volume of the history of CERN [22]. Because of the important role that nuclear chemists (together with physicists working in nuclear structure and with isotope separation, see sect. 9.4) played in creating ISOLDE, we give here a brief account of the start of nuclear chemistry at CERN. The science of nuclear chemistry was born and developed in Europe, notably in France, Germany and Great Britain, but the basic research associated with the nuclear programmes during the war led to a new blossoming of the field in the United States and Canada. Nevertheless it was a Norwegian nuclear chemist who brought this discipline to CERN. Alexis C. Pappas had been introduced to radiochemical techniques at the University of Oslo by Ellen Gleditsch, herself a student of Madame Curie, and had worked as a visitor at the Radium Institute in Paris. During a 2 1/2 year stay (1949-51) at MIT with the group of C D . Coryell, one of the leading experts on fission, Pappas had studied the

The early interest in nuclear physics at CERN

335

'delayed neutrons' emitted from certain fission products. (The word 'delayed' here refers to a decay mode proceeding via beta decay to particle-unstable excited levels so that the particles appear with the long lifetime characteristic of the weak interaction. Similar processes will be encountered again in sect. 9.4 and 9.6.) Back again in Norway, Pappas looked for international contacts and experimental facilities that would allow him to continue his research. Prompted by the British chemist Sir Geoffrey Wilkinson he wrote a letter (4 August 1952, in [13]) to Aage Bohr in Copenhagen and essentially offered his services: 'In Scandinavia there are very few nuclear chemists and I see it as one of my duties to spread knowledge about this branch of science and to train young scientists'. The reply (11 August 1952, in [13]) came immediately from Niels Bohr himself, who invited Pappas to Copenhagen and suggested that he should concentrate his efforts on studies of fission and spallation using the 170 MeV proton beam of the Uppsala synchro-cyclotron, which just had been completed and which 'had been placed at the disposal of The European Council for Nuclear Research', i.e. the embryonic CERN. This led to a fruitful collaboration with The Gustaf Werner Institute in Uppsala, later re-named the The Svedberg Laboratory, and involving the Swedish nuclear chemist Gosta Rudstam, the Norwegian Arve Kjelberg, Pappas's first research student, and others. An important collaborating partner at one of Europe's leading laboratories in the field of nuclear chemistry was Giinter Herrmann of the Institut fur Kernchemie at Mainz University. In a letter with a CERN letterhead, dated 21 October 1953, Niels Bohr on behalf of the Theoretical Study Group, located in Copenhagen and a forerunner of the Theory Division, invited Pappas to join the group as a consultant, an activity that lasted until 1957. It was therefore in all respects a logical choice when Wolfgang Gentner (see [22]) asked Pappas to help build up CERN's nuclear chemistry laboratory and to extend the research begun at Uppsala to higher energies. The laboratory was ready in 1958 with Rudstam as the first group leader (1959-65) and Kjelberg as the second (1965-70). Pappas continued to serve as a consultant for the Group. High-energy nuclear reactions, in general, produce many isotopes of each element, and in order to resolve these complex mixtures the nuclear chemists decided to take up a physical method, electromagnetic isotope separation (see sect. 9.4.1). The combination of this technique with chemistry provides samples selected in mass number A and in atomic number Z, thus consisting of only one radioisotope. The isotope separator [23] was designed by a small group including Goran Andersson, the specialist in this subject at Uppsala's Gustaf Werner Institute. The technique was to become the basis of the ISOLDE programme (see sect. 9.4). The scientific programme and policy of the Nuclear Chemistry Group as of 1961 was outlined in a memorandum by Gentner and collaborators [24] to Weisskopf. The main activity was cross-section measurements (fission and spallation) at 600 MeV and 24 GeV, mainly carried out in order to understand the mechanism of complex reactions. Some experiments also aimed at applications such as the understanding of radioactivities produced by cosmic rays in meteorites and the absolute determination of cross-sections that

336

The SC: ISOLDE and Nuclear Structure

could serve as beam monitors in other CERN experiments. The Group also carried out a number of experiments that exploited the extreme selectivity and sensitivity of the radiochemical technique to search for rare processes, in particular those involving the production of mesons. The main contribution during the early years of the Nuclear Chemistry Group was to the systematics of high-energy reaction cross-sections. A very successful attempt by Rudstam [25] to provide an empirical formula for spallation cross-sections is probably one of the most cited results of the group and one that has served as a guide in many later experiments. Radiochemical and mass-spectrometric research continued to be carried out at the SC and also at the PS, but in later years largely by external teams. As a particularly interesting example we mention the experiments by Raisbeck and Yiou [26] dealing with formation cross-sections and half-lives of presumably cosmic-ray produced light elements (Li, Be, B). 9.2.4 SOME OPEN PROBLEMS IN NUCLEAR PHYSICS IN THE SIXTIES AND SEVENTIES In the thirties and forties the nucleus had been viewed as an obscure, densely packed conglomerate of strongly interacting particles. This picture was behind the two most successful theories of the epoch, Niels Bohr's compound nucleus model and von Weiszacker's Hquid-drop model. Although they could explain many features of nuclear reactions and binding they offered little help in understanding the inside of the 'black box' that the nucleus continued to be. The 1948 shell model of M.G. Mayer and J.H.D. Jensen appeared as the great liberating miracle that opened the way to the understanding of nuclear structure and spectroscopy at low energies. On the heels of this followed the clarification by Aa. Bohr and B.R. Mottelson of the role of nuclear collective motion, the vibrations and rotations, and their relationship with the shell structure. The elaboration of the single-particle orbits of non-spherical nuclei in 1955 by S.G. Nilsson owed much to the emerging art of electronic computing for physics, an art that was to become essential to the development of a quantitative nuclear theory over the coming years, see Fig. 9.1. The book by Bohr and Mottelson [27] provides an overview of nuclear-structure theory in the beginning of the seventies. From the mid-sixties on it was becoming increasingly clear that although the shell model provided a convenient starting point, it was far from the final truth, and that it was of great interest to probe its limitations. Many experiments were undertaken to investigate precisely the nuclear charge and momentum distributions, the associated problem of twonucleon momentum correlations, and the role of sub-structures ('clusters') formed by groups of nucleons. Important tools were the scattering of electrons on nuclei and also the x-rays emitted from electronic and muonic atoms. Owing to the PauH principle, it is only at higher energy that it was possible to probe the deep-lying states of the nucleus, and reactions such as (p,2p), (e,e'p) and (TT, n) were used to this end.

The early interest in nuclear physics at CERN

337

Fig. 9.1 The success of the Nilsson-Strutinsky method in accounting for the energies and shapes of nuclei is commemorated in this ashtray, which Sven Gosta Nilsson had produced and distributed to friends. It shows the ground-state energy of the nucleus ^^^U as a function of an elongation (cigar-shape) parameter, running from upper left to lower right, and as a function of an asymmetry (pear-shape) parameter running from the mid-line to both sides. The calculation accounts for the following features: (i) The minimum to the upper left is the deformed ground state. The almost equally deep second minimum at larger deformations corresponds to a fission isomer, as discussed in the text, (ii) Along the symmetry line, the road to scission is blocked by a hill, but two symmetrically placed low passes favour the division of the nucleus into a small and a large fission fragment. This finally provided (see [29]) an explanation for the asymmetry in the mass distribution in fission, which at that time had been known for about 30 years.

The development was strongly stimulated by some unexpected experimental findings. The heavier nuclei turned out, in spite of their large Coulomb energy, which violated isospin symmetry, to have sharp isobaric analogue states which gave rise to a surge of interest in isospin structure in nuclei. This research was extended during the sixties and

338

The SC: ISOLDE and Nuclear Structure

seventies to other collective states at high energy (giant quadrupole resonance, GamowTeller resonance), which furnished other examples of persistent symmetries. Another group of open questions concerned nuclei 'far from stabiUty', that is nuclei with a composition very different from that of nuclei situated in the 'valley of stability', see Fig. 9.2. It is experimentally very difficult to produce and study such far-unstable nuclei. The valley corresponds to the minimum of energy for a given isobar and to stability against beta disintegration. Among the questions were the exact position of the boundaries to stability and what new decay modes and structural phenomena would show up there. In particular, there was hope of finding new regions in the N, Z plane with simple properties, such as new magic regions and new regions of strongly deformed nuclei. (The word 'deformed' here refers to so-called quadrupole deformations, that is cigar or pancake shapes). The first suggestion of such a possibility was made at a small conference in Copenhagen in the spring of 1961 by B.R. Mottelson, who proposed that the unexplored region with both N and Z smaller than 82 and bigger than 50 should show well-developed rotational bands. This was soon confirmed in an experiment by Sheline et al. [28], who found a drop in the energies of the first-excited 2^ states which was interpreted as indicating the onset of nuclear rotations. Of far-reaching importance was the discovery in 1962 by S.M. PoHkanov et al. of the 'fission isomers'. These are excited states of heavy fissionable nuclei. They have surprisingly long lifetimes for electromagnetic decays and equally surprisingly short lifetimes for spontaneous fission. For the latter the enhancement, as compared with normal nuclei of the same element and mass, amounted to factors of 10^^ or more. It was soon reahzed that these isomers represented states with extremely large quadrupole deformations (cigarshapes) and that this meant a very thin fission barrier and consequently a large probabihty for tunneling of the fission fragments through the barrier. The question was now why these shapes were so close to being stable. Techniques for calculating total binding energies and equihbrium shapes were developed, especially by W.J. Swiatecki, S.G. Nilsson and V.M. Strutinsky ('Strutinsky renormalization') ([29, 30], and Fig. 9.1). They also had great impact on the understanding of binding and masses in other regions of the nuclear chart (see Fig. 9.2). The nuclear physics community paid particular attention to the theoretical predictions of a region of possibly long-lived 'super-heavy' elements, isotopes with atomic number near 114 and neutron number near 184 (predicted [30] to be the magic numbers corresponding to the isotope^^^Eka-Lead). Many experiments were undertaken to search for these new elements, but the experiments were much harder than had been expected. It was only during the eighties that convincing evidence for the existence of relatively long-lived alpha-emitting radioisotopes with atomic numbers as high as Z=107, 108, 109. At the time of writing was obtained, largely by P. Armbruster, G. Miinzenberg and their collaborators at the G.S.I, in Darmstadt [31, 32]. (September 1992) the Group has decided to name these elements Nielsbohrium, Hassium and Meitnerium. Nuclear physics is a rich but also complex subject and it is not possible to identify a single frontier line for research similar to the high-energy frontier in particle physics. We

3'

h

Fig. 9.2 The nuclear chart, proton number Z as a function of the neutron number N (courtesy of Gottfried Miinzenberg, G.S.I.,Darmstadt). The dark squares

represent nuclides found in nature and the other signatures nuclei produced in the laboratory. The dashed lines represent estimated limits to stability set by spontaneous fission and proton and neutron emission. Those corresponding to B, and B, equal to zero are usually referred to as the drip lines.

w

\o

340

The SC: ISOLDE and Nuclear Structure

can maybe identify some of the discernible main lines, (i) The high Z frontier, i.e. that of the super-heavy elements just discussed, (ii) The isospin frontier, that is the regions in Fig. 9.2 with very high and low isospin projection Tz = (N-Z)/2. This research has been a major subject at ISOLDE and will be discussed in sect. 9.6. (iii) The energy frontier, the interactions of nuclei with high-energy probes such as pions, nucleons and fast heavy ions. Examples of such research at the SC will be discussed in sects. 9.3 and 9.5.5. (iv) The angular momentum frontier, largely the domain of heavy-ion accelerators at relatively moderate energies, (v) The low-spin frontier, concerned with spatial and momentum distributions of the nuclear ground state and low-lying excited states. This kind of research uses a large number of probes: electrons, muons, photons, pions. Examples of this research at the SC will be given in sections 9.3 and 9.6.

9.3 Experiments with muons and pions As early as the end of 1964 the scientific programme at the SC had become almost entirely nuclear, as may be seen from an example: In the NPRC meeting on 17 February 1965 Emilio Zavattini [33], gave a summary of experiments that would be on the floor during the coming six months. These included: (i) Studies of nuclear n~ capture at rest (Cernigoi), (ii) Pion production at 600 MeV (MichaeHs), (iii) Muonic x-ray studies (Backenstoss-Sens), (iv) Study of the reaction n^ +^ Li ^ 2p + a (Charpak), (v) Inelastic scattering of n~ on Hght nuclei (Meunier, Spighel and Stroot), and (vi) Background tests for a crystal spectrometer (Nilsson) intended for muonic x-rays. At the following meeting one more experiment had been added dealing with quadrupole interactions of muons with deformed nuclei (Macq). The tools for this research, the beam lines around the SC, have been described previously [2], so the following sections will deal with some of the physics that can be done with beams of muons and pions. 9.3.1 MUONIC X-RAYS The muon may be viewed essentially as a heavy electron. It has electromagnetic and weak, but not strong, interactions with nuclei, and its large mass, 207 electron masses, means that the muonic atoms formed by the negative muon have smaller dimensions and larger transition energies by a corresponding factor as compared with electronic atoms. It turns out that both sizes and transition energies are essentially on a nuclear scale, and for this reason the negative muon is an extremely valuable probe for nuclear structure. For light nuclei even the most bound states of muonic atoms have the muon well outside the nucleus and hence resemble the hydrogen atom, while for heavy nuclei the muon is mainly inside for the most bound states. At the energies discussed in this chapter the muonnucleus interaction is believed to be governed completely by the laws of quantum electrodynamics (QED) so that the interpretation of experiments is conveniently free from ambiguities. (Conversely, measurements on muonic atoms furnish some very accurate

Experiments with muons and pions

341

checks on QED.) The positive muon resembles from the point of view of atomic and molecular physics a Ught hydrogen nucleus; it has found applications in solid-state and molecular physics. The powerful new muon channel at the SC [34] had not escaped the attention of nuclear and atomic physicists, but the machine was crowded and 'machine time was allocated in hours rather than in shifts' to quote the German (Freiburg) physicist Gerhard Backenstoss [35], who was one of the young physicists around CERN biding his time for a go at the muonic atoms. He had worked in the United States at Bell Telephone Laboratories since at the time it was difficult to work in nuclear physics laboratories in the U.S.A, where clearance for foreign nationals had to be obtained. There he was inspired by a seminar by Sergio de Benedetti on pionic and muonic atoms. With the help of a CERN fellowship he finally could arrange a stay at Pittsburgh, where he learned that the leading lights in the field had left (M. and M.B. Stearns) or were spending some time at CERN's SC (J. Ashkin, L. Wolfenstein, S. de Benedetti), that just had come into operation. At CERN in 1959, Backenstoss had his first chance when Wolfgang Gentner, head of the SC, put him in touch with Peter Brix from Darmstadt. Brix together with Hans Kopfermann had, when they both were in Gottingen, discovered [36] the first cases of strong nuclear quadrupole deformations (in the rare earths, Z = 60-64) via the observation of very large isotope shifts in the atomic spectra. As one of Europe's leading experts on nuclear sizes and shapes, he had the right background for launching the first experiment [37] in Europe to study charge distributions from the x-rays emitted from muonic atoms. The weak point, however, was the gamma detection, made with thallium-activated sodium iodide crystals. The study concentrated on the 2 p ^ l s transition but the resolution was insufficient for resolving the fine structure (2p3/2,2pi/2) splitting, which could be observed only in the 3d-^2p transition and only for the heaviest elements. In a game where precision was absolutely essential this was clearly an unsatisfactory situation, as could also be seen from parallel and previous American experiments [38, 39]. Another physicist who was keeping an eye on the field was J.C. (Hans) Sens from Holland, who had obtained his Ph.D. at the University of Chicago working with V.-L. Telegdi on pr capture in nuclei. From his review of muonic atoms given at the 1963 Conference mentioned in sect. 9.2.1, it is clear that Sens had followed the subject closely and that he was thoroughly famihar with its theory. The possibility for a break-through came in 1964, when nuclear physicists began to use Uthium-compensated germanium diodes ('Ge(Li) detectors') and later pure ('intrinsic') germanium diodes for gamma-ray spectroscopy. At CERN this new technique had a quick start. A letter [40] submitted as early as January 1965 reported some early results on both spherical and deformed nuclei obtained with a small (2 mm thick) commercial Ge(Li) detector with quite mediocre resolving power. It was, however, essential quickly to get better detectors. Both Sens [41] and Backenstoss [35] emphasize the important role played by Ernst Baldinger from the University of Basel, who at that time was studying radiation damage to transistors. He agreed to attempt to make germanium detectors, and within 2-3 months succeeded in fabricating specimens with a thickness of 6 mm. (Thickness is above all

342

The SC: ISOLDE and Nuclear Structure

essential for stopping the photoelectron inside the sensitive volume.) With these, much better results were obtained, first for spherical nuclei [40] of 18 elements ranging from CI to Bi. With a resolution of the germanium detector that was still much inferior (20-24 keV full width at half maximum) to what could be achieved just a few years later, there was no longer any problem in resolving the fine structure, and the paper gave a detailed discussion of the intensity rules, governed mainly by statistical weights, but where there were some significant deviations. The main thrust of the paper was, however, the determination of the parameters for the nuclear charge distributions, which were parametrized as the so-called Fermi distribution p{r) = N{1 + exp[41n3(r - c)/t])-^ where c is the radius at one half of the central charge density, t the skin thickness, i.e. the distance over which the nuclear charge density drops from 90% to 10% of the central charge density, and N a normalization constant. The correlations between the two parameters were demonstrated in (t,c) plots, similar to the way previous electron-scattering data had been presented. The point is that a single transition energy for a given isotope determines a curve in the (t,c) plane. An intersection between two curves defines a parameter set that is consistent for the two transitions. A general area of best fit, approximately valid for all nuclei studied, was t = 2.2 fm and c = 1.12- A~^^^ fm, in excellent agreement with the values previously obtained in electron scattering. Somewhat similar results were found in a subsequent study [42] of deformed nuclei in the lanthanide and actinide regions. For the lightest nuclei (B-Cl) the muon is mainly outside of the nucleus, and the x-ray energies are no longer sensitive to the details of the charge distribution and give [43] the mean value of the square of the charge radius as the only information, exactly as is the case for the corresponding optical transitions in (electronic) atoms (see sects. 9.4.6 and 9.6.2). In this first phase of muonic-atom experiments the main purpose was to use muons to learn about the radial distribution of nuclear charge. The results were important in providing a confirmation, by another technique with different sources, of systematic errors in the picture already arrived at from scattering of high-energy electrons on nuclei. However, since no great surprises emerged, it is understandable that the programme soon changed character. Sens decided to take up experiments at the PS, and Backenstoss, as we shall see shortly, to an increasing degree initiated experiments involving x-rays from the capture of negatively charged hadrons in nuclei. Around this time Brix's group from Darmstadt, which we encountered at the beginning of this section, re-appeared on the scene. In a proposal presented by Roland Engfer on 31 January 1967 the group expressed its wish to conduct a second programme on exotic atoms. From the minutes (PH III-67-1) it appears that the Committee was hesitant about permitting a second independent effort at the same machine and in a fast-moving and very competitive field. It recommended tests together with Backenstoss's group to be followed by a review of 'whether there should be one or several groups in this area'. It was the second solution that was to prevail in a spirit of good collaboration between the groups.

Experiments with muons and pions

343

9.3.2 PIONS AND NUCLEI While the muon provides a clean probe for studying nuclear problems, the pion (or nmeson) is itself part of the problem. It interacts strongly with the nucleons, is spinless and carries isospin 1 and hence forms an isospin triplet TC", TT^, TT"^. Identified early as Yukawa's particle and carrier of the strong force, the charged pion's mass of 273 electron masses implies that the long-range part of its field has a decay length of the order of its Compton wave length H/mj^c :^ 1.4 fm, a quantity corresponding roughly the range of the nucleonnucleon force and to the internucleon distance in a nucleus. For a pion interacting with a nucleus, the pion field therefore has additional contributions from the virtual pions in the nuclear medium. This is a problem analogous to that of the propagation of a photon through a dielectric medium. Modern particle physics teaches that the pion is not an elementary particle but, like all mesons, composed of a quark and an anti-quark. Thus the negative pion has the formula (ud) and it is not point-Hke but has a root-mean-square charge radius of 0.66 fm. One would therefore tend to believe that this would mean that a description of nuclei in terms of quark structures would be more effective, but this does not seem to be the case for low excitation energies, say below 1 GeV. The reason is that the essential degrees of freedom at low energies involve only the lowest states of the hadron spectrum. For the mesons these are 7r(140) and the two vector (spin 1) mesons p(770) and co(783), and for nucleons the ground state N(938) and first excited state, the broad A(1232) which has both spin and isospin equal to 3/2. With these states as the essential ingredients modern medium-energy theory is able to describe a wide variety of phenomena in pion-nucleus interactions as can be seen from the recent book on this subject by Ericson and Weise [44] and from which we cite two examples. The deuteron is the classical example of a loosely bound system in nuclear physics, as the root-mean-square distance between the two nucleons is as large as 4 fm. For this reason, the properties of the deuteron are described very accurately by the simplest pion field, the one-pion exchange potential (OPEP), which is responsible for the nucleon-nucleon force at large distances. For more dense systems collective spin-isospin modes of low frequency appear; we have already in sect. 9.2.4 had occasion to mention the Gamow-Teller giant resonance. The SC played a central role in the early development of Ti-nucleus physics. As outUned briefly in sect. 9.2.4, the main emphasis in nuclear physics in the early sixties was on nuclear spectroscopy, which served to test nuclear models, and there was no particular reason to beHeve that a rare and expensive projectile such as the pion could give information that would not be readily obtained with the more abundant conventional projectiles. As mentioned in sect. 9.2.1, at the conference [6] in February 1963, Torleif Ericson had given arguments why pions were especially interesting for exploring the nuclear interior, together with a first presentation of his and Magda Ericson's theory [45] for the propagation of pions in nuclear matter. He pointed out that the important experiments were pion scattering from nuclei and measurements of x-rays from pionic atoms. We give here and in the following two sections some examples of how the ex-

344

The SC: ISOLDE and Nuclear Structure

perimentalists responded to this challenge. More information can be found in a recent article by Ericson [46]. The observation of x-rays from pionic atoms permits the study of the Ti-nucleus interaction at zero kinetic energy. The formation of pionic atoms with the emission of x-rays had been observed by a number of groups (see the review by Backenstoss [47] and also a recent retrospective [48]) but as in the case of muonic atoms, it was only with the advent of the lithium-drifted germanium counter that more precise investigations became possible. A first round of experiments [49] studied the 2 p ^ l s transitions of Ught elements and demonstrated that the pionic x-rays involving the Is state are shifted in energy and also dramatically broadened by the strong interaction, see Fig. 9.3. The pace was fierce in this early boom of exotic-atom research: quite similar results had been obtained just before by the Berkeley group [50]. For the heavier nuclei, the s-states become too broad to permit the observation of x-rays connecting to these states, and a subsequent experiment [51] succeeded in observing shifts and widths for the 3 d ^ 2 s transitions in the elements Al to Zn. The results were in good agreement with the theory of Ericson and Ericson [45]. Subsequently the 4f-^3d (Z = 49-59) and 5g^4f (Z = 73-83) transitions were studied [52]. It is maybe worth pointing out that for the cases in which the line broadening is too small to be observed directly, it may still be possible (see [47]) to determine the level widths via the line intensities, which reflect the competition between radiative decay and absorption. The pionic atom data could be analyzed in terms of the parameters of the pion-nucleus interaction potential. The systematics of the real and imaginary parts of this potential have been discussed by Hiifner et al. [53]. 9.3.3 TEST OF QUANTUM ELECTRODYNAMICS AND THE MASSES OF THE PION AND THE MUON The theory of quantum electrodynamics (QED) is believed to be exact as has been shown in a number of precise experiments, see e.g the review by Mohr [54]. These experiments, of which 'g-2' discussed in [2] is one example, can best be performed on simple atomic systems, for which accurate predictions are possible. The classical example is, of course, the 2p 1/2-2s 1/2 energy difference in the hydrogen atom, which led to the discovery of the Lamb shift and to the subsequent development of QED theory. Since the main terms in the Lamb shift involving self energy and vacuum polarization corrections depend strongly on the atomic number Z it is interesting to perform tests in the strong electric field of heavier nuclei. Although these effects are observable in the x-ray transition energies of neutral atoms the theory of a many-electron system cannot be exact, and the most precise tests require hydrogen-Hke systems. (Presently such experiments are being performed on highly stripped heavy ions at high energies.) Muonic atoms offer the advantage that they are always hydrogen-Uke because the muon is much nearer to the nucleus than the electrons so that electron screening of the field is neghgible or a small correction. Since we have seen in sect. 9.3.1 that the transition energies can be very sensitive to the nuclear size, it would seem that this effect would be a

Experiments with muons and pions

345

^3p-1s

-10^

T T ^

^l4p-1s

^h

3h

^3p-1s

^4p-1s

KO

150

160

170

180 kcV

Fig. 9.3 The 2p^ls x-ray transitions in pionic ^^'^^O appear as broad lines (F = 7.6 ± 0.5 and 8.7 ± 0.7 keV for the two cases). The pionic lines are strongly reduced in intensity by the competing process of nuclear absorption, which explains why the background of muonic x-rays is so prominent. The muon contamination in the beam was actually only a few percent. Note also that the pionic lines do not appear at the same energy, which impUes that the interaction depends on isospin [49].

346

The SC: ISOLDE and Nuclear Structure

serious limitation, but it can usually be avoided by studying transitions between states with high angular momentum, and for which the muon wave function at the nucleus is essentially zero. The effect of the nuclear size was, in fact, the main limitation in an ingenious experiment on the 2p3/2-2si/2 fine structure of muonic helium carried out at the SC by Emilio Zavattini, Jean Duclos and their collaborators [55, 56]. This experiment represented a longhaul effort begun around 1970. The basic idea is simple. The 2s state"* lies below the 2p state and it is long-Uved because one-photon decay to the Is ground state is forbidden. (Electric dipole radiation is excluded by the parity selection rule, and magnetic dipole radiation by the orthogonality of the Is and 2s wave spatial wave functions.) The level decays mainly via the beta decay of the muon and to about 20% via the emission of two photons. It was shown that this state is formed in the capture of muons in helium. The 2p3/2 level lies about 1.5 eV higher, an energy difference due predominantly to the contribution from vacuum polarization while those from the fine structure and nuclear size are about an order of magnitude smaller. The essential trick was now to induce the 2si/2 ^2p3/2 transition by means of a powerful pulsed laser operating in the infrared (the transition energy corresponds to a wave length of 8100 A) and synchronized with the arrival of a muon in the helium target. The formation of the p state was revealed through the emission of the usual Ka x-ray. In a scan of x-ray count rate versus laser wave length a resonance was found with the expected width of about 1.5 meV (milli electron volt), a splendid energy resolution for a medium-energy physics experiment, and leading to a transition energy of 1527.5±0.3 meV. The theoretical value for the transition energy is 1535±9 meV based on a root-mean-square radius for "^He of 1.650 ± 0.0025 fm determined from electron scattering. If the validity of QED is assumed, the experimental result may also be read as an improved determination of (r^) for helium. Other experiments at the SC approached the problem of QED corrections via measurements on heavy atoms with germanium detectors, which offer an energy resolution of the order of 1 keV (kilo electron volt), comparable to the effect of 1-2 keV expected. Such experiments test vacuum polarization to several orders in the product of the fine structure constant (1/137) and the nuclear charge, and therefore the best signal is obtained from heavy atoms. The effects of nuclear size were avoided by studying transitions between circular orbits with high angular momentum such as 5g-^4f (for nuclei near lead) or 4f—>3d (for nuclei near barium). Early results by Backenstoss et al. [57, 58] found agreement with QED theory while Walter et al. [59] and also parallel work in North America found indications for a small deviation from theory, of the order of two standard deviations. Subsequent experiments at the SC by Ludwig Tauscher and collaborators [60], and with an energy resolution now improved to 450 eV, found agreement with theory within error limits of 12-16 eV, so that the QED corrections had been verified to a relative precision of 0.5%. Quite similar results were simultaneously obtained [61] by the Canadian-American group that previously had found discrepancies. The comparisons of measured and calculated transition energies in muonic atoms discussed here presupposes that the muon mass is accurately known from other sources. This

Experiments with muons and pions

347

is, in fact, the case today. The most accurate determination of the muon mass comes from the ratio of the magnetic moments of the muon and the electron, but older measurements are based on transition energies in muonic atoms, as can be seen from the compilation by the Particle Data Group [62]. Likewise it is possible to determine the charged pion mass from the energies of transitions in low-Z pionic atoms, for which the corrections to the Klein-Gordon equation (the appropriate relativistic equation for a particle with spin zero) for QED effects and strong-interaction shifts are manageably small. An early accurate measurement of the pion mass was reported by Backenstoss et al. [58]. The currently most accurate value for the ratio of the pion and electron masses has been measured [63] at the Swiss meson factory SIN to be 273.1268±0.0007. 9.3.4 SCATTERING AND PRODUCTION OF PIONS ON NUCLEI A process that quickly captured the imagination of many nuclear physicists was that of pion double charge exchange (DCE) such as ^Be {n~^n^) ^He. This process, discussed in detail in [44], must take place as a two-step reaction involving two pion-nucleon interactions. Its final states are, in general, highly excited continuum states and the crosssections for producing individual bound final states are usually small. (Nevertheless DCE has recently served to give information on states in the unbound and extremely neutronrich nucleus ^He, see [64].) The DCE process was observed early at the SC by the so-called MSS Group (an abbreviation for 'Meunier, Spighel and Stroot'), and they made a valiant attempt to find the tetraneutron [65] from a bombardment of helium. However, with the intensities available at that time it was impossible to observe DCE to individual final states. The MSS collaboration set out in 1963 [66] to develop a spectrometer capable of studying the scattering of pions. The task was a difficult one, not only because of the low intensity of the pion beam, but also because excellent resolution was needed in order to resolve individual final states in the nucleus. Over the following years the group succeeded in building an instrument that had sufficient resolving power to separate individual levels in certain light nuclei. The essential trick, which later became a standard feature for spectrometers in intermediate-energy physics, was to use a 'double achromatic spectrometer', that is one in which the beam of pions is analyzed in the first magnet and the scattered particles are re-focused by the second magnet, independently of their initial momentum since the total dispersion in the two arms of the spectrometer is zero. (The analogy with similar arrangements in optics explains why the instrument is called achromatic.) Particles that have suffered inelastic collisions in the target appear elsewhere in the focal plane, so that cross sections for several states are recorded simultaneously. In this way it was possible to measure final states with an effective momentum resolution of 0.5-1% although the incident beam from the first magnet had a momentum bite of 2%. The spectrometer was first used for a study of n~ scattering on carbon. The results shown in Fig. 9.4 show a characteristic diffraction pattern in which the interference becomes especially pronounced at 180 Mev kinetic energy [67] demonstrating that the pion Notes: p. 403

348

The SC: ISOLDE and Nuclear Structure

0.2

0.3

Fig. 9.4 Elastic differential cross sections for the scattering of TT" on ^^C as a function of the longitudinal momentum transfer in the centre-of-mass system and for pion kinetic energies from 120 to 280 MeV. The points indicated by OP represent the optical point calculated from the measured total cross-section. (From [67]).

Experiments with muons and pions

349

has a very short mean free path in nuclear matter at energies near the A resonance. This experiment was the first to demonstrate the role of the A in nuclei. A second experiment by the same group [68] studied Coulomb-nuclear interference across the resonance region. Another group, usually referred to as the Goteborg-Oxford group, studied the production of pions in nuclear collisions. One interesting result was the observation [69] of the capture of a proton into bound states with all the excess energy concentrated on the emerging pion. Such processes require a very large momentum transfer and had therefore been regarded as forbidden. The explanation clearly must involve the collective eifect of several nucleons, most simply in the form of the Fermi motion of the individual nucleons in a nucleus. Similar phenomena have since been observed in a number of other cases, notably in pion and kaon production in nucleus-nucleus coUisions (see sect. 9.5.5). The same group also investigated [70] effects of charge symmetry and Coulomb distortion in the scattering of positive and negative pions on Ught nuclei. 9.3.5 OTHER EXPERIMENTS WITH MUONS In addition to other work already mentioned, the Engfer-Kankeleit group focused on some of the more subtle features of the muon-nucleus interaction in order to learn about nuclear structure. We give a few examples of the flavour of this work. In the first experiments they studied not x-rays but nuclear gamma rays emitted from states in the target nucleus that have been excited by the x-ray cascade. These gamma rays are emitted while the muon is still present, so the total energy contains a contribution from the muonnucleus interaction. If the two states have different sizes, it is found that the transition energy is changed by an amount referred to as the 'isomer shift', a finite-size effect of the same kind as that encountered in muonic x-rays (sect. 9.3.1) and in optical transitions (sects. 9.4.6 and 9.6.2). This phenomenon is pronounced for the rotational first-excited 2"^ levels of strongly deformed nuclei (Z = 62-76), which are easily excited and which have [71] different transition energies to those of a free nucleus - or rather a nucleus surrounded by its electrons. (The high resolution for y-rays provided by the Mossbauer effect has permitted similar observations on 'electronic atoms'.) For the heavy element such as thallium (Z = 81), the coupling of the muon to the nucleus via the magnetic dipole interaction is strong enough for the doublet to be resolved [72]. To give an example of the order of magnitude of this effect, the ground state and 203.7 keV first excited state in 205jj ^j.^ gpjj^ by 2.3 keV and 1.1 keV, respectively [73]. Like other weak and electromagnetic processes in nuclei, the capture of muons is strongly influenced by giant-resonance phenomena, but is for technical reasons Uttle studied. Petitjean et al. [74] approached this problem for the isotopes of Europium by measuring delayed gamma rays and deduced neutron multiplicities, Hnked to the excitation energies. A survey of results from a large number of nuclei was given by Backe et al. [75]. During the sixties and seventies a group from Louvain headed by Jules Deutsch and Pierre Macq carried out a number of experiments on weak interactions in nuclei. We take as an example the one that they themselves presented at a recent festive occasion [76],

350

The SC: ISOLDE and Nuclear Structure

namely the measurement of the parity of the ^^Be ground state. The problem was that suspicion had arisen that this state, corresponding to that of the seventh neutron, was not characterized by the spin-parity combination l/2~, as would be expected from the shell model, but that it was rather 1/2"^. In order to determine the parity the group measured [77] the direct muon capture rates to the ^^Be ground and 320 keV first excited and found them to be forbidden and allowed, respectively. Since the target nucleus, ^^B, is known to have negative parity this means that the ground state was indeed 1/2"^. This was the first example of what today is called an intruder state. There was also during the sixties a growing interest in the possible application of muonic x-ray spectroscopy to studies of the solid state, for example by detecting shifts in the x-ray intensity ratios for pairs of transitions in the same element embedded in different chemical compounds. Similar observations were being made elsewhere at about the same time, see e.g. [78, 79]. A much more important application that today forms a major research field is the use of muon spin rotation, often abbreviated /iSR. This technique exploits the parityviolating asymmetric beta decay of the positive muon for detecting the precession of the muon in a magnetic field. (There are similar, but less important, applications of negative muons.) The primary parameters detected are the precession frequency (there may be more than one) and the attenuation of the correlation due to muon depolarization. The many appUcations of /xSR in solid-state physics and chemistry have been reviewed by Brewer and Crowe [80]. The first proposal to conduct such a programme at the reconstructed SC was made [81] to the Physics III Committee by Erik Karlsson, Ola Hartmann and LarsOlaf Norlin (Uppsala), just at the moment when the reconstructed SC was getting ready to receive users. During the second half of the seventies and until the mid-eighties a broad collaborative programme in /iSR was conducted at the SC by a number of groups including, to name just a few participants, Cesare Bucci (Parma), D. Richter (Jiilich) and E. Walker (the Rutherford Laboratory). A good impression of the versatility of this field can be obtained from the proceedings of specialized conferences [82, 83] covering the period in question. Applications of /iSR in metal physics have been reviewed by Karlsson [84]. Several broad reviews can be found in [85, 86]. 9.3.6 LOOKING BACK This section has given some examples of the contributions made by the muon-pion programmes at the SC during the golden period from roughly 1965 to 1975. An in-depth assessment of the impact of the work at CERN in this field would, however, have to look in detail at a broader time window and also at simultaneous activities elsewhere, something that clearly falls outside of the scope of the present paper. We note that muon-pion experiments with nuclei had their first beginnings in the U.S.A., and that the Chicago and Columbia cyclotrons and to a lesser degree other machines were very serious competitors throughout the period in question. Especially in the exotic-atom research, the groups were racing neck and neck as can be seen from several cases of similar and almost simultaneous publications. (The reason for this situation should be clear from sect. 9.3.1. The advent of

The early ISOLDE

351

one new technique, the germanium diode for gamma-ray spectroscopy developed in nuclear physics, suddenly opened the floodgates to a host of interesting problems waiting to be answered.) We also believe that some of the most valuable contributions made by the CERN muon-pion experiments are the programmes that they generated at subsequent machines. As early as around 1970 some of the physicists at CERN had begun to shift to the PS to do experiments on K", antiprotons and Z", and during the first half of the seventies the pion and muon experiments moved to the Swiss meson factory SIN (today the Paul Scherrer Institute in Villigen, Switzerland), where the intensities were much more favourable. At about the same time similar and also very powerful American and Canadian facilities (LAMPF, TRIUMPH) sprang into operation, and an important mediumenergy programme developed at SATURNE (Saclay). It is clear, however, that during the period discussed here, the SC groups working with muons and pions were very well placed, maybe leading, in the competition on a world scale. The strong interaction between experiment and theory was an important ingredient in this success. Although the present paper does not discuss the contributions made by theory, we can at this point at least try to mention some of the names of those, visitors and staff of CERN's Theory Division, who played an important role: J. Bernabeu, J. Blomqvist, M. and T.E.O. Ericson, J. Hiifner, M.P. Locher, F. Myhrer, E. Oset, W. Weise and C. Wilkin. To them and many others goes much of the credit implied in the remark made by Sens [41] to the effect that the experiments at CERN generally were well conceived and were better analyzed than those of the competing groups. In the next section we shall discuss the ISOLDE Programme during roughly the same time period of time, and we shall see that its characteristics were in almost all respects the opposite of those mentioned. ISOLDE was very much an isolated long-haul eff'ort with only modest competition on the world scale. No floodgates had opened, and the eff"ort in the early years was concentrated on difficult experimental problems which were only rewarding in the long run, and which had Uttle glamour and very limited theoretical support. My own view is that in the early period discussed in sections 9.3 and 9.4, roughly corresponding to 1965-73, the muon-pion programme clearly was more topical, more timely and more interesting than ISOLDE.

9.4 The early ISOLDE The new frontier represented by the boundaries of the nuclear chart (Fig. 9.2) was one that attracted many nuclear physicists and chemists in the mid-sixties. Theoretical ideas had emerged as to what new physics one might learn there (sect. 9.2.1) and new techniques were being developed [11]. Of these electromagnetic mass separation appeared especially promising because it offered the cleanest conditions and consequently high sensitivity to rare events. From the experimental point of view, however, the problem was difficult, but it was encouraging that already in 1950-51 one group had succeeded in carrying out a successful pilot experiment, which is described in sect. 9.4.1. The rest of the section gives

352

The SC: ISOLDE and Nuclear Structure

an account of the creation of the ISOLDE Collaboration and of its early research programme. 9.4.1 ON-LINE MASS SEPARATION, COPENHAGEN 1950-51 A wide variety of techniques are used for electromagnetic isotope separation; well known are the mass spectrographs used for measuring relative abundances of ions or for measuring atomic masses. Another variety is the large-scale isotope separators called calutrons that were used in the nuclear-weapons programmes. European laboratories were active during the fifties and sixties in developing an intermediate instrument, usually referred to as 'isotope separators', of laboratory size and to be used as a tool for nuclear physics research to purify mixtures of stable or radioactive isotopes. There was much international collaboration and much informal contact between the European physicists^ working in this field. The development of this specialty can be traced through a conference series on electromagnetic isotope separation, EMIS [87], and a number of those involved played a role in developing the techniques for studying far-unstable nuclei by on-line mass separators at CERN and elsewhere. In a historical perspective it is, however, fascinating to note that this early and very informal European collaboration also had an important influence on fields other than nuclear physics. Studies of the implantation of radioactivity into collectors and of sputtering phenomena in the production of thick targets led to a deeper interest in ranges of ions and atomic coUision phenomena in solids, and among other things to the discovery [88] of 'channeling' of ions in crystals. Out of the conference series mentioned above another branch developed, which was dedicated to 'Atomic Collisions in SoHds', still a very active field. Interesting enough there are again lines that lead to CERN. There have been studies of penetration and stopping powers of charged particles at the PS, at LEAR and the SPS, there are high-energy experiments that use channeling as a tool in particle detection, and there even exist plans to use channeling for beam extraction at the LHC, the large hadron collider that for the moment is foreseen as CERN's next new accelerator. For someone who would like to think about the importance of not defining physics too narrowly and about the value of international collaboration, the history of European isotope separation provides some interesting material. But I digress and must return to the on-line experiments. The first experiment in which an isotope separator was connected directly to an accelerator was carried out in Copenhagen in 1951 by Otto Kofoed-Hansen and Karl Ove Nielsen [89], both working at Universitetets Institut for Teoretisk Fysik (UITF, later renamed the Niels Bohr Institute). The experiment ran for a short time only but nevertheless played an important role as a demonstration of the feasibility of the on-line technique and of its great power for sorting out the components of a complex reaction mixture. Although simple, it incorporated all the same elements as a modern on-Hne experiment. The Copenhagen cyclotron produced fast neutrons from an internal beryllium target and these bombarded an external target consisting of 10 kg of a mixture of uranium oxide and

The early ISOLDE

353

baking powder (essentially (NH4)2C03). The decomposition products (NH3, CO2 and H2O) of the latter served to sweep volatile fission products, mainly krypton and xenon, the two noble gases in fission, along through a 5 cm diameter metal tube towards the electromagnetic isotope separator. Just before the ion source the carrier gases were removed in a cold trap. The experiment was further complicated by the necessity of keeping the long metal tube connecting the two machines at the acceleration voltage of the separator, 50 kilovolts. The measurements of radioactivity were carried out with very simple detection systems, essentially Geiger-Miiller counters, and permitted the discovery of several new isotopes of krypton and their descendants. The experiment came to an end somewhat prematurely. During the first part of the fifties the UITF was constructing new buildings and the cyclotron was moved to a new area where, unfortunately, it was too far away from the isotope separator to permit a continuation of this research, something that was frequently remarked on by visitors to the Institute in the coming years. The 25th anniversary of this experiment was celebrated in 1976 in Cargese (Corsica, France) during the 3rd International Conference on Nuclei Far From Stability, a sequel to the Lysekil Meeting (section 9.2.1). In a lively talk, the spirit of which is well preserved in the written version [89], Kofoed-Hansen contrasted the primitive experimental techniques of 1951 with those of 25 years later. In fact, said he, not even the term 'on-line' had been known in 1951. (It entered physics in the early 1960s with the use of digital computers). He also pointed out that the experiments had been pursued with a single well-defined aim, namely to discover new noble-gas radioactivities that could be used in experiments to detect the neutrino via its (missing) recoil momentum. Around 1950, Kofoed-Hansen and other workers at the UITF had carried out several experiments of this kind, which served to provide an underpinning for Pauli's 'neutrino hypothesis'. The point is here that the neutrino had been invoked to account for missing energy and angular momentum; consequently it was important to check that the hypothesis predicted the correct amount of missing linear momentum. One of the isotopes discovered (^^Kr) was, in fact, used in such an experiment [90], but we know today that its decay scheme is far too complicated to permit any simple interpretation of the results. The purpose of the Copenhagen experiment was thus not an all-out attack on the problem of the far-unstable radioactive isotopes; the problem as such was hardly recognized at the time, and the primitive detection methods of the period did not allow much information to be extracted from a complex decay with many beta- and gamma-rays. In fact, one technical reason behind the emergence of this problem in the mid-sixties was that solid-state detectors based on siUcon and germanium had just been developed and permitted studies of particles and gamma rays with high resolution and good efficiency. 9.4.2 THE ISOLDE COLLABORATION IS FORMED Although many physicists were interested in on-line mass separation, it was the nuclear chemists at CERN who had their hands on the best accelerator in Europe for such a purpose, the 600 MeV synchro-cyclotron. In 1963 the first outline of a plan for placing an Notes: p. 403

354

The SC: ISOLDE and Nuclear Structure

electromagnetic isotope separator in the external beam of the SC was circulated as an internal NP Division report by Rudstam and Andersson [91]. Following Weisskopf s call for proposals (see section 9.2.2) the Nuclear Chemistry Group organized a meeting at CERN on 10 April 1964 in which the scientific aims and organization of the project were discussed. There was general enthusiasm for the idea and it was among other things decided to have the separator planned by a working party^. Later other working parties appeared, one on target and chemical separation methods and one on data handUng and electronics. More will be said about the former in section 9.4.4. The minutes and progress reports from these various committees and sub-committees can be found in the ISOLDE files [92] and give a month-to-month picture of the development over the next 3 1/2 years, up to the first beam on target. In a series of meetings from May to September 1964 the Working Party arrived at what was essentially the final design (see Fig. 9.5). Here one should note that the target-ionsource unit is separated from the analyzing magnet by a drift tube which traverses a shielding wall, and which is displaced from the target plane in order to avoid fast neutrons streaming from the target into the experimental area. A second collaboration meeting [92] was held on 9 November 1964 and it was decided to submit a final proposal to CERN. Other important decisions were to set up a 'Finance Committee' to look after common funds and to let the construction work on the isotope separator commence in Denmark, probably at Aarhus'. The meeting also considered a name for the programme; among those suggested were EBIS (external beam isotope separator), COLIS (CERN on-line isotope separator) and ISOL (isotope separator on line). None of them were adopted. In a memorandum of 26 October 1964 the chairman of the Nuclear Structure Committee, Torleif Ericson, recommended the on-line isotope separator to the NPRC, saying that the technical support (from the external groups) was fully adequate, that western Europe was in a leading position in this field, and that the NSC considered 'the project to be of high scientific value'. The proposal was presented by Ericson in the NPRC on 2 December 1964 where it was approved [93], and on 17 December 1964 the Director General invited the groups to carry out the experiment. The 'Finance Committee' was subsequently set up with members Bernas, Gentner, K.O. Nielsen, Pappas and Rudstam, but already at its first meeting [92] on 24 April 1965 it decided that it was too small. In order to assure a reasonable degree of attendance at all meetings it was felt necessary to have two members from each of the six 'countries' (including CERN) leading to a total of 12 members. The term country here stands as an abbreviation for 'group of laboratories from a given country participating in the Collaboration'. There were five such groups: France, Germany and the three Scandinavian countries. Rudstam was elected chairman of the Committee. It was also realized that the name 'Finance Committee' had other connotations at CERN, and it was decided 'until a better name was found' to call the project ISOLDE (from isotope separator on line) and hence the committee the ISOLDE Committee. The financial basis for the collaboration was decided by fixing the contribution to common funds to one and the same amount for all: 60 000 S.Fr. per country per year. This money, a total of 360,000 SFr/year, was used

$ s

5

Fig. 9.5 A general view of the ISOLDE facility around 1967. The numbers denote (1) proton beam extracted from the SC, (2) bending magnet, (3) quadrupole lens, (4) switching magnet. (8) target, (9) proton beam dumps, (1 1) crane for target, (12) cave for storage of irradiated targets, (13) ion source, (14) acceleration chamber, (1 5 ) shielding wall, (17) separator magnet, (18) collector chamber, (20) control desk, (21-23) experiments inside the collector chamber, (24) experiment at external beam line, and (26) computer.

W

356

The SC: ISOLDE and Nuclear Structure

by the ISOLDE Committee to cover common expenditures, in particular for the isotope separator and its associated equipment. It should be remembered, of course, that the individual laboratories in addition had to bear the full cost of their experimentation at ISOLDE. Thus, in one meeting the Collaboration had arrived essentially at an organization and mode of operation that was to last for the whole of the period under discussion in the present paper. During the same meeting the Committee was also informed by K.O. Nielsen that the construction of the separator would start in Aarhus in July 1965 and that an engineer and a technician had been found for this job. Another important problem was brought up by the Deputy Division Leader of MSC, Ernst G. Michaelis, who together with Preiswerk attended part-time. He pointed out that the radiation levels outside the CERN site would exceed the permissible levels unless the proton beam were passed through a beam tunnel about six meters below ground level to an underground irradiation cave. Any other solution would limit the permissible running time to an unacceptable degree, especially in view of the possibility of an increase in the intensity of the extracted beam, maybe by an order of magnitude. The very far-sighted solution with the underground hall was studied further by the MSC and in due course adopted by CERN; it was an essential ingredient in making it possible to continue the programme (as ISOLDE-2) after the completion of the SC Improvement Programme (sect. 9.5). Another meeting of the ISOLDE Committee took place on 17 September the same year; it was concerned mainly with organizational and administrative matters. The ISOLDE Committee met again^ at CERN on 22 April 1966 and examined the progress in the construction of buildings and the separator, in target development and in electronics and data handling. A sign that the first experiments were well advanced was that the committee decided to appoint a coordinator for the experiments at ISOLDE. The choice fell on the Nuclear Chemistry group leader, the Norwegian Arve Kjelberg, a forceful personality with considerable diplomatic talents. On the same day the NSC Chairman T. Ericson joined the committee for a discussion of scientific priorities and the groups were asked to outline the research topics that they wished to tackle first. The most interesting result of this part of the meeting, however, was that a procedure was adopted for interfacing the Collaboration with the CERN scientific committees. The problems that made ISOLDE differ from other CERN experiments were clear enough. ISOLDE was not an experiment with a single purpose but a general tool, a 'faciHty', that could be called upon to provide a wide variety of radioactive beams. Some of these beams would be easy, some hard and some impossible to make. Furthermore it was already clear that the programme would be composed of many different experiments and that the final blend would have first to take both feasibility and scientific merit into account and also that some concessions would have to be given to the taste - or lack of the same - of the individual groups. The solution found by Ericson and the ISOLDE Committee was to demand the individual experimental teams to prepare internal proposals on the basis of which ISOLDE would set its priorities and prepare a menu, a joint proposal to be submitted annually or perhaps bi-annually to the NSC and from there on through the

The early ISOLDE

357

normal CERN channels. Thus, formally ISOLDE was one experiment requesting machine time, i.e. the proton beam, from CERN, just like any other experiment. In reality the situation was more delicate. The ISOLDE Committee would often during the years to come have to face external criticism that it was receiving 'block time' and that is was using the strong parts of the programme to let less significant parts tail-gate. Conversely there was occasionally muted internal criticism that ISOLDE was using CERN as a bogeyman to suppress certain parts of the programme, but it never happened that a group was sufficiently convinced of its case to appeal to the CERN committees, which would have been its right. The fact that this system was to function unchanged for 15 years is probably the best sign that it worked well and served the interests of all involved, and elements of it were retained when the re-organization came in 1981, after the end of the period covered in this Chapter. Proposals for the initial experiments at ISOLDE were received at the next committee meeting (21 October 1966) and formed the basis for a proposal [94] accepted by the Physics III Committee in its meeting on 31 January 1967. The time zero was now approaching and on 29 May 1967 the committee held its last meeting before the start of the experiments. As could be expected it was concentrated around monitoring the progress in the preparations. At Aarhus University there were now two teams working in parallel on the isotope separator, one doing mechanical tests and preparing parts for shipment, the other doing ion-optical tests. Beam Unes for the transport of a mass-separated beam from the exit of the dispersion chamber to the experiment were discussed by Rene Bemas and Ole Bent Nielsen, who had a first version under construction in Copenhagen. Two ion sources had already been delivered from Aarhus. The Division Leader of the MSC Division, Giorgio Brianti, reported that the underground building was now ready, and that the proton beam had been tested and was better than had been promised. A technical detail illustrates the care with which CERN worked. The health physics group had monitored the radiation background with the proton beam on and had found that it was acceptable except in one case, that of an accidental spill of the proton beam upstream in the long beam line. This would lead to dose rates up to 10 times the tolerance level. Brianti proposed to make the area fail-safe (and therefore accessible to personnel during runs) by extending the shielding wall by 40 cm to a total of 290 cm. To understand this point it should be remembered that the very conservative CERN safety practice did not permit the use of active safety systems, for example a monitor that would interrupt a beam under certain conditions. (No nuclear reactor would work without such techniques). Personnel safety was ensured by passive devices that excluded a faulty condition, for example by a beam blocker that was moved mechanically into the beam before personnel could enter a certain area. For the future work at the separator the free access to the experimental hall turned out to be vital; some of the more deUcate experiments at ISOLDE would require frequent or even constant supervision. Finally, the nuclear chemists were almost ready with the targets, which will be discussed in more detail in sect. 9.4.4. With beam-on less than five months away the programme was under control and the minutes of the next meeting of ISOLDE Committee show that the Notes: p. 403

358

The SC: ISOLDE and Nuclear Structure

first 3 shifts of tests with proton beam on the target went well. The ISOLDE documents do not mention the date of the event, which was 16 October 1967 according to the CERN Courier (7, 206). ISOLDE had successfully made the transition from a project to a running programme. We now turn to the techniques and the physics behind it.

9.4.3 THE ISOLDE FACILITY The installation that had come into being through 3 1/2 years of effort is shown schematically in Fig. 9.5, which is taken from the detailed report published by the collaboration following the first two years of operation of ISOLDE [95]. The long external beam line from the cyclotron served the ISOLDE target-ion-source unit placed behind a 3 m shielding wall separating the target area from the experimental area. The beam could be deflected onto a second target position and beam dump, foreseen for particle physics experiments. This was at the time a valuable addition to the capabilities of the SC since the other experimental areas around the machine did not have sufficient shielding to permit the use of the full proton beam. The radiation safety problems were severe in this inner sanctum of ISOLDE, and increasingly so over the years as progress was made in proton beam intensity and target techniques. Unlike other 'hot' spots at CERN the problem was not only external radiation but also the risk of severe radioactive contamination; after all, the targets served to release volatile radioactivity, including alpha emitters, in large quantities. From a safety point of view it was therefore somewhat unfortunate that access to the zones of high radiation levels necessarily passed through the main experimental area where many and, usually, rather undisciplined external users worked. As a first of many steps to improve safety, the original design had foreseen two cavities in the floor to serve for temporary storage of irradiated target units. Since these were highly radioactive it was convenient to let them cool there and then at a later time remove them to the chemistry laboratories for post mortems and possibly repairs. It is actually remarkable that in 23 years of operation there never were any serious cases of contamination, which must be credited jointly to the house group and to CERN's health physics services, for many years represented by Jan Tuyn, efficient but also level-headed and unbureaucratic. On the other side of the shielding wall was the main experimental area, see Fig. 9.5. The separator, its control console and high-voltage supplies together with the access paths from the lift (to the left) take up the larger part of the room and leave little place for the experiments. Fortunately some electronics including the on-line computer could be placed in the room above, that is at first-basement level. The isotope separator was described in a paper by G. Andersson, H.E. Jorgensen and K.O. Nielsen [96]. For the benefit of the reader more used to high energy experiments, it is maybe useful to note at this point that the beam steering of slow heavy ions is best done with electrostatic elements, which are smaller and cheaper than corresponding magnetic elements. An isotope separator therefore has only one magnetic element, the magnet that

The early ISOLDE

359

takes care of the momentum analysis. All other elements, deflectors and quadrupoles, are energy-focusing and all settings are independent of mass, i.e. they are at a fixed proportion of the acceleration voltage, the absolute value of which is unimportant to a first approximation. The main design features of the ISOLDE isotope separator were taken from the machine that had been constructed for the Nuclear Chemistry Group some years before [23] based on fringing-field focusing with a 55° bending angle. The mean radius of curvature was chosen as 1.5 m leading to a dispersion at the focal plane D = 1500/A mm, where A is the mass number of the central beam. In order to be able to run stable mass markers of a given element simultaneously with a far-unstable isotope the instrument had a very large momentum bite: ±15% relative to the central mass. The vacuum tank was constructed so that the dispersion chamber could be taken out without moving the magnet and collection chamber, which would have changed the alignment of the spectrometer. This feature was useful because radiation safety imposed periodical removal of disposable Unings placed inside the dispersion chamber to collect radioactive contamination. The almost parallel beams (of different masses) on the exit side and with a small convergence favoured simultaneous experiments on different mass components in the beam. Another feature of the geometry was that the focal plane was at an oblique angle (about 30°) to the beam direction, but as the arm of the spectrometer was long this did not lead to any practical difficulties, the beams being practically parallel and pencil-shaped. This can easily be appreciated from the drawings given by Camplan and Sundell [97]. The analyzing magnet of the separator was constructed as an H-type magnet with the yoke closed on both sides of the pole gap so that the magnetic stray fields were very small. This was done [96] so that it would be possible to operate magnetic spectrometers for beta rays and conversion electrons in the vicinity of the isotope separator. The design called for an acceleration voltage of 100 kV, somewhat higher than is usual for laboratory isotope separators. This choice had been made in order to reduce the effects of space charge (a more serious problem at ISOLDE because of the 3 m long transfer tube for the unseparated beam) and also to reduce the blow-up by scattering on residual gas. During the beam tests carried out by Camplan and Sundell [97] it turned out to be difficult to reach 100 kV and the tests and, in fact, all future running took place at 60 kV, and probably not much was lost by that. Part of the problem in going to higher voltages was condensation on water-cooled parts of the high-voltage end; the humid Geneva summers always brought with them a new high in high-voltage break-downs. The beam mapping showed that the machine worked well. Camplan and Sundell curiously enough refrained from citing a resolving power and only said that more measurements 'will be undertaken to give more representative data', probably to avoid offending sensitive souls by admitting that the nominal resolution of 1500 for M/AM had not yet been reached. From Figure 9.6 in [97] the resolution may be estimated to be around 700, not far from the typical value for the next many years of operation of ISOLDE. The cross-contamination was very low, with mass number 133 as the central mass it was of the order of 2 • 10""^ at mass positions 132 and 134.

360

The SC: ISOLDE and Nuclear Structure

9.4.4 THE HEART OF THE MATTER: TARGETS AND ION SOURCES The creation of ISOLDE as described in section 9.4.2 was essentially an application of known techniques in experimental physics, except for one Hnk in the chain. It was, to take one specific example, known technology to let the 600 MeV proton beam of the SC hit a kilogram of molten lead and produce the mercury isotope with mass 179 and half-life of 1 second at a rate of a few atoms per second. (This isotope was, of course, unknown before ISOLDE). Once this activity appeared as ions (^^^Hg+) in the acceleration gap of the machine it was also known technology to make a beam, to momentum-analyze it in a magnet and to steer it to experiments. The problem was the step that lay in between: to liberate the interesting atoms from all bulk material (which, if evaporated in appreciable quantities would suffocate the ion source) and from interfering radioactive impurities, to transport the interesting atoms and to ionize them, all within a second. This was the kind of problem the Nuclear Chemistry Group and its collaboration partners had offered to solve, and for which each chemical element posed a separate problem. The collaboration had set up a 'Working Party on Target and Chemical Separation Methods' which coordinated the research in the different groups. It held a first meeting at CERN on 21 April 1966 with 32 participants from 9 laboratories and later a 'Seminar on ISOLDE Chemistry Problems' two weeks after the first ISOLDE runs [98]. The result was a considerable number of ideas and trials. Early in 1967 there were a total of 11 different systems under investigation. It was also clear that under Kjelberg's and Rudstam's able direction great care was taken that the most promising devices, the so called 'cold' and 'hot' systems, would advance quickly and be ready in time. The ion sources were not at that stage of ISOLDE'S programme a subject of research. All the work was essentially done with a plasma ion source with oscillating electrons trapped in a magnetic field and with axial extraction of the ions, the so-called Nielsen source [99]. The noble gases were produced from the cold targets. Since emanation from radium is a noble gas (radon), it is not surprising that the release of this element from various compounds had been studied by the old radiochemists. Paul Patzelt, a radiochemist from Giinter Herrmann's group in Mainz, was familiar with the classical studies, which had shown that organic salts such as palmitates and stearates of the alkaline earths were the best emanators. He quickly realized that these compounds were too vulnerable to radiation damage and also too bulky to do the job and that hydrous oxides of elements with valency four (zirconium, cerium and thorium) were better, as could be shown in off-Une investigations. Once put on-line these systems turned out to give excellent yields of krypton, xenon, and radon, respectively [100] from (p,5pxn) reactions, which posed no problem at the high energy available at the SC. These targets then were little else than a vacuum container containing the pre-dried hydroxide, connected to and pumped through the ion source. The hot targets, primarily developed by Einar Hagebo and Stig Sundell [101], were contained in a small vacuum oven surrounded by a number of heat screens. The oven could be heated to 1500°, enough to melt a number of metals and to distil some volatile

The early

ISOLDE

361

Fig. 9.6 Laboratory test of the molten-metal ('hot') target system [101] with the oven containing the target trays to the left. The heated transfer Une (middle) connects the target to the ion source (right). The proton beam is intended to traverse the target axially. (Photo CERN).

metals. This arrangement was used for producing isotopes of mercury from (p,3pxn) spallation reactions on a target of molten lead, which was contained in graphite trays, and also for producing the chemical homologue cadmium from molten tin. To prevent the products from condensing, the oven had to be connected to the ion source via a heated transfer tube as shown in Fig. 9.6, which gives a deUghtful impression of the pioneering spirit behind this research. The hot systems also performed well on-line and together with the cold systems provided ISOLDE with the main workhorses for the coming years: Cd, Hg, Kr, Xe, and Rn, and, of course, all isotopes that could be formed as radioactive decay products of these five. During the first on-hne tests the Nuclear Chemistry Group studied [102] the important question of the delay between the production of an isotope and its ionization. Since the flight time of the ion, being about 50 microseconds, can be neglected, the delay came from the target-ion-source unit and could be studied on-line by interrupting the proton beam and observing the continued arrival of a long-lived product. For both types of systems the delay curve was a single exponential. In the case of the noble gases the mean delay time

362

The SC: ISOLDE and Nuclear Structure

was 15-30 seconds, apparently determined by geometrical factors, while for the hot systems, it was minutes or longer, and strongly temperature-dependent. In the latter case the corresponding activation energy for the release of cadmium from molten tin was 19 kcal/ mole, similar to the heat of evaporation of cadmium of 24 kcal/mole, which suggested that the rate-determining step was the release of cadmium from the tin surface. (It is perhaps useful to point out that these relatively long average delay times ta do not exclude the observation of much shorter average lifetimes t. The experiments then work on the small part of the radioactivity that comes out early, the yield being of order t/ta.) 9.4.5 THE FIRST EXPERIMENTS An overview of the achievements of ISOLDE for the whole period in question in this paper will be given later (sect. 9.6). The following paragraphs are an attempt to give an impression of the style and flavour of the early experiments. Although ISOLDE was created by a large collaboration involving external laboratories and CERN, it was clear from the beginning that a joint scientific utiHzation was unthinkable. Many different experiments were possible at the new facility, each requiring the effort of no more than a few scientists, the typical nuclear-physics group of the sixties. This meant that there were untold possibilities for internal competition and rivalries at ISOLDE, an aspect that had made the question of interfacing ISOLDE with CERN's committee system both so important and so delicate (sect. 9.4.2). Bearing in mind the problem of possible internal feuds the ISOLDE Committee had, even before the start of the experiments, made considerable efforts to identify potentially explosive issues and to defuse them. The ISOLDE Committee Meeting on 17 September 1965 even wondered whether it was necessary to provide ISOLDE with a 'convention'. Later, an internal agreement was reached on individual areas of main scientific interest, protected hunting grounds as it were, and the ordering of the names of authors on future papers became the subject of a Committee decision^ on 4 December 1967 [92], just after the start of the experiments. Some of the younger scientists in the collaboration, including the present writer, tended at the time to regard the committee's interest in rules and regulations as a sign of fussiness, but in retrospect the avoidance of unnecessary conflict was probably one important factor in shaping the extraordinary internal coherence that made it possible for ISOLDE to survive for such a long time at CERN. There may be something in this that reflects the strong Scandinavian^ contribution to ISOLDE during its early years. The start of ISOLDE was characterized by great enthusiasm and also by a keen feeHng of pressing internal competition. At the same time it was essential that all scientific and technical experience gained should be communicated immediately to the other groups. To this end the participating groups were requested to stay behind after the end of their machine time for what was called 'After-Run Meetings'. In these, all new observations were discussed and written summaries were later mailed to all ISOLDE users. (Note that many groups, maybe most, did not have permanent residents at CERN.) This was possible since the data taking was still simple (mainly multichannel analyzers) and key results such

The early ISOLDE

363

as half-lives of newly discovered isotopes would usually have already been extracted during the experiment. The conditions at ISOLDE during the early years is well illustrated by the following extracts from a preamble which accompanied an information newssheet concerning the experiments in January-February 1970. The Nuclear Chemistry (NC) Group Leader, Arve Kjelberg, wrote [103] under the heading 'Rules of the Game': 7. Too many participated simultaneously during some of the experiments! This made it next to impossible to keep the operation going in an effective, not to say safe, way. 2, Many of the participants were unknown to me when they came - and some when they left [...] 6. There was a radiation incident during the repair of the ion source during the last day of the radon run [...] 8. [,..] And do not bring any more equipment for the main ISOLDE room [..f Too many people try to do too many things at the same time without making sure that we all know the intention, with the result that none work well - and that temperaments get short - even mine! 9. The noise in the experimental hall has now reached insupportable levels [...] 10. The number of keys to the NC laboratories is restricted. Rotraud Mohr tries her best, by alternatively smiling and shouting, to get the keys back before the culprits leave. So, give back your key - or no more smile next time! From this you may deduce that you, dear visitors, are not loved so much as you were used to. I am afraid this is reflecting the problems foreseen on a global scale as a consequence of the population explosion. These days there are ways to improve such situations. We now turn to the experimental arrangements that were on the floor when ISOLDE went into operation in October 1967. Only one experimental set-up [104], labelled #24 in Fig. 9.5, was mounted at an external beam line. This technique, which gives maximum freedom for shaping the detector arrangement, was in just a few years to become the one and only way to do experiments at ISOLDE. The radioactivity contained in the mass-separated beam was collected on a tape that could be moved by a step-motor system to allow precise control of the collection and measuring times. Furthermore any long-lived daughter products or impurities associated with the beam were continually moved away with the tape and hence prevented from building up near the detectors. For a fixed setting of the isotope separator, the apparatus covered three mass numbers near A = 100 and five near A = 200, but larger movements required shifting the central mass of the separator, which could only be done freely if there were no other users working in parallel. Three other experimental arrangements, situated near #19,23 in Fig. 9.5 and described in [95], had been prepared to operate inside the collector chamber of the separator and hence had considerably more freedom to intercept any potentially interesting mass number. The fact that much ingenuity had gone into building these collection systems reflected the competitive situation as it was anticipated by the individual groups. The socalled tape collector system intercepted the beam in the focal plane of the separator and Notes: p. 403

364

The SC: ISOLDE and Nuclear Structure

moved the radioactivity to beta and gamma detectors placed outside the vacuum chamber. A second system built by the Gothenburg group [105] also operated in the focal plane and was designed for discovering particle emission (alphas and protons). Named the tau-meter, this instrument collected the radioactivity on tiny metal discs which subsequently were dropped in front of a cooled solid-state detector. The third system, the so called end-strip collector, consisted of an aluminium foil that covered the area where the comb of massseparated beams hit the rear end of the collector chamber. This arrangement was originally meant as a disposable lining that would allow radioactive contamination to be removed periodically from the separator, but it was soon modified so that the foil could be exchanged via an air-lock during runs. These foils were a prolific source of samples for offline experiments with radioactivity with half-lives longer than a few minutes. In the early years of ISOLDE operation it was probably foils from the end-strip collector that supported the largest volume of research. Although the experimental arrangements operating inside the collector chamber were a transient phenomenon, characteristic of the early ISOLDE, they were important in augmenting the scientific output in a period when machine time was scarce. The point was that once a beam of one particular mass was in use at a given beam port, then all other masses were available essentially for free inside the chamber. A fourth arrangement of this kind was added a Uttle later by an Aarhus-CERN-Gothenburg team [105]. In this several masses of presumed short-lived proton emitters were intercepted on a spinning disc and carried in front of nuclear emulsion plates. The half-Hfe of a new emitter could now be deduced from the angular distribution of the protons on the plate and the proton energy spectrum from an analysis of the track lengths. This experiment must surely represent one of the last applications of emulsions as spectrometers in nuclear spectroscopy. The first tests with proton beam used the cold targets (sect. 9.4.4) to produce isotopes of xenon (16 October 1967) and radon (5-6 December 1967). The performance of ISOLDE was extremely satisfactory. During the radon run the yields were scanned across the mass range from A = 201 to A = 226 and were found to be distributed as shown in Fig. 9.7. The bell-shaped yield curve with a fast drop to zero at low and high mass values is typical of isotope production in high-energy reactions, and we give here a brief explanation of it. The dominant reaction of 600 MeV protons on a heavy element such as thorium (Z = 90) is fission, which cannot produce radon. About one in a hundred of the struck thorium nuclei escapes fission and undergoes the so-called spallation process, which may be thought of as proceeding in two stages. The first step is a fast collision cascade in which nucleons and larger fragments are removed from the target nucleus. The residue from this will usually be in a highly excited state and will cool primarily by the evaporation of neutrons, whereas proton evaporation is suppressed by the Coulomb barrier. When the composition of the residue approaches that corresponding to the proton drip line, the neutron binding energies have increased to 12-14 MeV and the proton binding energies decreased to almost zero. Proton evaporation now sets in and halts the production of more neutron-deficient isotopes, thus creating the sharp drop in the yields at the low-mass end of the distribution. The neutron-rich products can only be produced in rare events in which primarily protons

The early k1i,-¥LL

ISOLDE

!

-

|—

ilL+li " !

1

1

1

11?. AQ .

•

--••••^ ^

-

mm

B A

\

k

.

1

••

^

•

A

A

•

A

1

• •

1 1

A

•

1

1Fj.A
•

A

•

-

*

•

•

.

1Fj.lWk

365

A

:

•

A

IP'.A'S _

• June 1985

11?.A'> _ 11?.Ai _

• Target La •

A Dec. 1967

1

A Target UC

-

lE+00 -

195

Fig. 9.7

200

205

210 215 Rn mass

220

225

230

115

120

125

130 135 Cs mass

140

145

150 155

Beam intensities in atoms/s of mass-separated isotopes of radon (Z = 86, left) measured on 5 December

1967 (lower left). The result was obtained with a target of 275 g of hydrous thorium oxide and the proton beam intensity was 2.10^^ protons per second. For comparison the corresponding yield curve measured at ISOLDE-2 is shown and, to the right, ISOLDE-2 yields of a lighter element (caesium, Z = 55) produced from spallation of molten lanthanum metal and from high-energy fission of uranium carbide at high temperature. (Courtesy of H.L. Ravn, CERN).

have been knocked out in the fast cascade, and in which the residue is left with very Uttle excitation energy, so that it cannot loose neutrons by evaporation. This explains the fast drop on the high-mass side. For spallation on Ughter targets the fission competition is absent and the spallation yields are higher, as can be seen from the yields for producing caesium (Z = 55) from a lanthanum (Z = 57) target shown in Fig. 9.7 (The measured yields are also influenced by decay losses in the target. This aspect was touched upon in sect. 9.4.4.). The first year of operation of ISOLDE was spent surveying the isotopes of six elements, four noble gases (Ar, Kr, Xe, and Rn) from the cold targets, and mercury and cadmium from the hot targets. During this period about 15 new isotopes were discovered and significant new information was found for about 40 other isotopes. One interesting observation was that beta-delayed emission of protons, impeded by the Coulomb barrier, turned out to be detectable for extremely neutron-deficient isotopes of elements as heavy

366

The SC: ISOLDE and Nuclear Structure

as xenon (Z = 54) and mercury (Z = 80) [105]. It was decided first to publish jointly all this information on gross decay characteristics. ISOLDE'S first research paper [106] had 29 authors, a number that nobody would find strange today, but which caused some lifted eyebrows when it appeared in Physics Letters in January 1969. The publication was, of course, nothing but a comprehensive collection of raw data with no explicit physics point attached to it, but it was a powerful demonstration of the strength of the new experimental facility that had come into being at CERN. The topical orientation of the research was now left to the individual collaborations. Several concentrated on gamma-spectroscopic studies of level schemes of the many radioactivities that had come within reach. There were studies of decay schemes in the xenon and cadmium regions and a French collaboration headed by Roger Foucher concentrated on decays in the platinum-mercury isotopes and emphasized particularly the 'soft' (or transitional) aspect of the nuclear shapes in this region. (These isotopes are situated between the strongly deformed (elongated) rare earths and spherical ^^^Pb.) As an example we cite the comprehensive results [107] for the level structures in even-A platinum isotopes. Other groups aimed at more specialized information such as nuclear masses from beta-decay Q-values and alpha energies, the systematics of alpha widths and the search for new cases of proton emission from nuclei following beta decay, the particular interest of the Gothenburg group headed by Goran Andersson. Finally, the Aarhus-Copenhagen collaboration had suggested that in view of the high energy release in the beta decay of farunstable nuclei and the ensuing complexity of the spectra, it would be interesting to study the strength-function^^ aspects of nuclear beta decay. This line of research soon merged with the studies of highly excited levels via proton emission. Some examples of results from the different lines of research will be given in section 9.6. 9.4.6 RADIATION-DETECTED OPTICAL PUMPING (RADOP) COMES TO ISOLDE The early scientific programme was, apart from the work on targets and ion sources, based on well-established techniques from nuclear physics and chemistry. A seminal event in the further development of ISOLDE'S research programme was the presentation on 10 May 1968 of a new proposal [108] entitled 'Determination of spin and nuclear moments of mass-separated, short-lived isotopes by optical pumping'. Its author, Ernst W. Otten from the Physikalisches Institut der Universitat Heidelberg, was a new face in the ISOLDE collaboration, though he had completed two somewhat similar experiments at the Heidelberg cyclotron the previous year. These experiments, based on an ingenious mixture of atomic, nuclear and weak-interaction physics could, for certain elements, give precise information on the spins, moments and charge radii of nuclear ground states and longlived isomers. Otten was now looking for a clean and abundant source of short-lived radioactive atoms, and his Heidelberg colleague Bogdan Povh, who on some occasions had substituted for Gentner on the ISOLDE Committee, had drawn his attention to the experimental possibiHties at ISOLDE.

The early ISOLDE

367

The proposed experiment was based on optical pumping, an important technique in atomic physics, which had been introduced by Alfred Kastler^^ (Nobel prize in 1966). The principle of optical pumping is that the interaction of the atom with polarized light at the resonance energy leads to a transfer of angular momentum to the valence electron and hence via the hyperfine-structure (hfs) coupling to a polarization of the nuclear spin. Otten's idea (see [110]) was to detect nuclear polarization via the celebrated beta asymmetry originating from parity non-conservation. The light source for the experiment was a mercury lamp equipped with a Xjl bi-refringent plate. The resonance condition could be met by placing the lamp inside a magnet, so that the magnetic Zeeman splitting shifted the frequency of the light. (One polarization component, say G^ corresponding to the change in magnetic quantum number Amp = + 1 , goes up in frequency, the other goes down. This also provided a way to control systematic errors, simply by shifting from G^ to cr", which inverts the polarization.) The experimental apparatus is shown in Fig. 9.8. Otten's proposal was quite brief, and in addition to a summary of the general principles of the technique it simply gave a Usting of the groups in the periodic table that would be suitable for such experiments: la,lb, 2a, 2b, 5a, and the elements with half-filled electron shells. To this he added the for him characteristic remark, that it was not a coincidence that the list largely coincided with those elements that seemed favourable for ISOLDE, since atoms in S states were those most easily evaporated. The point of the remark was that for non-S states the polarization is destroyed by coUisional relaxation. Confronted with this remarkable collection of tricks, the ISOLDE Committee was preoccupied, maybe understandably so, with the feasibility of the experiment and it ended up requesting a more detailed analysis. What yields, count rates could one hope for, and which cases were the most promising? Oral tradition at CERN has it that P. Preiswerk, head of CERN's NP Division and not a committee member, remarked after the meeting that he personally had found that the experiment was so beautiful that it ought to have been accepted, even if one had possessed the certain knowledge that it would fail. A second and more detailed proposal [108] supplied the missing numbers and pointed to cadmium and mercury as the best early candidates for the experiment. The programme was accepted at the meeting on 17 December 1968. The experiment turned out to be very difficult. After some initial attempts with the cadmium isotopes it was decided that mercury would offer better possibilities and the effort was concentrated on ^^^Hg, which was produced at ISOLDE in good yields. When at long last an anisotropy signal was obtained [112] it was very weak, which seemed a bad omen for experiments on lighter (and more rare) isotopes. Furthermore the main result, the nuclear charge radius, was no surprise at all as it continued the almost linear trend from the heavier isotopes. A completely different picture emerged from the next experiments [113], deaUng with the isotopes -^^'^^^'^^^Hg, as may be seen from the more complete systematics given in sect. 9.6.2. Not only did the lighter isotopes give a much better anisotropy signal but the isotope shifts indicated that the three nuclei were very much larger than ^^^Hg; they had roughly the same charge radius as ^^^Hg. This was (correctly) seen as the discovery of a new and unexpected class of deformed nuclei. The whole picture, which emerged later from Notes: p. 404

368

The SC: ISOLDE

m

and Nuclear

Structure

)il-heotin9

got-.psssss|r^2:i Vocuum Mo-foil I i-ioo beom

M

KWSSSSSWS^llAS

100 Torr He regutotad X/2 birefringtnf plote

HzO cooling Hg light source

Fig. 9.8 Experimental arrangement for the RADOP experiments. (From [112]). The upper part of the figure shows, to the right, the collector for the radioactive mercury atoms from ISOLDE. After each collection it is turned and the mercury is evaporated into a buffer gas contained in a quartz cell, which is heated to prevent condensation of mercury on the walls. The holdingfieldfrom the Helmholz coils serves to maintain the polarization. The lower part of thefigureshows the mercury lamp placed in a magnet to allow Zeeman scanning, as described in the text.

new data from atomic and nuclear spectroscopy and from a host of theoretical papers, was even more interesting and involved the phenomenon of shape co-existence (see the brief comments in sect. 9.6.2 and for more detail the review by Otten [110]).

The early

ISOLDE

369

The RADOP experiment was the first salvo in a research effort that was to become a major Hne at ISOLDE after 1974. It also furnished an instructive example of a purely experimental discovery and maybe a lesson for those who in committee meetings clamour for theoretical arguments. When Otten presented his proposal no theoretical predictions pointing to the light mercury isotopes existed although theoretical explanations became available in large numbers after the event. It will be clear from the above that the Heidelberg group selected the experiment because it was one of the few, possibly the only one at all, that was feasible at the time. It should be remembered that at the time ISOLDE had not yet developed techniques for separating alkali and alkaline-earth metals. 9.4.7 WHY AT CERN? It should be emphasized that ISOLDE was far from alone in the field nuclei far from stabiUty. The period 1965-90 saw a large number of experiments by different techniques in many laboratories all over the world. Table 9.2, based on information from [114, 115], Usts Table 9.2 On-line mass-separation^^ programmes at different machines At high-energy proton accelerators

At heavy-ion accelerators

Orsay - CERN PS (MS) IRIS - Leningrad (LCS) ISOLDE 2 - CERN SC (LCS) ISOCELE - Orsay (MC) ISOLDE 3 - CERN SC (MC) TISOL - TRIUMF (MC)

Montreal (MS) Orsay (MS) Tokyo (MS) DOLIS-Daresbury (LCS) GSI-Darmstadt (LCS) Jyvaskula (LCS) LISOL - Leuven (LCS) OASIS - Berkeley (LCS) PINGIS - Stockholm (LCS) Stockholm (LCS) POLARIS - Princeton (LCS) RAMA - Berkeley (LCS) SARA - Grenoble (LCS) Tohoku (LCS) Tokai (LCS) UNISOR - Oak Ridge (LCS) Chalk River (MC) BEMS 2 - Dubna (MC) EMSONHIB - Dubna (MC)

At reactors or neutron generators GODIVA - Los Alamos (MS) SOLAR - Richland (MS) OSTIS - Grenoble (MS) Copenhagen (LCS) ARIEL - Grenoble (LCS) Kyoto (LCS) OSIRIS - Studsvik (LCS) SOLIS - Soreq (LCS) TRISTAN I - Ames (LCS) TRISTAN II - Brookhaven (LCS) Mainz (LCS) INEL - Idaho Falls (LCS) lAELE - Buenos Aires (MC) SIRIUS - Strassbourg (MC)

a) MS: mass spectrometer; LCS: low-current isotope separator. MC: medium current isotope separator.

370

The SC: ISOLDE and Nuclear Structure

those using on-line mass separation. It is characteristic of most of these that they were set up to serve the scientific interests of a small group of people. Many of the experiments produced excellent physics but it is probably fair to say that, in general, they did not aim for a very broad and continually renewed programme such as was the case for ISOLDE. They were usually also limited by their accelerators. At this point we may ask why the world's largest installation for producing secondary beams of radioactive nuclei in their ground states came into existence at a laboratory dedicated to particle physics at the highest energies^^ and why laboratories of a similar capacity were not created elsewhere? We shall have more to say about the second question in sect. 9.7.3. For the present we suggest the simple answer that it was due to a coincidence of several fortunate circumstances. CERN first of all possessed a high-energy proton machine almost ideally suited to the task and permitting a much broader programme than did reactors and smaller accelerators. It also had developed the organization and tradition that could assemble the necessary specialists in subjects such as target chemistry, ion sources and mass spectroscopy together with research teams from atomic, nuclear and soHd-state physics. This second point is important for understanding why in principle free and independent external groups could maintain the sense of duty and loyalty to CERN and to the collaboration that ensured the stabiUty of the programme over many years. And finally CERN provided an in-house group with engineers, technicians and some research posts for staff"*^, associates and fellows, a group that had as its first priority serving the external users.

9.5 The SC improvement programme (SCIP) In 1967, the year that the new underground hall for the SC was completed and ISOLDE went into operation, the SC Machine Division (MSC) headed by Giorgio Brianti was far advanced with a plan for major improvements in the performance [117] of the synchrocyclotron. The main aims were to obtain an increase of the internal beam intensity by a factor 10, to about 10 //A, and the highest possible increase in the extraction efficiency leading to an external beam of at least 1 /xA. These studies were continued under the new MSC Division leader, Ernst G. MichaeUs, who took office in 1968. In what follows a brief description is given of the physics and technology of SCIP followed by a more detailed account of the technical and poHtical turmoil that this project gave rise to. 9.5.1 THE PLANS FOR UPGRADING THE SC An account of the planned upgrading can be found in a paper presented at the Cyclotron Conference in Vancouver in 1972 by MichaeUs [118], who also prepared a complete Hst [119] of SCIP Uterature including internal reports and specifications for the use of the SCIP Advisory Panel (see sect. 9.5.4).

The SC improvement programme (SCIP)

371

One essential ingredient in the SCIP programme was to replace the radiofrequency system based on a tuning fork with a rotary condenser, a solution that had already been considered in the early planning of the SC [34]. For the new project a small-scale prototype was built, and further ideas for improvements concerned the central region and the ion source. The rotary condenser as it looked when it had reached completion is shown in Fig. 9.9. The swing of the cyclotron radiofrequency (RF) during one cycle, from 30.0 MHz at injection to 16.8 MHz at extraction, was produced by the change in capacitance when the rotor blades, 3 rows of 16 teeth each, passed through the 4 rows of pecuUarly shaped stator blades. In order to obtain the highest possible beam intensity the frequency as a function of time had to follow closely the ideal curve, which could be approximated by tapering the stator blades. One advantage of this system of modulation was that the back-swing of the frequency was fast so that most of the time was used for acceleration. The acceleration cycle could be made even shorter by having a high peak voltage in the RF power. As an additional advantage this brings a larger distance between each turn of the spiral orbit, and hence the possibility of single-turn extraction so that beam losses inside the machine are reduced. This is beneficial both for the machine (radiation safety) and for its users (more protons available). For these reasons the design voltage between stator and rotor was as high as 18 kV at a minimum gap distance of only 1 mm, reached at the end of the cycle. To have such a high voltage gradient would clearly be impossible with a static high voltage; it can be achieved with radiofrequency if the surfaces are so clean that a discharge does not have time to build up during one cycle. The one impurity that high-voltage experts fear most is traces of hydrocarbons, so the final machining of the rotor and stator parts was to be done without lubrication oil and the parts were to be assembled under very clean conditions. The construction furthermore had to be such that the rotor vacuum was isolated by a separately pumped duct from the vacuum of the rotor bearings, which were oil-lubricated, and from the acceleration chamber, which contained traces of oil-vapour. The stator blades were held by an outer support ring, which via a set of insulators held an inner ring, which via further sets of insulators held the drive motor, the latter sitting in the very centre of the unit to provide mechanical equilibrium. The motor (under atmospheric pressure!) and various other parts had to be provided with cooling circuits, so the final construction was a complex intermingUng of seals, ducts, pipes, pressures, and voltages, the engineer's delight and the mechanic's nightmare. It is very much to the credit of the people^^ in charge that this device in the end worked well and served the SC for 15 years. A contract for the construction of the radiofrequency system was signed [120] with the company A.E.G.-Telefunken in February 1969 with delivery foreseen for August 1971. In the light of the events that followed, one may ask why the most complex, delicate and essential piece in the SC upgrade was placed in the hands of a private manufacturer? After all, experience, for example with the bubble chambers, had shown that CERN was capable of doing excellent technological development work. The explanation was that CERN was following a poHcy of farming advanced projects out to industry in the member countries in Notes: p. 404

372

The SC: ISOLDE and Nuclear Structure

Fig. 9.9 The rotary condenser for the SC radiofrequency system with the endplate removed. Note the 16 sets of three rotor blades that pass through the peculiarly shaped stator blades (16 sets of four). (Photo CERN).

order to allow the firms to develop their know-how in the field of accelerators. The accelerator branch of the company in question had originally solicited an open-ended research contract in connection with the ISR, but the final decision by the CERN management was to let them handle the rotary condenser for the SC and at a fixed price [121]. Other important improvements concerned the orbit dynamics of the cyclotron and in particular the central region, the domain of the Orbit Dynamics Group under N. Vogt Nilsen. The original SC used an open ion source dictated by the rather small energy gain per turn. The absence of axial focusing and the slow acceleration allowed space-charge forces to blow up the beam leading to a poor beam quality and hence to low beam intensity and low extraction efficiency. The condition for using a hooded ion source giving a well-defined beam is then that the beam must go clear of the ion source on its first turn.

The SC improvement programme (SCIP)

373

The group, with R. Galiana and R. Giannini working on the ion source and central region, found that with the improved RF system and a modified central region, which had been studied in models, this could be reached so that the cyclotron would have separated orbits. Another modification was that the ion source was inserted through a 20 cm diameter hole drilled from below to the centre of the magnet. The extraction channel was in the hands of B. Hedin, S. Lindback and A. Susini, who hoped that the well-defined orbits would allow single-turn extraction with high efficiency, maybe 5-7%, an order of magnitude over the old value. The actual values achieved in the end were yet an order of magnitude higher: 50% in slow extraction and 70% in fast extraction. The occasion was also used to replace the field coils and the vacuum tank. The SC upgrade was, however, beginning to be dangerously close in time to a new generation of proton accelerators, called the meson factories because their primary purpose was to dehver very intense secondary beams of muons and pions for experiments like those described in sect. 3. The leading contenders in this field were: (i) LAMPF, the Los Alamos Meson Physics Facility, nominal 800 MeV protons at 1 mA and negative hydrogen at 100 /xA, completion foreseen 1972, (ii) the Canadian TRIUMF in Vancouver with 530 MeV H " at 100 /lA (1973), and (iii) the Swiss Institute for Nuclear Research, SIN with 580 MeV at 100 /lA (1974), all target dates being cited from the documents in [119]. Any delay would therefore again raise the question of whether the SC was needed. It will be remembered [34] that this issue had already come up in Weisskopf s time. In his reply to a memorandum from the MSC Division Leader P. LapostoUe dated 29 January 1962 Weisskopf had written [119]: 'I was also very interested in your remarks regarding future plans with the SC. It seems to me that these problems can perhaps be divided into two. One comprises attempts to improve the present machine by major alterations and the other [...] ideas of meson factories. It seems to me that the first kind of things would certainly fall within the terms of reference of your Division; about the second one I am not so clear myself.' Weisskopf s remark is interesting as an indication that already as early as January 1962 CERN was prepared to leave a large part of the subject of muon and pion physics to whoever wanted to take it over. In view of the new and more powerful accelerators appearing on the horizon and, no doubt, further stimulated by the technical and commercial difficulties, to which we shall return in a moment, the debate about the future of the SC resumed in CERN's inner circles towards the end of 1970. This can be seen from a draft document [122] from 9 November 1970 that Michaelis discussed with Ericson and Kofoed-Hansen, but which was never circulated wider. 9.5.2 SCIP IS DELAYED: POLITICAL, COMMERCIAL AND TECHNICAL DIFFICULTIES By 1970 technical difficulties began to appear, heralded by an announcement by E.G. Michaelis at the meeting of the Physics III Committee 2 November 1970 of a 6-8 months delay in the delivery of the new radiofrequency parts. By 30 June 1971 CERN had re-

374

The SC: ISOLDE and Nuclear Structure

ceived a revised estimate of the time plan from the manufacturer, and MichaeUs informed [123] the Director General that the delay had grown to a total of 47 weeks, so that the new deUvery date for the equipment would be 10 July 1972. Some of this time could be recuperated by starting the dismantling of the cyclotron before the parts had been delivered and tested, but at the risk of a long, unplanned and very uncomfortable shut-down if further delays occurred or if the high-voltage tests were unsatisfactory. According to Michaelis this solution would also make CERN's threats of canceling the contract after its 'ultimate delivery date' look less credible. He himself favoured avoiding any major dismantling operation until the test results were known, foreseeably in April 1972. A small meeting [124] to discuss these options was held on 8 July 1971 at the initiative of J. Steinberger, Director of Physics I. It is characteristic, however, that the meeting was not with engineers and administrators to discuss the technical, legal and commercial aspects of the problem but with the users^^ of the SC. Steinberger opened the meeting by asking 'if, under these conditions, the users maintained their interest.' They did, and asked that all should be done to reduce the length of the shutdown in preference to advancing the startup date. The meeting agreed that the physics programme should be scheduled to run to 1 April 1972 with a further programme prepared 'to continue operation into 1972 'if a failure of the tests necessitated an abandonment of the Improvement Programme'. The future of the machine was clearly now very much in question; the wording of the conclusion implies that CERN was ready to let the quality of the workmanship of one commercial supplier decide the future of one of its programmes. This might appear to be in contradiction to CERN's usual record of superb technical control, but it should be remembered that the SC by then was used almost exclusively by physicists from CERN's member countries. This was one machine that the aristocracy of CERN, to borrow an expression coined by Pestre [125], could well be without. It would also not have been the first time at CERN when technical arguments were used to obscure the real issues. One who had no difficulty in seeing what the real issues were was Sir Denys Wilkinson from the University of Oxford, the chairman designate of the Physics III Committee. Kofoed-Hansen's term as chairman was coming to its end and in a letter of 25 May Jentschke had asked Wilkinson to take over. Sir Denys replied [126] from his sabbatical retreat in Seattle (Washington): 'I am very pleased to accept and shall look forward to doing my best for the SC and nuclear structure programme of CERN (and to defend them against predators).' In the spring of 1972 a small conference 'on the future of medium-energy physics' [127] was held at CERN in order to prepare the ground for the coming battle. Meanwhile, during the autumn and winter 1971-72 new delays in the manufacture of the rotary condensers had occurred and the new target date of April 1st was long past when MichaeHs reported to the Physics III Committee [126] at its open meeting on 14 June 1972. He said among other things that 'we cannot hope for decisive information before [...] the end of September. [...] Past experience suggests that the earliest date is unlikely to be met [...] In conclusion I regret that I am still unable to give a definite date for the SCIP shutdown.' Wilkinson commented that the continuing delays and uncertainties were bound to

The SC improvement programme (SCIP)

375

raise the question of the wisdom of continuing the SC Improvement Programme and that it was necessary for the members of the Physics III community to express their opinions on this point. In Wilkinson's view it was not right to arrive at conclusions immediately as many of the people concerned were not present at the meeting, but he proposed to send out a letter asking for written statements. In the discussion that followed Hans Hofer (Bern) and Jean Pierre Stroot (Bruxelles) both suggested that CERN should take over the responsibihty and finish the job inhouse, the solution that, as we shall see, emerged in the end. Ernst Otten, the Chairman of the ISOLDE Committee, pointed to the plight of ISOLDE that was already rebuilding its facility in preparation for the SCIP. Others felt that more pressure should be brought to bear on the manufacturer of the rotating condensers, to which the Director of the Administration, G.H. Hampton, said he had found the company utterly impervious to all threats, legal or commercial. The letter [128] from the Physics III Chairman, dated 17 July 1972, Hsted a number of technical options, competing accelerators etc. and asked for consideration of the action to take. It was now up to the SC users to provide input for the next Physics III Committee meeting, in which recommendations would be made. 9.5.3 CONFLICTING VIEWS: SHOULD THE SC BE SHUT DOWN OR UPGRADED? While the debate in the Physics III Committee, with a few honourable exceptions, had followed the line that CERN had taken, namely that the issue was one of commercial and technical problems in connection with the manufacture of the two rotary condensers, other committees that met during the same week had gone straight to the poUtical aspects. The Scientific Policy Committee met [129] on 13 June 1972 and 'the eventual^^ closure of the SC was examined again'. It became clear during the discussion that, if groups now working on the SC wanted to work at SIN around 1976, they would be expected to contribute to the operating costs, and such a contribution would be of the same order of magnitude as the cost of SC operation. According to a statement made by B. Hahn, the SIN authorities would welcome it if any move of this kind were coordinated by CERN. The Director General of Laboratory II (J.B. Adams, head of the SPS machine construction) remarked to this that it was 'difficult not to consider priorities'. In the following discussion E. Amaldi, L. Leprince-Ringuet, V.F. Weisskopf and D.H. Wilkinson emphasized that it would be very bad for CERN to exclude low- or medium-energy physics from its activities, in particular with an eye to the way CERN was used by the smaller member countries. They argued that it was in CERN's interest not to separate high-energy physics from low- or medium-energy physics and the question was not which priority should be allotted to low-energy physics but that of fixing priorities between the various parts of the high-energy physics programme. At the Council Meeting on 15-16 June 1972 the British Delegate, Sir Brian Flowers, questioned the conclusion of the SPC. He 'remained unconvinced that the work done on Notes: p. 404

376

The SC: ISOLDE and Nuclear Structure

nuclear structure at the intermediate energies was of the same quahty and significance as high-energy particle physics. [...] The question was important not only in its own right but also in view of the need for economy in order to finance an extremely important^^ venture' (i.e. the SPS) [130]. It should be added that much support to ISOLDE and the SC, often in the form of unrecorded private interventions, came from delegates to CERN's Council and Finance Committee, especially from Professors A.C. Pappas and W. Gentner. About two weeks later Denys Wilkinson was again at CERN and one senses that he was influenced by the views prevailing in the CERN Management and also by the outgoing PH III Chairman, Otto Kofoed-Hansen, always a man in favour of sweeping and radical solutions. Following the visit to CERN, Wilkinson travelled to the construction site of the Swiss meson factory SIN at Villigen near Brugg. The following is an extract of the letter [131] that he wrote on 14 July 1972 to the Director of SIN, Jean-Pierre Blaser: May I review very briefly the extremely tentative programme that I had discussed with Jentschke just before I visited you and about which I told you: (i) Physics III meeting on 3 October at which, hopefully, Physics III will endorse the idea of an ultimate transfer to SIN and closure of the CERN SC if the right conditions can be obtained. (a) Shortly following (i) informal but explicit talks between you, Jentschke, myself and interested officers on possible ways of implementing the transfer from CERN to SIN. The most striking feature of the proposed procedure is that it implies the closure of the SC and the transfer (of certain programmes?) to SIN before the economic and other consequences of this transfer had been studied. It appears that Kofoed-Hansen, who was at CERN as a personal adviser to Jentschke, was given the task of putting some substance into these ideas. On 25 July, just before going into hospital, he provided the Directorate with a hand-written draft [132] for a memorandum 'On the phasing out of the S C , in which he argued that Europe would be better served by having the SC available all the time up to the start of SIN. Savings in money and manpower could be used for what he called the 'internationalization of SIN' and for an early realization of SIN's plans for an improvement programme to take the machine to higher beam intensities. He pointed out that it would be important to help ISOLDE to optimal conditions for the transfer. Kofoed-Hansen's proposals were criticized by Michaelis [133, 134] for being unreaUstic with respect to time and money. Still, in retrospect one probably has to admit that Kofoed-Hansen had one valid point, namely that European intermediate-energy physics, or maybe simply physics, could have been served better in an ideal world with a closer interaction between CERN and SIN, the latter in many respects the best of the world's meson factories. As we shall see, there were in the non-ideal world that we live in, two opposing currents that were to prevail. The outside users representing non-particle-physics communities were reluctant to give up their share in CERN, which they considered an important part of the European physics^^ scene, and CERN's owners and its permanent physics staff saw Httle use in spending money at SIN just in order to serve non-particle physicists better.

The SC improvement programme (SCIP)

311

9.5.4 THE USERS ARE HEARD: PHYSICS III AND THE SCIP ADVISORY PANEL Not surprisingly there was no immediate response to Sir Denys's request (section 9.5.2) for viewpoints on the future of the SC and its improvement programme. The letter of 17 July with an implicit September deadline was sent out at a time that to university physicists means end of term, travel to conferences, private holidays etc. The present writer, who at the time was one of the few outside users actually present at CERN, has a vivid recollection of having spent a good fraction of August and September making telephone calls to colleagues as they returned home, suggesting that they should begin opening their mail. In the end a total of 34 letters [135, 134] bearing the names of 57 physicists were received from the Physics III community. There was an overwhelming majority in favour of continuing the SCIP programme. The recurring argument was that an activity at intermediate energies was important if CERN were to be maintained as a meeting ground for high-energy and nuclear structure physicists, the original goal of Weisskopf s initiative of 1963 (sect. 9.2.1). Many, among them Gerhard Backenstoss (Basel), made clear that they were positive to a close cooperation with SIN provided that active nuclear-structure research remained at CERN. In a different vein, Ingmar Bergstrom (Stockholm), who at the time was collaborating with Backenstoss on SC and PS experiments on exotic atoms, stated that his laboratory in Stockholm was not using CERN just because of the existence there of 'a certain beam with certain properties' but rather because of the intellectual and technical stimuU that it provided to visitors and visiting groups. He asked whether CERN would be prepared to take the political consequences of a decision that made it 'a rather exclusive laboratory for privileged particle physicists?' A long debate took place at the Physics III meeting on 3 October 1972. Its meanderings through sub- and side-issues may be followed from a lucid summary prepared by the Committee's secretary, A.J. ('Freddy') Herz [136]. At the proposal of Wilkinson it was finally decided to set up a panel^^ [137] to work on a week-by-week basis with MichaeUs to advise the Ph III Chairman on the date to be recommended for the start of the SC shutdown and to advise and inform both the Physics III Committee and the MSC Division on all matters of interest to intending SC users. A monthly report on the progress was to be sent out jointly by Michaelis and the Chairman of the panel. It was decided that, initially, the panel should meet every two weeks. Soon thereafter, at the next meeting [138] of the Scientific Policy Committee on 7 November 1972, the CERN Management had decided to maintain the SC. Jentschke announced that the shutdown, expected to last a year, would take place in March. The intention was to continue to operate the SC until it ceased to be a really modern tool for nuclear structure research. If the rotating condenser failed, the plan would have to be reconsidered. Wilkinson added that this decision was in line with views expressed by a large majority of users. Even in the case of a possible technical failure, he still saw strong arguments for a partial improvement programme including the acceleration of helium ions. Barring technical mishap it had thus been decided to keep the SC. Although the proponents of SCIP saw this as a victory, the reaUty was rather that the views had converged. Notes: p. 404

378

The SC: ISOLDE and Nuclear Structure

Let us try at this point to summarize the arguments: (i) It was in CERN's interest to hold on to its role as Europe's most prominent physics laboratory by having a broad scientific programme, and (ii) this also broadened the science-poUtical support base in the member countries, notably the smaller ones (iii) which were interested in institutionalized access to a big-science laboratory with its intellectual climate and technical know-how. Finally (iv) some of those initially opposed to SCIP had come to fear that a transfer of activities to SIN would imply a direct or indirect transfer of funds to SIN in an amount that would exceed the cost of continued SC operation. The SCIP Advisory Panel held its first meetings on 3 and 10 October and when it met a third time on 21 October three members (Boschitz, Hofer and Nielsen) had visited the manufacturer of the rotary condensers in Berlin. They had come back with a clear impression that the work going on there was technically sound but also that the manufacturer had lost his motivation and feared to be trapped by the very exacting specifications for these devices. (The company's position is stated very clearly in a letter to the CERN Administration [139]). The first joint report from Michaelis and the panel to the Physics III Committee [140, 141] ended on a significant note: 'Discussions are in progress both within CERN and with AEG with the aim of finding contractual solutions which will enable the technical work to go ahead undisturbed.' The following meetings began to reveal that, in addition to the resistance to SCIP inside CERN and the commercial dispute with Berlin, there was a third problem in that the always correct and cautious Michaelis was quite happy to see the most delicate element in the SCIP placed outside his responsibiUty. By the time of the ninth meeting of the panel on 24 January 1973 a clear picture of the situation had emerged, and in a discussion, in which Wilkinson participated, it was decided to take action. On the following day the panel recommended to Physics III '(i) that CERN take over full responsibility for the first Rotco [...]. Moreover we do not think it is necessary to insist on a completed full-power test before this happens. We further recommend (ii) that the shut-down should start on April 19th', a recommendation that Wilkinson endorsed and took to the Director General. On 4 April 1973 the NPRC [33] decided to fix the shut-down for 31 May. The additional delay had been included to allow two physics groups to complete their experiments, one of them being the experiment on the fine structure of muonic helium (sect. 3.3). The shut-down finally took place on 7 June 1973 and was followed five days later by a flooding of some machine areas during a thunderstorm. Some physicists took this as an indication that divine intervention had been prepared in the event that the MSC Division had continued to procrastinate! The SCIP Advisory Panel continued to monitor the Improvement Programme during the following year. On 1 October 1974 protons were accelerated for the first time out to full radius with an intensity of 0.6 fxA at a repetition rate of one pulse in 16. One basic goal had thus been reached. The first experiments began in December and scheduled operation from January 1975. At the 24th and last meeting of the SCIP Advisory Panel on 24 February 1975 it was decided to recommend the dissolution of the panel as the main design aims of SCIP now had been attained [141]. The experience over the coming years showed that the

The SC improvement programme (SCIP)

379

most stable operation was achieved with a reduced repetition rate (1:2) on the rotary condenser, corresponding to an internal beam of about 4 /lA. With 70% extraction efficiency in the fast mode this meant about 3 juA proton beam on ISOLDE'S target. The success of the SCIP was due to the competence of the CERN engineers and technicians working on the floor. Although Denys Wilkinson and the members of his SCIP Advisory Panel had spent two years leaning over drawings of rotary seals, cooling ducts and other technicalities their contribution had been essentially a politico-technical one, i.e. that of de-fusing the technical arguments that were being used to stop the SCIP. The situation had many features in common with that described by Pestre [116] covering the time when the 'truck teams' disappeared. Those outside physicists who were running independent programmes at CERN and not just acting as a source of auxiliary labour were forced to unite against what they felt was passive - and occasionally active - resistance by the CERN establishment. 9.5.5 POST-SCIP DEVELOPMENTS: THE ACCELERATION OF ^He AND HEAVY IONS In 1973 it was pointed out by Hohbach [142] that with relatively small modifications to the radiofrequency system it should be possible to accelerate deuterons and doublycharged ^He and ^He. During 1973-75 the studies continued and were extended [143] to the possibilities for accelerating multiply-charged, partially-stripped ions such as ^"^N^"*". The possible acceleration of trans-protonic projectiles was discussed repeatedly in the SCIP Advisory Panel [141] and it was brought to the attention of the Physics I Department [144]. ISOLDE was mainly interested in ^He with a total energy of 900 MeV as this projectile was expected to give larger cross-sections for deep-spallation reactions than a 600 MeV proton beam, both because of the increased energy and also because a composite projectile was expected to deposit a larger part of its energy in the initial colUsion. Heavy ions, on the other hand, were not thought to be a competitive production tool for ISOLDE. For this reason a limited modification involving only the helium beam was discussed early in 1975 between the R F Group (H. Beger and A. Fiebig) and ISOLDE (P.G. Hansen) [145]. Later in the year Beger submitted an outline [146] of such a project to the Physics III Committee. At the s e c Meeting on 1-2 December 1975 a sub-committee with P.G. Hansen, R. Klapisch and O.B. Nielsen as members was set up to state the physics case for ions and to discuss the technical aspects with the MSC staff. In their presentation on 10 March 1976, summarized in [147], they emphasized that the job was cheap, essentially 150 kSFr for a new intermediate line for the radiofrequency, and that the gains could be great, but that a determination of the relevant cross-sections required on-line mass separation, possible only at ISOLDE. The modification was approved and the CERN Annual Report mentions that the extension to the connection Dee-Rotco was ordered the same year, 1976. From other groups there also emerged an interest in the helium beam, primarily for experiments attempting to observe the production of K- and pi-mesons and especially in

380

The SC: ISOLDE and Nuclear Structure

so-called coherent reactions. In these a large part of the necessary momentum is supplied by the nuclear structure, in the simplest form by the tails of the Fermi-momentum distribution in the nucleus [148]. Similar processes had already been seen with protons (sect. 9.3.4). During the Workshop on Intermediate Energy Physics [149] held at CERN in 1977, the interest in heavier ions was again voiced by several groups doing counter experiments and the acceleration of ^^C"*^ and other ions with Q/A= 1/3 was one of the recommendations emerging from the meeting [150]. This modification was also approved and the realization, including changes in the ion source and in the extension line, began in 1978. The workshop also considered the possibility of studies with post-accelerated radioactive ions but concluded, as we know today wrongly, that although there were interesting applications, these were of no major interest in nuclear physics. The ion programme was from the beginning seen as being in a time window before more powerful beams with up to 100 MeV/nucleon became available at the French national accelerator laboratory GANIL (for Grand Accelerateur National des Ions Lourds) in Caen and in an energy window above the 10 (later 20) MeV/nucleon available at the German heavy-ion centre GSI in Darmstadt. The SC beams attracted a large number of good experimental groups, which made substantial contributions to the understanding of heavy-ion reactions at intermediate energies. As foreseen much of the effort was concentrated on pion production at energies well below the free N N threshold, a subject that had earlier been studied in proton-nucleus coUisions (see sect. 9.3.4). Among the laboratories that took part in the programme can be mentioned Cagliari, Copenhagen, Darmstadt, Frankfurt, Heidelberg, Lund, Saclay, Stony Brook, Strasbourg and Turin. The reviews [151-153] give a good impression of the themes and status of the heavy-ion field, and include references to much of the SC work. Among the many papers on pion production we cite as examples Johansson et al. [154] for work on charged pions, and Grosse et al. [155] for work on neutral pions and direct photons. It gives a striking impression of the importance of collective effects in the pion-production mechanism to note that n^ production has been observed with heavy ions with as low a laboratory energy as 20 MeV/ nucleon, where the threshold for NN collisions, also on a target at rest, would be around 290 MeV kinetic energy. The ion experiments came to an end around the mid-eighties, when more powerful machines took over. The helium beam continued to be used by ISOLDE until 1990 and gave in some cases gains approaching an order of magnitude in production rate (see [115]), though it is probably fair to say that the beam did not become the magic bullet that its proponents had hoped for.

9.6 The evolution of the scientific programme at ISOLDE In this section we give examples of how the ISOLDE FaciUty for slow radioactive beams has permitted studies of a wide variety of topics in nuclear, atomic and solid-state physics. A much more complete picture may be obtained through the proceedings of the series of

The evolution of the scientific programme at ISOLDE

381

specialized conferences [156-159] that followed the original Lysekil Meeting of 1966 (see sect. 9.4.2) and through review papers [160-168] prepared for other conferences and books. Volume 8 of Bromley's Treatise on Heavy Ion Science [169] has been dedicated to the subject of nuclei far from stability and gives an excellent up-to-date coverage of both the physics and the experimental techniques. The first years of ISOLDE were a learning period during which the users got to know the machine. They found out what new problems it could be used for, and which experimental techniques were best suited for the purpose. On the way there were many practical problems that had to be solved, e.g. reaUzing that the new isotopes of argon that had been discovered in one run in fact were well-known but doubly-charged isotopes (and hence appearing at mass A/2) of the next heavier noble gas, krypton. It was activities like this that earned the ISOLDE physicists the reputation, in some cases undeserved, of being a collection of isotope and gamma-ray hunters. Not unUke biological evolution, the new conditions brought about new species that for a while seemed to have an edge in the struggle for survival. A pertinent example, already mentioned in sect. 9.4.5, was the highly mobile collection systems designed for operating upstream in ISOLDE'S beams, systems that in the long run were too inflexible to allow more sophisticated experiments. (We shall see below that after SCIP it was possible to serve several users in parallel in a better way.) Conversely, there were also old estabUshed techniques that, dinosaur-like, turned out to have no future under the new conditions. An example of this was provided by the Aarhus-Copenhagen group, which during the preparations for ISOLDE had constructed a large magnetic six-gap electron spectrometer, a so called 'orange' with very large transmission, one of the most powerful tools for nuclear spectroscopy at the time. It was never used and that for several reasons. First of all physics had changed and precise and detailed spectroscopy was less interesting than it had been a decade earUer. To this was added a continual shortage of machine time, which made an instrument based on point-by-point scanning inefficient^^. Starting with the machpe's targets, ion sources, lay-out and beam Hnes and continuing with the various experiments, we shall now try to give some indication of the evolution during the period 1967-81. 9.6.1 THE ISOTOPE SEPARATOR AND ITS BEAMS From 1971 ISOLDE began to give priority to the preparation of the post-SCIP experiments and about half of the available machine time was devoted to tests of new systems [170]. The importance of this research effort was generally acknowledged and the delay in the start of SCIP actually turned out to be a blessing in disguise since it allowed the tests to be done more safely (with weaker beams). The in-house group, now called the CERN-ISOLDE Group (group leaders P.G. Hansen, 1970-78, and B. Jonson, 1978-83) had been joined by the talented experimentalist and engineer, Helge Ravn, who set out to make a wider range of elements available and also to make more systematic studies of the delay between the production of a radioactive nucleus and its arrival in the experiment. Notes: p. 404

382

The SC: ISOLDE and Nuclear Structure

The evolution of the scientific programme at ISOLDE

383

The first results concerned alkali elements, which because of their low first ionization potential can be ionized on a hot metal surface, a technique that had first been exploited for on-line mass separation by Bernas and his collaborators [171] and since had served in a series of experiments at the PS [160]. The experiments at ISOLDE incorporated a number of new developments such as the use of molten metals or very hot powders of refractory metals as target material and a new design of the ion source. Over the following years the techniques were extended to give beams of the earth alkalies, of the rare earths and, later, also of the halogens produced selectively as negative ions by surface ionization. The use of various designs of plasma ion sources together with the new molten-metal or powder targets also played an important role in improving the production of the ISOLDE classics, the noble gases and mercury, cadmium and zinc. We shall not go into details here concerning this fascinating research, which involves a mixture of experimental physics, accelerator technology, metallurgy, engineering and chemistry, but refer simply to some review papers [161, 172, 115]. The progress brought about by the combination of this work with SCIP is illustrated in Fig. 9.7, where roughly a factor 60 in the improvement in production rate arises from the increased proton beam intensity at the re-built cyclotron. A second goal in the preparations for SCIP was to introduce more advanced engineering, a task handled by the engineers Erich Kugler and Stig Sundell in collaboration with Ravn. The new high-temperature systems had no oven and the target container, usually made of tantalum, was heated directly by Ohmic losses in the construction material - and soon also to a considerable degree by the proton beam. The targets were made from a modular design (the module is visible in Figs. 9.10-9.11) to allow many variations in the configuration to suit individual experiments. Thus, the same (mass-produced) parts could be fitted with different ion sources (surface-ionization or plasma) and with various accessories such as hot or cold connections between target and ion source (in order to transmit or not transmit less volatile elements) as well as devices for admitting stable isotopes as mass markers into the beam. Another aim of the standardization was to make the systems cheap - the group knew that the high radiation levels after SCIP would not permit any repairs, so that any irradiated unit would be discarded at the first break-down. Still, the cost of expendable target units was to become a major item on ISOLDE'S budget. The target area was designed so that the modules could be brought in and out by remote control, in the first version via rail to a shielded cave (Fig. 9.10) and a few years later by an

Fig. 9.10 Lay-out of the ISOLDE area with the experiments as of 1978. (1) Magnetic quadrupoles and X-Y steering magnets for the proton beam, (2) target module, (3) magnet, (4) switchyard (see Fig. 9.12), (5) external beam Hnes with electrostatic quadrupole lenses, (6) experiment on beta decay of exotic nuclei, (7) high-resolution mass spectrometer (8,9) nuclear spectroscopy, (10) range measurements of ions in gases, (11) optical pumping and laser spectroscopy, (12) atomic-beam magnetic resonace, (13,14,15) collection stations for long-lived radioactive samples for off-line work, (16,17) experiments on beta decay and neutron detection. The control console of the separator can be seen to the left of (17).

384

The SC: ISOLDE

and Nuclear

Structure

Fig. 9.11 The industrial robot, height about 160 cm above floor level, holding a target module. The operation is surveyed by the TV camera placed on the arm of the robot. Note on the target the vacuum lock and the set of standardized quick-coupling connectors for supplies. Irradiated targets and spares are stored on the shelves behind. The resemblance of the target vacuum container with an aluminium cooking pot is not accidental; to save money the target containers were mass-produced by welding aflangeonto a 40 SFr kitchen utensil bought in large numbers directly from the manufacturer. (Photo CERN.)

industrial robot (Fig. 9.11). The supplies (voltages, cooling water, carrier gas) to the target module were all provided from the (fixed) separator front-end and acceleration stage via automatic couplings designed to serve the needs of all systems. A third but equally essential problem in the preparations for SCIP was the lay-out of the whole area including the interfacing of the separator with the experiments. A number of discussions took place involving the house group at CERN, the external users and the engineers. There were two major issues of which one was space. Any extension of the underground hall would have been very costly and it was decided instead to add a large hall at ground level (top left on Fig. 9.10), to be used mainly for electronics and data taking and also to place some experiments in this hall and in the floor below it. Still, it was clear that it was essential to make the best possible use of the lowest level (the hall next to the separator) and also to add more shielding. It was Erich Kugler [173] who found the

The evolution of the scientific programme at ISOLDE

385

solution that met these requirements. The essential elements, which can all be seen by comparing Fig. 9.10 with Fig. 9.5, were (i) to move ISOLDE'S target back by about five meters to the beam foreseen for particle physics experiments and (ii) to suppress the 3 m drift tube, which the Group had come to beheve was not essential. The machine, effectively eight meters shorter, now (iii) ended before the existing shield and (iv) an additional shielding wall with mid-plane iron could be constructed around the analyzing magnet and part of the dispersion chamber. A more modern beam-handling system was designed by Kugler, who replaced the 'einzel-lenses' of the Copenhagen design (sects. 9.4.2, 9.4.3) by electrostatic quadrupoles. Finally the experience with the first ISOLDE had shown that it was important to preserve some possibiHty of parallel operation in order to economize beam time. Kugler and Goran Andersson [173] (Gothenburg) reahzed that the almost parallel geometry of the fan of beams in the dispersion chamber would allow the interception of individual masses by four movable electrostatic deflectors, which would swing the beams into four external beam fines. The resulting switchyard, shown in Fig. 9.12, gave rich possibifities for several

Fig. 9.12 The switchyard of the isotope separator with the top flange removed to show the four electrostatic deflectors, which are movable along the spindles. The exit ports and the quadrupole lenses can also be seen. (Photo CERN.)

386

The SC: ISOLDE and Nuclear Structure

experiments to operate in parallel. During the first years of ISOLDE-2 operation there were on average three experiments taking data when beam was on. 9.6.2 NUCLEAR MASSES, SPINS, MOMENTS AND RADII One fundamental experimental question posed at ISOLDE was whether new structural phenomena would appear in the regions of the nuclear chart now available to experiment. The spectroscopists had believed that the proper, maybe even the only, way to answer this question was through the detailed spectroscopy of excited nuclear levels, but experience had taught them that this path was laborious and very demanding in machine time (sect. 9.4.5). Otten's experiment, deaUng with the ground state properties of four mercury nuclei (sect. 9.4.6), had, on the other hand, given very convincing evidence for a new and unexpected phenomenon, which it took many subsequent measurements, nuclear as well as atomic, to clear up. It is therefore not surprising that a number of groups from 1975 onwards mounted dedicated experiments to scan the properties of nuclear ground states and long-lived isomers. The fine structure of the nuclear mass surface (as a function of N and Z) provides detailed insight into nuclear structure as demonstrated e.g. by the overviews of mass data given by Zeldes in [156] and [158]. Early work at ISOLDE had obtained masses via the determination of the energy release in radioactive decays (see papers in [158]) but a more direct and comprehensive approach was developed by a group [174] from the Rene Bernas Laboratory^^. The experiments, carried out first at the PS and later at ISOLDE, used a (velocity-focusing) Mattauch-Herzog spectrometer and were based on the principle that if the magnetic field is kept fixed, then two ions of masses MA and MB will follow the same trajectory in the instrument provided that all electric potentials V obey the relation MA/MB = VB/VA. Thus, the measurement of the mass is converted to a precise measurement of the ratio of the two electrostatic potentials that will bring the two ions into focus. The experiments gave evidence for new regions of deformed nuclei near N,Z = 20,11 (although 20 is a magic number normally associated with spherical shape), 60,40 (known from spectroscopic studies, see sect. 9.6.3) and 90,55 (slightly below the familiar deformed rare-earth region). Unfortunately this research line came to an end with the studies of alkalies, mainly for technical reasons, and it is only within the last few years that the technique that seems destined to replace the classical mass spectrometer, namely the use of ion traps, has begun to emerge [175]. Another experiment, carried out by Ekstrom and his collaborators [176], studied spins and moments in long chains of isotopes by means of the atomic-beam magnetic-resonance method (ABMR). Their spin spectrometer was designed so that for a given element and given settings only one spin value was transmitted, so that the spin value of a given radioisotope could be determined in 5-6 measurements, which makes the technique extremely fast. By scanning the transmission as a function of the radiofrequency setting at somewhat higher magnetic fields it was also possible to measure magnetic and electric moments. The detailed comparison [176] of spin and moment data with predictions from

The evolution of the scientific programme at ISOLDE

387

theoretical models demonstrates very convincingly the insight that this systematic information gives. The original optical-pumping experiment on mercury (sect. 9.4.6) was based on the detection of nuclear polarization and hence could not provide any information on the radii of the (spinless) even-even isotopes. In a second experiment Otten and his group (see [110]) used tunable lasers together with frequency doubling in order to get into the UV range of wavelengths necessary for mercury, and measured the resonantly scattered light from a cell containing the radioactive vapour. The results, together, with those of later work, are shown in Fig. 9.13 demonstrating that the i82,i84pjg ^^ ^^^ j^^^^^ ^j^^ anomalously large radii that characterize their (strongly deformed) odd-mass neighbours and also that the isotope ^^^Hg has a second low-lying isomeric state of presumably spherical shape. The favoured theoretical explanation (see [110]), is the coexistence at low energy in these nuclei

'[fm']

•

ground sfafe

o

isomer

A

droplet model 305

DROPLET HF.BCS 30.0

29.5

NEUTRON NUMBER 100

102

104

106

108

110

112

IK

116

118

120

122

12*. 126

128

130

132

Fig. 9.13 The mean value of the nuclear charge radius in the isotopic sequences of Au, Hg and Pb. The absolute scale (the experiments determine the differences in (r^» has been fixed from the droplet model. (From [110]). Notes: p. 404

388

The SC: ISOLDE and Nuclear Structure

of two families of states with very different wave functions, one corresponding to almost spherical shape and one corresponding to a strong quadrupole deformation. Nuclear spectroscopic studies of ^^"^Hg have identified a low-lying 0"^ state, which has a welldeveloped rotational band and which must be the deformed partner to the ground state (see the review by Hamilton [177]). It is only for the heavier elements that it is possible to study hyperfine structure via the optical spectroscopy of atoms in a gas cell, such as in the experiments described in the previous paragraph and in sect. 9.4.6. Already for somewhat lighter elements the thermal Doppler broadening of the lines exceeds the hyperfine splittings and isotope shifts, and it becomes mandatory to use Doppler-free techniques. One solution used by a collaboration involving the Rene Bernas and Aime Cotton laboratories (both Orsay) was to stop the ions from ISOLDE and to re-evaporate them as a coUimated atomic beam, which interacted with a laser beam crossing at a right angle. The polarization transfer was now detected with a magnetic six-pole (Stern-Gerlach analyzer) followed by an ionizer and a small mass spectrometer. This technique has given a wealth of interesting results for rubidium, francium and caesium (see e.g. [178, 179] and also the reviews [164, 110]). Owing to the losses connected with re-evaporation and re-ionization of the atoms, the method could not readily be adapted to elements other than the alkalies. The general solution to the Doppler broadening problem turned out to be collinear laser spectroscopy, a technique invented by Kaufman [180] and independently by Wing et al. [181] and developed for studies of radioactive atoms at ISOLDE by the Otten Group [182]. The basic technique is to deflect the ion beam from the separator so that it travels parallel to and inside the Hght beam from the laser and, in the simplest version shown in Fig. 9.14, to measure the resonantly scattered light in the observation region. Although the fast beam obviously implies a large Doppler shift, there is the surprising and extremely important corollary that the Doppler spread becomes very small. This is because the spread in the kinetic energy E is not changed by acceleration through a constant potential. Denoting the atomic mass and velocity by m and v we can relate the energy and velocity dispersion dE = S(mv^/2) = mvSv = constant , showing that a large velocity is associated with a small Doppler spread. The reduction factor turns out to be of the order of 1000 for an ion-source temperature of 2000 °K and an acceleration voltage of 60 kV. The collinear scheme has been used for a large number of experiments on different isotopes. It allows many modifications which are discussed in Otten's review [110]; suffice it to mention here the possibiUty of neutralizing the ions by inflight coUisions with alkah vapour, a variant that is of prime importance because most ions in their ground states do not have transitions in the region of visible Ught, the frequency range that can most easily be reached with lasers. The optical techniques have been used to measure radii, spins and moments for about 400 ground states and isomers of about 20 elements, and a similar number of spins and

389

The evolution of the scientific programme at ISOLDE Jeflector

Quadrupole triplet

Retardation system

Charge - exchange cell

Observation regton

^3i LSI 11

I

Photomultiplier

Fig. 9.14 The principle of coUinear-laser spectroscopy with fluorescence detection. The ion and laser beams are merged at the deflector and the ions neutralized in collisions with caesium vapour in the charge-exchange cell. The resonantly scattered light is detected with the photomultiplier. (From [110]).

moments have been measured by the ABMR method. These tools from atomic physics represent without doubt the most important appUcation of on-line mass separation until now. 9.6.3 NUCLEAR SPECTROSCOPY Traditional nuclear physics allowed the exploration of nuclear structure close to the nuclear species that occur in nature, that is along the Une of beta stability, shown in Fig. 9.2. An important motivation, mentioned in section 9.2.4, for undertaking spectroscopic studies away from the stability Une was to search for new structures: new deformed regions and new combinations of magic numbers. As we have just seen atomic methods for probing nuclear ground states were soon to provide a more general - and model-independent - tool for probing nuclear sizes and shapes. The proton-rich nuclei have gradually become accessible to experiment all the way out to the limit of proton instability, the proton 'drip line', which for the lighter nuclei lies close to the Z = N line, fundamental for its relation to the quantum number isospin, in nuclear physics denoted T with projection^^ T^ = {N — Z)/2. The nuclei with negative isospin projections are of special interest in nuclear physics as they are (with a few exceptions) the only ones in which beta decay can manifest itself with maximum matrix elements, the so-called 'superallowed transitions'. The progress in this research has been summarized in the review [183]. As an example it can be mentioned that the first case of a nucleus with Tz = —2, the isotope ^^Ar with 18 protons and 14 neutrons, was discovered at ISOLDE in 1977. Some eight years later it could be produced in sufficient quantities at ISOLDE to be used in a precision experiment that served to illuminate the strength and the limitations of the nuclear shell model. This model in its modem form (based on effective interactions) could reproduce the spectrum of the weak-interaction decay up to 10 MeV excitation energy but not the absolute scale, which is reduced by a factor of two by sub-nuclear effects Unked in various ways to the pion field in nuclei (see [184]). Notes: p. 404

390

The SC: ISOLDE and Nuclear Structure

A large number of studies have dealt with the nuclear structure of the heavier nuclei by electron- and gamma-spectroscopic methods (see especially the review by Hamilton [177] and eariier work cited therein). We mention just a few examples [185] of the intricate interplay between shapes and shells, which would not have been observed without comprehensive studies that cut across the nuclear chart. Whereas the magic nucleon numbers (2,8,20,28,50,82,126) of the classical shell model favour spherical shapes, other nucleon numbers have a 'chameleon character'. Thus the proton numbers 38,40 (Sr,Zr) when combined with the magic neutron number 50 favour spherical shapes so that ^^Zr is very much Uke a double-closed-shell system. On the other hand the light (N:^40) and very heavy (N>60) isotopes are strongly deformed and have well-developed rotational bands. In some cases (especially ^^Zr) it has been possible to detect the co-existence of spherical and deformed states at low excitation energies in the same nucleus analogous to the findings from studies of nuclear sizes and moments mentioned in the previous section. Another example is provided by the proton number 64. Gamma-spectroscopic experiments have also been extremely important for the understanding of the Os, Pt, Hg, Pb region. This is hardly the place to give a more detailed picture of the vast amount of knowledge collected in 30 years of research on the spectra of nuclei away from stability, but it is tempting to try to draw a sort of balance sheet. It is the impression of the present writer that spectroscopic research has been consistently underrated because it requires a large, systematic and often tedious effort that has little 'committee appeal'. It is only when all the bits of information come together that it is possible to see that a much more interesting and nuanced picture of nuclear structure has emerged; it is noteworthy that many of the most interesting features were not foreseen by theory although they were usually abundantly explained after the fact. 9.6.4 EXOTIC DECAYS, STRENGTH-FUNCTION PHENOMENA AND STATISTICAL ASPECTS In sect. 9.6.3 examples were given of how new facets of nuclear structure appear when the nuclear composition is varied. We now turn to examples of how nuclei near the nuclear drip lines show properties that nuclei do not possess near stability. These phenomena are linked to the asymmetry in the binding energies. While beta-stable nuclei necessarily have roughly equal binding of protons and neutrons, typically 6-8 MeV, the nuclei at, say, the proton drip line have nearly zero binding of the protons while the neutrons are bound by 10-12 MeV. This means that even quite low-lying excited levels are unstable with respect to proton (and usually also alpha) emission, which can therefore be excited in beta decay. This process is usually referred to as beta-delayed particle emission and has already been encountered in sect. 9.2.3. It was also used for detecting the very proton-rich Hght systems mentioned in sect. 9.6.3. Soon after the start of the first ISOLDE, beta-delayed proton emission was seen in nuclei as heavy as xenon and soon after in mercury. After the start of ISOLDE-2 the

The evolution of the scientific programme at ISOLDE

391

(much weaker) competing process of beta-delayed alpha emission from proton rich nuclei was also found. These spectra and the corresponding spectra of neutrons from very neutron-rich nuclei were important in giving information about the density of beta transitions to very high-lying states, the so-called beta strength function, defined in a footnote to sect. 9.4.5. and reviewed in [163, 183]. These processes and similar excitation phenomena following muon capture (see sect. 9.3.3) are interesting in that they are dominated by giant-resonances not unUke those encountered in electromagnetic excitation processes. It is also a giant-resonance phenomenon that explains the different beta decay behaviour of nuclei with positive and negative isospin projections (sect. 9.6.3), namely that superallowed beta decay is encountered essentially only for T^ < 0. The main features of the very complex particle spectra following beta decay of the heavier nuclei could be understood on the basis of a statistical theory containing reasonable estimates of the strength functions involved [186]. It was soon realized that some experiments also saw a pronounced fine structure that reflected the fluctuations in the composition of the nuclear wave function of the individual levels [109], and that the classical statistical model of the nucleus due to E.P. Wigner and others gave very definite predictions for the intensity (and its variance) of the emitted particles and gamma rays. Measurements of the fine structure of particle spectra has in some cases allowed the determination of nuclear level densities at high excitation energy (see the review by Jonson [187]). An interesting application of beta-delayed protons pioneered by the Canadian physicist J.C. Hardy was the use of coincidences between the protons and K x-rays (from electroncapture beta decay) for measuring lifetimes in the 10"^^ s region. The x-ray energy is larger if the proton is emitted after the x-ray so that the branching ratio ties the proton Ufetime to the (known) atomic K-shell lifetime. (See e.g. [188].) The Ught neutron-rich nuclei [168] have been found to display a number of interesting exotic decay modes such as the emission of two and even three neutrons following beta decay, first observed [189] in the decay of ^^Li with a half-Ufe of only 8.6 milUseconds via the use of time-correlation techniques with a large neutron detector. Multi-neutron emission has also been detected in the sodium isotopes ^^"-^^Na, and recent experiments find rare decay modes involving charged particles such as deuterons, tritons and ^He (see e.g. [190, 191]). It was clear from the start that the energy spectra of these particles reflected a very special aspect of nuclear structure, namely spectra where all excited states except a few low-lying ones were unbound, and decayed with very large particle decay widths. The detailed investigation of these structures, however, was very difficult and was not pursued with much energy. In the last few years it has, however, become clear that the neutron-rich nuclei have extremely interesting properties and a large number of theoretical and experimental papers on this subject have appeared. (For a popular presentation see e.g. [192]). It has turned out that the extremely low neutron binding near the neutron drip line permits the last neutron or pair of neutrons to travel far away from the core via quantum-mechanical tunneUng so that it forms a neutron halo that may extend to several times the normal nuclear radius.

392

The SC: ISOLDE and Nuclear Structure

Due to the physical separation of the neutrons from the protons, these nuclei violate some of the most basic rules in nuclear physics: The mass and charge radii are no longer identical and certain electromagnetic and beta-decay processes appear with essentially their full single-particle strength and are no longer quenched by giant-resonance phenomena. 9.6.5 APPLICATIONS TO ATOMIC AND SOLID-STATE PHYSICS The atomic beam and laser techniques discussed in sect. 9.6.2 were put to the service of atomic physics in a search for optical transitions in the alkali element francium (Z = 87). In 1978 Sylvain Liberman and his collaborators [193] succeeded in observing its D2 line at a wavelength of 717.7 nm. (The D Hues of francium represent the transition 7s^7p, spUt by the fine structure into components Di and D2. Such valency-electron transitions are characteristic of all alkali elements.) Francium, appropriately named after the country of origin of this group, is a rare radioelement, which until then had remained the only element with Z<100 for which no optical transition had been reported^^. The reasons why such a measurement had not been done earlier were the short half-lives of the francium isotopes (the longest is 22 minutes), and also the low production rates in most laboratories. ISOLDE'S 10^ atoms/s of Fr thus provided a decisive advantage in this experiment, which in turn opened up studies of properties of nuclei of francium through hyperfine-structure spectroscopy. Later experiments have also observed the Di line [194] and the second finestructure doublet, the D' lines (in the blue) representing the 7s-^8p transition [195]. In another series of atomic-physics experiments, in which the high production yields at ISOLDE also played a central role, the relative energies of some atomic K x-rays of medium-weight and heavy elements were measured with a precision of 10-100 meV (milUelectronvolts), that is to within one thousandth of the natural line width. The experiments compared the energies of x-rays from intense sources of electron-capture (EC) radioactivities produced at ISOLDE with each other, and with those of sources from photoionization. Shifts in the energies of 0.1 to 5 eV were observed [196], and turned out to arise from contributions that had not been considered previously. One of these effects was the hyperfine shift (analogous to that observed in muonic x-rays and in optical spectra, sects. 9.3.2 and 9.6.2). The hyperfine shift became observable in the ISOLDE experiments because the x-rays from beta decay are subject to a previously unnoted angular-momentum selection rule that leads to a non-statistical population of the hyperfine components. Another effect was a small increase in the energies of x-rays from photo-ionization due to final-state excitations ('shake-off^). A third series of experiments demonstrated a shift reflecting the fact that an element undergoing (EC) beta decay has one valency electron more than the daughter atom. This leads to very characteristic shifts in the energies of the K-series of x-rays. The experiments showed that for the rare-earth metals the additional electron was located in the 4f level. This is exactly where chemists and solidstate physicists would Uke it to be in this case, but the method offers a more general tool for testing electron assignments.

The last defence of the Cyclotron: 1979-81

393

In the mid-seventies several solid-state physics groups began to take an interest in implanting the radioactive beams from ISOLDE into solids with the purpose of using the radioactive nucleus as a probe for the internal fields in the host material. The main detection methods used were the Mossbauer effect and perturbed angular correlations, the latter based on the observation of an (often minute) shift in the angular correlation between successive radiations. This shift arises from the precession of the nuclear magnetic dipole and electric quadrupole moments in the ambient fields. The methods are attractive because of their high sensitivity; a total of 10^^ impurity atoms will suffice in many cases and the signal corresponds to the conditions on a single location, something that no macroscopic method can match. The solid-state appUcations at ISOLDE have continued to grow in importance to this time, when they account for about 25% of all experiments at ISOLDE. The blossoming of nuclear solid-state physice at ISOLDE came mainly after the period covered in the present paper; we refer to the reviews by Haas and by Weyer [197] for an account of, and references to, much early work in this field of applications. 9.7 The last defence of the Cyclotron: 1979-81 9.7.1 THE PLANS FOR SIN-ISOLDE By 1978 CERN was heading towards an approval of LEP, the Large Electron-Positron Collider, which was to be built with 'constant budget'. This effectively meant that there should be no decrease in budget after the SPS construction period. Still, there was a need to make economies, real and symbolic sacrifices that could convince the member states that the management was earnest. The Directors General, John Adams and Leon van Hove, proposed to Unk the construction of LEP to a closing of the ISR and the SC, which permitted the happy formulation that 'CERN would be closing two accelerators in order to build one'. They suggested that ISOLDE should investigate the possibilities for a continuation of its programme at the Swiss meson factory SIN. ISOLDE responded by setting up an ISOLDE-3 Working Party^"^ to study the technical and scientific aspects of this suggestion and contact was made with the SIN Director, JeanPierre Blaser, who appointed John Domingo as the Unkman for this project. It was reaUzed that the possibilities were very attractive. Since the running would always be in parallel with other users, the beam itself would cost little and operation corresponding to 500 eight-hour shifts per year would be possible, thus fulfilling a long-standing wish of the collaboration. After a planned upgrading of SIN, the 600 MeV proton beam was expected to reach an intensity of 1-2 mA, so that without causing major disturbance to other users it would be permissible to divert 20 //A of these to ISOLDE for about 400 shifts and 100 juA for 100 shifts per year. The improvement over the existing ISOLDE would then amount to factors of 3 and 16 in the two cases. It also emerged that it would be possible to take the beam out in a pulsed mode, which would lower the background and give higher intensities in experiments in which the separator beam has to be gated off during the Notes: p. 404

394

The SC: ISOLDE and Nuclear Structure

measurement period. The last advantage was finally achieved when a new ISOLDE went into operation at the PS Booster in 1992. Technical studies of lay-out, radiation safety, and remote handling of the very radioactive target-ion-source units were carried out [198, 199] during the following months. The design preferred by the Working Party was one with two separators and two target areas connected directly to a handling bay with industrial robots for safe handling of very large amounts of radioactivity. This solution made it possible to operate the two systems alternately^^ (in 'push-pull'), so that the radioactivity had time to 'cool off for a longer period before interventions by personnel in the target areas. A lay-out with one target area was proposed as a cheaper but also more risky alternative. Domingo from SIN looked into the economic aspects of the move. He assumed [200] that SIN would provide office and general laboratory space (at least 600 m^) for an on-site load of 50-60 persons and the use of all general services such as the electronics pool and purchasing office. The in-house group of about 25 persons would be provided by CERN. It was left open who should pay for the most expensive items, the building (11-15 MSFr) and its separators, hot-cells etc., but a sharing in some form between SIN, CERN and the ISOLDE collaboration was tacitly assumed. The technical plans were presented in a condensed form in a paper by Domingo et al. [201]. Figure 9.15, adapted from this paper, gives a good impression of the scale of the proposed installation. It is probably useful to look briefly at two precedents in order to understand the CERNSIN-ISOLDE relationship that was tacitly assumed in these deliberations. SIN had obtained an agreement that quantified the participation of German and Austrian research teams in its programme and had in return obtained financial contributions towards its operation from the two countries. The question was now whether it would be justified for CERN to sponsor ISOLDE in a somewhat similar way. Technically the answer was clearly yes, since, at the time when the 70 GeV accelerator at Serpukhov (U.S.S.R.) was the world's largest proton machine, CERN had participated in the construction of equipment for experiments and had maintained a team there for an extended period. An entirely different question was whether CERN would find such a solution desirable, which raised the issue of whether CERN had a responsibility for this area of research? ISOLDE had not forgotten Adams's 'priorities' and the final outcome of the 1972 debate (sects. 9.5.3 and 9.5.4) and had begun to fear that it was being lured into an alley that would lead via an ambitious proposal to general praise of the proposed programme's scientific merits and finally to a flat rejection on financial grounds. This would be the outcome that some, most Hkely, had hoped for from the start. This explains why the final proposal [170], which was adopted by the ISOLDE Committee on 6-7 November 1979 and immediately forwarded to the PSCC Committee, incorporated an alternative, which was the continued use of the SC as a dedicated injector for ISOLDE. The discussion of economy in the document shows that the problem was real enough. Although the SIN solution would become cheaper in the long run owing to its smaller operational costs, it showed a peak in investments during 1982-85, just in the middle of the LEP construction period. Both the document and its covering letter expressed the view that for the long-term

k

v,

2 c

Fig. 9.15 View of the SIN-ISOLDE building, planned as a side wing to the accelerator hall at SIN (Villigen, CH). The hot bay for handling very large radioactivities (left) has separate access and is completely separated by large amounts of shielding from the secondary-beam area and electronics huts (right). (See [2011).

396

The SC: ISOLDE and Nuclear Structure

future of the field, the SIN faciUty would be the ideal installation, but also that in the short run, defined as the next 5-7 years, the SC-ISOLDE would produce more physics. The letter also stressed the notion of responsibility: that the existing ISOLDE programme had become possible only because of European cooperation within the framework of CERN and that it was essential for its continuation at SIN that ISOLDE should remain a CERN activity. A couple of months later estimates of construction costs for the SIN project were submitted to the CERN Management by the EP Division Leader, Erwin Gabathuler [202]. For the solution with two separators the total cost was estimated to be 23.4 MSFr of which the building cost was 15 MSFr. The total cost for a facility with one separator was 17.3 MSFr. Apparently it was only a year later when the pendulum had begun to swing the other way that the PS Division Leader, Gordon Munday, was asked to provide forecasts of SC staff and running budgets for a continued operation at different levels of exploitation [203]. 9.7.2 THE DISCUSSIONS IN CERN'S COMMITTEES The PSCC met on 14 November 1979 under the chairmanship of Robert Klapisch. Its discussion about ISOLDE concluded (i) that the community centered around CERN had an undisputed leadership in its specialty and (ii) that CERN had a responsibility for maintaining this field, since there was no laboratory in the member states in a position to support an effort of the necessary magnitude. The PSCC therefore proposed that formal negotiations with SIN and the Swiss authorities should be undertaken immediately. It also decided to launch a call for 'declarations of interest' including also laboratories outside the ISOLDE collaboration. And finally the PSCC announced its intention to appoint external referees to review the programme that would emerge from this procedure. The last step was unusual for CERN but not unheard of, and the idea had, most likely, been cleared with van Hove. The point was that essentially all physicists at CERN who were knowledgeable in matters pertaining to ISOLDE were also actively involved, including, of course, Klapisch himself. The committee therefore felt that it would be more certain to be of service to CERN if its final recommendations were based on a peer review by nuclear physicists unconnected with ISOLDE. On the following day the Research Board^^ accepted the PSCC recommendations and also accepted to include in the CERN planning the possibility of a continued, reduced operation of the SC for a few years in a mode dedicated to ISOLDE. The latter decision meant that the possibility of the continuation of the programme, perhaps only during a transition period, was kept open. The future of the ISOLDE was discussed in a series of meetings of the Scientific Policy Committee. On 16-17 September 1980 [204] there was a presentation of the plans by Klapisch followed by a summary by Blaser of SIN's position and by a long general debate. One of the questions was whether the increase in beam intensity would have a major impact on the programme, to which representatives of ISOLDE (Hansen and Jonson),

The last defence of the Cyclotron: 1979-81

397

who had been invited for this part of the meeting, answered that there were several arguments in favour of a transfer to SIN: (i) The beam would be cheap because a meson factory is a very cost-efficient way of accelerating protons, and (ii) a more modern and safer facility would also produce more physics. Finally, (iii) a gain in intensity of one, maybe two, orders of magnitude was obviously important, but the scientific programme would not be changed qualitatively, at least not in the first five to seven years of operation. Klapisch added that only recently had experiments emerged at ISOLDE that required high intensity, such as some of the optical experiments and the work on x-rays (see sects. 9.6.2 and 9.6.6). Ingmar Bergstrom referred to a debate that had taken place in the Swedish CERN Committee shortly before. Its conclusion had been that ISOLDE should remain at CERN. He said that there was a danger of breaking up a collaboration that it had taken two decades to create, and also, very much in line with his position in the 1972 debate (sect. 9.5.4), that the contact with CERN was an important source of scientific and technical inspiration for the national laboratories in the member countries. He saw no need for any independent evaluation of ISOLDE'S activities. On the last point the Research Director General replied that he was in favour of an evaluation for two reasons. The first was that ISOLDE was used by only five of CERN's member states and the second that, to quote the minutes of the meeting, 'while in no way doubting the scientific merits of ISOLDE, one could ask why a facility of such quality had not been built elsewhere'. The last argument brings to mind the tendency of many at CERN during its first decades to have an inferiority complex towards the U.S.A.; in fact, on the tape recording of the discussion one hears that van Hove asked 'why didn't others do it, for example in the States?' The Director General designate, H. Schopper, was in favour of a continuation of operation of ISOLDE at CERN at the level foreseen in the scientific activities document (CERN/SPC/456/Rev.) since it 'would be many years before the costs arising from the transfer and upgrading of ISOLDE could be offset by the savings made from the closure of the S C . Not surprisingly, it was his view that was to prevail. ISOLDE was discussed again in the SPC on 29 October [205], in which Klapisch summarized progress. He felt that it would be a mistake to miss the opportunities offered by SIN and suggested that in order to reconcile 'the short term and long term^^ requirements', the new projects should be shifted in time so that any major capital outlay would be incurred after LEP construction. At the meeting of the Research Board on 29 January 1981 it was decided that further information was needed, but from the notes taken during the meeting by Y. Goldschmidt-Clermont [206] it was clear that Schopper favoured a continuation at CERN in the short term, followed in the long term by SIN under other (meaning non-CERN) arrangements. This meant, as pointed out by Klapisch, the necessity of finding 'a responsible third body with a budget'. The next important discussion [207] in the SPC took place on 25 February 1981 and was opened by a presentation by Klapisch, who reported that the external referees 'had confirmed that the importance of ISOLDE was beyond doubt'. Two members (Cabbibo, Notes: pp. 404 ff.

398

The SC: ISOLDE and Nuclear Structure

Bergstrom) requested more detailed information on the contents of the letters from the referees. The Chairman, V.L. Telegdi, said that the SPC should be given an opportunity to study them before a decision was reached although it would mean a further unfortunate delay. In retrospect it appears surprising that these letters, which had been taken to be of such key importance at an early stage, had not been made available to the SPC. It is tempting to guess that the new CERN management, which Klapisch himself was soon to join as a Research Director, had found the letters too positive, i.e. that they would justify larger expenditures than a Directorate, which saw LEP as its one and only essential task, was prepared to make. 9.7.3 A DECISION ON THE FUTURE OF ISOLDE For the next SPC Meeting a collection of documents [208] had been prepared including extracts of PSCC and RB documents and a list of the 31 'Letters of Interest' received from interested scientists. The most enlightening part from an historical point of view, however, is the collection of letters from the eight referees^^, two nuclear theorists, four nuclear experimentalists, one atomic physicist and one solid-state physicist, letters which provide a rare picture of how this research was viewed by eminent outsiders, who in the past had had Httle or no contact with ISOLDE. The programme obtained very positive comments from all the referees; three of them were in favour of an all-out effort to construct the ultimate facility, the SIN-ISOLDE. The others, for a variety of reasons, preferred continued activity under CERN's auspices. The following are extracts from the comments given by two of the most perspicuous of the majority. D. Allan Bromley, at the time science adviser at the White House to President George Bush, wrote: (1) f...J On several occasions within the last years when I have been asked to provide a review of the most challenging and significant developments in worldwide nuclear science, I have had occasion to take a look at the ISOLDE output and, in each case, found examples for which I was searching in that work. Obviously, the facility was well conceived initially, and it has attracted to it an outstanding international group of nuclear scientists who have, on the whole, selected very wisely, in terms of problems for study [...] (2) The question sometimes arises as to why other major activities of the scope of ISOLDE have not been mounted in the U.S. and elsewhere. I believe that the answer is rather simple and is connected to my comment above. The ISOLDE group got such a head start on the rest of the world activity in this field that people were very reluctant to attempt to mount a competitive operation. The largest such activity in the U.S. is clearly the UNISOR project associated with Oak Ridge National Laboratory accelerators, but this is very much smaller than that at ISOLDE [...] (3,4) [...] it is clear that almost without exception one can find some aspect of the program that would benefit from the proposed move to SIN, (but) I would not consider that the

The last defence of the Cyclotron: 1979-81

399

change, in any case, would represent a quantum jump, [...] (and) I have not been overwhelmed by examples of totally new science that the move would make possible... (5) It is also clear [...] that there is still excellent science to be done with the existing facility at CERN, particularly if it were possible to obtain more running shifts and more research space [...] (7) [...] I do not find evidence of the dedicated, experienced, group of people who would actually accomplish the move to SIN [...] Without such a dedicated group of people, all of whom are prepared to devote several years of their professional careers to this move, largely for the public good, the whole project would appear doomed. It may well be that such a group exists. I have not, however, seen any evidence for it [...] W ["•] (J) y^ould suggest that ISOLDE should stay at CERN [...] (10) [...] The experimental work shows real elegance and expertise, and I have the feeling that the science could be even more sharply pointed toward questions of central topical interest, if more theorists were directly associated with the project [...] It will be seen that Bromley inadvertently answered the question that had been raised by van Hove (sect. 9.7.2). The following are extracts from the comments made by Hans J. Specht: [...] if the nuclear physics history of the seventies will be written, the wealth of results obtained on nuclei off stability at ISOLDE will take a very prominent place, comparing with those from the seemingly more glamorous field of heavy ion physics [...] I therefore strongly plead for a continued and substantial support of the project [...] Any geographical change should not lead to a years long interruption [...] Reading through the impressive number of letters of interest it is noteworthy that the majority of them argues about the virtues of an increased current in rather vague terms (quite often beam time seems to be the problem). [...] only (the x-ray experiment) makes a convincing case [...] Much higher gain factors than 3-16 may be buried in future developments of the target-ion-source system [...] (to) put it in radical terms - if the same manpower [...] needed for the installation at SIN were put into the target-source problem, where would be the greater pay-off? [...] I favour, in conclusion, a continuation of the ISOLDE 2 physics programme for the next few years [...] a decision on the site could be delayed by another 1-2 years without hurting progress in physics. [...] detailed thoughts could be given to an integration of an accelerator for radioactive ions into the concept right from the start [...] Specht elaborated his views on the acceleration of radioactive ions in a footnote, in which he suggested that a workshop should be arranged on the subject. In hindsight it is regrettable that this suggestion was neglected by all who knew of it. As has been mentioned in sect. 9.5.5, the idea had been considered and rejected at the 1977 Workshop on Intermediate Energy Physics. It came to Ufe again in the late eighties under the impact of important experiments in nuclear physics carried out with the Bevalac (Berkeley) and GANIL (Caen) and by the realization that these techniques had important appUcations in

Notes: p. 405

400

The SC: ISOLDE and Nuclear Structure

nuclear astrophysics. At the time of writing^^ there is a considerable number of working experiments and projects in this field. At its Meeting [208] on 28 April 1981 the SPC then, as a final conclusion, 'approved the idea to postpone moving ISOLDE outside CERN, specifically to SIN, and persisted in its previously formulated recommendation, that the beam time of 4000 hours at the SC be preferentially used by ISOLDE'. The management interpreted this as favouring a continuation of heavy-ion and fiSR activities 'at a modest level' to be decided by the PSCC [209]. 9.7.4 EPILOGUE The final decision came as no surprise to those involved. People at both SIN and ISOLDE had felt for some time that the whole procedure was a ritual dance and that the SIN-ISOLDE project was doomed. Doomed at CERN because neither the old nor the new Directorate were willing to invest in strengthening this field, and doomed at SIN, if I may permit myself to conjecture, because no major Swiss physics groups had shown serious interest in joining ISOLDE, so that the Federal Government in Bern for this reason alone was unlikely to sponsor a costly construction programme. In any case the communication lines between ISOLDE and SIN had already been silent since the autumn of 1980. The LEP construction period 1981-88 was a lesson for those at ISOLDE and SIN who still felt that an opportunity had been missed. CERN's economy was stretched to the limit. The laboratory took large loans, cut services to physics users to a minimum, stopped maintaining buildings and equipment, and took risks on the operational safety of all machines so that it was no longer uncommon for an outside team to loose important parts of its machine time because stand-by duty for a CERN accelerator technician, who could have fixed a technical mishap, was no longer paid for. ISOLDE managed to scrape through, but would have been badly off" with a costly and ambitious new programme at a moment when the internal attitude was, to quote a senior member of the administration, 'Let the last person leaving switch off the lights'. The long discussion about the future of ISOLDE had cost much eff*ort for everybody involved, but it had also cleared the air for a long time to come. The main immediate consequence was that ISOLDE was allowed to build up a second experimental area in the zone designated 'proton experimental room' in Fig. 4.3 on p. 108 of ref. [2] and to place the target for the second isotope separator, a high-resolution spectrometer referred to as ISOLDE-3, inside the cyclotron hall [199]. This solution had been a long-standing wish of ISOLDE, but had always been refused because of the non-negligible risk of a major radioactive contamination in the area of the cyclotron itself. With ISOLDE taking over the role as the principal user, this risk was now acceptable. This installation served a large number of users during the eighties, and shortly before the final shutdown of the installation in 1990 the high-resolution separator was for the first time used to separate mass doublets, namely the pair ^^K and ^^Ca, where the latter, produced in minute quantities,

Concluding remarks

401

happened to be the isotope of interest [210]. The careful weighing of all arguments that had taken place during 1979-81 probably also had paved the way for the final decision in 1989 to transfer ISOLDE to the PS Booster [211]. 9.8 Concluding remarks The present account of how some low- and medium-energy physicists interacted with CERN is not impartial. I have chosen to view the events from the angle from which I saw part of them some years back, that of an external physicist who is at CERN, not as a volunteer but to work on his own projects. I hope that it is absolutely clear that I consider the opposite angle both legitimate and necessary, in other words that a management must ask 'Do we really need these people? Is what they are doing interesting?' I also hope that the vehemence of the external users will be viewed as an indirect tribute to the important role as a centre of excellence that CERN has played and continues to play in European university physics and higher education. Science policy and the making of decisions concerning the SC have been given a prominent place in the present chapter because, as mentioned above, this is an essential part of modern science, which cannot be pursued by free individuals in their spare time and at their own cost. Those wishing to participate must accept the conditions: that conflicts of interest exist, that a case must be made, that independent experts will be consulted, and that arguments will be considered and decisions taken. Many university physicists will only admit with much hesitation that such a procedure, in their words 'bureaucratic', is perhaps necessary in big science, but in my experience the principles of documentation, openness and an impartial hearing are valuable at all levels. They allow for a more fair and better balanced making of decisions than is usual in the civil service and at the universities, where quick decisions and nepotism have a freer run. In this respect CERN has had a beneficial influence on the style of physics management in some of the member countries. There is maybe a side benefit in that the transparent structure of a modern scientific organization makes it possible to retrace the events, as has been done in the present paper. The pessimist will add that the closed system also has its advantage; mistakes are forgotten as discretely as they were made. Figure 9.16 is a quantitative illustration of how the utilization of the SC developed over the years, but it also serves as a reminder that there are many fundamental activities in science that are so difficult that the appropriate unit of time is one generation. To take two famous examples, two generations later we have not yet finished with the boson that lies behind Fermi's theory of beta decay, nor with the transuranic elements for which he was awarded the Nobel Prize. As an example from ISOLDE'S area it may reasonably be argued that the research on far-unstable nuclei began 30 years before the start of the time scale in Fig. 9.16, namely with the discovery [212] in Copenhagen in 1936 of ^He, the first case of a nucleus situated at the neutron drip line. The second nucleus at the neutron drip Une appeared exactly 30 years later, and it is almost another 30 years later again that it is Notes: p. 405

402

The SC: ISOLDE and Nuclear Structure

800

600H

40(H

200H

Fig. 9.16 Operating statistics for the SC from 1967 to the final shut-down on 17 December 1990 (courtesy H. Haas, CERN). The operating time for ISOLDE was limited during the later years by the capacity of the operating group rather than by the machine time available. This was the main motivation behind the wish for a second, independent area and 'push-pull' operation. (See sect. 9.7.1).

becoming clear that this class of nuclei has a very special character (see the remarks in sect. 9.6.4). The SC, with 33 years of active service [5] is one of the accelerators to have served the longest in front-line research. It made essential contributions to particle physics very early, and it continued to support important programmes in atomic, nuclear, intermediateenergy and soHd-state physics until the day when it was worn out. What happened was not that it no longer could be repaired, every piece being individually designed and manufactured, but rather that it represented a technology that had become outdated and which consumed too much manpower. The SC was one of the last and largest of a type of accelerator that will no longer be built, and it was representative of the engineering and science of the fifties, based on mechanics (see Fig. 9.9) and on analogue regulation, where modem technology favours electronics and digital control. For these reasons it was briefly discussed whether it would be possible to preserve the cyclotron in its vault as a museum (see the correspondence in [8]). Very much in line with other events told here, it seemed for a short while that the museum solution had a chance because it would be cheaper than a 'de-commissioning' as this process is called in officialese. On second thoughts, however, the metal value of the iron in the cyclotron yoke got the upper hand, and the machine will

Notes

403

go the same way as most European medieval castles, which ended up serving as quarries for the surrounding villages. I am indebted to Maria Fidecaro for advice on the CERN Committee system, to Roswitha Rahmy for help with the CERN archives, and to Alexis C. Pappas for correspondence and for the loan of documents from his personal archives. Throughout the long time that I have been involved with CERN, Torleif Ericson has been an invaluable source of information on physics, poUtics and people and I have greatly appreciated his help during all phases of the present task. I wish to thank him and also Bjorn Jonson, John Krige, Geoffrey Oades and Karsten Riisager for advice on the contents and presentation of the final manuscript.

Notes 1. Present were, according to the minutes [13]: G. Backenstoss, Aa. Bohr, G. Charpak, L. Dick, P.M. Endt, T. Ericson, L. Foldy, W. Gentner, K. Gottfried, P. LapostoUe, E.G. Michealis, A. Pappas, P. Preiswerk, G. Rudstam, J.C. Sens, K. Siegbahn, V. Soergel, P.G. Sona, I. Talmi, J. Teillac, J. Thirion, L. van Hove, J.D. Walecka, V.F. Weisskopf and D. Wilkinson. 2. We note for the uninitiated that NP stands for nuclear physics', and that the Division was responsible for CERN's counter experiments. Thus 'nuclear' here as well as in the name CERN itself and in the name NPRC mentioned above could be translated as 'subatomic'; it has nothing to do with the sense in which we talk about nuclear physics in the present chapter. 3. According to the minutes [19] of this, the seventh and last, meeting of the NSC, the following were present: Backenstoss, Brianti, Ericson, Herz, Kjelberg, Michaelis, Nielsen, Paul, Soergel. 4. We remind readers not famiUar with atomic physics that states with orbital angular momentum /= 0,1,2,3,4... are denoted s,p, dj,g... 5. Among those involved were O. Almen (Gothenburg), G. Andersson (Uppsala, later Gothenburg), I. Bergstrom (Stockholm), R. Bernas (Paris, later Orsay), J. Kistemaker (Amsterdam), K.O. Nielsen (Copenhagen, later Aarhus), W. Paul (Bonn), and many others. 6. The members of the working party were: G. Andersson (chairman), R. Bernas (Orsay), B. Hedin (CERNSC, see [2] pp. 98-100), K.O. Nielsen (Aarhus), and O. Skilbreid (Copenhagen). Among the other participants in the meeting were R. Foucher (Orsay), T. Ericson (CERN), E. Hageb0 (Oslo), A. Kjelberg (Oslo), O.B. Nielsen (Copenhagen), A.C. Pappas (Oslo), G. Rudstam (CERN), S. Sundell (CERN) and R.J. Walen (Orsay), as can be seen from the minutes in [92]. 7. Present at this meeting were: G. Andersson (Gothenburg), R. Bernas (Orsay), R. Brandt (Heidelberg), G. Brianti (CERN), A. Kjelberg (CERN), K.O. Nielsen (Aarhus), O.B. Nielsen (Copenhagen), A.C. Pappas (Oslo), B. Povh (representing W. Gentner, Heidelberg) and G. Rudstam (Studsvik). 8. The ordering was to be alphabetical by home institute, a system that has persisted until quite recently. From the same meeting dates the tradition, still surviving to this day, to let the name ISOLDE Collaboration appear, usually as a 'corporate author', on the title page of papers. 9. Scandinavians view themselves as shy of conflict. They, in general, prefer to suffer silently rather than to run the risk of being branded troublemakers. In addition, they are able to remember their grievances over remarkably long periods, somewhat Uke the Pope's mule in Daudet's short story.

404

The SC: ISOLDE and Nuclear Structure

10. This concept is taken from statistical nuclear physics, see e.g. Lynn [109]. A strengh function is the product of the level density with the average reduced transition probability to (or from) the family of closely spaced levels in question. 11. In 1987 Ernst W. Otten became the first German recipient of the Gentner-Kastler Prize awarded jointly by the French and German physical societies [111]. The role played by Wolfgang Gentner in the early development of ISOLDE has been mentioned in sects. 9.2.2, 9.2.3 and 9.4.2. 12. The late Sven Gosta Nilsson, mentioned previously in sect. 9.2.4, occasionally referred to ISOLDE as 'an underground church in the heathen temple of high-energy physics', a joke referring mainly to the location of the experimental area (Figs. 9.5 and 9.10). 13. The fact that the research staff frequently was on loan from the home laboratories and never permanently appointed probably also helped to avoid some of the friction that occasionally plagued the relations between CERN and its users [116]. See also Krige (this volume). 14. The engineering behind the rotary condenser was in the hands of H. Beger (RF group leader), S. Talas (mechanical design), A. Fiebig, R. Hecken and R. Hohbach (theory and models), and C. Hill (vacuum). 15. The three users present were G. Backenstoss, J. Deutsch and P.G. Hansen. Two more, V. Soergel and E. Zavattini, had been invited but were unable to come. Also present were the Director General W. Jentschke, the NP and MSC Division Leaders H. Schopper and E.G. MichaeHs, and O. Kofoed-Hansen, who had replaced G. Ekspong as Chairman of the Physics III Committee. 16. As is most often the case when the words eventual, eventually appear in a CERN context, it is here impossible to see whether they are used in their English meaning of 'ultimately resulting' or in the more loose, hypothetical meaning that similar words have in e.g. Danish, Dutch, French, German, Swedish - and that eventual had in EngHsh until the end of the 18th century i.e. 'possible'. 17. It is probably evident that Adams's and Flowers's weighing of the SPS against SCIP left out the fact that the former was one hundred times more expensive than the latter. This is the gambit that in scientific politics is called 'setting priorities'. 18. The same latent conflict is symbolized by the recent re-naming of the Experimental Physics Division (EP) to Particle Physics Experiments (PPE). 19. The final composition of the panel was: G. Backenstoss (Karlruhe), E.T. Boschitz (Karlsruhe), C. Cernigoi (Trieste), P.G. Hansen (Aarhus and CERN, Chairman), H. Hofer (Bern, later Zurich), O.B. Nielsen (Copenhagen), V. Soergel (Heidelberg), N.W. Tanner (Oxford) and E. Zavattini (CERN). 20. The appearance of more efficient but less selective and far less discriminating spectrometers based on silicon solid-state detectors could also be mentioned, but was probably less important. 21. Bernas, who had been one of the founders of ISOLDE (see sect. 9.4.2), had died in July 1971. 22. The sign convention for T^ is opposite from that used in particle physics. 23. In its presentations the group often pointed out that the experiment also represented the first discovery of a new alkali D-line since Bunsen and Kirchoff" discovered the corresponding transitions in rubidium and caesium around 1860. It is almost overwhelming to consider the number of new tools and concepts in physics that were on the 'critical path' to this next, in principle simple, step. 24. Members of the ISOLDE-3 Working Party were B. Jonson (Chairman), E. Kugler, H.L. Ravn, S. Sundell, all from the CERN-ISOLDE group, F. Blythe from the SC Engineering Office, and P.G. Hansen (Aarhus), who participated as the Chairman (1979-81) of the ISOLDE collaboration. 25. The ISOLDE coordinator, Bjorn Jonson, had in 1977 studied an extension involving a second target area in the proton hall of the SC. The arrangement that finally resulted at the SC also incorporated two separators, the old one (ISOLDE-2) and one in the proton hall (ISOLDE-3), a high-resolution instrument [199]. A similar lay-out was chosen for the facility constructed from 1990 onwards at the PS-Booster. 26. We remind readers that this committee consists of CERN management, committee chairmen, coordinators (when necessary), and some external representatives. It is essentially equivalent to its predecessor, the NPRC, mentioned earlier in this chapter.

References

405

27. Towards the mid-eighties, as high-energy physics was becoming increasingly commercial, the same phenomenon would have been referred to as a 'cash-flow problem'. 28. The referees were D.A. Bromley (Yale), V. Gillet (Saclay), P. Kienle (TU Munich), S. Lundquist (Chalmers), B. Mottelson (NORDITA), O. Nathan (Niels Bohr Institute), G. zu Putlitz (Heidelberg), and H.J. Specht (Heidelberg). 29. This was written in 1992. An accelerator for radioactive ions connected to the ISOLDE Facihty at the PS Booster was approved by the Research Board on February 9, 1995. This machine, designed for experiments in nuclear and astrophysics and called REX-ISOLDE, is currently under construction.

References The number(s) in curly brackets {} refer to the section(s) in which this reference appears. [1] A. Hermann, J. Krige, U. Mersits, D. Pestre and L. Weiss, History of CERN, Vol. II, Building and Running the Laboratory 1954-65, (North-Holland, Amsterdam 1990) pp. 1-880. {1} [2] Ulrike Mersits, The 600 MeV synchro-cyclotron: constructing CERN's smaller accelerator and the machine's role in the scientific programme, in ref. [1] pp. 95-137. {1, 7.4} [3] D. Pestre, The organization of the experimental work around the proton synchrotron, 1960-65, the learning phase, in ref [1] pp. 429-502 {1,2.2} [4] W.F. Weisskopf, in CERN rapport annuel 1965, (1966) p. 21. {1} [5] Proceedings of the SC 33 Symposium held at CERN, April 22nd, 1991 (ed. G. Fidecaro), Physics Reports 225 (1993) 1-191. {1, 8} [6] International Conference on High Energy Physics and Nuclear Structure, CERN February 25-March 1, 1963 (T. Ericson ed.) CERN Report 63-28, July 1963. {2.1, 3.2} [7] T. Ericson and T. Mayer-Kuckuk, Ann. Rev. Nucl. Sci. 16 (1966) 183. {2.1} [8] Discussion on the Future of the ISOLDE Programme 1979-81. P.G. Hansen file. Extract from the personal files of A.C. Pappas (Oslo). Notes and correspondance. Memoranda and Correspondence in Connection with the Debate about the SC Improvement Progranmie. Taped interviews with G. Backenstoss, T. Ericson, J.C. Sens, and J.P. Stroot.. CERN Archives SYSNO 0012990. {2.3, 7.1} [9] T.E.O. Ericson, interviewed by P.G. Hansen at CERN, 17 October 1991. Tape in CERN Archives, ref. [8]. {2.1} [10] I. Bergstrom, Why and How Should We Investigate Nuclides Far Off the StabiUty Line?, Nucl. Instr. Meth. 43 (1966) 116 and 129. {2.1} [11] Lysekil Conference 1966. Nuclides Far Off the Stability Line, (eds. W. ForsUng, C.J. Herrlander and H. Ryde), (Almqvist and Wiksell, Stockholm) 686 pp. Also pubUshed as Arkiv for Fysik 36 (1967) 1-686. {2.1,4} [12] T. Ericson, Possibilities for nuclear structure research at CERN, Internal CERN note 3 February 1964, in ref. [92]. {2.1, 3.3} [13] Alexis C. Pappas, extract from his personal files with a handwritten summary (six pages, letter to P.G. Hansen) dated September 1990 in ref. [8] {2.1, 2.3} [14] Minutes of the 1st meeting of the Emulsion Experiments Committee held at CERN on December 15th, 1960, doc. EmC 61/1 of 1 March 1961, in the A.J. Herz file, EMC Documents 1961-62. The functions of the committees had been defined in Council Document 344 Rev. 4, 1960, Nov. 14th. {2.2} [15] Memorandum from T. Ericson and P. Preiswerk to the Director General, 'Proposal for a Nuclear Structure Committee', 27 August 1964, in ref. [92]. {2.2} [16] L. van Hove file. CERN/ARCH/TH/44, A 801, TH22204. This contains the minutes of NSC meetings No. 2, 3, 5, 6 and 7. The 7th and last meeting was held on 13 June 1966. {2.2}

406

The SC: ISOLDE and Nuclear Structure

[17] L. van Hove, memorandum of 10 March 1966 with an enclosed preliminary proposal, addressed to T. Ericson and A.J. Herz, in ref. [92]. {2.2} [18] Draft niinutes of the meeting of the CERN Emulsion Experiments Committee held on 24 May 1966 (EmC 66/3) in the A.J. Herz file, EMC Documents 1963-66. {2.2} [19] Minutes of the seventh meeting of the Nuclear Structure Committee held on 12 June 1966, in ref. [92]. {2.2} [20] Contrary to this, the EEC never had a 'Preparatory Conmiittee' (M. Fidecaro, personal communication 1990) but according to Pestre in ref. [3] p. 467 the decisions, at least during certain period, were left to Treiswerk and a few of his staff...assisted by an external member, who reviews the situation periodically.' Maria Fidecaro suggests that this should be interpreted to mean that PP handled running business and the preparations for meetings. {2.2} [21] M. Hai'ssinsky, La chimie nucleaire et ses applications, Masson et Cie, Paris (1957) pp. 1-651. {2.3} [22] Ulrike Mersits in ref. [2] pp. I l l , 115-6. {2.3} [23] G. Andersson, B. Hedin and G. Rudstam, Nucl. Instr. Meth. 28 (1964) 245 {2.3} [24] W. Gentner, K. Goebel, A.C. Pappas and G. Rudstam, The Activity of theNuclear Chemistry Groups at CERN, memorandum to Professor V.F. Weisskopf, 15 December 1961, pp. 1-15. (The plural in the title is significant. Goebel's activity, mainly aiming at determining absolute monitor cross-sections, was considered an independent branch, occasionally referred to as the Spallation Group.) in ref. [13]. {2.3} [25] G. Rudstam, Z. Naturforsch. 21a (1966) 1027. {2.3} [26] G.M. Raisbeck and F. Yiou, Phys. Rev. Lett. 27 (1971) 875 and 29 (1972) 372; Phys. Rev. C 6 (1972) 685. {2.3} [27] Aa. Bohr and B.R. Mottelson, Nuclear Structure, (Benjamin Inc., N.Y.), Vol. I (1969) pp. 1^71 and Vol. II (1973) pp. 1-748. {2.4} [28] R.K. SheHne, T. Sikkeland and R. Chanda, Phys. Rev. Lett. 7 (1961) 446; see also R.K. Sheline, Revs. Mod. Phys. 32 (1960) 24. {2.4} [29] S.G. Nilsson and J. Damgaard, Physica Scripta 6 (1972) 81. {2.4} [30] Superheavy Elements - Theoretical Predictions and Experimental Generation (S.G. and N.R. Nilsson eds.), Physica Scripta lOA (1974) 1-184. {2.4} [31] P. Armbruster, Ann. Rev. Nucl. Part. Sci. 35 (1985) 135-194. {2.4} [32] G. Miinzenberg, Rep. Prog. Phys. 51 (1988) 57-104. {2.4} [33] Decisions of the NPRC, in CERN/ARCH/NP/45, 1960-74, (NP 22888). {3, 5.4} [34] Ulrike Mersits in ref. [2] pp. 100-103, 114, 123-126. {3.1}{5.1} [35] G. Backenstoss, interviewed by P.G. Hansen in Basel, 21 October 1991. Tape in CERN Archives ref. [8]. {3.1} [36] P. Brix and H. Kopfermann, Z, Physik 126 (1949) 344. {3.1} [37] P. Brix, R. Engfer, U. Hegel, D. Quitman, G. Backenstoss, K. Goebel and B. Stadler, Phys. Lett. 1 (1962) 56. {3.1} [38] M.B. Steams and M. Steams, Phys. Rev. 105 (1957) 1573. {3.1} [39] C.S. Johnson, E.P. Hincks and H.L. Anderson, Phys. Rev. 125 (1962) 2102. 3.1 [40] H.L. Acker, G. Backenstoss, C. Daum, J.C. Sens and S.A. De Wit, Phys. Lett. 14 (1965) 317; Nucl. Phys. 87(1966) 1-50. {3.1} [41] J.C. Sens, interviewed by P.G. Hansen at CERN, 14 October 1991. Tape in CERN Archives, ref. [8]. {3.1, 3.4} [42] S.A. De Wit, G. Backenstoss, C. Daum, J.C. Sens and H.L. Acker, Nucl. Phys. 87 (1967) 657-702. 3.1 [43] G. Backenstoss, S. Charalambus, H. Daniel, H. Koch, G. Poelz, H. Schmitt and L. Tauscher, Phys. Lett. 25B (1967) 547. {3.1} [44] T. Ericson and W. Weise, Pions and Nuclei, Clarendon Press, Oxford (1988), pp. 1-479. {3.2, 3.4} [45] M. Ericson and T.E.O. Ericson, Ann. Phys. (N.Y.) 36 (1966) 323. {3.2} [46] T.E.O. Ericson, Pion-Nuclear Interactions at the SC and Beyond, Lecture given at the SC-33 Memorial Symposium, 22 April 1991. In [5]. {3.2}

References

407

[47] G. Backenstoss, Ann. Rev. Nucl. Sci. 20 (1970) 467-508. {3.2, 3.3} [48] G. Backenstoss, Lecture given at the SC-33 Memorial Symposium, 22 April 1991. In [5]. {3.2} [49] G. Backenstoss, S. Charalambus, H. Daniel, H. Koch, G. Poelz, H. Schmitt and L. Tauscher, Phys. Lett. 25B (1967) 365. {3.2} [50] D.A. Jenkins and K.M. Crowe, Phys. Rev. Lett. 16 (1966) 667; D.A. Jenkins et al., ibid. 17 (1966) 1. {3.2} [51] G. Poelz, H. Schmitt and L. Tauscher, G. Backenstoss, S. Charalambus, H. Daniel and H. Koch, Phys. Lett. 26B (1968) 331. {3.2} [52] H. Schmitt and L. Tauscher, G. Backenstoss, S. Charalambus, H. Daniel, H. Koch and G. Poelz, Phys. Lett. 27B (1968) 530. {3.2} [53] J. Hixfner, L. Tauscher and C. Wilkin, Nucl. Phys. A231 (1974) 455.{3.2} [54] P.J. Mohr, Atomic physics tests of quantum electro dynamics, in Atomic Physics 5 (eds. R. Marrus et al.). Plenum Press, New York (1977) pp. 37-62. {3.3} [55] E. Zavattini in ref. [85] pp. 43-74. {3.3} [56] A. Bertin, G. Carboni, J. Duclos, U. Gastaldi, G. Gorini, G. Neri, J. Picard, O. Pitzurra, A. Placci, E. Polacco, G. ToreUi, A. Vitale, E Zavattini and K. Ziock, Phys. Lett. 55B (1975) 411; G. Carboni et al. Nucl. Phys. A278 (1977) 381.{3.3} [57] G. Backenstoss, S. Charalambus, H. Daniel, Ch. Von der Malsburg, G. Poelz, H.P. Povel, H. Schmitt and L. Tauscher, Phys. Lett. 31B (1970) 233. {3.3} [58] G. Backenstoss, H. Daniel, H. Koch, Ch. Von der Malsburg, G. Poelz, H.P. Povel, H. Schmitt and L. Tauscher, Phys. Lett. 43B (1973) 539. {3.3} [59] H.K. Walter, J.H. Vuilleumier, H. Backe, F. Boehm, R. Engfer, A.H.von Gunten, R. Link, R. Michaelsen, C. Petitjean, L. Schellenberg, H. Schneuwly, W.U. Schroder and A. Zehnder, Phys. Lett. 40B (1972) 197. {3.3} [60] L. Tauscher, G. Backenstoss, K. Fransson, H. Koch, A. Nilsson and J. De Raedt, Phys. Rev. Lett. 35 (1975) 410. {3.3} [61] M.S. Dixit, A.L. Carter, E.P. Hincks, D. Kessler, J.S. Wadden, C.K. Hargrove, R.J. McKee, H. Mes and H.L. Anderson, Phys. Rev. Lett. 35 (1975) 1633. {3.3} [62] Particle Data Group, Review of Particle Properties, Phys. Lett 204B (1988) 1^86. {3.3} [63] B. Jeckelmann, T. Nakada, W. Beer, G. de Chambrier, O. Elsenhans, K.L. Giovanetti, P.F.A. Goudsmit, H.J. Leisi, A. Ruetschi, O. Pillier and W. Schwitz, Phys. Rev. Lett. 56 (1986) 1444. {3.3} [64] P.G. Hansen, Nature 328 (1987) 476. 3.4 [65] L. Gilly, M. Jean, R. Meunier, M. Spighel, J.P. Stroot, P. Duteil and A. Rode, Phys. Lett. 11 (1964) 244; 19 (1965) 335. {3.4} [66] J.P. Stroot, interviewed by P.G. Hansen at CERN, 18 October 1991. Tape in CERN Archives, ref. [8]. {3.4} [67] F. Binon, P. Duteil, J.P. Garron, J. Gorres, L. Hugon, J.P. Peigneux, C. Schmit, M. Spighel and J.P. Stroot, Nucl. Phys. B17 (1970) 168. {3.4} [68] F. Binon, V. Bobyr, P. Duteil,M. Gouanere, L. Hugon, J.P. Peigneux, J. Renuart, C. Schmit, M. Spighel and J.P. Stroot, Nucl. Phys. B33 (1971) 42. {3.4} [69] J.J. Domingo, B.W. AUardyce, C.H.Q. Ingram, S. Rohlin, N.W. Tanner, J. Rohlin, E.M. Rimmer, G. Jones and J.P. Girardeau-Montaut, Phys. Lett. 32B (1970) 309. {3.4} [70] C. Wilkin, C.R. Cox, J.J. Domingo, K. Gabathuler, E. Pedroni, J. Rohlin, P. Schwaller and N.W. Tanner, Nucl. Phys. B62 (1973) 61. {3.4} [71] R. Baader, R. Engfer, K. Hesse, E. Kankeleit, U. Schroder, H.K. Walter and K. Wien, Phys. Lett. 27B (1968) 425. {3.5} [72] R. Baader, R. Engfer, E. Kankeleit, W.U. Schroder, H.K. Walter and K. Wien, Phys. Lett. 27B (1968) 428. {3.5} [73] H. Backe, R. Engfer, U. Jahnke, E. Kankeleit, R.M. Pearce, C. Petitjean, L. Schellenberg, H. Schneuwly, W.U. Schroder, H.K. Walter and A. Zehnder, Nucl. Phys. A189 (1972) 472. {3.5}

408

The SC: ISOLDE and Nuclear Structure

[74] C. Petitjean, H. Backe, R. Engfer, U. Jahnke, K.H. Lindenberger, H. Schneuwly, W.U. Schroder and H.K. Walter, Nucl. Phys. A189 (1972) 472. {3.5} [75] H. Backe, R. Engfer, E. Kankeleit, R. Link,R. Michaelsen, C. Petitjean, L. Schellenberg, H. Schneuwly, W.U. Schroder, J.L. Vuielleumier, H.K. Walter and A. Zehnder, Nucl. Phys. A234 (1974) 469. {3.5} [76] J.P. Deutsch, Lecture given at the SC-33 Memorial Symposium, 22 April 1991. In [5]. {3.5} [77] J.P. Deutsch, L. Grenacs, J. Lehmann, P. Lipnik and P.C. Macq, Phys. Lett. 28B (1968) 178. {3.5} [78] L. Tauscher, G. Backenstoss, S. Charalambus, H. Daniel, H. Koch, G. Poelz and H. Schmitt, Phys. Lett. 27B (1968) 581. {3.5} [79] H. Daniel, Die Naturwissenschaften 55 (1968) 314. {3.5} [80] J.H. Brewer and K.M. Crowe, Ann. Rev. Nucl. Part. Sci. 28 (1978) 239-326. {3.5} [81] E. Karlsson, O. Hartmann and L.-O. Norlin, Local Magnetic Fields in Ferromagnets Studied by Positive Muon Precession, PhIII-74/59 of 4 December 1974. {3.5} [82] Muon Spin Rotation (Proc. 1st Topical Meeting), eds. F.N. Gygax, W. Kiindig and P.F. Meier, Hyperfine Interactions 6 (1979) 1^50 {3.5} [83] Muon Spin Rotation (Proc. 2nd Topical Meeting), eds. J.H. Brewer and P.W. Percival Hyperfine Interactions 6 (1979) 1^50 {3.5} [84] E. Karlsson, Physics Reports 82 (1982) 271-338. {3.5} [85] Exotic Atoms. Proceedings of the First Course of the International School of Physics of Exotic Atoms, Erice 1977 (G. Fiorentini and G. TorelU eds.), publ. by Laboratori Nazionali di Frascati (1977) pp. 1-510. {3.3,3.5} [86] Exotic Atoms *79. Fundamental Interactions and Structure of Matter (K. Crowe et al. Eds.), Plenum Press, New York (1979), pp. 1^03. {3.5} [87] Electromagnetic Isotope Separators and Their AppHcations (eds. J. Koch and K.O. Nielsen), Nucl. Instr. and Methods 38 (1965) pp. 1-325. {4.1} [88] E. B0gh, J.A. Davies and K.O. Nielsen, Phys. Lett. 12 (1964) 129; J. Lindhard, Mat.-Fys. Medd. Dan. Vid. Selsk. 34 (1965) No. 14. {4.1} [89] O. Kofoed-Hansen and K.O. Nielsen, Phys. Rev. 82 (1951) 96; Kgl. Danske Videnskabernes Selskabs Mat. Fys Medd. 26 (1951) No. 7; O. Kofoed-Hansen, Proc. 3rd International Conference on Nuclei Far From Stability, CERN Yellow Report 76-13 (1976) 65. {4.1} [90] O. Kofoed-Hansen and P. Kristensen, Phys. Rev. 82 (1951) 95: Kgl. Danske Videnskabernes Selskabs Mat. Fys Medd. 26 (1951) No. 6. {4.1} [91] G. Rudstam and G. Andersson, NP Internal Report 63-12, 19 November 1963, in ref. [92]. {4.2} [92] Minutes of Meetings of the ISOLDE Committee and Sub-Committees, 1963-73 (two volumes), P.G. Hansen files. CERN Archives SYSNO 0012983/4. {4.2, 4.5} [93] Decisions of the thirty-ninth meeting of the NPRC held on 2 December 1964, in CERB/ARCH/NP/45, Nov. 1960 to Sep. 1974, file NP 22888. {4.2} [94] ISOLDE Proposals and Selected Documents 1964-70, File of P.G. Hansen. CERN Archives SYSNO 0012985. {4.2} [95] The ISOLDE Isotope Separator On-Line Facility at CERN (A. Kjelberg and G. Rudstam eds.), CERN Yellow Report 70-3 (19 January 1970) pp. 1-140. {4.3} [96] G. Andersson, H.E. Jergensen and K.O. Nielsen, in ref. [95] pp. 19-30. {4.3} [97] J. Camplan and S. Sundell, in ref. [95] pp. 33-37. {4.3} [98] Minutes of a Meeting of the Working Party on Target and Chemical Separation Methods, CERN, 21 April 1966; Abstracts for a Seminar on ISOLDE Chemistry Problems, CERN, 2-3 November 1967. Both in ref. [92]. {4.4} [99] K.O. Nielsen, Nucl. Instr. Meth. 1 (1957) 289; O. Almen and K.O. Nielsen, Nucl. Instr. Meth. 1 (1957) 302. {4.4} [100] P. Patzelt in ref. [95] pp. 83-91 {4.4} [101] E. Hageb0 and S. Sundell, in ref. [95] pp. 65-80. {4.4}

References [102] [103] [104] [105]

[106]

[107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119]

[120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130]

409

E. Hagebo, A. Kjelberg, P. Patzelt, G. Rudstam and S. Sundell, in ref. [95] pp. 95-107. {4.4} A. Kjelberg, memorandum to ISOLDE users, February 1970, in ref. [92]. {4.5} A. Lindahl, O.B. Nielsen and G. Sidenius, in ref. [95], p. 55. {4.5} M. Alpsten, G. Andersson, A. Appelqvist, B. Bengtsson, E. Borgenthun and B. Jonson, in ref. [95] p. 39; E. Hagberg; P. Homshoj, K. Wilsky, P.G. Hansen, B. Jonson, M. Alpsten, G. Andersson, A. Appelqvist, B. Bengtsson and O.B. Nielsen, Phys. Lett. 34B (1971) 591; P. Hornshoj et al. Nucl. Phus. A187 (1972) 599; P.G. Hansen, B. Jonson, B.G.G. Jorgensen, E. Kugler and T. Mowinckel, Nucl. Phys. A208 (1973) 309. {4.5} P.G. Hansen, P. Homshoj, H.L. Nielsen, K. Wilsky, H. Kugler, G. Astner, E. Hagebo, J. Hudis, A. Kjelberg, F. Miinnich, P. Patzelt, M. Alpsten, G. Andersson, Aa. Appelqvist, B. Bengtsson, R.A. Naumann, O.B. Nielsen, E. Beck, R. Foucher, J.P. Husson, J. Jastrzebski, A. Johnson, J. Alstad, T. Jahnsen, A.C. Pappas, T. Tunaal, R. Henck, P. Siffert and G. Rudstam, Phys. Lett 28B (1969) 415. {4.5} M. Finger, R. Foucher, J.P. Husson, J. Jastrzebski, A. Johnson, G. Astner, B.R. Erdal, A. Kjelberg, P. Patzelt, A. Hoglund, S.G. Malmskog, and R. Henck, Nucl. Phys. A188 (1972) 369. E.W. Otten, Determination of Spin and Nuclear Moments of Mass-separated, Short-Lived Isotopes by Optical Pumping, Proposal May 1968 and Supplement, December 1968, in ref. [94]. {4.6} J.E. Lynn, The Theory of Neutron Resonance Reactions, (Clarendon Press, Oxford 1968) pp. 1-504. {6.4} E.W. Otten, Nuclear Radii and Moments of Unstable Isotopes, in ref. [169] pp. 515-638. {4.6, 6.2} Bulletin de la societe francaise de physique, juillet 1987, pp. 29-31. {4.6} J. Bonn, G. Huber, H.-J. Kluge, U. Kopf, L. Kugler and E.W. Otten, Phys. Lett. 36B (1971) 41. {4.6} J. Bonn, G. Huber, H.-J. Kluge, L. Kugler and E.W. Otten, Phys. Lett. 38B (1972) 308; E.W. Otten, J. Physique 34 (1973) CoUoque C4, 63. {4.6} Electromagnetic Isotope Separators and Techniques Related to their AppUcations (eds. H.L. Ravn, E. Kugler and S. Sundell), Nucl. Instr. Meth. 186 (1981) 1^98. {4.1, 4.7} H.L. Ravn and B.W: AUardyce, On-line Mass Separators, in ref. [169] pp. 363-439. {4.7, 5.5, 6.1} D. Pestre in ref. [1] pp. 444-450. {5.4} CERN Annual Report 1967, pp 53-56; also MSC Internal Reports 67-5 and 67-6. {5.1} E.G. MichaeUs, Proceedings of the Sixth International Cyclotron Conference, Vancouver (B.C.), (1972). {5.1} SCIP Advisory Panel, the files of P.G. Hansen, Supplementary Material and Background Information in Connection with the SC Improvement Programme (SCIP), 1972-74. CERN Archives SYSNO 0012986. {5.1} CERN Annual Report 1969, p 44. {5.1} K. Zilverschoon, personal communication during the public presentation of the plans for The History of CERN, Vol. 3, on 14 May 1991. {5.1} E.G. Michaelis, Notes on the possible closing down of the CERN SC. Draft document dated 9 November 1970. In the personal files of T.E.O. Ericson; copy in ref. [119]. {5.1} E.G. MichaeUs, memorandum to the Director General, CERN Laboratory I (MSC-2.2C/754) of 30 June 1971./« ref. [119]. {5.2} Notes of a discussion on the SC Improvement Programme held on 8th July 1971. (MSC-3.2/792) of 12 July 1971. in ref. [92] and ref. [119]. {5.2} D. Pestre in ref. [1] p. 466, 483. {5.2} Archives of the Physics III and Proton Synchrotron and Synchro-Cyclotron (PSCC) Committees, 1966-90. (In the office of Dr. M. Fidecaro). {5.2} Invited lectures given at the meeting on the future of intermediate-energy physics, CERN 16-17 March 1972. Ph.III-72/41/Rev. of 11 October 1972. Also in ref. [119]. {5.2} D.H. Wilkinson, Letter of 17 July 1973 to the PH III Community, PH III-72/50. Copy in ref. [134]. {5.2} Draft Minutes CERN/SPC/328/Draft of 18 September 1972. {5.3} Draft Minutes of the 48th Session of the CERN Council, 15-16 June 1972, p. 13. {5.3}

410

The SC: ISOLDE and Nuclear Structure

[131] D.H. Wilkinson, Letter of 14 July 1973 to J.P. Blaser, CERN Archives DIRADM-20269. Copy in ref. [134]. {5.3} [132] O. Kofoed-Hansen to the CERN Directorate, handwritten draft for a memorandum dated 25 July 1972. In ref. [134]. {5.3} [133] E.G. Michaelis, memorandum to the Director General, CERN Laboratory I, Future policy regarding the CERN S C . In ref. [134]. {5.3} [134] SCIP Advisory Panel, the files of P.G. Hansen, SCIP and anti-SCIP. CERN Archives SYSNO 0012987. {5.3, 5.4} [135] Letters to the Chairman in reply to his request for opinions on the future of the CERN SC and of intermediate-energy physics at CERN, PH III-72/68 of 2 November 1972, in ref. [134] and ref. [126]. {5.4} [136] Debate on the SC Improvement Progranmie and the Future of Intermediate-Energy Physics at CERN. Notes taken by A.J. Herz. PH III-72/69 of 22 December 1972. in ref. [134], [126]. {5.4} [137] Memorandum to the NPRC from Secretary, Physics III Committee, PH III-72/R of 5 October 1972, in ref. [134]. {5.4} [138] Draft Minutes CERN/SPC/334/Draft of 7 November 1972. {5.4} [139] Letter to the CERN Department of Administration from Dr. A. Schuller, Vorstandsmitglied AEG-Telefunken, 10 November 1972, in ref. [119]. {5.4} [140] Memorandum on 'SCIP Information' to the Physics III Committee from P.G. Hansen and E.G. Michaelis dated 11 November 1972 in ref. [141]. {5.4} [141] SCIP Advisory Panel, the files of P.G. Hansen, Minutes and Notes of the Panel, 1972-75. CERN Archives SYSNO 0012988. {5.5} [142] R. Hohbach, Study on the feasibihty of a conversion of the improved SC to accelerate also deuterons, alphas and He^, CERN-MSC-73-2, 5 February 1973. In ref. [119]. {5.5} [143] R. Galiana and P. Mandrillon, in PH III-74/25, in the SCC files. {5.5} [144] Memorandum from P.G. Hansen to P. Falk-Vairant and E. Picasso, 18 December 1974. In ref. [141]. {5.5} [145] H. Beger, Minutes of a meeting about ^He and a acceleration in SC-2. MSC/SD/3975 of 16 January 1975. In ref. [147]. {5.5} [146] H. Beger, Ph III 75/17, in ref. [147]. {5.5} [147] Heavy-ion and ^He Acceleration in the SC. The file of P.G. Hansen 1973-78. CERN Archives SYSNO 0012989. {5.5} [148] B.W. Allardyce and G. Dellacasa, Search for kaon production with the ^He beam at the CERN SynchroCyclotron, Letter of Intent CERN/SCC/76-12, 18 May 1976; E. Aslanides and F. Hibou, Search for TT^ production on nuclei with the ^He beam.... Letter of Intent CERN/SCC/77-5, 3 March 1977; E. Aslanides, T. Bressani, G. Dellacasa, P. Fassnacht, F. Hibou and M. Panaghini, Search for ii^ and K"^ mesons with the ^He beam.... Proposal CERN/SCC/77-19, 30 August 1977. Also in ref. [147]. {5.5} [149] CERN Workshop on Intermediate-Energy Physics 26-30 September 1977, PS-CDI/77-43, in ref. [147]. {5.5} [150] P.G. Hansen, Conveners Report Group 1, CERN Workshop on Intermediate Energy Physics 26-30 September 1977, PS-CDI/77^3, in ref. [147]. {5.5} [151] V. Metag, Nucl. Phys. A488 (1988) 483c-502c. {5.5} [152] C.-K. Gelbke and D.H. Boal, Prog. Part, and Nucl. Phys. 19 (1987) 33. {5.5} [153] P. Braun-Munzinger and J. Stachel, Ann. Rev. Nucl. Part. Sci. 37 (1987) 97-131. {5.5} [154] T. Johansson, H.A. Gustafsson, B. Jakobssson, P. Kristiansson, B. Noren, A. Oskarsson, L. Carlen, J. Julien, C. Guet, R. Bertholet, M. Maurel, H. Nifenecker, P. Perrin, F. Schussler, G. Tibell, M. Buenerd, J.M. Loiseaux, P. Martin, J.P. Bondorf, O.B. Nielsen, A.O.T. Karvinen and J. Mougey, Phys. Rev. Lett. 48 (1982) 732. {5.5} [155] E. Grosse, P. Grimm, H. Heckwolf, W.J.F. Miiller, H. Noll, A. Oskarsson, H. Stelzer and W. Rosch, Europhys. Lett. 2 (1986) 9. {5.5}

References

411

[156] Proc. 2nd International Conference on Nuclei Far From Stability, Leysin 1970, CERN Yellow Report 7030 (1970), Vols. I-II. {6, 6.1} [157] Proc. 3rd International Conference on Nuclei Far From Stability, Cargese 1976, CERN Yellow Report 76-13 (1976). {6} [158] Proc. 4th International Conference on Nuclei Far From Stability, Helsing0r 1981, CERN Yellow Report 81-09 (1981). {6, 6.2} [159] P.G. Hansen, in Proc. Int. Conf. on Properties of Nuclear States, Montreal 1969 (Univ. of Montreal Press 1969) p. 189. {6} [160] R. Klapisch, Ann. Rev. Nucl. Sci. 19 (1969) 33. {6, 6.1} [161] R. Klapisch, On-Line Mass Separation in Nuclear Spectroscopy and Reactions (ed. J. Cemy), (Academic Press, 1974) Part A, pp. 213-242. {6, 6.1} [162] P.G. Hansen, Nuclei Far Off the Stability Line, in Proceedings of the International School of Nuclear Structure, Alushta (U.S.S.R.) 1972, published as Dubna report JINR-D-6465 (1972) pp. 365-397. {6} [163] P.G. Hansen, The Beta Strength Function, in Advances in Nucl. Phys. 7 (1973) 159. {6, 6.4} [164] P. Jacquinot and R. Klapisch, Rep. Prog. Phys. 42 (1979) 773-832. {6, 6.2} [165] J.H. Hamilton, Probing Nuclei Far From StabiHty With Heavy Ions, in Heavy Ion Collisions, Vol. 3 (R. Bock ed.). North Holland Publ. Co. (1982) pp. 575-665. {6} [166] R. Neugart, CoUinear Fast-beam Laser Spectroscopy, in Atomic Spectroscopy, Part D (H.J. Beyer and H. Kleinpoppen eds.). Plenum, N.Y., (1987) pp. 75-126. {6} [167] J. Aysto and J. Cerny, Proton-Rich Light Nuclei, in ref. [119] pp. 206-258; A.A.Oglobhn and Yu.E. Penionzhkevich, Very Neutron-Rich Light Nuclei in ref. [169] pp. 260-360. {6} [168] C. Detraz and D.J. Vieira, Exotic Light Nuclei, Ann. Rev. Nucl. Part. Sci. 39 (1989) 407-65. {6, 6.4} [169] D. Allan Bromley (Ed.), Treatise on Heavy-Ion Physics. Vol. 8: Nuclei Far From StabiUty, (Plenum Press, New York, 1989), pp. 1-727. {6} [170] P.G. Hansen and B. Jonson, On the Future of the ISOLDE Programme, with a covering letter dated 7 November, CERN-PSCC 79-39/M31/November 1979, also in ref. [8]. {6.1, 7.1} [171] I. Amarel, R. Bernas, J. Chaumont, R. Foucher, J. Jastrzebski, A. Johnson, R. Klapisch and J. Teillac, Ark. Fys. 36 (1967) 77. {6.1} [172] H.L. Ravn, Phys. Repts. 54 (1979) 201-259; T. Bjornstad, E. Hagebo, P. Hoff, E. Kugler, H.L. Ravn, S. Sundell and the ISOLDE Collaboration, Physica Scripta 34 (1986) 578-590 {6.1} [173] E. Kugler, The beam handling system for ISOLDE-2, in Proc. 8th International EMIS Conference (G. Andersson and G. Holmen eds.), published 1973 by the Institute of Physics, Chalmers University of Technology, Goteborg, Sweden (1973) p. 382; G. Andersson ibid. p. 356. [174] M. Epherre, G. Audi, C. Thibault, R. Klapisch, G. Huber and F. Touchard, Phys. Rev. C19 (1979) 1504; G. Audi, M. Epherre, C. Thibault, A.H. Wapstra and K. Bos, Nucl. Phys. A378 (1982) 443; G. Audi, A. Coc, M. Epherre-Rey-CampagnoUe, G. le Scomet, C. Thibault, and F. Touchard, Nucl. Phys. A449 (1986) 491. {6.2} [175] H. Stolzenberg, S. Becker, G. BoUen, F. Kern, H.J. Kluge, Th. Otto, G. Savard, I. Schweikhard, G. Audi and R.B. Moore, Phys. Rev. Lett. 65 (1990) 3104. {6.2} [176] C. Ekstrom, Nuclear Single-Particle Structure Derived from Spins and Moments of Long Isotopic Chains, in ref. [158] p. 12. {6.2} [177] J.H. Hamilton, Structures of Nuclei Far From StabiHty, in ref. [169] p. 3-98. {6.3} [178] A. Coc, C. Thibault, F. Touchard, H.T. Duong, P. Juncar, S. Liberman, J. Pinard, M. Carre, J. Lerme, J.L. Vialle, S. Btittgenbach, A.C. Mueller and A. Pesnelle, Nucl. Phys. A468 (1987) 1. {6.2} [179] C. Thibault, F. Touchard, S. Buttgenbach, R. Klapisch, M. de Saint Simon, H.T. Duong, P. Jacquinot, P. Juncar, S. Liberman, P. Pillet, J. Pinard, J.L. Vialle, S. Buttgenbach, A. Pesnelle and G. Huber, Phys. Rev. C23 (1981) 2720; C. Thibault, F. Touchard, S. Buttgenbach, R. Klapisch, M. de Saint Simon, H.T. Duong, P. Jacquinot, P. Juncar, S. Liberman, P. Pillet, J. Pinard, J.L. Vialle, A. Pesnelle and G. Huber, Nucl. Phys. A367 (1981) 1. {6.2}

412

The SC: ISOLDE and Nuclear Structure

[180] S.L. Kaufman, Opt. Comm. 17 (1976) 309. {6.2} [181] W.H. Wing, G.A. Ruflf, W.E. Lamb, Jr. and J.J. Spezewski, Phys. Rev. Lett. 36 (1976) 1488. {6.2} [182] A.C. Mueller, F. Buchinger, W. Klempt, E.W. Otten, R. Neugart, C. Ekstrom and J. Heinemeier, Nucl. Phys. A403 (1983) 234. {6.2} [183] P.G. Hansen, Nuclei Far Away From the Line of Beta Stability, Ann. Rev. Nuc. Part. Sci. 29 (1979) 69119 {6.3,6.4} [184] T. Bj0mstad, M.J.G. Borge, P. Dessagne, R.-D. von Dincklage, G.T. Ewan, P.G. Hansen, A. Huck, B. Jonson, G. Klotz, A. Knipper, P.O. Larsson, G. Nyman, H.L. Ravn, C. Richard-Serre, K. Riisager, D. Schardt and G. Walter, Nucl. Phys. A443 (1985) 283; M.J.G. Borge et al. Physica Scripta 36 (1987) 218. 6.3 [185] L Ragnarsson, S.G. Nilsson and R.K. Sheline, Physics Reports 45 (1978) 1-87; P. Kleinheinz, A.M. Stefanini, P.J. Daly and M.R. Maier, in ref. [157] p. 382; see also the series of papers in ref. [158] pp. 542556. {6.3} [186] P. Hornshoj, K. Wilsky, P.G. Hansen, B. Jonson and O.B. Nielsen, Nucl. Phys. A187 (1972) 609. {6.4} [187] B. Jonson, E. Hagberg, P.G. Hansen, P. Horashoj and P. Tidemand-Petersson in ref. [157]. A review of more recent developments in the applications of statistical theory to nuclear spectroscopy has been given by P.G. Hansen, B. Jonson and A. Richter, Nucl. Phys. A518 (1990) 13. {6.4} [188] P. Asboe-Hansen, E. Hagberg, P.G. Hansen, J.C. Hardy, B. Jonson and S. Mattsson, Nucl. Phys. A361 (1981) 23. {6.4} [189] R.E. Azuma, L.C. Carraz, P.G. Hansen, B. Jonson, K.-L. Kratz, S. Mattsson, G. Nyman, H. Ohm, H.L. Ravn, A. Schroder, and W. Ziegert, Phys. Rev. Lett. 43 (1979) 1652; R.E. Azuma et al. Phys. Lett. 96B (1980) 31. {6.4} [190] M. Langevin, C. Detraz, M. Epherre, D. Guillemaud-Mueller, B. Jonson and C. Thibault, Phys. Lett 146B (1984) 176. {6.4} [191] M.J.G. Borge, M. Epherre-Rey-Campagnolle, D. Guillemaud-Mueller, B. Jonson, M. Langevin, G. Nyman and C. Thibault, Nucl. Phys. A460 (1986) 373. {6.4} [192] P.G. Hansen, Nuclear Physics News 1 (1991) 21. {6.4} [193] S. Liberman, J. Pinard, H.T. Duong, P. Juncar, J.L. Vialle, P. Jacquinot, G. Huber, F. Touchard, S. Biittgenbach, A. Pesnelle, C. Thibault and R. Klapisch, Compt. Rend. Acad. Sci. Ser B286 (1978) 253; Phys. Rev. A22 (1980) 2732. {6.5} [194] N. Bendali, H.T. Duong, P. Juncar, S. Liberman, J. Pinard, J.L. Saint-Jalm, J.L. Vialle, S. Biittgenbach, C. Thibault, F. Touchard, A. Pesnelle and A. Mueller, C.R. Acad. Sci. Paris 299 (1984) 1157. {6.5} [195] H.T. Duong, P. Juncar, S. Liberman, A.C. Mueller, R. Neugart, E.W. Otten, B. Peuse, J. Pinard, H.H. Stroke, C. Thibauh, F. Touchard, J.L. Vialle, K. Wendt, Europhys. Lett. 3 (1987) 175. {6.5} [196] G.L. Borchert, P.G. Hansen, B. Jonson, H.L. Ravn, O.W.B. Schult and P. Tidemand-Petersson, Phys. Lett. 63A (1977) 15; G.L. Borchert et al. Phys. Lett. 65A (1978) 297 and 66A (1978) 347. See also the review by P.G. Hansen, B. Jonson, G.L. Borchert and O.W.B. Schult, Mechanisms for Energy Shifts of Atomic K x-rays, in Atomic Inner-Shell Physics (B. Crasemann ed.). Plenum Publ. Co. 1985, pp. 237-280. {6.5} [197] H. Haas, Quadrupole Interaction in Metals: Nuclear Methods, Z. Naturforsch. 41a (1986) 78; G. Weyer, Ion Implantation, Hyperfine Interactions 27 (1986) 249. {6.5} [198] E.Kugler, Lay-out of ISOLDE-3, Working Party Internal Report (WPIR 1), 24 July 1979; H.L. Ravn and S. Sundell, The SIN-ISOLDE Target Handling Facility (WPIR 2), 27 July 1979; H.L. Ravn, Dose Rates Around the SIN-ISOLDE Target (WPIR 3), 9 July 1979; all in ref. [8]. {7.1} [199] B.W. AUardyce and H.L. Ravn, Nucl. Instr. Meth. B26 (1987) 112. {7.4} [200] J. Domingo, note in ref. [8]. {7.1} [201] J. Domingo, P.G. Hansen, B. Jonson, E. Kugler, H.L. Ravn, S. Sundell and C. Tschalar, Nucl. Instr. Meth. 186(1981)79. {7.1} [202] Note of 19 March, marked EP/EG-kl, in ref. [8]. {7.1} [203] G. Munday, memorandum of 19 February 1981 to G. Brianti with attached note, in ref. [8]. {7.1}

References

413

[204] Draft Minutes of the Meeting of the Scientific PoHcy Committee 16 and 17 December 1980, CERN/SPC/ 464/Draft, 464/Draft/Corr, and 464/Draft/ANNEX. {7.2} [205] Draft Minutes of the Meeting of the Scientific Policy Committee 28 and 29 October 1980, CERN/SPC/467/ Draft. {7.2} [206] Y.Goldschmidt-Clermont, Protocol of the Meetings of the Research Board, CERN/ARCH/YGC/81. YGC 23581. {7.2} [207] Draft Minutes of the Meeting of the Scientific Policy Committee 24 and 25 February 1981, CERN/SPC/ 469/Draft. {7.2} [208] Minutes of the Meeting of the Scientific Policy Committee 27 and 28 April 1981, CERN/SPC/474; Documents Relative to the ISOLDE Programme, CERN/SPC/473, 31 March 1981. {7.3} [209] CERN/PSCC/81-56; PSCC 18 of 20 May 1981. {7.3} [210] A. Garcia, E.G. Adelberger, P.Y. Magnus, H.E. Swanson, O. Tengblad, D.M. Moltz and The ISOLDE Collaboration, Phys. Rev. Lett. 67 (1991) 3654. {7.3} [211] CERN/PSCC/89-31, PSCC 60 of 8 September 1989; CERN/DG/RB 89-144. {7.3} [212] T. Bjerge and K.J. Brostrom, Nature 138 (1936) 400. {8}

This Page Intentionally Left Blank

CHAPTER 10

Experimental Studies of Weak Interactions Klaus WINTER

Contents 10.1 Introduction 10.2 Neutrino physics 10.2.1 Discovery of the weak neutral current interaction 10.2.1.1 Why did it take more than fifty years to discover weak neutral current interactions? 10.2.1.2 Structure of the neutral current 10.2.1.3 Neutrino identity 10.2.1.4 Lorentz structure 10.2.1.5 Neutrino electron scattering 10.2.1.6 Isospin structure of the neutral quark current 10.2.2 Structure of the weak leptonic charged current 10.2.3 The quark structure of matter 10.2.3.1 Scaling violations and QCD 10.2.3.2 New weak currents and the GIM mechanism 10.3 Discovery of the bosons of the weak interactions W and Z 10.4 CP violation 10.4.1 Discovery of KL -^ n^n~ decays: CP violation or alternative explanations? 10.4.2 Other manifestations of CP noninvariance 10.4.3 Precision experiments 10.5 The weak hadronic current 10.5.1 Introduction 10.5.2 Experimental studies of hyperon decays 10.5.3 The AS/AQ rule in kaon decays 10.5.4 Generalization of the Cabibbo theory References

415

416 420 420 423 424 425 426 429 431 432 436 441 443 445 450 450 454 454 459 459 461 465 467 469

10.1 Introduction The previous period of 1960-1965 (volume II) was marked by important contributions of CERN to the understanding of the weak interaction. We recall them very briefly. There was the discovery of the pion decay into an electron and a neutrino at the SC and a measurement of its rate [1]. The V-A theory of the weak interaction had previously been in difficulty because eariier experimental results had failed to show the existence of that decay mode with the predicted branching ratio of 1.2 • 10""*. Thus, this important experiment can be considered as the cornerstone of our understanding of the V-A interaction. A further important experiment, also performed at the SC, made the first observation of the pion beta decay, W^ -^ n^e^v [2], and measured a branching ratio of ~ 10~^. The corresponding decay rate could be predicted theoretically from the measured rate of the super-allowed beta-decay O^"* -^ N^^*e"*'v using the hypothesis of the conserved vector current (CVC). This was the first step towards a full theoretical understanding of the weak hadronic current. The next step came with the notion of quark mixing from Cabibbo and later from Kobayashi and Maskawa. In the period from 1966-1980 a series of beautiful experiments on hyperon and kaon decays was conducted at CERN which, through its high precision results, established the validity of the quark mixing scheme. Another important confirmation of the V-A theory had come through a measurement of the helicity of the muon resulting from n -^ fiv decay [3] at the PS. It was based on the measurement of the helicity asymmetry in the scattering of muons on electrons in magnetized iron. In 1964 the success of the V-A theory with its exact CP symmetry was shaken with the discovery of the unexpected decay K L -^ 2n. This decay mode is not allowed if CP invariance is exact. Its observation at Brookhaven [4] thus showed that our understanding of the weak interaction was not complete (Fig. 10.1). In particular, the smallness of this violation (2 • 10"^) compared to maximal violation of parity and charge conjugation invariance was difficult to understand. Intense experimental activity started on the study of CP violation effects, in which CERN played an important role. Initially, a number of suggestions had been made which allowed one to avoid having to accept CP violation. Among them was the possibility of a long-range cosmological vector field which would introduce a small K^ — K^ mass difference. The resulting strong energy dependence of the decay rate (KL —> 2n) was however not found experimentally [5]. The beautiful and precise experiments at CERN (1966-1980) which were of key importance for the phenomenological analysis of K^ —• 2n decay led to the important conclusion that CP violation was accompanied by a violation of time reversal invariance T by an amount compatible with CPT invariance, whereas CPT vio416

417

Introduction

^^sbcTc

Fig. 10.1 Cartoon shown by N. Cabibbo at the 1966 Int. Conf. on High-Energy Physics, Berkeley: Where we stand [112].

lation was ruled out. Experimental studies which aim at understanding the origin of CP violation continue at CERN to the present day [6]. By measuring with high precision the double ratio

Y{Y.l-^2n^)/n}Ll-^n^n-) r(K«s-27rO)/r(K«s-^^^-) they have detected a direct CP violation in the decay amplitude at the three standard deviation level. This important result indicates that CP violation may be induced by the Cabibbo-Kobayashi-Maskawa quark mixing matrix and would give a natural explanation for the smallness of the violation in terms of a product of three small mixing angles and a CP violating phase angle. However, this result requires further experimental confirmation and a new experiment is under construction at CERN [7] which can reduce the error by an order of magnitude. The most important part of the weak interaction work at CERN were the neutrino physics programmes. While a first attempt to compete with Brookhaven, in searching for the second neutrino flavour, the muon neutrino, had not led to a success, the great results achieved at CERN in the period 1966-1980, under consideration here, were the result of careful planning and of efforts consistently pursued over many years. The first successful intense neutrino beam at CERN, built in 1961-63 under the leadership of Colin Ramm, used the new techniques of ejecting the PS proton beam onto an external target and of

418

Experimental Studies of Weak Interactions

focussing positive or negative beams of pions and kaons towards the decay region and the detectors by a new device, the magnetic horn invented by Simon van der Meer [8]. At the PS these plans involved the increase of the PS intensity through the addition of the booster and the construction of a high quality neutrino beam with a compact iron shield. The first series of neutrino experiments had demonstrated the superiority of heavy Uquid bubble chambers. It was therefore decided to build a very large heavy liquid bubble chamber in France following a proposal by A. Lagarrigue, P. Musset and A. Rousset. This chamber was installed at CERN and started data taking in 1971. Figure 10.2 shows this bubble chamber called Gargamelle and its environment. The results obtained with Gargamelle at the PS are well known [9]. The most prominent result is the discovery of weak interactions of the neutral current type. The first evidence for this new phenomenon came from the observation of one event of antimuon neutrinoelectron scattering in 1973. Soon after, the experiment gave evidence for the existence of neutral current interactions in neutrino-nucleon processes. Not since the early thirties had a new type of fundamental force been discovered. A unified gauge theory of weak and electromagnetic interactions with spontaneous symmetry breaking had been proposed independently by Weinberg and Salam in 1967-68, following earlier pioneering work by Schwinger and Glashow. When its renormaUsability was proved by 'tHooft in 1971 it was an extremely attractive theory of the weak interactions. Neutral current weak interactions are an intimate part of this theory and a sizeable effect had to be seen in neutrino processes. There they were discovered by Gargamelle in 1973. Experiments with Gargamelle achieved several other important results. Among them is the observation of a linear rise of the total neutrino-nucleon cross section [10]; it revealed the point-Uke nature of the nucleon constituents involved in high energy neutrino reactions. Later it was shown that these constituents can be identified with the quarks and antiquarks, and their momentum distribution could be determined from deep inelastic neutrino scattering. A spark chamber set-up built by an Aachen-Padova collaboration was added in this beam line in 1972 and made a pioneering attempt to study neutrino-electron scattering. A new programme with a neutrino facility of very high quahty was planned at the SPS. It again involved a neutrino beam of the wide energy band type successfully developed at the PS and in addition a new type, a so-called narrow energy band beam, with parents of selected momentum in a narrow momentum band. This new type of beam provided an important new tool for the continued study of the quark structure of nucleons in deep inelastic neutrino scattering and for detailed experiments on the Lorentz and isospin structure of the neutral current weak interaction. Despite its late start in 1977 compared to the start in 1972 of an accelerator of similar energy at Fermi National Laboratory near Chicago, the 400 GeV SPS neutrino programme made a very strong impact almost immediately. The SPS neutrino beam line in the West Area is an impressive installation. It emerges at an angle of 42 mrad from the underground target area and crossed successively several detectors, first BEBC, the Big European Bubble Chamber filled either with hydrogen, deuterium or with a neon-hydrogen mixture, the massive electronic detector of WAl designed mainly for the study of deep inelastic neutrino scattering by weak charged

XPANWN VALV

. * . . . .. .. .

.- . .- . ,

.

. ... . ' . . .. . . . . . . ~~

t

tat

lb)

Fig. 10.2 The Gargamelle Bubble Chamber at CERN [47]. (a) Plan view of the chamber; (b) schematic view of the installation,

420

Experimental Studies of Weak Interactions

current processes, the fine-grained electronic detector of WA18 aimed at a detailed study of weak neutral current processes and, until 1978 (when it sprang a leak due to material fatigue), the Gargamelle bubble chamber. Later, in 1985, the new electronic detector of WA79 replaced the other two electronic detectors. Its design aimed at a precise study of neutrino-electron scattering. The next step towards verifying the unified theory of the electroweak interaction was a search for the weak intermediate bosons. Measurements of the electroweak mixing parameter sin^ 0w in neutrino-induced neutral current processes led to predictions of m^ and mz in the 80-90 GeV mass range. Here again, through important technical advances in the stochastical cooUng concept invented by Simon van der Meer [11] and in its use for an antiproton accumulator and pp colUder in the SPS ring conceived by CUne, Mclntyre and Rubbia [12], and careful planning, CERN has achieved a high-quaUty physics facility which led to the discovery of the intermediate bosons W and Z in 1983. The advances in detector concepts and techniques which led to their discovery by the UAl and UA2 experiments are irrevocably linked to this great success [13]. With the discovery of the weak neutral current interaction and the intermediate bosons CERN has led the field of elementary particle physics to the next step, the large e+e" collider LEP operating at the laboratory since 1989 at the Z^ pole. At this installation the unified theory is being put to a series of high precision tests. The existence of the hypothetical Higgs boson which induces spontaneous symmetry breaking is being searched for at LEP and has not been detected at the time of writing. If its mass would be larger than 80 GeV this search may have to be pursued at the LHC, CERN's next large research facility, a 15 TeV pp collider to be added in the LEP tunnel in 2004. 10.2 Neutrino physics 10.2.1 DISCOVERY OF THE WEAK NEUTRAL CURRENT INTERACTION In 1973 a new weak interaction induced by neutral currents was discovered at CERN in neutrino processes in Gargamelle. The story of this discovery has been told in detail by P. Galison [14]. One event of elastic scattering of an antimuon neutrino on an electron was found at Aachen in early 1973 [15] and evidence was growing of neutrino-Hke interactions without a muon or an electron. While the v^e event was unambiguous (see Fig. 10.3) because of the spiralling electron which recoiled at a small angle with respect to the neutrino beam direction, the interpretation of the hadronic events of the type v(v)N -^ v(v) + hadrons was more difficult because of the neutron background created by neutrino interactions in the body of the bubble chamber. The main challenge of the experiment was to show that

Neutrino physics

421

Fig. 10.3 A candidate for v^e scattering found in Gargamelle in 1973 [47].

the muonless events were not due to stray neutrons. This demonstration was difficult because the lateral dimensions of the chamber were not much larger than the neutron mean free path in the freon filling it. However, after nearly a year of painful work and long discussions, the neutron background could be separated from neutrino induced muonless events. This was possible because of the energy difference of neutrino and neutron induced events, and because neutrino events are distributed uniformly along the chamber, whereas the neutron events decrease exponentially along the axis of the chamber as expected for the neutron mean free path in freon (see Fig. 10.4) [16]. Not everyone was convinced by this evidence; Jack Steinberger [17] wrote in his Nobel lecture: 'I myself was a sceptic for a long time, and I lost a bottle or two of good wine on this matter.' Confirmation came slowly, initially in a controversial way, from the electronic experiment E l A of Chne, Mann, Rubbia and co-workers at Fermi National Laboratory. Despite the considerable advantage of ten times higher neutrino beam energy, the discrimination of pions and muons was difficult and led to some uncertainty in the fraction of muonless events with respect to variations of the fiducial volume. Finally, in March 1974 the Fermilab Collaboration pubhshed new and convincing evidence [18]. Weak neutral currents were here to stay. The neutral current interaction was thought to be mediated by a neutral boson, the Z^. Unfortunately, this very important discovery has remained unrewarded by a Nobel prize, perhaps because of the untimely disappearance of Andre Lagarrigue (1924—1974). What previously had been considered a weakness and a handicap of the work at CERN, the multinational collaboration of many university groups (Aachen, Brussels, Ecole Polytechnique Paris, Milano, Orsay, University College London) with CERN, turned into a triumph. Viktor F. Weisskopf wrote in his biography. The Joy of Insight [19]:

422

Experimental Studies of Weak Interactions

^

^M

®

NC Ev«ntt

i-jji^ fA^ji/r

\j\

Fig. 10.4 Distribution of the origins of muonless events in Gargamelle along the neutrino beam axis, for NC candidates and for neutron stars [47].

*much was accomplished during my tenure at CERN, but more could have been done. Because the European scientists were acquiring experience so slowly, we were prevented from fully exploiting the possibilities offered by the new equipment'.

This may have appHed to the period preceding the discovery of neutral currents at CERN. Later, however, the careful planning and the superiority of the neutrino beams and the detectors at CERN together with the new 'style' of international collaboration led to a fundamental discovery.

Neutrino physics

423

10.2.1.1 Why did it take more than fifty years to discover weak neutral current interactions? Neutral current interactions do not change the flavour of quarks; for this reason they remained undiscovered in decay processes because they are completely masked by electromagnetic processes in the form of gamma ray emission. But even in neutrino reactions it took ten years to discover that there are neutral current reactions at the level of 30% of the charged current processes. This is also reflected by the poor showing of a search for neutral currents in the priority Ust of Gargamelle [14]. There were two reasons for this; one was based on the low limit placed at CERN in 1967 on strangeness-changing neutral currents [20],

nK

/i+/i-

nK - all)

< 1.6 10-^(90%C.L.);

the other is based on experimental upper limits on the ratio of elastic neutrino scattering [21], o"(v^p -^ v^p)/o"(v^p -^ /x~p) and on the exclusive channel v^p ^> V^TC^P [22], which were reported, and seemed to exclude the phenomena predicted by the gauge theory of a unified electro weak interaction [23]. Figure 10.5 shows Gilberto Bernardini reporting in

Fig. 10.5 G. Bernardini reporting in 1964 on results from the neutrino programme at CERN (From '25 years of CERN').

424

Experimental Studies of Weak Interactions

1964 on the results of the first neutrino experiment at CERN. On the right-hand side of the blackboard he has written the limit on neutral currents that excluded the predicted phenomena. On the other hand, owing to the small lateral dimensions of the detectors in the first generation of neutrino experiments at accelerators as compared to the neutron mean free absorption path, and despite a persistent rumour of a 'background' of events of unidentified origin, inclusive neutral current neutrino events could not be distinguished from neutron interactions, and remained uncovered. Suddenly, in the spring of 1971, following the proof of the renormalizibihty of the Weinberg-Salam theory by 'tHooft [24], theoreticians and experimentaUsts took a new interest in neutral currents and calculated the experimental consequences of the theory. Glashow, IHopoulos and Maiani postulated in 1970 [25] a mechanism invoking a fourth quark (charm) to suppress strangeness-changing neutral currents in K^K^ mixing to explain the small Kj - K2 mass difference. Now, only two years later, the GIM mechanism was seen to fit naturally into the Weinberg-Salam model, allowing AS = 0 neutral currents while suppressing those with AS 7«^ 0. In a more recent publication Cundy et al. 1970 [26] withdrew the original result on elastic scattering by neutral current interaction. The way was open for a new search and, finally, for the discovery of neutral currents.

10.2.1.2 Structure of the neutral currentl Following the discovery of a new weak force in muon-neutrino elastic scattering on electrons and in inelastic neutrino scattering on nucleons, its Lorentz and isospin structure were determined from further neutrino experiments and from electron-positron annihilation experiments. The existence of/i/i and TT neutral currents was deduced from the observation of a weak forward-backward charge asymmetry in the annihilation of electrons and positrons at the PETRA collider at DESY [27] in 1982. The existence of other neutral quark currents, for example, ss and cc, was deduced from the analysis of the inelasticity distribution of deep inelastic neutral current neutrino scattering on nucleons [28] and from J/^ production [29], respectively. Also the neutral current VgVe has been observed in neutrino experiments at CERN [30]. So far, only diagonal neutral currents have been observed that do not change the flavour of the particles involved. With three families of leptons and quarks, the standard theory [31] predicts the existence of six diagonal neutral lepton currents and six diagonal neutral quark currents. The neutral current has a more complex helicity structure than the charged current. Experiments, for example, measurements of the inelasticity distribution of deep inelastic neutral current neutrino scattering [32, 33], have shown that coupling to both left-handed and right-handed quarks exist. This observation shows directly the existence of a unified, electroweak force. Its existence was demonstrated by the observation of interference of

425

Neutrino physics

amplitudes with y and Z^ interchange, for example, in the helicity asymmetry of electrondeuteron scattering [34] and in the optical activity of Bismuth and Cesium vapour [35, 36]. The structure of the current as deduced from these experiments implies that left-handed fermions transform as doublets under a weak isospin rotation group and right-handed fermions transform as singlets. The Standard Model of the electro weak gauge theory predicted this structure of neutral currents and it successfully describes a large amount of experimental data [37, 38, 39, 40, 41] which are all consistent with universal strength of the forces g2 and gi associated with the SU(2) and U(l) symmetry groups, respectively. The fundamental quantities of the Standard Model, the coupling constants gi and g2, and the masses of the weak bosons mw and mz are related to the angle 0w that describes the mixing of the two local symmetries by the relations ^—

gl§2

. n

-In

1

: = g2 sm ^w 5 sm ^w = 1

V^TKBI

^W

m|

y •

The value of the mixing angle is not predicted by the Standard Model. Grand unified theories predict a value of sin^ 0w = i ^t the unification mass. The occurrence of a nonzero mixing angle defines both the structure and the strength of the neutral currents. The left-handed 'up' particles of the weak isospin doublets couple with a coefficient (5 — Q sin^), where Q is the electric charge of the particle. The coupling coefficient of the right-handed states is —Qsin^^w Hence, the value of sin^^w can be deduced from all neutral current-induced processes. 10.2.1.3 Neutrino identity Since the discovery of the neutral weak current, it has generally been believed that in neutrino-induced processes

the neutral lepton in the final state (v') is identical with the incident neutrino. The identity is suggested by the assumption that the neutral neutrino current (v^v^) and the neutral electron (e"^e~) and the quark currents (uu, dd, etc) couple by exchanging a neutral intermediate boson, in analogy with the CC coupUng. The possibility of nonidentity has been excluded in two ways. One source of information is the behaviour of the differential cross sections of v and v induced processes in the limit Q^ ^ 0 for exclusive reactions or y = 1 —Ey/Ev^ -^ 0 for inclusive reactions. We expect dcr(v) = dcr(v)

426

Experimental Studies of Weak Interactions

as q^, y -> 0 if V = v'. Experimental data obtained by the CDHS (WA 1) Collaboration led by J. Steinberger [42] and by the CHARM (WA 18) [43] Collaboration led by K. Winter at CERN are compatible with this equaUty and, hence, assuming only V, A interactions, support the concept of neutrino identity. The other source of information is electron-neutrino scattering on electrons. Observation of interference of amplitudes from NC and CC interactions again supports the concept of neutrino identity [44].

10.2.1.4 Lorentz structure Observation of an asymmetry of the scattering cross sections of left-handed and righthanded electrons on deuterons at SLAC (Stanford) in 1978 [45] demonstrated that the interaction of the ee neutral current is parity violating. In terms of the space-time structure of the current, because of the interference with the electromagnetic interaction this is direct evidence for vector (V) and axial vector (A) ee currents. This was confirmed by the observation that the plane of polarization of a beam of circularly polarized laser light passing through Bismuth or Cesium vapour is rotated [46]. Is the Lorentz structure of the neutrino NC interaction of the helicity-conserving vector (V, A) type, or of the helicity-changing scalar, pseudoscalar or tensoriel type? Elucidating this question for the CC weak interaction took nearly 25 years of experimental investigation. In neutrino-induced reactions the answer is further obscured by the so-called confusion theorem. The cross section ratios

T%

^v

r%

V

y

V

are given in the electroweak theory in terms of the mixing parameter (Weinberg angle) sin^ 0w On the basis of these ratios the Gargamelle experiment yielded a first measurement of sin^ 0w [47]. The neutrino beams of higher energies that became available at CERN with the 450 GeV SPS machine made more precise measurements possible. The separation of NC and CC reactions was much cleaner because of the higher muon energy and greater muon penetration. Electronic detection techniques gained several advantages over the bubble chamber technique. Among them is fast timing to ehminate the associated neutron background that plagued the Gargamelle experiment, the large detector mass and dimensions compared to the interaction length of hadrons, and the calorimetric measurement of hadron energy with high resolution (AE/E ~ 50%/Y^E/GeV) owing to the fine segmentation of the target plates. The results, given in Table 10.1, show good agreement between data obtained by the CDHS and CHARM collaborations at CERN.

427

Neutrino physics Table 10.1 Values of cross section ratios R, R, and id r and vali values of sin^ 0w (radiative corrected for nit = 45 GeV and nin = 100 GeV) derived from them R

Experiment CDHS [48]^ CHARM [49]^

R

0.3072 ± 0.0032 0.3093 ±0.0031

0.382 ±0.016 0.390 ±0.013

r 0.494 ±0.013 0.486 ±0.013

sin^^ 0.225 ±0.005 0.236 ± 0.005

Note: nic = 1.5 GeV The common theoretical uncertainty is Asin^ 6^ = ±0.003. ^Event-length method. ^^Event-by-event method.

The combined value with radiative corrections for mt = niH = 100 GeV is sin^ 0w = 0.230 ib 0.004(exp) ± 0.003(theor) . This result defines both the structure and the strength of the neutral currents and predicts the masses of the intermediate bosons mzo (predicted) = 91.6 ± 0.9 GeV mw (predicted) = 80.2 ± 1.1 GeV . The ratio of the NC coupUng to right-handed and left-handed quarks can also be derived from these measurements of cross section ratios. However, it is evident that one cannot demonstrate the handedness of the fermions participating in the NC interaction by measurements of scalar quantities. Using the approach by Llewellyn-Smith [50] relating the differential cross sections of neutrino and antineutrino scattering on isoscalar targets (equal numbers of neutrons and protons) by the NC and CC interaction d^NC _ „2 d^^cc , ^2 dec dy

"^^

dy "^^^ V

d<^NC _ ^2 dtr^c , ^2 d 4 c dy " ^ ^ dy "^^L dy

the NC coupling to left-handed quarks (gL) and to right-handed quarks (g^) has been determined by the CHARM collaboration [51]. In neutral current neutrino reactions the outgoing neutrino (v') cannot be observed and, hence, the inelasticity y = Eh/(Eh + Ev^) cannot be determined on an event-by-event basis. One must resort to a sign and momentum selected parent beam, a so-called narrow band beam. A high quality beam of this type had been built for the first time at the CERN SPS. Owing to the dominant two-body decays n -^ [xv^ and K ^ )uv^ that produce the neutrinos, a measurement of the neutrino direction implies a determination of the neutrino energy, apart from the TT, K ambiguity.

Experimental Studies of Weak Interactions

428 1.0

"1

1

\

1

r

0.3

L

0.0

charged current

>-^~-. 0.0 00

I

0.2

. I

0.4

0.6

-J

0.8

1.0

0.0

y

0.2

0.4

0.6

0.8

1.0

y

Fig. 10.6 Differential cross sections of v^N and v^N deep inelastic scattering by neutral current and charged current interaction (CHARM Collaboration) [51].

The neutrino direction can be inferred from the distance of the neutrino interaction point from the beam axis. The differential cross sections of CC and NC deep inelastic scattering, thus determined, are shown in Fig. 10.6; from a fit to the Llewellyn-Smith relations the CHARM collaboration determined [51] gl = 0.287 ± 0.008

A

0.042 ±0.010

in good agreement with the values determined from sin^ 0^^ = 0.230 in the context of the electro weak theory [52]. The NC coupling of right-handed quarks (g^) is shown to be nonzero at the four G level. The value of the electroweak mixing parameter sin^ 6^ determined from deep inelastic neutrino scattering affected also the discussions about Grand Unification Theories (GUT) into which the electroweak gauge groups SU(2) x U(l) would be embedded. The minimal SU(5) group proposed as a candidate for GUT by Georgi and Glashow predicted a value which is 3(7 below the experimental result. Together with the absence of proton decays at the predicted rate this led to abandoning minimal SU(5) as a GUT candidate and to new interest in other theories like supersymmetry which predicted additional mass states and a larger value of sin^ 9y/,

429

Neutrino physics 10.2.1.5 Neutrino electron scattering

In the standard SU(2) x U(l) electro weak theory, all left-handed fermions are assumed to transform as doublets with respect to weak SU(2), and right-handed fermions as singlets. Neutral current data can directly measure the SU(2) x U(l) properties of the fermions. The cleanest approach in principle to this goal would be by measuring the cross section of v^e and v^e scattering as this process proceeds by neutral current interaction alone and involves only leptons. However, the cross sections are small, some 10~^^ • Ev[cm^/GeV], smaller than those of hadronic processes by the ratio me/mp because of the smaller c m . energies, and, consequently, the event rates are low and the background large. 'tHooft, then a young physicist at the University of Utrecht has derived the expressions for the differential cross section in the framework of the SU(2) x U(l) gauge theory [52]: 9

1

1

9

9

9

^iy^i^) =-;rEv j g l + gR 2 where y = Ee/Ey, gL = gy + gA' gR = gy ~ gA ^^^ ^^'^ nominal cross section slope is ^0 = p2 ^ ^

^ 8.6 • 10-^2 cmVGeV

assuming p = G N C / G F = 1-

A fourfold ambiguity for exchanging gy and g^^ remains if these cross sections are measured. Two solutions can be eliminated by VgC or VgC scattering experiments, a third solution by measurements of the forward-backward asymmetry in the reaction e"^e" -> pC^iT under the assumption that weak neutral current processes are dominated by the exchange of a single Z^. A first attempt to measure the cross sections was made by an Aachen-Padova collaboration led by H. Faissner and M. Baldo-Ceolin [53] at the CERN PS. An array of aluminium plate optical spark chambers with a fiducial weight of 18 tons was operated in an unbiased way by pulsing the spark chamber high voltage on every accelerator pulse. In total 12 v^e candidates and 10 v^e candidates with a signal to background ratio of about 1:2 were observed. Following this early pioneering attempt the CHARM (CERN-Hamburg-Amsterdam-Rome-Moscow) collaboration made measurements [54] at the CERN SPS using marble target plates of 70 tons of fiducial mass and proportional tube chambers and scintillator hodoscopes of fine segmentation. In total 200 v^e and v^e event candidates were observed, after subtraction of a background of similar magnitude. Combining them with data from PETRA (DESY, Hamburg) [55] and with VgC data from a nuclear reactor [56] this result resolved for the first time the fourfold ambiguity and determined

430

Experimental 1.0

"I

Studies of Weak

I I I I I

Interactions I

r

I

I

I I

I I

e*e" --vl e ^ =

0.5

•yf 0

-0.5

'

-1.0

'

'

•

1 >

-0.5

«

t^ '

0

\ \ \ \ \ \ \ \ \ 0.5 1.0

Fig. 10.7 Electroweak electron couplings determined from e-^e" annihilation [55] and from neutrinoelectron scattering [54] by the CHARM Collaboration.

g\ = -0.57 ± 0.04 (stat) ib 0.06 (syst) in agreement with the SU(2) doublet local symmetry scheme (see Fig. 10.7). The original guess was thus confirmed experimentally. As the Standard IVLodel does not distinguish between families of fermions it was natural to take the same doublet assignment of muons and tauons as well. These were confirmed by measurements of annihilation processes at PETRA [55] and LEP [58]. More recently, another step in the precision of measuring the total and the differential cross sections of v^e and v^e scattering has been achieved by the CHARIVI-II Collaboration at CERN led by K. Winter. Using a new detector of low Z target material (glass) with 500 tons fiducial mass and finer segmentation and detector elements of smaller width they improved the statistics to 4500 v^e and v^e candidates. From the ratio of the cross sections they determined sin^ 0w and from the absolute diff'erential cross sections the values of the coupling constants g\ and g^ [59]. The result is compared with those on the crossed diagram e+e" -^ e+e" which has been studied at LEP [58]. The agreement is remarkable, keeping in mind the difference in energy scale, a cm. energy of ~ 100 MeV in v^e scattering and of 90 GeV at LEP. Radiative corrections due to the running of the fine structure constant a and the neutrino charge radius tend to cancel each other when calculated in the electroweak theory. Compared to the divergent electromagnetic corrections in the Fermi theory, the progress is very significant.

Neutrino physics

431

10.2.1.6 Isospin structure of the neutral quark current Measurements of inclusive neutral-current neutrino scattering on isoscalar targets determine two combinations of the chiral coupling constants of the u and the d quarks, UL + dL and u^ -f d^. Measurements of inclusive neutrino scattering on protons and neutrons were required to determine the coupling of the u and the d quark separately. These measurements remained the exclusive domain of the Big European Bubble Chamber (BEBC) built at CERN by a collaboration between CERN, France and Germany which had been set-up and operated through the initiative and under the guidance of W. Jentschke, F. Perrin and V.F. Weisskopf. Originally built for the 28 GeV Proton Synchrotron this chamber had been adapted to the needs of neutrino physics at the 450 GeV SPS by equipping it with new electronic devices, an external muon identifier, a veto plane and an internal picket fence (see Fig. 10.8). The chamber was filled, successively, with hydrogen, deuterium and with a mixture of neon and hydrogen. Inside this heavy mixture a track sensitive target, filled with hydrogen or deuterium had been installed for some time, with the aim of using the heavy liquid as a detector for y-rays carrying a large fraction of the hadron energy in inclusive deep inelastic neutrino reactions. Simultaneous measurements of four ratios of NC and CC cross sections, of neutrinos and antineutrinos on protons and neutrons have been performed by one collaboration [60] using BEBC filled with deuterium. The target particle could either be a proton or a neutron. The cases were distinguished by the number of detected tracks; events with odd (even) numbers of tracks correspond to interactions with protons (neutrons). Two effects, due to Fermi motion and to rescattering are not described by this simple scheme. A correction is appUed for them.

EMI (Outer plane) EMI (Veto plane)

Fig. 10.8 The big European bubble chamber (BEBC) at CERN with external muon indentifier (EMI), veto plane and internal picket fence (IPF).

432

Experimental Studies of Weak Interactions

Another collaboration [61] used BEBC with a track sensitive Hquid hydrogen target and measured the ratio of n^/n" in the four NC and CC reactions on protons induced by neutrinos and antineutrinos. The ratio TT^/TT" is sensitive to the quark composition produced in the primary neutrino-quark interaction and, although somewhat model dependent, it gives better precision than the cross section ratios. The results are summarized in Table 10.2, together with the Standard Model predictions for sin^ 0w = 0.230. The relative signs of the chiral coupHng constants cannot be determined from inclusive experiments. They have been determined from exclusive channels (elastic NC reactions, vp —> vp and vp -^ vp, v^A -^ V^TT^A, Vgd —> Vepn). The overall sign is determined from interference between Z^ and photon exchange in electron-deuterium scattering and atomic parity violation. Except for dR that is determined with large uncertainty the agreement with the Standard Model is excellent. In later years and in particular with the high precision results obtained from e"^e~ annihilations at LEP the Standard Model became a reference from which no deviation was seen. The situation was in many ways similar to that of tests of QED in the 1960's. Although not a complete theory, the Standard Model will have to be part of that theory. 10.2.2 STRUCTURE OF THE WEAK LEPTONIC CHARGED CURRENT The main subject of experimental neutrino physics, following the seminal paper by T.D. Lee and C.N. Yang in 1960 [64], had been a search for the bosons W='= which mediate the weak charged current interaction. The rise of the cross section of point-like particles such as neutrino-electron scattering would, in the four-fermion-point-interaction picture, reach, at a center of mass energy of v^ = yJn/G ~ 320 GeV the s-wave unitarity limit of a = G/n ~ lO"-'-^ cm^. Thus, at small distances, corresponding to these energies, Lee and Yang argued, the weak interaction must be modified in order to avoid a violation of unitarity. Such a modification could be obtained by the propagator effect of a non-locaUty introduced by a finite mass intermediate boson. Lee and Yang had calculated the cross

Table 10.2 Values of neutral current quark coupling constants determined from neutrino experiments Coupling constant UL

dR UR

dR

Value 0.339 -0.429 -0.172 -0.011

±0.017 ±0.014 ±0.014 +0.081 -0.057

Standard Model prediction 0.345 -0.427 -0.152 -0.076

Note: The Standard Model prediction is given for sin^ 0w = 0.230. Source: [62; 63].

Neutrino physics

433

section for neutrino production of the W in the Coulomb field of a heavy nucleus of charge Z v^Z -^ /i-W+Z . The cross section has a strong dependence on the W mass. 'If experimentally no W=^ is found,' they wrote, 'it would be possible to set a lower limit on the value of mw' [64]. Following the discovery of a second neutrino associated with the muon - the muon neutrino - at Brookhaven in 1962 by L. Lederman, M. Schwarz, J. Steinberger and collaborators [65], a new neutrino program was started at CERN in 1963. Using a spark chamber set-up and a heavy liquid bubble chamber exposed to the new high quality neutrino beam (see Fig. 10.9) the discovery of the muon neutrino was confirmed with high statistics [66]. Also some events due to electron-neutrino interactions were observed, at the rate expected from K"^ -^ Tr^e+Vg decays. Another important result was obtained by focussing negative pions and kaons by the horn, thus producing a beam of antimuon neutrinos. Their interactions were observed to produce exclusively positive muons [67] in agreement with the notion of lepton number conservation. Left-handed muon neutrinos produce negative muons, whereas right-handed antimuon neutrinos produce positive muons. The energy of the PS neutrino beam is peaked in the region of a few GeV and was, thus, suitable to search for the production of the W+ with a mass below 2 GeV. The leptonic decay modes of the W"^

W+ ^ e+Ve were searched for as they provide the cleanest signature. A few candidates of events with the topology /i~e"^ and ^~pi^ were indeed observed in the spark chamber set up [68]. One event is shown in Fig. 10.10. In a moment of uncertainty these events were interpreted as candidates of W decays. However, after careful caUbration a lower limit of mw > 1.8 GeV was quoted. The bubble chamber [69] gave a model independent lower limit by integrating over all decay modes of mw > 1.5 GeV. Later, Helmut Faissner, who was one of the leaders of the spark chamber detector, said that the events, which had been tentatively attributed to W decays, may have been the first candidates of charm particle decays. The search of W=^ remained at the top of the list of physics motivations for the construction of Gargamelle at CERN and for the construction of Experiment lA at the Fermi National Accelerator Laboratory in the U.S.A. Following the discovery of neutral current weak interactions in 1973, the theory of electro weak interactions of Glashow, Salam and Weinberg made, for the first time, a prediction of mw ~ 80 GeV. This large value was out of the reach of the neutrino beams at the CERN SPS and the FNAL 400 GeV accelerators and the subject was dropped. The CDHSW Collaboration led by Jack Steinberger made

Concrete shielding

i

-Y

Path

Focuslng magnetk horn

,,Mag,netkreflector

',,

Internal ... .- amton M

s 3

I cltatbnI

G W

R

Fig. 10.9 The horn focussed neutrino beam at CERN.

Neutrino

physics

435

Fig. 10.10 An example of a (^e) event [68] observed in the 1964 neutrino experiment at CERN.

an attempt to search for the W propagator effect in the cross section dependence on q^ [70]. But the interpretation remained ambiguous because of similar effects introduced by scaUng violation (see Sect. 10.2.3). From studies of beta-decay processes in nuclei in the MeV domain the charged current weak interaction had been found to be of the V-A type. With the advances in particle accelerators it became possible to test the structure of weak charged currents at higher energies and higher momentum transfers in the GeV domain. The improvement of neutrino beams at the CERN SPS and the existence of the two large detectors, that of the CDHS collaboration and that of the CHARM collaboration, made it possible to measure the helicity of the positive muons produced in the reaction v^N

/ i +X

The positive helicity of the antineutrino would be preserved if the interaction was of V and A type, whereas interactions of the S(scalar), P(pseudoscalar) and T(tensor)-type would flip the heUcity. Such an experiment therefore constitutes a very direct test. The experimental set-up consisted of two parts [71], the target and the polarimeter. The neutrino detector of CDHS served as an active target. The CHARM detector was used as a muon polarimeter. Muons stopped in the (marble) plates, chosen to minimize depolarization effects, and the muon spin precessed in a magnetic field with a period of 1.3)us. The time dependent forward-backward asymmetry of high energy positrons from muon decay was measured (see Fig. 10.11) and its phase and magnitude was found to correspond to initially fully right-handed muons. An upper limit of CTS^P/O-TOT < 7 % (95 % C.L.) was

Experimental Studies of Weak Interactions

436 0.600

0.100.

Fig. 10.11 Observed time dependence of the oscillating forward-backward asymmetry of positrons from polarized muons [71].

given. It can be concluded that the weak leptonic charged current remains dominantly composed of V and A currents at momentum transfers of several GeV^. The reaction

is a purely leptonic process mediated by charged currents. A measurement of its cross section can complement the precise measurements of muon decay, /x"^ -> e"^VeV^, the inverse reaction. Assuming left-handed neutrinos the measurements [72] found good agreement with V-A coupHng, whereas right-handed neutrinos or S, P coupling were excluded at the 6 standard deviation level. 10.2.3 THE QUARK STRUCTURE OF MATTER In the first publication in 1964 of neutrino results obtained in the CERN heavy liquid bubble chamber [73], a 'marked increase of the inelastic cross section with neutrino energy' was reported (see Fig. 10.12). This phenomenon was also discussed by Perkins [74] and by Bell, Lovseth and Veltman at the 1963 Sienna Conference [75]. Perkins reported, The total inelastic neutrino cross section rises rapidly with neutrino energy, perhaps as Ej , but the energy spectrum of the flux enters and this is still quite uncertain.' He is also asking for possible explanations for this rise and gives two: (1) the form factor of the scattering may be associated with a hard nucleon core, (2) increase of the inelasticity. Bell et al. remarked

Neutrino physics

437

14 fe CD 12

Q. CM

E 10 o

o o

CD CO

4

01

en

CO

2 o

8

Evis(GeV)

10

12

Fig. 10.12 Cross section of inelastic events observed in the CERN heavy liquid bubble chamber in 1964 [69].

[75]: 'this rise in the inelastic cross section is one of the most striking features of the experiment.' Hence, both experimentahsts and theorists were alerted by this very unusual phenomenon. Never before had a total cross section been observed to rise linearly with energy. If this was due to the opening up of new channels with higher mass one would expect the cross section to level off at some higher energy. Perkins with the proposal of a hard core had come very close to the later interpretation. Bell, in a seminar on neutrino physics [76] in 1963 at CERN, had calculated that the cross section of neutrino electron elastic scattering was expected to rise linearly with Ev owing to the point-Uke nature of the leptons and of the 4-fermion-interaction involved, but in October of the same year, at Sienna, he did not make the connection with the rising total cross section. Later, in 1969, following the discovery of very similar phenomena in deep inelastic electron scattering at the 2-mile linear accelerator SLAC (Stanford, U.S.A.), Perkins [77] reported at a Topical Conference on Weak Interactions organised by J. Bell at CERN, 'another, and quite different way to arrive at point-Uke cross sections is to postulate pointlike constituents in the nucleon. These constituents can be imagined as 'bare' quarks if anyone can imagine such objects.' He continued by saying, 'If one sums over all elastic and inelastic channels the total cross section will be given by the elementary lepton-quark elastic cross section, i.e. da/dq^ = constant. This model is almost unbelieveably crude, and, as K. Gottfried has remarked [78], no well educated person should be expected to accept it. Yet, it at least has the virtue of making rather definite predictions.' Again, in 1969, at the Lund Conference, J. Steinberger [79] referred to the rise with neutrino energy of the total neutrino cross section and compared it to the elastic cross section. 'The levelling off of the elastic cross section already below 1 GeV, consistent with form factors

438

Experimental Studies of Weak Interactions

V TOTAL CROSS SECTIONS

X Freon 63/6^ • Propone 67 10^ K — K — <

I"

/^asE^

/

o

/

b

t •

^7\\

y
Fig. 10.13 Energy dependence of elastic and of total neutrino cross section [79].

of the same general behaviour as the electromagnetic form factors, while the total cross section is still seeming to increase linearly up to neutrino energies of '^ 12 GeV, consistent with a point interaction (see Fig. 10.13) made the greatest impression on me.' Neutrinos are ideal projectiles for investigating this structure, owing to the large mass of the intermediate boson and the corresponding nearly point-like interaction, and also because neutrinos are scattered differently by quarks and antiquarks owing to the V-A nature of the weak currents. Scattering of neutrinos on quarks and on antiquarks can therefore be distinguished whereas in electron or muon scattering this is not possible. The quark model makes definite predictions for neutrino-nucleon scattering which were

Neutrino physics

439

beautifully confirmed experimentally. Although the merit of the discovery of the quark structure and the Nobel prize for it went to Friedman, Kendall and Taylor who were leading the experiment at SLAC, the role of CERN in confirming the predictions of the quark model was very important. The proton contains three so-called 'valence' quarks, two up-quarks and one downquark. In addition it contains a 'sea' of virtual quark-antiquark pairs. Sea quarks and antiquarks necessarily have identical distributions as a function of the Feynman scaling variable x which has a physical interpretation as the fraction of the nucleon momentum or mass carried by the quark. For the neutron, u and d quarks change their roles whereas the sea quarks are the same. In the simple quark model, describing the scattering cross section of neutrinos and antineutrinos on quarks, the absence of a finite size of quarks translates into an absence of a dependence on q^, the momentum transfer from the neutrino to the muon, in the inclusive processes v^N - > / / " + hadrons v^N -^ li^ -\- hadrons . This property, also called 'scaling' by Feynman and Bjorken [80], is experimentally evident everywhere, e.g. in the linear rise of the total cross sections with neutrino energy [81], in the uniformity of the average inelasticity y with respect to the neutrino energy [81]. These striking scaUng properties are a consequence of the point-Uke interaction of the quark. In these experiments, one measures the momentum and angle of the muon and the kinetic energy of the hadrons using sampling calorimeters. The invariants describing the kinematics of the inclusive reactions can be calculated in terms of these measured quantities: Ev = Ehadron + E^ Q 2 = 4E^Ev sin^ 9^/2 X = Q^/2mpEhadron y = Ehadron/Ev

The y dependence of the cross sections directly reflects the heUcity of the neutrino and of the spin 1/2 quark which interact. A claim for a y-anomaly (so-called high y anomaly) by a Harvard-Pennsylvania-Wisconsin-Fermilab group was reported [82] in 1976 for antineutrino scattering at high energies. The apparent flattening of the antineutrino y distributions along with a rapid rise of the ratio of antineutrinos and neutrino total cross sections at high energy reported by the same group [83] led to considerable conjecture about possible new phenomena at high energies. However, the CERN results of the CDHS collaboration [81] and results obtained by a Caltech-Fermilab experiment [84] contradicted these claims. The observed energy independence of the average fraction of the neutrino energy transferred to the hadronic final state, y and the slow variation of the ratio of R = Gy/o^ did not support these claims.

440

Experimental Studies of Weak Interactions

However, there appeared another disagreement, in the values of the Unear slopes of the rise with neutrino energy of the total cross sections. The Caltech-Fermilab experiment [84] reported values which are 15% higher than those measured by the CDHS collaboration at CERN. This conflict was resolved by later experiments at CERN [85] using new monitoring equipment for determining the neutrino flux; they confirmed the earlier CaltechFermilab results. The disagreement was traced back to errors in the secondary hadron beam intensity measurements at CERN [86]. Combining data from neutrino and anti-neutrino scattering one can determine structure functions which are related to the quark structure of the nucleon. F2 (x, Q^) is reflecting the total quark and anti-quark distribution, q(x) + q(x); XF3 (x, Q^) is related to the valence quark distribution, q(x)-q(x). Comparing F2 as determined from deep inelastic electron or muon scattering (F2(x)) and from neutrino scattering (F2(x)) from isoscalar nuclei we expect them to be proportional to the same quark distribution, q(x) + q(x)). They are therefore related by the average of the squared electric charges of the down- and up-quarks.

F|(x)^l F^(x)

2

(-OMf)^

5_ 18

The agreement in shape and in magnitude of the measurements of F^Cx) at SLAC [87] and of F2(x) at CERN [88] supported the quark picture and demonstrated that quarks have fractional electric charges This remarkable confirmation of the quark model of the nucleon was first reported at the 1972 Rochester Conference at Batavia and Chicago. Following the demonstration at SLAC that partons have spin 1/2, the remaining most decisive question was: What is their electric charge? Theoretical work of Llewellyn-Smith [90] at CERN had led to the prediction of the ratio of neutrino and antineutrino total cross sections and of the structure functions F2. The electric charge of the quarks, if there were any in the nucleon, could be read off" the deep inelastic electron and neutrino scattering. Experimental results obtained by the Gargamelle collaboration could finally be compared to the electron data from SLAC. But the important conclusion that the comparison indeed agreed with fractionally charged quarks was only given in the discussion following the report on the neutrino experiment [91] and immediately acclaimed by Feynman. Perkins reported the result in his rapporteur talk at this conference [92]. From data on neutrino and antineutrino scattering the number of valence quarks in the nucleon can be determined. Gross and Llewellyn-Smith working at CERN [93] derived a sum rule for the structure function F3. In the parton model, they argued, F3 is a measure of the average baryon number and an integral of / F s d x = 3 is expected in the simple quark model, corresponding to the number of valence quarks. Although the experimental demonstration was not without problems all experiments [93] gave a value near 3, actually below 3, with typical uncertainties of r^ 10%. The neutrino experiments are unique for measuring, independently, the quark and antiquark distributions in the nucleon. Together with the charged-lepton inclusive ex-

Neutrino physics

441

periments they leave no doubt about the vaUdity of the quark picture of nucleon structure. If quarks were the only nucleon constituents one would expect the integral of F2 to be equal 1, / F2(x)dx = / x[q(x)+q(x)]dx = Experiments [94] found a value of /F2(x)dx ~ 0.50 di 0.02, indicating that about one-half of the nucleon momentum is carried by other constituents which do not interact with neutrinos. The gluons that are binding the quarks are expected to carry the missing half of the nucleon momentum. This point of view had first been taken by Llewellyn-Smith [95]. But the question why quarks are confined and why they behave like bosons remained obscure at that time. 10.2.3.1 Scaling violations and QCD Once the dominant scaling property of inclusive lepton-nucleon scattering had been uncovered some deviations from the predictions of the simple quark model were observed and called 'scaUng violations'. Such violations of scaling, due to the strong interactions between quarks, manifest themselves through the fact that the structure functions depend not only on x but also on q^. These violations turn out experimentally to be weak, especially at large q^, as beautifully explained in Quantum Chromodynamics (QCD), the theory of the gluon-quark interaction by the colour charge, through the property of asymptotic freedom. QCD predicts logarithmic deviations from scaUng and these effects should appear in high energy neutrino data and manifest themselves as a 'shrinking' of the structure functions towards smaller x as q^ increases. This was indeed observed experimentally, as can be seen from Fig. 10.14. ScaUng is only approximately true for the structure functions. Measurements of F2(x) in three different energy domains exhibit shrinking (Fig. 10.14), as expected in the QCD theory. In that theory the 'shrinking' is the consequence of the emission of gluons in the scattering process. The rate of their emission can be calculated and the q^ evolution of the structure function can thus be predicted and compared with the measurements. Relations between different moments of the structure functions gave first evidence for logarithmic scahng violations. The bubble chamber analysis, combining data from BEBC and Gargamelle [96] was spanning the widest q^ range, and found agreement with the predictions of QCD (see Fig. 10.15). The data from the electronic experiment of the CDHS collaboration [97] covered only the domain of high q^ values and lend further support to this confirmation of QCD because of its high statistics. Let us pause here to examine to what extent these results may be affected by experimental uncertainties. It is important to note that data at large q^ and x < 0.1 were not available because of the energy limitation of the neutrino beams; the lower moments could therefore not be evaluated. The higher moments are strongly dependent on data

Experimental Studies of Weak Interactions T——T

0.09

1—I—I—r ^ ? I

!

r

• CDMS }eCBC/GGM

0.01

0.05

oxx

JL

0.05

JL

0.1

1

»

i

0.5

Moments Fig. 10.14 (left) Scaling violations. Measurements of F2(x) in three different energy domains show shrinking, as expected in QCD [89]. Fig. 10.15 (right) Relations between moments of the structure function xFa are well described by a power law as predicted by QCD [96, 97].

with X > 0.5 and are therefore subject to experimental resolution effects which require important corrections. Other effects, such as Fermi motion of the nucleons in the target nucleus and radiative corrections, are also large. Since, however, the main concern is the q^ dependence of the structure functions and of their moments, these effects are negligible in comparison with the other uncertainties. In summary, there was consistency with the QCD predictions, but the quality of the test did not yet give compelling evidence for spin 1 gluons. In the case of xFs, the valence quark distribution, the theoretical predictions have only one free parameter, the QCD parameter A in the q^ evolution ('running') of the strong gluon-quark coupling constant (for 4 flavours) as

n

12

25^n(qVA0

443

Neutrino physics

In the case of F2(x) the q^ evolution is coupled to the gluon distribution G(x, q^). The experimental results on the q^ evolution of F2 and XF3 (from charged lepton and neutrino scattering) can be adequately described by the theory (see Fig. 10.16) with a value of ^MS ^ ^^^ MeV, corresponding to as(M|) ^ 0.113. 10.2.3.2 New weak currents and the GIM mechanism Neutrinos offer a unique way of producing particles with new quantum numbers by changing the nature of the quark with which they interact. Produced singly, not in pairs, the new quark cannot disappear or annihilate in a final state interaction. This was reaUzed when a new class of events was discovered in the HPWF experiment at Fermilab [98] in 1975, consisting of two muons of opposite charge and a hadron shower. Rubbia showed that these events were due to the decay of a new particle produced at the hadron vertex. Was this naked charm? Hidden charm had been discovered by Richter and Ting in 1974 in the form of the J/i/^ charmonium. The observation at Fermilab was soon studied in detail in the CDHS experiment at CERN [99]. These di-muon events occur with ^1/100 of the rate of all single-muon events. Their study confirmed the weak isospin doublet structure of quarks as proposed by Glashow, Iliopoulos and Maiani (GIM) [100] which is fundamental to the electroweak theory. In the GIM model, the charm-producing reactions are due to new quark flavourchanging currents, in analogy to the mixing of s and d quarks introduced by Cabibbo,

(1) (2) (3) (4)

vd -^ pre vs —> )U~c vd->iU+c vs -^ fi^c

CrossSection xd(x) sin^ 0^ xs(x) cos^ 6c xd(x)sin^0c xs(x) cos^ 9c

with the subsequent decays c -^ jU+vs and c -^ fi~vs. The attribution of dimuon events to charm decays is experimentally supported by the following facts: (a) opposite-sign muon pairs are produced, but no Uke-sign muon pairs; (b) the extra muon has less energy than the leading one; (c) the extra muon is correlated to the hadron shower. The cross sections are proportional to sin^ 6c for d and d quarks and to cos^ 6c for s and s quarks. The Cabibbo angle was known, with cos^ 6c close to one and sin^ 6c = 0.05, very small. Reactions (1) and (2), or (3) and (4) are not experimentally distinguishable because the target nucleon contains both d and s quarks. In the antineutrino case reaction (4) dominates (3) because of the smallness of sin^ 6c. The x distribution for antineutrino dimuon events therefore measures the amount and the distribution of the strange sea quarks (see Fig. 10.17a). The two contributions to the neutrino dimuon events are roughly equal. Using the shape of s(x) determined from antineutrino dimuon events and of d(x)

444

Experimental Studies of Weak Interactions 0.2

I I I I I I I I

I I I I I I I I I I I I I I

(a)

SLAC + BCDMS Hg Dg

0.1 U

"b

:

,190 MeV

B -0.1 5

Aj5is=260 MeV

-0.2 U

330 MeV

-0.3 h

-0.4

i I I I I I I I I

0.2

I I I I I I I L-

0.4

1.0

0.8

0.6 X

0.2

r" L

T"~"

1

1

1

1

1•

r

£

0

"O CO U. X

1

1

1

1

1

1

i j

1

CDHSW

1

\i

\ 1 ^^^^ ^•fj '•. i i

L^

^^'^^'^ni

_

A

1 J

^ ^ * * ' * ^ T Vr * • • ^***«s.J^"*'J * • • .

c -0.1 —

"O

50 MeV

|1

•>

"1 * *

•

^ H

*^* • . ^ 1

AMs=100MeV

-0.2

^ ^ * » . ^ -|

1

fd [J '-j

7 ^

200 MeV

-0.3

-0.4

:

0

1

Q 2 > 5 GeV2, V > 23 GeV

ii

'

1

(b)

Q 2 > 2 GeV2, V > 5 GeV

h ". i 1 1

0.1 h:

1

i \

1

0.1

1

J

0.2

\

1

1

0.3

1

0.4

1

1

0.5

1

1

0.6

1—J

0.7

X

Fig. 10.16 q2 evolution (a) of F2 (x) from charged lepton [86] and (b) of xF3(x) from neutrino scattering [85] as compared with QCD.

Discovery of the bosons of the weak interactions W and Z 300

"I 1 r 1 v „ * N - M**M"*X

r

1

1000

COHS

800

1

1

1

v^ • N -

1

1

1

1

M'^ji** X

445

1

b)

1

CDHS

1

1

axslx) • bxqix)

1 ^ L

J

shape of x s i x ) or x q l x )

Z 600h

•' \ J ^

f '( 400 200

03 x

0.4

05

0.6

0

J

1

"••••^^^^--w 1

0.2

shape of x q ( x )

I ^ -'\' V Vl \t v/

'' 0.1

\

0.1

1

02

1

* ••i--..

1

1

0.4

0.5

0.6

03

1 r H

0.7

X

Fig. 10.17 The x-distributions of opposite-sign dimuon events: source [99]. (a) For antineutrinos (b) for neutrinos.

from normal charged current events one can fit the observed shape (see Fig. 10.17b). The ratio of the two contributions is a measure of Oc The Cabibbo angle obtained in this way agrees, within errors, to 6c measured in strange particle decays, as proposed in the GIM model. Further support for the GIM model was provided by the y distributions. They were found to be flat, reflecting equal helicities of the neutrino and the struck quark. This is particularly striking in the antineutrino case, where the single muon events have a falling, (1-y)^, distribution, because of opposite neutrino and quark helicities. A spectacular event observed in BEBC involving the formation of a D* charmed vector meson which decays in a D meson and a pion, is reproduced in Fig. 10.18. The D meson then decays into a K meson and pions, the K meson colUdes with a proton and produces a E hyperon. Worth a special mention is the first determination of the Ufetime of charmed particles in an experiment [101] combining BEBC and the emulsion technique. The measured lifetime, roughly 5 • 10~^^s, agreed with theoretical expectations. 10.3 Discovery of the bosons of the weak interactions W and Z First experimental evidence favoring a unified description of the weak and electromagnetic interactions had been obtained in 1973 with the discovery of neutral current interactions of neutrinos at CERN [15, 16]. Within the framework of the Standard Model, this experiment gave a first estimate of the electroweak mixing parameter sin^ 0w which led to the first prediction of a new mass scale, that of the W boson ranging from 60-80 GeV/c^ and that of the Z boson ranging from 75-92 GeV/c^. This mass range was not accessible to any of the accelerators in operation at that time. An e^e" collider is the ideal machine to

446

Experimental Studies of Weak Interactions AACHEN - BONN - CERN - MUNICH - OXFORD - COLLABORATION WA21 EVENT 294/0995 vp-^D*pM.LDOTC+

Vu+v Ue+v U+p-*X'7C+ UriTC-

U+p-».np

IIP *

NEUTRINO BEAM MOMENTUM

Fig. 10.18 Production and decay of a charmed D* meson in a neutrino proton interaction in BEBC [101].

produce the Z^ boson in e"*"e" annihilations and to study its properties, and the W boson in pairs (e"^e~ -^ W"^W~) at total energies in excess of 2mwc^. A large e"^e~ collider came into operation at CERN in 1989 and has contributed to the study of the reaction e"*'e" -^ Z with large statistics. The threshold of W pair production is expected to be reached in 1995. While colHders of this type were already being considered and designed in the 1970's, a quick and relatively inexpensive way of producing W and Z bosons (if they existed) was proposed by Rubbia, Cline and Mclntyre [102]. Their proposal was to transform the existing 450 GeV CERN Superproton synchrotron (SPS) into a proton-antiproton collider. In this scheme, a proton and an antiproton beam, each of energy E, circulate on identical orbits in the same ring of magnets in opposite directions, providing head-on coUisions at a total centre-of-mass energy of 2E, a value much larger than that achieved by coUiding one beam with a proton at rest. The proposal met initially with scepticism; machine builders, in particular, were hesitant to have their brand-new SPS transformed into a test ground for the pp collider. Carlo Rubbia stood alone against nearly everyone else in trusting that the collider would work and succeeded, after a while, to convince them. This scheme was adopted at CERN in 1978. The directors-general of CERN at the time, John Adams and Leon van Hove, put the full technological power of CERN behind this

Discovery of the bosons of the weak interactions W and Z

447

ambitious project. The main difficulty was to obtain a sufficiently high pp collision rate for producing W's and Z's by fusing together a quark from a proton and an antiquark from an antiproton. To achieve the required luminosity for producing the intermediate bosons at an observable rate, antiproton beams of high particle density had to be obtained. Since the cross section for producing the W and Z particles at centre-of-mass collision energies of about 500 GeV was calculated to be of the order of a few nanobarns (1 nanobarn = 10"^^ cm^), a luminosity in excess of 10^^ cm"^s"^ was necessary to produce a few intermediate bosons per day of coUider operation. Antiprotons are produced in proton-nucleus collisions at a low rate, typically 10~^ — 10"^ antiprotons per incident proton. They have therefore to be accumulated in a special storage ring over several hours. However, although sufficient in number, the accumulated antiproton beam has a very small phase-space density resulting from the typical 'temperature' of 300 MeV for particles produced in proton-nucleus collisions. It is, therefore, necessary to apply a 'cooUng' technique to increase the p density to values close to those of the proton beam. The technique of stochastic cooling, invented by Simon van der Meer in 1972 [103] was adopted (see also Crowley-Milling, this volume). It makes use of the fluctuations of the average beam position in phase space that occur because the beam contains a finite, though large number of particles. These fluctuations are detected by means of pick-up electrodes around the antiproton accumulator ring. Correction signals are then generated and applied, over a period of time of several minutes, at other points of the ring to either accelerate or decelerate the beam according to the prevaiHng average beam position detected. In this way lO^^p's per day have been accumulated and cooled, accelerated together with protons to 26 GeV in the CERN Proton Synchrotron (PS), transferred to the SPS and accelerated to 270 GeV and after 1984 to 315 GeV (see Fig. 10.19). First pp coUisions at 2E = 540 GeV were observed in 1981 [104]; by the end of 1982 the coUision rate was high enough to permit the observation of W ^ ev decays [105; 106]. In the following year the decays Z^ -^ e"^e~ and Z^ -^ pi^pr were observed [107; 108]. For a detailed report see e.g. L. DiLella in ref. [109]. Here we shall limit ourselves to a brief description of the experiments and of the main results. Detectors at particle colUders consist, in general, of many successive layers of different kinds of detectors, surrounding the interaction region and aiming at a complete detection of all particles produced in the collision. Two detectors were designed and built at CERN for the pp collider. The UAl collaboration, led by Carlo Rubbia built a complete detector [110] consisting of a central tracking detector in a strong magnetic field of 0.7T, an electromagnetic calorimeter, a hadronic calorimeter and a muon detector, all with large angular coverage. The importance of the hermeticity of the detector for the energy flow measurements emerged during the early analysis [110]; it permitted the detection of missing transverse energy carried away by a neutrino which remains of course undetected. In this way the 2 body decay of the W into e+v could be recognized and the W mass of about 80 GeV reconstructed. The second detector was built by the UA2 collaboration [111] led by Pierre

448

Experimental Studies of Weak Interactions

TT70 526 GcV/c ^ '

PS ISR PSB SPS AA —

26 GeV/c PROTON SYNCHROTRON INTERSECTING STORAGE RINGS PS BOOSTER 500 Ge V/c PROTON SYNCHROTRON ANTIPROTON ACCUMULATOR TRANSFER TUNNELS

pO -• 26 GeV/c

100 meters Fig. 10.19 Layout of the three machines involved in the operation of the pp coUider at CERN [109].

Darriulat. It had full calorimetric coverage over the polar angle interval 20^ < 0 < 160^ but no muon detection and a magnetic field in only a part of the solid angle. When searching for Z^ particles the decay modes e"'"e~ and ii^^~ allowed direct determination of the Z mass by measuring the energies of the two leptons and the angle between their directions. Early results [105; 106] which established the existence of the intermediate bosons are shown in Figs. 10.20 and 10.21. Among the properties of the intermediate boson W it is its spin J =\ which is most intimately related to its presumed role as the mediator particle of weak interaction. As a consequence of the V-A coupling, the helicity of the quarks and antiquarks which fuse to form the W is - 1 and -h 1, respectively, and the W spin is polarized in the direction of the p beam. Helicity arguments applied to the decay W —^ eve predict that the leptons (e~ or Ve) should be preferentially emitted opposite to the W polarization direction, and antileptons (e"*" or Vg) along it. The observed angular distribution of electrons with respect to the p beam [112] is shown in Fig. 10.22. It has been shown by Maurice Jacob [113] that the mean value of cos 0* is directly related to the W spin J: (cos0*) = (A)(/i)/J(J+l) where k and pi are the total heUcities of the initial qq and of the final ev states, respectively. The value measured by the UAl collaboration [112]

Discovery of the bosons of the weak interactions W and Z EVENTS

0

WITHOUT

10 Transverse

JETS

20 electron

449

30 energy

1.0

GeV

(GeV)

Fig. 10.20 Early results of the UAl collaboration at CERN [105] establishing the existence of the intermediate W boson.

(cosr) = 0.43 ±0.07

demonstrated that the W spin is one and that the initial and final fermion states have maximal helicity, (A) = (/i) = ±1. Later, more precise values of the masses were measured and confronted with the Standard Model predictions derived from precise measurements of sin^ 0w from deep inelastic neutrino scattering (see Table 10.3). The quantitative success of predicting the Fermi mass scale has been one of the triumphs of the Glashow-Salam-Weinberg theory and also of CERN's contributions to the study of the weak interaction. The outstanding contributions of Carlo Rubbia and of Simon van der Meer were rewarded by the 1984 Nobel Prize for Physics.

Experimental Studies of Weak Interactions

450

1

L zo-- • e ' ^ e -

UAl

L

(a)

L 24 EVENTS

\A

\A_

h

J

CO

H 2 W c > ^-

/

0

70

^

y'

1

T

r-

1-]

"T

149 EVENTS Background subtracted

and

60 "

A

50

A

40

J

acceptance corrected

i

V

H

-4

30

A 20

V _S

1 . 90

T

A

["^zO'= 93.1 GeV/c2

fs

70

1

A A 110

(l+cosdJ)2

/

/

/

/

H

/

-H

\

10 n -0.8

L_J1

0.4

-0.4

1f

0.8

Fig. 10.21 (left) Early results of the UAl collaboration establishing the existence of the Z^ boson [106]. Fig. 10.22 (right) Angular distribution of electrons from W —> ev decays with respect to the p beam direction demonstration that the W has spin one (from UAl [112]).

10.4 CP violation 10.4.1 DISCOVERY OF KL -^ TT+TT" DECAYS: CP VIOLATION OR ALTERNATIVE EXPLANATIONS? The phenomenon of CP violation in decays of neutral K^ mesons was discovered by Christenson, Cronin, Fitch and Turlay [114] in 1964 at the Brookhaven National Laboratory. They were studying the phenomenon of Kj regeneration from a beam of K2. This Table 10.3 Values of mw and mz from measurements by UAl and UA2 and predicted from neutrino scattering experiments.

mw (GeV) mz (GeV)

experiment

reference

predicted

80.8 ± 0.4 ± 0.8(scale) 90.9 ± 0.3 ± 0.2(scale)

[109] [109]

80.2 d= 1.1 91.6 ±0.9

CP violation

451

phenomenon is one of the consequences of the strangeness oscillation scheme of K^ and K^ worked out by Gell-Mann and Pais [115]. It predicts two components, Ki and K2 with short and long Ufetimes respectively. The set-up of the Princeton group was composed of two magnetic spectrometers for detecting the two-pion decay of Kj. Sparkchambers were used to track the pions through the spectrometers. The tungsten regenerator was placed in a Helium filled bag to minimize interactions of K2. To check the background from decays in Helium they removed the regenerator. Some events which were compatible with Kj -^ n^n~ decays remained. Which phenomenon could produce K? in Helium? The authors took nearly one year trying to eliminate those events or to understand their origin. In their pubUcation [114] they wrote T h e events from the gas appear identical with those from the coherent regeneration in tungsten in both mass and angular spread' and concluded that K2 decays to two pions with a branching ratio R = (K^ ^ 7r+7r-)/(K^ -^ all charged modes) = (2.0 ± 0.4) • 10"^ . They emphasized that any 'alternative explanation required highly nonphysical behavior of the three-body decays of the K2. The presence of the two-pion decay mode implies that the K2 meson is not a pure eigenstate of CP but requires an admixture of a CP even amplitude of \e\^2' 10"^' From the experimental point of view confirmation was of course required and some improvements in the detection scheme allowed one to eliminate the 'alternative explanations'. The first confirmation came from Europe. A group at CERN [116] led by Klaus Winter and Marcel Vivargent (Orsay) set out (1) to search for K2 -^ n^n' decays in vacuum, as the preceding experiment had been done in Helium, and to identify the decay particles, using a Cerenkov counter and an iron absorber, and (2) to search for an energy dependence of the two-pion decay rate. They confirmed the result of Cronin and Fitch and eliminated the 'alternative explanations' due to anomalous behavior of the three-body decays of the K2. This fast action at CERN (six months between the publication of Cronin-Fitch and the submission of the paper from CERN) was made possible by Victor Weisskopf granting special priorities to the setting up of the detector. The sparkchamber pictures were analysed by a computer-assisted flying spot device which had been built at Orsay by P. Scharff*Hansen and collaborators under the leadership of Marcel Vivargent. This new technique enabled the group to perform the analysis in a record time. If the two-pion decay of the K2 was induced by a new weak and long-range cosmological field as hypothised by Bell [117] and by Bernstein et al. [119], a branching ratio of 1.6 • 10"^ instead of 2.10"^ would have been observed for the mean K2 momentum of 10 GeV/c at CERN compared to 1.1 GeV/c at Brookhaven. This increase was not found. Physics Today [118] pubUshed a sparkchamber picture of the CERN experiment on the front page and the head line: 'Fifth force finished?' All alternative explanations were

452

Experimental Studies of Weak Interactions

finally eliminated by the observation of quantum mechanical interference between the K^ -^ W^n- ampUtude and the ampUtude of K? -> n^n~ from coherent regeneration. The interference phenomenon demonstrated unequivocally that the long-Hved Kj^ state contains an ampUtude e which is identical and indistinguishable from the Kg -^ n^n~ ampUtude, and, hence K?^ = eK? + K^, or K2 -^ In directly. Val Fitch reported at the 1966 International Conference on High Energy Physics in Berkeley [120] on two types of experiments which were successful in demonstrating this interference phenomenon. One had been done by his own group [121]. They distributed regenerator material over the decay volume of their detector to obtain roughly equal ampUtudes of regenerated Kg -^ jt^n- and of Kj^ -^ n^n- decays. The other results came from the CERN-Orsay group of Winter and Vivargent [122] and from a CERN group led by Rubbia and Steinberger [123]. They measured the time dependence of two-pion decays behind regenerators of different thickness and obtained the relative phase and the beat frequency of the two amplitudes which is proportional to the Kg-Kj^ mass difference. While the method of Fitch was very robust, that of the CERN groups was more delicate but gave much higher precision. The interference term unfolded from the CERN-Orsay experiment (see Fig. 10.23) was shown in the talk of Fitch to demonstrate the power and the beauty of the method. 6=0480^ yf* - 87.5» r:0j900

Seconds

Fig. 10.23 Observed time dependence of the interference between Kg -> TC+TT" and Kj^ -^ TT+TC" amplitudes behind a regenerator unfolded from data of the CERN-Orsay experiment [122].

CP violation

453

A first estimate of the phase of the ratio of K L —> n^n~ and Kg -^ n^n" ampHtudes,
A value of A = +(7.2 it 2.8)% had been reported by a Columbia-Stony-Brook bubble chamber experiment [127] lead by Paolo Franzini from Columbia University and interpreted as evidence for charge-conjugation noninvariance in the decay of the rf^ meson. A CERN-Saclay-Ziirich group led by G. Finocchiaro performed a counter-sparkchamber experiment at CERN [128]. This type of experiment, in general, has more possibilities for asymmetric biases than bubble chamber experiments. However, because of the larger statistics and the previous experience of the group with analysis of cloud chamber data on K^ decays, more checks were accessible to the experimenters. 'In this case'. Fitch reported [120], 'the experiment has obviously been carefully performed and the data treated in a meticulous fashion'. The mass resolution of the instrument was better than that of the bubble chamber and the background therefore substantially lower. The experiment gave a result compatible with no asymmetry and a much smaller error, A = +(0.3 ± 1 . 1 ) % , at variance with Franzini's result and in support of C invariance in rf decay. However, Fitch concluded, if C invariance were violated in if decay, one would expect, on theoretical grounds, an asymmetry of less than 1 % and that question therefore remained open. Later, in 1974, a Rutherford-Westfield College-Sussex group reported [129] on a new experiment, performed at the NIMROD Proton Synchrotron which confirmed the earlier result with an improved error of 0.25%.

454

Experimental Studies of Weak Interactions

There remains, even today, one other experimental search for T violation outside the weak interaction. This is a search for an electric dipole moment of the neutron which is being conducted by Ramsay, and by Lobachov and collaborators. However, at the time of writing this report, no positive effect has been reported. The present limit is d < 12 • 10"^^ e.cm (95% CL) [130]. 10.4.2 OTHER MANIFESTATIONS OF CP NONINVARIANCE Two other manifestations of CP noninvariance in K^ decays are possible, an asymmetry of the rates of the decays KL —»Tieve and KL -^ TT/IV^ according to the electric charge of the pion, and KL decay into 2n^. The value of the asymmetry in KL -^ ntv^ decays depends on the validity of the AS/AQ rule (see Sect. 10.5) and on the real part of the CP even admixture in long-lived neutral kaons, Ree. The rate of KL -^ 2n^ decays can give, in principle, when compared to decays to TC+TT" , decisive information on the question of direct CP violation in the K^ —> nn amplitudes of different isospin. The existence of a charge asymmetry of the K^3 and Ke3 decay modes was first demonstrated in two counter experiments at the 30 GeV Proton Synchrotron of Brookhaven National Laboratory, under the leadership of M. Schwartz [131] and J. Steinberger [132] respectively. The values found were smaller than the maximum, 2|e|, approximately onehalf that value, implying that the CP even admixture e of KL has a non-zero imaginary part, or more generally, that the long-lived and short-lived K^ states are not orthogonal. A measurement of the charge asymmetry behind a regenerator can also determine the phase of the Kg regeration amplitude. This method was pioneered by the CERN-Orsay [133] group but quantitative results were obtained by the Brookhaven group of Steinberger [134]. Combining this knowledge with the results of the interference experiments of K^ -^ n^n~ decay amplitudes behind a regenerator gave a more reliable, but not more accurate, estimate of the phase _,._. The decay KL -^ n^'nP turned out to be much more difficult to observe and to measure because of the difficulty of combining the needs of kinematical reconstruction, in particular the direction of the four photons from TT^ decays, with good detection efficiency. In 1968, at the 14th International Conference on High Energy Physics at Vienna, J.W. Cronin described the situation with the following words [135]: 'At this conference a spectrum of results on KL -^ 'nP'nP has been presented which range from a maximum of \riQQ\ • 10^ = 4.3 down to zero'. He concluded by saying 'the existence of the CP violating decay KL -^ rfin^ is now established. However, the important question remains unanswered, is Y\QQ different from ^+_?'.

10.4.3 PRECISION EXPERIMENTS Following the first demonstrations that the decay KL -^ n^n^ indeed occurs [136] new experimental efforts led to consistent and precise results.

CP violation

455

A CERN-Orsay-Rutherford group detected all four photons from K L -^ 2n^ -^ 4^ decay in thick plate sparkchambers (borrowed from the first CERN neutrino experiment) and determined their direction from the pairs produced and their energy by spark counting. They observed interference of K L and Kg -^ In^ amplitudes behind a regenerator [136] and determined the absolute value and the phase of f^oo- The authors performed [137] a phenomenological analysis of their results and those obtained on ^^_. They decomposed the K^ -^ 2n ampUtudes into a T violating and CPT conserving part and a CPT violating and T conserving part. The data clearly estabHshed T invariance violation at a lOo- level while no evidence for CPT violation was found. However, the important question: 'is J/QQ different from Y\^_\ remained without answer. An Aachen-CERN-Torino group [138] designed a new detector guided by the idea of measuring accurately the energies of all four y rays and the direction of at least two y's of the four from K L —> TT^TT^ -^ 4y decay. The upstream part of the detector was the directionmeasuring region with their converter foils and sparkchambers while in the downstream part the remaining y's are converted and their energies measured in total absorption leadglass counters (see Fig. 10.24). This approach gave results of higher precision. The use of the new technique of multi-wire proportional chambers invented by Charpak [139] improved the position resolution and made a revolutionary change in the data analysis (see also Gambaro, this volume). Track positions were recorded electronically at the time of the experiment, the time consuming measurements of spark positions from films, either manually or by flying spot techniques, became obsolete. A CERN-Heidelberg group led by Jack Steinberger recognized the power of this new technique and built a new detector for K^ decays [140] using these multiwire proportional

61 Leadglass Blocks

Anticounter

Counter Hodoscope

1m

.^1 Anticounter

K? Beam

3.8 m Converter Foils Chamber Modules containing 2X-Y Chambers (0° 90° 2U-V

(45M35**

Coordinates) "

)

Fig. 10.24 Apparatus of the Aachen-CERN-Torino group for the measurement of the Kj^ —^ 2n^ decay rate [138].

456

Experimental Studies of Weak Interactions

chambers (see Fig. 10.25). A vast increase of statistics resulted in a corresponding improvement in precision. In order to be free of the compHcations of regenerators and of the phase of regeneration Rubbia and Steinberger [141] proposed a new technique. In proton coUisions with a nuclear target an excess of K^ mesons over K^ is produced. A K^ state is a coherent superposition of Kg and KL amplitudes. Because of their different lifetimes and In decay rates maximal interference occurs about 12-14 Kg lifetimes away from the target. The phases of r\^_ and ^QO ^^d their absolute values can therefore be directly determined with high precision. An example of such a high precision measurement is shown in Fig. 10.26. At the time of the 16th International Conference on High Energy Physics, Carlo Rubbia [142] concluded that data on ^QO were now consistent and, when compared with those on ^_i__, they excluded a large number of theoretical models proposed to explain CP violation. Only two classes of models survived, the so-called superweak model, postulating a very weak CP violating interaction with AS = 2 [124] and milliweak models invoking a small part (10~^) of the normal AS = 1 weak interaction as the source of CP violation. No significant deviations from the prediction of the superweak CP violation theory

were observed and no theory of milliweak CP violation gave a reliable estimate of how much it would expect to differ with these predictions. It was therefore difficult to assess which precision was needed to confirm or reject either of the two possibilities. In 1973 Kobayashi and Maskawa proposed a specific milliweak model within the Standard Model [143]. At the time of the discovery of CP violation, only 3 quarks were known, and there was no possibility of explaining CP violation as a genuine phenomenon of weak interactions. However, the picture changes if six quarks exist in nature. Then the quark mixing of Cabbibo can be extended to a 3 x 3 mixing matrix containing three mixing angles and a phase. CP violating weak amplitudes can be constructed invoking box diagrams with transitions between quark flavors and famiUes. A necessary consequence of this model of CP violation is the non-equality of ^^_ and ;/oo- This 'direct CP violation' is due to so-called Penguin diagrams for K^ -^ In decay with an amplitude e'. The two models of CP violation differ significantly with respect to the value of e': the superweak model predicts e' = 0, and therefore ri_^_ = rjoQ = e, while in milliweak models one expects e' ^ 0. In the Kobayashi-Maskawa model the value of e' can be estimated by inferring the magnitude of the mixing angles from other experiments. Typical values for the measurable quantity are [144] Re(e'/e) = (1 - |»;oolVl'/+-P)/6 ~ (1 - 2) • lO'^. A measurement of this quantity to this level of precision therefore becomes a challenge for our understanding of CP violation. A measurement of the double ratio

MAGNET TARGET

6 MIRRORS

COLLIMATOR 8 SWEEPING MAGNET

lm

Qg. zg MULTl WIRE PROPORTIONALCHAMBERS

COUNTERS

COUNTERS

Fig. 10.25 New type of detector for KO decays using multiwire proportional (Charpak) chambers built by a CERN-Heidelberg group [140], (a) side view, (b) top view.

P 4

ul

458

Experimental Studies of Weak Interactions

15

20 x(10-''0s)

Fig. 10.26 Example of precise interference experiment using K^ states produced by proton-nucleus interaction [141].

R =

l^/ool' ^ r(KL ^ 27rQ)/r(KL -> 71^71-) |^^_|' r(Ks -^ 27rO)/r(Ks -^ n^n')

to a precision of 0.5% or better is therefore required to distinguish the remaining two models of CP violation and to test the Standard Model prediction. At the time of writing this report, five precise experiments have reported results [145] with a mean value of Re(e7e) = (1.5±0.5)-10 - 3 This result is in good agreement with the range of presently available predictions within the Cabibbo-Kobayashi-Maskawa Standard Model. Further improvements on the experimental side are underway at CERN and Fermilab aiming at a precision of ±0.2 • 10"^ [146].

The weak hadronic current

459

10.5 The weak hadronic current 10.5.1 INTRODUCTION Around 1960 it had become quite evident that the notion of universality of the weak interaction could not be extended to strange particle decays, while in the decays of baryons and mesons without strangeness this concept worked well, except for a five percent discrepancy between G^ and Gp, the Fermi coupling constants deduced from muon decay /I -^ evv and O^"^ -^ N^'^*e"v decay, respectively. At the time of the 1962 High Energy Physics Conference held at CERN there was much discussion about the validity of the AS/AQ = 1 rule. Viki Weisskopf [147] discussed violations of the rule which were reported and showed a cartoon (Fig. 10.27) in this connection, illustrating the uneasiness felt about this matter. In K meson decays the situation was particularly complicated. While no AS = —AQ signal was seen in Ke4 decays [148], a considerable fraction of AS = -AQ decays had been reported in Ke3 and K^3 decays [149]. In the baryon sector AS = +AQ decays A -^ pe~Ve and 2~ -^ ne~Ve were observed with rates [150] which were about twenty times smaller than those predicted by the simplest extension of the universal weak interaction. How could the cherished idea of universality be saved? ewAwwtt vt oiWMM » i m t f KW tewmi

"T/H'S could be the discovery of the century. Depending, of courset on how far down it goes." Fig. 10.27 Cartoon shown by V.F. Weisskopf [147] at the 1962 High Energy Physics Conference in connection with possible violations of the AS/AQ rule.

460

Experimental Studies of Weak Interactions

The idea of baryon octets and decuplets and meson octets as manifestations of an approximate flavour SU(3) invariance of the strong interactions was introduced by GellMann and Ne'eman [151] in 1961. Attempts to introduce these ideas into the classification of weak hadronic currents met with two vital problems: (1) to what extent does the AS = +AQ rule hold in strangeness changing leptonic hyperon and meson decays? (2) Do the AS = 0 leptonic decays of E hyperons have a rate comparable to that predicted by the universal weak interaction or are they also suppressed by an order of magnitude? Answers to these questions came out of close collaboration between experiments at CERN and Nicola Cabibbo who spent the year 1962-63 at CERN. The 28 GeV CERN Proton synchrotron (PS) make it experimentally possible to build an intense separated beam of K~ that stopped in a hydrogen bubble chamber. Stopping K" mesons are a beautiful source of Z"^ hyperons through the reactions K - p -^ S^TT^ .

Such a beam was built in the new North hall of the PS allowing a short distance from the target to the bubble chamber to minimize the loss of K" mesons by decays in flight. CERN designed and built electrostatic separators [152]. The 81 cm hydrogen bubble chamber of Saclay and Ecole Polytechnique Paris was moved from the South hall into this beam and took data starting in December 1962. Already in a test run one event of the AS = 0 leptonic Z hyperon decay Z~ —> Ae~Ve had been observed. A team from CERN with H. Courant and W. Willis as visitors and the Maryland University bubble chamber group led by G. Snow collaborated on the analysis of the AS = 0 and AS = 1 leptonic decays of Z hyperons and reported first results at the Washington Meeting of the American Physical Society in April 1963 [153]. Final results were pubHshed in 1964 [154]. Ten events of the rare AS = 0 decay Z~ -^ Ae"Ve were found and many examples of AS = +AQ Z~ -^ ne~Ve and Z~ -^ n//~Ve decays but no definite example of AS = -AQ Z"*" decays. N. Cabibbo used these results to develop the ideas published in his famous paper 'Unitary Symmetry and Leptonic Decays' [155] (received 29 April 1963). He assumed that the weak current of strongly interacting particles J^ transforms according to the eightfold representation of SU(3), and 'neglected currents with AS = -AQ, or AI = 3/2, which should belong to other representations' if they existed. He also assumed that the vector part of the current is in the same octet as the electromagnetic current. For AS = 0 processes this assumption is equivalent to vector current conservation in the V-A theory for weak interactions [156]. This assumption was supported by the results on the rate of pion beta decay n^ -^ n^t^v as compared to the rate of O^"^ beta decay [2]. Together with the octet of vector (V) currents, j ^ , he assumed an octet of axial vector (A) currents, g^. In each of these octets there is a current with AS = 0 (no change of strangeness), and a current with AS = AQ = 1, and hence

The weak hadronic current

461

The usual, strong form of universality which failed to describe AS = 1 decays would correspond to a = b = 1. Cabibbo introduced a weaker form of universality by requiring that J;^ has 'unit length', i.e. a^ + b^ = 1 and a = cos 0, b = sin d. This hypothesis implies that GF

= G^ • cos 9 ,

thus linking the small difference between Gp and G^ to the small strangeness changing amplitude. On the other hand, since J^ as well as the baryons and the pseudoscalar mesons belong to the octet representation of SU(3), one obtains relations between processes with AS = 0 and AS = 1. Cabibbo estimated the value of 0 from a comparison of the rates for K+ -^ fi-^v and 7r+ -^ /i+v, and obtained 0 = 0.257. For baryons in the SU(3) octet the axial vector matrix element could then be expressed as a function of two parameters, F and D, corresponding to the two ways (odd and even) of forming an octet out of (8) x (8). The two AS = 0 processes, n -^ pe"Ve and Z " -^ Ae"Ve, could then be used to determine the values of F and D; together with the value of 6 and vector current conservation (D^ = 0) this allows one to predict the rates of all three AS = +AQ transitions for which data existed. It worked ! A plot in the publication of the CERN data [154], (see Fig. 10.28) shows how well the available hyperon semileptonic decay data agreed with the Cabibbo hypothesis. The subsequent development is marked by further and more precise experimental studies of hyperon decays using electronic techniques and a hyperon beam (Sect. 10.5.2). Cabibbo's choice of neglecting AS = —AQ currents was fully justified by further experimental work on kaon decays (Sect. 10.5.3) which estabUshed the vaUdity of the rule at the 1% level. Finally, the extension of the Cabibbo theory to six quarks by Kobayashi and Maskawa [157] will briefly be described in Section 10.5.4. 10.5.2 EXPERIMENTAL STUDIES OF HYPERON DECAYS While the early experiments which led to the basic assumptions of the Cabibbo theory were performed in bubble chambers, further tests of the theory and improved precision came from electronic counter experiments [158]. At CERN these experiments were pioneered by a CERN-Heidelberg group led by Heintze and Soergel. They designed an experimental set-up which allowed one to detect electrons from hyperon beta decays and to discriminate them from pions by using a large focusing Cerenkov counter [159]. Tracks were measured using wire chambers. The main advantage over bubble chamber techniques was the trigger which selected events of the reaction K - p -^ S-K+ by requiring a backwards going K+ and a H decay to an electron in coincidence.

Experimental Studies of Weak Interactions

462

0.3

0.4

03

o5

0.7

0.8

o!5

10

1.1

1.2

1.3

Fig. 10.28 A plot of allowed values of F and D showing the constraints on the Cabibbo theory imposed by the various measurements. The shaded bands indicate the experimental errors. The data shown are from the hyperon beam experiment at the CERN SPS [161]. Eariier experiments [154] did already show agreement with the theory.

The set-up, shown in Fig. 10.29, was operated in an enriched K~ beam of 1.65 GeV/c momentum. At each Cycle of the accelerator 7000 K~ and lOO'OOO n~ crossed the detector without problems of event superpositions owing to the short sensitive time of microseconds of sparkchambers compared to the millisecond sensitivity of bubble chambers. The first experiment performed by the CERN-Heidelberg group [159] managed to log 17 events of S~ -^ A(Z^)e~Ve and gave a branching ratio of (6.8 di 2.2) • 10""^ in good agreement with the prediction of the Cabibbo theory (6 • 10~^) derived from other hyperon decays. Several experiments studied extensively the decay A —> pe"Ve during the prehyperon beam era. We refer here to another experiment performed at CERN by the CERNHeidelberg group [160] using the reaction TTN ^> AK just below the SK threshold (P;c ~ 1.1 GeV/c) as a source of polarized A. The detector was the same as that used for studying S" beta decay [159]. About a thousand A beta decay events were observed, and the decay rate and the asymmetry parameters ae, ap and ay of the angular distributions with respect to the A spin were measured as well as the electron-neutrino angular correlation. Good agreement with the Cabibbo model was found and no deviations from the underlying V-A theory, e.g. no second class current, no time reversal violation nor S or T contributions.

The weak hadronic current I

463

PM

"CZK] Fig. 10.29 Experimental set-up for studying H" -^ Ae"Ve and A -^ pe~Ve beta decay at the CERN PS [159]. The S~ and its decay products are observed in the optical spark chamber SP3. T is a focusing Cerenkov counter to discriminate between electrons and pions. Counters 1-6 and Mi-Mn are plastic scintillators, Ci a high pressure ethylene Cerenkov counter for 7r-suppression, C2 a FC75 liquid Cerenkov counter and C3 is a cyUndrical plexiglass Cerenkov counter. The tracks of the incoming K~ and the outgoing K"*" are localized in the wire chambers SPi, SP2 and in the cylindrical wire chambers SP , which have magnetostrictive readout. The target region is shown in detail in the upper left corner.

The construction of hyperon beams, first at the AGS of Brookhaven National Laboratory and the CERN PS, and more recently at the CERN SPS has given the next advance in the field of hyperon beta decay studies. High statistics experiments, with 10^ to 10^ events and up to 10^ events in the case of the A -^ pev decay, have been performed. Hyperon beams are secondary beams of particles produced by striking a target with the primary proton beam of the accelerator. In the case of negative beams they contain X~, S~ and Q~ hyperons and a background of TT". The beam built at the CERN SPS [161] is shown in Fig. 10.30. The main design problem is the short decay length of the hyperons. For example, at 100 GeV/c the decay lengths of E", S~ and Q" are 3.7m, 3.7m and 1.5m, respectively. Therefore, the beam has to be as short as possible. Fluxes of 5000 L~ and 500 H~ hyperons per pulse have been achieved. These hyperons were identified by a compact Cerenkov counter (DISC) developed at CERN. A decay region of 10m length was followed by a magnetic spectrometer and electron identification devices, a lead glass array, a Cerenkov counter and transition radiation counters. Multiwire proportional chambers and drift chambers were used to measure tracks.

P

m

P

Fig. 10.30 Plan view of the apparatus of the CERN SPS hyperon beam experiment [161]. He: helium bags; Li: Lithium radiators; Xe: Xenon proportional chambers; DC: drift chambers.

The weak hadronic current

465

The results of these studies have been analysed in the frame work of the Cabibbo theory in terms of three parameters 0, F and D (see Sect. 10.5.1). We give here the results from the CERN hyperon decay experiment based on five hyperon beta decays [158]. The q^ dependence of the form factors and radiative corrections have been included in the analysis and give a completely consistent picture for the following values F = 0.477 ±0.012 D = 0.756 ±0.011 sine = 0.231 ±0.003 To what extent the different decays constrain these results is shown in Fig. 10.28. The widths of the bands indicate the experimental errors; they overlap in a common region as predicted by the Cabibbo theory. For the beta decay of the Z " hyperon, S " -^ ne'Ve? the Cabibbo theory, based on the other hyperon decay data, predicts a ratio of form factors gA/gv = —0.28 ± 0.02. Earlier experiments had given a positive sign [160], but a more recent experiment [162], performed at FNAL near Chicago, has obtained a beam of polarized E~ hyperons of 250 GeV/c momentum derived at an angle of 3 mrad. From a sample of 90'000 decays they determined, experimentally, gA/gv = —0.327 ± 0.02, in excellent agreement with the prediction, and equivalently, an up-down asymmetry of the angular distribution of electrons with respect to the S spin polarization of OLQ = -0.53 ± 0.14. 10.5.3 THE AS/AQ RULE IN KAON DECAYS Following the wise attitude of Cabibbo to neglect early evidence for AS = - A Q decays [163, 164] and in view of the success of his model [155] in describing hyperon beta decay there was new interest to establish the limits of validity of the AS = AQ rule with higher precision. Such limits can only be determined in a study of semileptonic decays of neutral kaons, K^ and K^. Studies of Ke4 decays [169] K"^ -^ 7r"^7r+e"v which violate the rule can only be used to search for events of the AS= — AQ type; however if none is found they do not determine the limits of validity of the AS = AQ rule. In neutral kaon decays we can have AS = AQ decays, K ^ ^ n'e'^Ve and K^ -^ Tr+e'Vg and AS = —AQ decays, K^ —> Ti'^e'Ve or K Q ^ ' n'e'^Ve. Early bubble chamber experiments [163, 164] performed in the Ecole Poly technique (Paris) heavy liquid bubble chamber at CERN had indicated a sizeable violation of the rule. C. Rubbia had summarized [165] the combined results by stating that they impUed the existence of AS = - A Q currents at the 15% level compared with the octet, AS = +AQ currents; the evidence had a 3 standard deviation statistical significance. A new study of these decay modes was performed by a CERN-Orsay-Vienna collaboration at CERN [166] led by K. Winter and M. Vivargent. They produced an initially pure K^ state in the inelastic charge exchange reaction

466

Experimental Studies of Weak Interactions K+p -^ K^p7r+

using an enriched K+ beam of 2.4 GeV/c momentum. The initial K^ state is propagating by the weak interaction eigenstates Kg and KL and an ampUtude of K^ is building up as a function of the eigentime T elapsed since the K^ production. Using the notation N+ = N(7r-e+v) N" = N(7r+e-v) and the ratio of AS = -AQ to AS = AQ ampHtudes x, one expects the decay rates to vary as a function of eigentime T in the form

N^(T)^i Ml+xlV^s^ + l l - x l V ^ L ^ ±2(1 - |x|^)cos Amre"^^ - 4Imx sin Amre"^^ where Am = mL — ms = 0.54 • lO^^s"^ is the difference of the KL and Kg masses, FL and Fs are the KL and Kg decay rates and F = ^ (FL + FS). The momentum of the initial K^ state was determined from the kinematics of the reaction K"^p —> K^pTr"^. The directions of the p and n^ were measured in a cylindrical spark chamber set-up surrounding the hydrogen target (see Fig. 10.31) and the charged decay products of K^ were analysed in a magnetic spectrometer. One of the decay products can be an electron; the other is a pion. Electrons were identified in a large 14-cell Cerenkov counter; their charge was determined by the magnet spectrometer. The time distribution of a sample of 4778 K^ —> Tcev events is shown in Fig. 10.32. It shows excellent agreement with the expected evolution of K^ and K^ states in the strangeness oscillation scheme predicted by Gell-Mann and Pais [167] and no evidence for weak hadronic currents with AS = -AQ at the 2% level. A result of similar precision was obtained for the real part of x from a measurement of the charge asymmetry in KL —> Trev decays in an electronic experiment by S. Bennett et al. [168] which was discussed in Sect. 10.4.3. A new high statistics search for AS = -AQ K+ -> Tt^Ti^f^'v decays was performed in another electronic experiment at CERN by a Geneva-Saclay group [169] led by R. Mermod and R. Turlay and, again, found no evidence. A detailed review of kaon decays by Chounet et al. [170] helped to clarify the situation. Further evidence for the validity of the V-A theory for kaon decays came from measurements of the branching ratio r(K+^e+v) r(K+^/i+v) •

467

The weak hadronic current " Cw

BCH1 I (~

_

_ ~ '1 2

TH CCH I-L Target

I

(~H 1-5 ~/~ _

Magnet

H ~

/

(~.

)Hm

BHI

~-

,~

---___j-

,,

I I I

Fig. 10.31 Plan view and elevation of apparatus used to detect the production of the initial K° state and its subsequent decay into different modes [166].

The predicted value R = 2 . 1 . 1 0 -5 for axial vector interaction was confirmed by an Oxford group [171] and with the highest precision by the CERN-Heidelberg group [172] at C E R N who found R = (2.45 4- 0.11) 10 -5. These kaon decays are well described by stating, in addition, that the ratios

r(K +

-~ ev)/r(~

+ --+

ev) and F ( K + ~ . + ~ ) / r ( ~ + -~ .+~)

are consistent with the value of sin 0e = 0.231 derived from hyperon beta decays. 10.5.4 G E N E R A L I Z A T I O N OF T H E CABIBBO T H E O R Y While all leptons have the same weak coupling constant this is not so for different quark flavours. Cabibbo had introduced a linear combination of quark states as the weak interaction eigenstate that couples to the u quark with the universal strength. With the discovery of six quarks this quark mixing was generalized by Kobayashi and Maskawa [143]; they introduced a matrix V which describes this mixing by a unitary transformation of the mass eigenstates (d, s, b) into the weak interaction eigenstates (d', s', b'):

468

Experimental Studies of Weak Interactions

8-10''s

Fig. 10.32 Time distribution of observed decays in the N^(7c'^e^v) and in the N (yr^e v) mode. Also shown is the prediction for x = 0, AS = AQ decays [166].

ycd yes y c b \ \ s ytd

yts

ytb

U

This matrix can be parametrized by four parameters, three angles 9i and one CP violating phase d (see Sect. 10.4). Values of these parameters have been determined [173] from nuclear beta decay rates, from muon decay, hyperon beta decay and kaon decay rates; charm-quark couplings have been determined from measurements of single charm production in neutrino processes, yielding |Vud| = 0.9744 ±0.0010 and |Vus|= 0.2205 ±0.0018 and in antineutrino induced reactions, yielding |Vcd| = 0.21 ± 0.03. The coupling Vcs has been determined from the decay rate of D"^ -^ K^e"^v with the result |Vcs| = 0 . 9 6 ±0.10. The coupling ub can, in principle, be determined from the rate of direct quark decays b -^ ue~v, and the coupling cb from the lifetime of b quark hadrons and their semileptonic branching ratio.

References

469

Using these data and constraints one obtains a pattern with a hierarchy in which the mixing angle of the first two quark famiUes, On is larger than that connecting the second and third generations, 0235 and this is again larger than ^13. This pattern remains to be explained by theories beyond the Standard Model, maybe in relation with the quark masses. No experimental evidence for lepton mixing has been found to date [174], but mixing of the neutrino flavours cannot be excluded either. A search for this phenomenon remains one of the great challenges of experimental particle physics. The author gratefully acknowledges the help he received from a large number of physicists who worked at CERN during the period under review. Amongst them he would like to thank in particular the following: P. Darriulat, D. Denegri, L. DiLella, H. Faissner, J.M. Gaillard, K. Kleinknecht, C.H. Llewellyn-Smith, G. Myatt, D. Perkins, K. Schultze, R. Turlay and H. Wahl.

References [1] T. Fazzini, G. Fidecaro, A.W. Merrison, H. Paul, and A.V. ToUestrup, Phys. Rev. Letters 1 (1958) 247. [2] P. Depommier, J. Heintze, A. Mukhin, C. Rubbia, V. Soergel, and K. Winter, Phys. Letter 2 (1962) 23; P. Depommier, J. Duclos, J. Heintze, K. Kleinknecht, H. Rieseberg, and V. Soergel, Nucl. Physics B4 (1968) 189. [3] G. Backenstoss, B.D. Hyams, G. Knop, P.C. Marin, and U. Stierlin, Phys. Rev. 129 (1963) 2759. [4] J.H. Christenson, J.W. Cronin, V.L. Fitch, and R. Turlay, Phys. Rev. Letters 13 (1964) 138. [5] X. de Bouard, D. Dekkers, B. Jordan, R. Mermod, T.R. WiUitts, and K. Winter, Phys. Letters 15 (1965) 58. [6] H. Burkhardt et al., Phys. Lett. B206 (1988) 169. [7] H. Wahl et al., CERN Proposal SPSC/90-22/P253, approved as NA 48. [8] Simon van der Meer, CERN 62-16. [9] For a review see: P. Musset and J.-P. Vialle, Neutrino Physics with Gargamelle, Physics Reports 39C (1978) 1. [10] T. Eichten et al.. Physics Letters 46B (1973) 274. [11] S. van der Meer, CERN-ISR-PO 72-31 (1972). [12] C. Rubbia, D. Cline, and P. Mclntyre, Proc. Int'l. Neutrino Conference, ed. H. Faissner, H. Reithler, and P. Yerwas, Vieweg, Braunschweig (1977) p. 683. [13] UAl Collaboration, C. Albajar et al., Z. Phys. C44 (1989) 15. [14] P. GaUson, Rev. Mod. Phys. 55 (1983) 477. [15] F.J. Hasert et al., Phys. Letters 46B (1973) 121. [16] F.J. Hasert et al., Phys. Letters 46B (1973) 138. [17] J. Steinberger, CERN-EP/88-180. [18] A. Benvenuti et al., Phys. Rev. Lett. 32 (1974) 800. [19] V.F. Weisskopf, The Joy of Insight, New Zork, Basic Books, 1991. [20] M. Bott-Bodenhausen et al., Phys. Letters 24B (1967) 194. [21] M. Block et al., Phys. Letters 12 (1964) 281. [22] W. Lee, Phys. Letters 40B (1972) 423. [23] J.S. Bell, J. Lovseth, and M. Veltman in Proc. Int'l. Conference on Elementary Particle Physics, Sienna 1963, ed. G. Bemardini, G. Puppi (Societa ItaHana di Fisica, Bologna) Vol. 1, p. 555.

470 [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64]

Experimental Studies of Weak Interactions G. 'tHooft, Nucl. Physics B33 (1971) 173. S.L. Glashow, J. Iliopoulos, and L. Maiani, Phys. Rev. D2 (1970) 1285. D.C. Cundy et al., Phys. Letters 31B (1970) 478. S.L. Wu, Rapporteur Tal., Proc. Int'l. Symp. on Lepton and Photon Interactions at High Energies, Hamburg, ed. W. Bartel (1987) 39. CHARM Collab., M. Jonker et al., Phys. Lett. B107 (1981) 241. H. Abramowicz et al., Phys. Lett. B109 (1982) 115. CHARM Collab., J. Dorenbosch et al., Phys. Lett. B180 (1986) 303. S.L. Glashow, Nucl. Phys. 22 (1961) 579; A. Salam and J. Ward, Phys. Lett. 13 (1963) 168; S. Weinberg, Phys. Rev. Lett. 19 (1967) 1264. K. Winter, Proc. Thirteenth Int'l. Conf. on Neutrino and Astrophysics, World Scientific, Singapore (1988) 403. J.V. AUaby et al., CHARM Collab., Phys. Lett. B231 (1989) 317. C.Z. Prescott et al., Phys. Lett. B (1978) 347; B84 (1979) 524. M.A. Bouchiat et al., Phys. Lett. B134 (1984) 46 and M.A. Bouchiat and C.A. Picketty, J. Phys. (France) 46 (1985) 1897. M.C. Noecker et al., Phys. Rev. Lett. 61 (1988) 310. U. Amaldi et al., Phys. Rev. D36 (1987) 1385. G. Costa et al., Nucl. Phys. B297 (1988) 244. G.L. FogH and D. Haidt, Z. Phys. C40 (1988) 379. J.E. Kim et al.. Rev. Mod. Phys. 53 (1981) 211. L.M. Seghal, Progress in Particle and Nuclear Physics ed. A. Faesler, vol. 14, Pergamon Press (1981) 1. M. Holder et al., CDHS Coll., Phys. Lett. B72 (1977) 254. J.V. AUaby et al., CHARM Coll., Z. Phys. C38 (1988) 403. R.C. Allen et al., Phys. Rev. Letters 64 (1990) 330. C.Z. Prescott et al., Phys. Lett. B77 (1978) 347; B84 (1979) 524. M.A. Bouchiat et al., Phys. Lett. B134 (1984) 46 M.C. Noecker et al., Phys. Rev., Lett. 61 (1988) 310. P. Musset, J.-P. Vialle, Phys. Reports 39C (1978) 59. H. Abramowicz et al., CDHS Collab., Phys. Rev. Letts. 57 (1986) 298. J.V. Allaby et al., CHARM Collab., Z. Phys. €36(1987)611. C.H. Llewellyn-Smith, Nucl. Phys. B228 (1983) 205. J.V. Allaby et al., CHARM Collab., Phys. Lett. B231 (1989) 317. G. 'tHooft, Phys. Lett. B37 (1971) 195. H. Faissner et al., Phys. Rev. Lett. 41 (1978) 213. J. Dorenbosch et al., CHARM Collab., Z. Phys. C41 (1989) 567. S.L. Wu, Proc. Int. Symp. Lepton and Photon Interactions at High Energies, Hamburg, ed. W. Bartel (1987) 39. F. Reines, H. Gurr and H. Sobel, Phys. Rev. Lett. 37 (1976) 315. G.H. Georgi and S.L. Glashow, Phys. Rev. Lett. 32 (1974) 438. see e.g. F. Dydak, Proc. Int. Conf. High Energy Physics, Singapore 1990 and J.R. Carter, Proc. Int. Conf. on Lepton-Photon Interactions at High Energy, Geneva 1991. D. Geiregat et al., CHARM II Collab., Phys. Lett. B259 (1991) 499 and P. Vilain et al., Phys. Lett. B281 (1992) 159. D. AUasia et al., WA25 Collab., Nucl. Phys. B307 (1988) 1. N. Armenise et al., BEBC-TST Collab., Paper C023, Neutrino 88, Boston 1988. U. Amaldi et al., Phys. Rev. D36 (1987) 1385. P. Langacker, Proc. 24th Int. Conf. High-Energy Physics, Munich, Springer Verlag (1988), p. 190. T.D. Lee, C.N. Yang, Phys. Rev. Lett. 4 (1960) 307.

References

471

[65] G. Danby et al., Phys. Rev. Letters 9 (1962) 36. [66] M.M. Block et al., Phys. Lett. 12 (1964) 281 J.K. Bienlein et al., Phys. Lett. 13 (1964) 80. [67] T. Eichten et al., Phys. Lett. 46B (1973) 274. [68] G. Beraardini et al., Phys. Lett. 13 (1964) 86. [69] M.M. Block et a l , Phys. Lett. 12 (1964) 281. [70] J.G.H. de Groot et al., CDHS CoUab., Z. Phys. CI (1979) 143. [71] M. Jonker et al., CHARM CoUab., Z. Phys. C17 (1983) 211. [72] D. Geiregat et al., CHARM II CoUab., Phys. Lett. 247B (1990) 131. [73] M.M. Block et al., Phys. Lett. 12 (1964) 281. [74] D. Perkins, Proc. 1963 Int. Conference on Elementary Particle Physics, G. Bemardini, G. Puppi, ed., Societa Italiana di Fisica, Bologna, p. 555. [75] J. Bell, J. Lovseth and M. Veltman Proc. 1963 Int. Conference on Elementary Particle Physics, G. Bernardini, G. Puppi, ed., Societa Italiana di Fisica, Bologna, p. 584. [76] J. Bell, The 1963 NPA Seminars, The Neutrino Experiment, C. Franzinetti, editor, CERN 63-37, (1963), p. 1. [77] D. Perkins, Proc. Topical Conference on Weak Interactions, J. Bell, editor, CERN 69-7, (1969), p. 1. [78] K. Gottfried, Phys. Rev. Lett. 18 (1967) 1174. [79] J. Steinberger, Proc. Europhys. Conf. High Energy Physics, Lund 1969, p. 41. [80] J.D. Bjorken, Phys. Rev. 179 (1969) 1547 R.P. Feynman, Photon-hadron interactions (Benjamin, New York, 1972). [81] J.G.H. De Groot et al., CDHS CoUab., Z. Phys. CI (1979) 143 H. Abramowicz et al., CDHS CoUab., Z.Phys. C12 (1982), C17 (1983) 283. [82] A. Benvenuti et al., Phys.Rev. Letters 36 (1976) 1478. [83] A. Benvenuti et al., Phys. Rev. Letters 37 (1976) 189. [84] B.C. Barish et al., Phys. Rev. Letters 39 (1977) 741, 1595. [85] P. Berge et al., CDHS CoUab., Z. Phys. C35 (1987) 443, Z. Phys. C49 (1991) 187 J. Dorenbosch et al., CHARM CoUab., Z. Phys. C38 (1988) 403. [86] M. Virchaux, A. MUsztajn, Phys. Lett. B274 (1992) 221. [87] A. Bodek et al., Phys. Rev. D20 (1979) 1471. [88] P. Musset, J.P. Vialle, Phys. Reports C39 (1978) 29. [89] D. Perkins, Introduction to High Energy Physics, second edition, Addison-Weslez 1982, Fig. 8.21(a). [90] C.H. Llewellyn-Smith, Nucl.Phys. BIT (1970) 277. [91] K. Schultze, Proc. XVI Int. Conf. High Energy Physics, Batavia-Chicago 1972, vol. 2, p. 207. [92] D. Perkins, Proc. XVI Int. Conf. High Energy Physics, Batavia-Chicago 1973, vol. 4, p. 189. [93] D.J. Gross and C.H. Llewellyn-Smith, Nucl. Phys. B14 (1969) 337. [94] See e.g. in K. Winter, editor. Neutrino Physics, Cambridge Univ. Press 1992. [95] C.H. Llewellyn-Smith, Nucl. Phys. B17 (1970) 277 and Phys.Rev. D4 (1971) 2392. [96] P.C. Bossetti et al., Nucl. Phys. B142 (1979) 1. [97] J.G.H. de Groot et al., CDHS CoUab., Z. Phys. CI (1979) 143. [98] A. Benvenuti et al., Phys. Rev. Letters 34 (1975) 419 C. Rubbia, Proc. 1975 Int. Conf. on Lepton and Photon Interactions at High Energies. Stanford Univ., W.T. Kirk, editor, p. 1049. [99] M. Holder et al., CDHS CoUab., Phys .Lett. 69B (1977) 377 H. Abramowicz et al., CDHS CoUab. Z. Phys. C15 (1982) 19. [100] S.L. Glashow, J. Iliopoulos, L. Maiani Phys. Rev. D2 (1970) 1285. [101] C. Angelini et al., Phys. Lett. 84B (1979) 150. [102] C. Rubbia, P. Mclntyre, and P. CUne Proc. Int. Neutrino Conference, Aachen 1976, Vieweg, BraunSchweig 1977 (ed. H Faissner, H. Reithler, P. Zerwas) p. 683.

472 [103] [104] [105] [106] [107] [108] [109] [110] [Ill] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150]

Experimental Studies of Weak Interactions S. van der Meer, CERN-ISR-PO 72-31 (1972). The staff of the CERN proton-antiproton project Phys. Lett. 107B (1981) 306. UAl Collab., G. Arnison et al., Phys. Lett. 122B (1983) 103. UA2 Collab., M. Banner et al., Phys. Lett. 122B (1983) 476. UAl Collab., G. Arnison et al., Phys. Lett. 126B (1983) 398. UA2 Collab., P. Bagnaia et al., Phys. Lett. 129B (1983) 130. L. DiLella, in Neutrino Physics, Cambridge Univ. Press 1992, ed. K. Winter, p. 445. UAl Collab., A. Astbury et al., Phys. Scripta 23 (1981) 397. UA2 Collab., B. Mansoulie, Moriond Workshop, 1983 Edition Frontieres, p. 609. UAl Collab., C. Albajar et al., Z. Phys. €44 (1989) 15. M. Jacob, Nuovo Cimento 9 (1958) 826. J.H. Christenson, J.W. Cronin, V.L. Fitch and R. Turlay, Phys. Rev. Lett. 13 (1964) 138. M. Gell-Mann, A. Pais, Phys. Rev. 97 (1955) 1387. X. de Bouard et al., Phys. Lett. 15 (1965) 58. J.S. Bell and J.K. Perring, Phys. Rev. Letts. 13 (1964) 348. Physics Today, April 1965. J. Bernstein, N. Cabibbo and T.D. Lee, Phys. Letts. 12 (1964) 146. V. Fitch, Proceedings Int. Conference on High Energy Physics, Berkeley 1966, p. 63. V. Fitch, R. Roth, J. Ross and W. Vernon, Phys. Rev. Lett. 15 (1965) 73. M. Bott-Bodenhausen et al., Phys. Lett. 20 (1966) 212. C. Alff-Steinberger et al., Phys. Lett. 20 (1966) 207. L. Wolfenstein, Phys. Rev. Lett. 13 (1964) 562. T.D. Lee, Proc. Int. Conf. on High Energy Physics, Berkeley 1966, p. 75. R. Friedberg, T.D. Lee, M. Schwartz (unpubhshed) J. Bernstein, G. Feinberg, T.D. Lee, Phys. Rev. 139 (1965) B 1650. C. Baltay et al., Phys. Rev. Lett. 16 (1966) 1224. A.M. Cnops et al., Phys. Lett. 22 (1966) 546. J.M.R. Jane et al., Phys. Lett. 48 (1974) 260. Review of Particle Properties, Phys. Lett. 239B (1990) 11.18. D. Dorfan et al., Phys. Rev. Lett. 19 (1967) 987. S. Bennett et al., Phys. Rev. Lett. 19 (1967) 993. M. Bott-Bodenhausen et al., Phys. Lett. 24B (1967) 438. S. Bennett et al., Phys. Lett. 27B (1968) 238. J.W. Cronin, Proc. Int. Conf. on High Energy Physics, Vienna 1968, p. 280. J.C. Chollet et al., Phys. Lett. 31B (1970) 658. K. R. Schubert et al., Phys. Lett. 31B (1970) 662. M. Holder et al., CDHS Collab., Phys. Lett. 408(1972)141. J.H. Dieperink et al., Proc. Int. Conf. on Instrumentation for High-Energy Physics, Dubna 1970, p. 251. C. Geweniger et al., Phys. Lett. 48B (1974) 487. A. Bohm et al., Phys. Lett. 27B (1968) 321 and Nucl. Phys. B9 (1969) 605. C. Rubbia, Proc. 16h Int. Conf. High Energy Physics, Chicago and Batavia 1972, vol. 4 p. 157. M. Kobayashi, T. Maskawa, Prog. Theor. Phys. 49 (1973) 652. see e.g. J.M. Gerard, Proc. Int. Conf. Lepton-Photon Interactions at High Energy, Geneva 1991. K. Kleinknecht, Comments on Nucl. Particle Physics, (to be pubUshed). G.D. Barr et al., NA 48 experiment at CERN. V .F. Weisskopf, Proc. Int. Conf. on High-Energy Physics, Geneva 1962, p. 929. A Barbaro-Galtieri et al., Phys. Rev. Lett. 9 (1962) 26. G. Alexander et al., Proc. Int. Conf. on High-Energy Physics, Geneva 1962, p. 448. R.P. Ely et al., Proc. Int. Conf. on High-Energy Physics, Geneva 1962, p. 445.

References

473

[151] M. Gell-Mann, Cal Tech Report CTSL-20, 1961 (unpubHshed) Y. Ne'eman, Nucl. Phys. 26 (1961) 222. [152] C. Germain, R. Tinguely, Proc. Int. Conf. on Instrumentation for High-Energy Physics, CERN-Geneva 1962, p. 21. [153] W. Willis et al.. Bull. Am. Phys. Soc. 8 (1963) 349. [154] W. WiUis et al., Phys. Rev. Letters 13 (1964) 291. [155] N. Cabibbo, Phys. Rev. Letters 10 (1963) 531. [156] R.P. Feynman and M. Gell-Mann, Phys. Rev. 109 (1958) 193 R.E. Marshak and E.C.G. Sundarshan, Phys. Rev. 109 (1958) 1860. [157] M. Kobayashi, T. Maskawa, Prog. Theor. Phys. 49 (1973) 652. [158] For a review see J.M. Gaillard and G. Sauvage, Ann. Rev. Nucl. Part. Sci. 34 (1984) 351. [159] J. Duclos et al., Nucl. Phys. B32 (1971) 493. [160] K.W. AlthoflFet al., Phys. Lett. 37B (1971) 531, 537 and Phys. Lett. 43B (1973) 237. [161] M. Bourquin et al., Z. Phys. C12 (1982) 307 1; C21 (1983) 1, 17 and 27. [162] S.Y.H. Sueh et al., Phys. Rev. Lett. 54 (1985) 2399. [163] B. Aubert et al., Phys. Lett. 17 (1965) 59. [164] M. Baldo-CeoUn et al., Nuovo Cim. 38 (1965) 684. [165] C. Rubbia, Proc. Topical Conf. Weak Interactions, CERN 69-7. [166] F. Niebergall et al., CERN-ORSAY-VIENNA Collaboration, Phys. Lett. 49B (1974) 103. [167] M. Gell-Mann, A. Pais, Phys. Rev. 97 (1955) 1387. [168] S. Bennett et al., Phys. Lett. 29B (1969) 317. [169] M. Bourquin et al., Geneva-Saclay Collaboration, Phys. Lett. 36B (1971) 615. [170] L.M. Chounet et al., Phys. Reports C4 (1972) 199. [171] D.R. Botterill et al., Phys. Rev. 171 (1968) 1402. [172] J. Heintze et al., Phys. Lett. 60B (1976) 302. [173] K. Kleinknecht, Proc. Int. Conf. on High-Energy Physics, Munich 1988, p. 98. [174] See e.g. S.M. Bilenky in Neutrino Physics, ed. K. Winter, Cambridge Univ. Press 1991, p. 177.

This Page Intentionally Left Blank

PART III

Technologies

This Page Intentionally Left Blank

CHAPTER 11

The Development of Accelerator Art and Expertise at CERN: 1960-1980. Twenty Fruitful Years Michael CROWLEY-MILLING

Contents 11.1 Introduction 11.2 Accelerator designs and major improvements 11.2.1 New accelerators 11.2.1.1 ThelSR 11.2.1.2 TheSPS 11.2.1.3 SCISR 11.2.1.4 LSR/SISR 11.2.1.5 MISR 11.2.1.6 CHEEP 11.2.1.7 LEP-100 11.2.1.8 Antiprotons 11.2.1.9 LEP-70 11.2.1.10 LEP 11.2.1.11 Two contrasting stages in accelerator design at CERN 11.2.2 What is involved in designing strong focussing accelerators and storage rings? 11.2.3 Improvement programmes 11.2.3.1 SC improvement 11.2.3.2 PS improvement 11.2.3.3 ISR improvement 11.2.3.4 SPS improvement 11.3 The proton-antiproton collider (p-pbar) 11.3.1 Cooling 11.3.2 Rubbia's proposal 11.3.3 The definitive design 11.3.4 The project approved

477

479 481 481 481 481 484 484 484 486 487 489 489 489 490 492 494 496 496 498 498 499 499 501 504 508

11.4 Beam instrumentation and its use 11.4.1 The needs 11.4.2 The instruments 11.5 Accelerator components 11.5.1 Magnets 11.5.1.1 Iron-cored magnets 11.5.1.2 Superconducting magnets 11.5.2 Magnet power supplies 11.5.3 Radio-frequency systems 11.5.4 Vacuum systems 11.5.5 Beam extraction 11.5.5.1 Fast extraction 11.5.5.2 Slow extraction 11.5.5.3 Further developments 11.5.6 Control systems 11.5.7 Aligning the machines 11.6 Relations with industry 11.6.1 Mutual advantage 11.6.2 Working with industry 11.6.3 Development in industry 11.6.4 Does CERN demand too much? 11.7 Concluding remark Notes References

512 512 518 521 522 522 525 527 529 535 538 538 539 539 541 545 547 547 548 548 550 552 552 553

478

11.1 Introduction The development of accelerator art and expertise is a continuous process and a new development is often the result of work done in more than one laboratory. Someone has an idea for an improvement and this may be developed right away in the same or another laboratory, or it may not be immediately appUcable and Ue dormant until either the need for it becomes apparent or advances in technology render it practicable. In many cases an idea or development is started in one laboratory, modified or improved in another and then perhaps further improved or its use extended in a third. This means that it is often difficult to sort out which laboratory has made the major contribution to a given development. This chapter will attempt to describe the contribution that CERN has made to accelerator art in both these areas: new ideas that have been put forward by CERN personnel and ideas that may have originated outside CERN but which have been put into practical use for the first time at CERN, together with the continued development and improvements in all types of accelerator components. In the first part we look at the contribution that CERN has made to the design of accelerators as a whole, the design methods and the improvement programmes, followed by a more detailed description of one of the most original and successful developments, the proton-antiproton collider. The problems of accelerator instrumentation and its use are sufficiently important to warrant a separate section. We follow this with a review of the advances and developments in the component parts that go to make up an accelerator. Finally, we add a few remarks on the relationship between CERN and industry. Although this chapter is mainly concerned with the developments at CERN in the period after the start-up of the CERN proton synchrotron (PS or CPS), it should not be forgotten that significant innovations in accelerator technology were made right from the formation of the provisional CERN. The CERN synchro-cyclotron (SC), although it was conceived as a conventional machine to get some physics experience at the new European laboratory before the proton synchrotron was built, was not just a Chinese copy of existing machines. It incorporated a number of new developments, the major one being the use of a giant 'tuning fork' to vary the frequency of the RF system during the acceleration cycle, instead of the more conventional rotating capacitor. This enabled the machine to run at a high repetition rate and avoided many difficulties, such as rotating joints in vacuum. That said, it was not without its own troubles, as is related in section 4.2.2 of Volume II of this history. In the case of the PS, although the principle of alternating-gradient strong focussing had been proposed elsewhere [1], it was the members of Coward's team, then working at 479

480

The Development of Accelerator Art and Expertise at CERN: 1960-1980

Harwell before moving to Geneva, that pointed out the limitations of the original proposals and offered possible methods of circumventing them [2]. Despite the uncertainties as to whether such a strong focussing machine would work, Odd Dahl, who was then in charge of the Proton Synchrotron Division, proposed the adoption this new principle for the CERN machine and the Council agreed to it. Commenting on this decision, John Adams, at a meeting called to pay tribute to Dahl's 70th birthday, said: 'Undoubtedly this attitude of Dahl, so very characteristic of the man, largely determined the future success of CERN. It would have been so much easier to have advocated the safe course and to persuade the Council of CERN to accept it, but had CERN gone on to build a 10-15 GeV scaled-up Cosmotron, it would probably not have attained its present high standing in the world of elementary particle physics. It was also a very unselfish attitude for Dahl to take, because the whole nature of the Proton Synchrotron Group's work changed thereafter. Instead of being essentially an engineering group scaUng up an existing machine based on well-established principles, it became a physics group studying the theory of accelerators, and only later did it return again to engineering design. Dahl [...] saw his function largely as a mechanical engineer leading an engineering group, but as a result of advocating the new focussing principle he thereby made himself responsible for a quite different kind of project.' [3]

In order to ensure the required precision of the magnetic field around the machine, it was essential to have uniformity between the 100 magnets concerned, and to secure the longterm accuracy of their position around the ring to within a fraction of a millimetre. When CERN's engineers found that the properties of the sheet steel for the magnet laminations varied between the batches by a greater amount than was allowable, they decided to obtain all the laminations before making any of the magnets and to shuffle them. In this way each magnet contained laminations from many batches, so limiting the variation from magnet to magnet [4]. The possibility of changes in the positions of the magnets was taken very seriously, a survey of possible ground movements was made, and a number of possible ways of minimising their effects were explored. The solution chosen was to mount the magnets on a heavy concrete annulus, which in turn was supported onflexiblemounts at the top of concrete pillars which went down into the stable molasse rock. Water was circulated through pipes embedded in the concrete annulus to minimise temperature differences round the ring. It was pointed out that this might be an 'overkill', but in view of the unknowns and the cost of the machine, it seemed a reasonable precaution [5]. The whole period of construction of the PS was one of constant development on a scale and an order of magnitude larger than anything before in this field. Several of the participants have commented on the remarkable spirit of pioneering that gripped the whole team - each new problem was attacked with vigour. Hildred Blewett, a physicist from Brookhaven who was visiting CERN at the time, caught the mood and wrote a very graphic description of the day when the PS reached 25 GeV for the first time [6].

Accelerator designs and major improvements

481

11.2 Accelerator designs and major improvements 11.2.1 NEW ACCELERATORS As already discussed in Section 12.1.1 of volume II of this history, the papers given at the 1956 CERN Symposium on High Energy Accelerators and Pion Physics showed that CERN, preoccupied with building the PS and SC, was not keeping up with new ideas for future accelerators that were coming from other laboratories. On John Adams' initiative, at its December 1957 meeting the Council agreed to the setting up of a small group under Arnold Schoch within the PS Division to carry out research into theory and developments in the accelerator field. This group looked into a number of exotic possibilities. The progress from plasma accelerators to Fixed Field Alternating Gradient (FFAG) machines and then to the proposals for building both the ISR and the 300 GeV proton synchrotron as complimentary machines for CERN has been recorded in detail in Volume II. That account terminates with the approval of the ISR and the postponement of a decision on the 300 GeV. 11.2,1 J The ISR The first definite proposals for storage rings for the PS were widely published [7] some four years before the project was approved, after the difficulties that have been recorded in Volume II of this history. The construction and operation of the ISR are covered by Russo in this volume. There were a considerable number of scientific and technological advances made during this period and some of these will be treated in the sections dealing with beam instrumentation and with the individual components. 1L2.L2

The SPS

Pestre (this volume) has related the events leading up to the approval of the 300 GeV machine. Here we add a few more technical details to the story. As a result of the criticism of the earUer design [8] made after R.R. Wilson's plans for the American machine became known, the ISR Division carried out a study which compared the costs of their original design using combined-function magnets (performing both bending and focussing functions) with a machine of the same energy but using the separated-function design (separate bending and focussing magnets) proposed by Wilson. They came to the conclusion that there would be very little difference in cost, but that the separated-function machine could be about 15% smaller in diameter. Since a 'green field' site provided free by a member state was being considered, this did not seem to matter and the combined-function design was retained^ When it seemed likely that the 300 GeV project would be approved, and Adams returned to CERN, he re-examined the earUer design and looked at all options. He refined Notes: p. 552

482

The Development of Accelerator Art and Expertise at CERN: 1960-1980

the cost comparison between the two types of machine and, although there was Uttle difference between the two figures, he showed a preference for the separated-function design. It allowed what he called the 'missing magnet' option: to install all the quadrupole focussing magnets but only half the dipole bending magnets. This would give half the final energy more rapidly and for less initial outlay [9]. Another important reason for this proposal was that it could stave off calls from some quarters to delay the project and to wait for suitable superconducting magnets to be developed. The missing magnet positions, he argued, could be filled by superconducting ones if they became available later. The attraction of a smaller diameter for a given energy may not have played a part in his choice at that time. It certainly did later when, after the impasse caused by the position taken by the German government, he proposed building the machine in an underground tunnel alongside CERN. In the early discussions, starting in 1961, when synchrotrons of 100 to 150 GeV were first being talked about [9a], Colin Ramm was a strong advocate of such a machine being built next to CERN. The main difficulties were that, if it was built on the surface like the PS, it would involve considerable local disturbance and the deviation of roads etc. Alternatively, if it was put in an underground tunnel, large underground experimental areas would have to be built, as internal targets were still the norm at the time. Some test borings were made that showed that it would be possible to bore a circular tunnel, 1.2 km across, some distance down in the good molasse rock which lay under the unstable moraine on the surface. This size would be sufficient to attain at least 150 GeV. However, at that time the feeling, especially amongst the Council members, was that CERN was big enough anyway and that any large new machine should be built elsewhere in Europe. By the time that Adams was reconsidering building the machine at the CERN site, one of the disadvantages of a deeply buried machine had disappeared. The techniques of both fast and slow extraction of the whole beam from a synchotron had been developed in the intervening period, so that an underground accelerator could feed beams to experimental areas at or near the surface. When he made the proposal for 'Project B' (see Pestre), Adams used the results of the earlier borings, from which he concluded that the maximum diameter that could be safely accommodated was 1.8 km. Under pressure from the physics community, he took the risk of proposing an increase of diameter to 2.2 km even before the results were available for further borings in some doubtful areas. This, together with the savings obtained by using the PS as the injector (a possibiHty which had been considered earlier but only then brought out into the open), as well as the possibiHty of using the West Hall for experiments at lower energy and three years earlier, carried the day at the vital ECFA meeting in May 1970. The support of the physics community, which was necessary for final approval, was thus ensured. The final layout chosen is shown in Fig. 11.1. When the 300 GeV Programme was endorsed it included the construction of a synchrotron with the potential to go to 400 GeV, now christened the Super Proton Synchrotron (SPS), and its experimental areas. There were a number of technical innovations in the design and construction of the SPS and some of these are covered in the later

I he proposed 3(X) OeV site layout The indicated points are as follows A-main rinff. B-injection tunnel, C-eject ion tunnel to West Experimental Hall, D-ejection tunnel to North Experimental Area, t -main control F-mam elettrnal suhitation, (>power house. H —laboratories and office buildings, I-assembly hall, L —water reservoir and pumping station, M —pipeline bringing in cooling viuter from the lake. I to 6 —au\iliar\ buddings and IK cess shafts

300 GeV

*

iili- • ^ -

-----dif

1'-

•-••fc>--.••-

•••.>^" , . . / j /

Fig. 11.1 The final position chosen for the SPS (CERN Annual Report, 1970, p. 145).

484

The Development of Accelerator Art and Expertise at CERN: 1960-1980

sections on the accelerator components. A good description of the construction of the SPS has been pubUshed [10]. 77.2.7.5 SCISR Even before the SPS was finished, the ISR accelerator designers who were not involved in SPS construction were thinking of the next step, and discussing what kind of machine should be built. With the successful operation of the ISR, their first thoughts turned to a higher energy ISR using superconducting magnets, to be built in the ISR tunnel [11]. This would enable the energy to be increased to about 150 GeV per beam. During the first workshop on ISR physics in 1974, it was recommended that a design study should be started on a superconducting ISR, which was now called SCISR [12]. A very detailed study was made and a design evolved which used as many as possible of the existing ISR components (Fig. 11.2). Using a dipole field of 5.12 Tesla, which was considered to be well within the capability of superconducting magnets for DC or slowly varying fields, a beam energy of 120 GeV should have been attainable. The calculated luminosity in the low beta intersections was 4 x 10^^ cm"^ s~* [13]. 77.2.7.4

LSR/SISR

Another possibility that was considered early on was that, since CERN was to have a 400 GeV proton accelerator, the addition to it of a pair of 400 GeV storage rings (LSR) would have interesting physics possibiUties. A small group started studying this towards the end of 1973. The first phase was directed towards a machine using normal iron magnets, to establish the basic scaling features and the limitations of proton storage rings in this energy range. The results of this work [14] indicated that such an LSR could be built and would have a high performance, but at the cost of very high power consumption and an uncomfortably large circumference. Therefore the eff*ort was transferred to a version using superconducting magnets which came to be called SISR. A set of parameters was determined early in 1974 and a review of the physics interest and possibilities was carried out [15]. A detailed proposal was published in 1977 which showed that a luminosity of up to 10^^ cm~^ s~^ should be obtainable in two out of the six interaction regions [16]. These would be provided by undulating the two rings, as shown in Fig. 11.3. No cost estimate was published. 77.2.7.5 MISR A second workshop on future ISR physics was held in October 1976, when another idea was put forward. This was to use the magnets from both rings of the ISR to make a 60 GeV storage ring to collide with the SPS. This was called MISR (Merged ISR) and it would require a new tunnel to be bored, intersecting the SPS tunnel at one point. A

Accelerator designs and major improvements

Injection kickers

Injectk^n kickers

General purpose straight sections

General purpose straight sections

485

Injection septum magnets

Injection septum magnets

Fig. 11.2 The layout for SCISR in the ISR tunnel (CERN Yellow Report 77-20, p. 86).

detailed study was made and a report issued in January 1978 [17]. The work was estimated to cost about 110 MSF and to take just over 3 years to carry out, requiring a 9-month shut down of the SPS towards the end of this period. Three possible locations for this faciUty round the SPS were proposed (see Fig. 11.4).

486

The Development of Accelerator Art and Expertise at CERN: 1960-1980 GP

LB

.

HB

V

Fig. 11.3 Schematic layout of the LSR (CERN Yellow Report 77-21, p. 20).

1L2.L6

CHEEP

Another proposal, made in 1976, was aimed at a different range of physics. This was to put an electron ring in the SPS tunnel and to collide 25 GeV electrons with 270 GeV protons [18]. As a result, early in 1977 an ECFA Study Group was formed, with a strong CERN participation. The aim was 'to assess the physics interest of a high-energy electronproton facility, identify possible experimental problems and investigate the detectors needed to exploit the physics, and to establish the technical feasibility of the scheme put forward'. The report of this study group [19] stated that such a facility, now called CHEEP, would substantially extend the kinematical region accessible to observation, compared to the then possible neutrino and muon experiments. A detector to fit into the SPS tunnel that would cover a great variety of events was described and the design of the electron ring and its intersection with the SPS refined. A 5 GeV electron synchrotron was needed for injection into the electron ring and the possibility of building such a facility was taken sufficiently seriously for an agreement to be made with the Daresbury Laboratory, where the electron synchrotron NINA was being shut down. It was arranged for the NINA magnets to be put in store rather than scrapped, in case they might be needed for CHEEP. No cost estimates were published for this faciUty. A possible location for the electron synchrotron is shown in Fig. 11.5.

Accelerator designs and major improvements

487

Fig. 11.4 Possible locations for MISR (CERN Yellow Report 78-01, p. 62).

77.2.7.7 LEP-100 Meanwhile, the opinion in the physics community as to where the emphasis should be put for future experiments was evolving towards the verification of the theory which would unify the electromagnetic and the weak interactions. The most direct way of producing the heavy intermediate bosons postulated in the theory was to collide beams of electrons and positrons, each with an energy of about 100 GeV. This emerged clearly in the review mentioned above [15] and two groups were set up to look into possible machines and

488

The Development of Accelerator Art and Expertise at CERN: 1960-1980 Proton Synchrotron 26GeV

to LSS6 of SPS

Fig. 11.5 Possible locations for the electron/positron injector for CHEEP (CERN Yellow Report 78-02, p. 182).

experiments. At its meeting in May 1977, ECFA decided to recommend to the CERN Scientific Policy Committee (SPC) that 'an electron-positron storage ring of about 200 Gev cm. energy, possibly with an initial phase of 140 GeV, be considered by the highenergy physics community as the prime candidate for a major European project in the 1980's'. The team gathered together to study such a machine was truly international. Half were CERN staff but the others came from the Rutherford Laboratory in England, from SLAC in the USA and from KEK in Japan. The problems of designing such a machine (LEP) were by no means trivial and, in August 1977, the team pubHshed a report [20]. In the introduction to this it was stated that:

'Some of us feel that there are even more unanswered questions now than there were at the beginning of the study; nevertheless we have obtained a much clearer picture of the difficulties associated with building an electron-positron storage ring in the energy range recommended by ECFA.'

Accelerator designs and major improvements

489

These difficulties included a great sensitivity to closed orbit distortions of only a few millimetres, severe beam-loading effects and a very low field at injection which precluded the use of distributed ion-pumps for the vacuum system. 11.2.1.8 Antiprotons When the proposal for the collision of protons and antiprotons (p-pbar) in the SPS was put forward (see Krige, this volume, and expanded in Section 11.3 below), all the proposals for new or improved ISR were dropped. The work on LEP continued however, since the p-pbar collider was considered simply as an experiment that might show the existence of the intermediate bosons. Physicists judged that LEP was needed to explore this and other fields in greater depth. 11.2.1.9 LEP-70 A new LEP study group was formed in 1977 which called on the help of a total of 49 CERN staff*, 11 from LAL, Orsay and three from other laboratories. As well as the difficulties shown in the eariier study, the estimated cost was thought to be too high, and so a machine about half the size, 22 km in circumference, with about 70% of the nominal energy was considered. Since the energy lost per turn by synchrotron radiation increases as the fourth power of the particle energy, the radius of these large electron-positron colliders has to increase by at least the square of the energy if the RF power needed is to be kept within reaUstic limits. In the case of the machine then being considered, the maximum energy of each beam with conventional copper RF cavities would be 70 GeV for the initial operation. On the other hand, if the work being carried out on superconducting cavities was successful, these could replace the copper ones and the energy could then be taken up to 100 GeV. The initial magnet and vacuum systems would be designed to cater for this increased performance without modification. A very detailed report was issued [21]. This design was discussed in detail by experimental and machine physicists at the LEP Summer Study at Les Houches, organised jointly by CERN and ECFA [22]. The main conclusions of this meeting were that, in view of the prime importance attached to the study of W particles, it was considered that the machine should reach the energy needed for their pair production with 'conventional' equipment. This energy was now estimated at 85 GeV per beam. An increase in the size of some of the proposed experimental areas was also requested. 11.2.1.10 LEP As a result of the meeting at Les Houches, a new study was made for a machine 30 km in circumference, which could reach 86 GeV per beam with copper cavities and eventually go to 130 GeV with superconducting ones. This new study involved 60 CERN personnel

490

The Development of Accelerator Art and Expertise at CERN: 1960-1980

and twelve from other laboratories and was able to draw on the experience gained in the running-in of PETRA at DESY. A report was issued in August 1979 which stated 'Owing to several improvements and to novel construction techniques, the cost increase for this 40% bigger machine has been kept down to 20%.' It went on to propose construction by stages to avoid any increase in the annual budget compared with the earUer design. Only one third of the RF equipment would be installed at first to give an energy of 62 GeV per beam, followed later by the installation of the remainder, to give 86 GeV. The final stage would be the change to superconducting cavities [23]. This design was discussed at a meeting of ECFA held in Rome in September 1979, where it was approved and CERN was requested to proceed with its construction as fast as possible. In the light of pressure from the member states to reduce the cost, and of statements that DESY could build such a machine much cheaper, further ways of saving money were explored. The original plan for a 22 GeV electron/positron synchrotron injector was replaced by modifications of the PS and SPS to accelerate electrons and positrons to 3.5 and 22 GeV respectively. These particles would be provided by a new 600 MeV Hnac and accumulation ring, ACR [24]. The number of experimental areas was reduced from eight to four, the number of klystron galleries reduced from four to two and the initial RF installation from one third to one sixth. This was known as LEP 1/6. Later, the circumference was reduced to about 27 km and the ring tilted from the horizontal and moved so as to reduce the length of tunnel under the foothills of the Jura mountains, where faults in the limestone rock could be expected. This change in position is shown in Fig. 11.6. The difficulties later experienced in boring this part of the tunnel, due to incursions of water at high pressure, showed that this was a wise move. The approval of this version and the construction of LEP is outside the scope of this review. 77.2.7.77 Two contrasting stages in accelerator design at CERN In the above description of the work on new machines at CERN two contrasting stages can be seen. The first stage was the period when the SPS, proposed as the jewel in the crown of CERN and only authorised after years of discussion, was under construction and beginning to start up with a massive experimental programme ahead. The question might be asked why, during this period, no less than five major proposals for new machines, or a massive update of an existing one, came to the surface, were worked out in great detail and actively canvassed amongst the physics community. Certainly one of the reasons was that it had become clear that it took about ten years from the concept of a new large project to it becoming reality, so designers and builders were looking well ahead. A second reason could be that ideas in the high-energy physics community were in a state of flux. However, the main reason seems to be that a highly expert team of machine designers had been gathered together to design and build the ISR and only a few of them had moved on to build the SPS. Although the ISR had some problems to be solved, they still had plenty of time to look into all possibilities, to canvas physics support for them and to respond to every suggestion for a new design study.

Accelerator designs and major improvements

Fig. 11.6 The earlier (dotted) and final (solid) positions for LEP (CERN Annual Report, 1981, p. 20).

492

The Development of Accelerator Art and Expertise at CERN: 1960-1980

In the second stage, the push for the p-pbar and LEP came from the physics community and not the machine designers. Once the CERN management had been convinced of their importance, a much more massive effort was put into the design studies, both inside and outside CERN. Although these two machines were Umited in the type of experiments that could be carried out on them, as were the earlier ISR proposals, these experiments were considered to be of such vital importance in establishing the vaUdity of the current theories that their construction was justified. Adams still thought that an investment as expensive as the LEP tunnel should have more than one use, and insisted that it should be made large enough to house a second machine, a prevision that will become reality if the construction of the proposed Large Hadron Collider (LHC) in the LEP tunnel is approved. 11.2.2 WHAT IS INVOLVED IN DESIGNING STRONG FOCUSSING ACCELERATORS AND STORAGE RINGS? Soon after the discovery of AG focussing it was realised that, while the linear theory could be used to determine the basic trajectories of particles injected into a perfect machine, any practical machine would have defects that would introduce non-linearities that could result in instabilities and the consequent loss of particles. Although the linear equations can be solved analytically, most of those involving nonUnearities require numerical solutions. Nowadays the designers require more and more sophisticated computer programs to provide these solutions, since as the machines become larger and the accelerated currents higher, more and more possible causes of instabilities have to be taken into account and ways found to avoid them. However, computers were only in their infancy when CERN started and the most powerful available for public use was that at the National Physical Laboratory in England. This was used by the Harwell team to look into the effect of non-Unearities in a simple model, but it was expensive to use. It is interesting to note that in the CERN Annual Report of 1965 it was estimated that to perform a full set of calculations for the PS on this computer: 'using the series expansion method and an adequate number of starting conditions, perturbations, working points inside the working diamond and sizes of non-Hnearity [...] would cost about twice the total budget of the PS machine [...]. With work to reduce this cost by careful choice of working conditions, it seems possible to reduce this by a factor of 100, when it would not exceed 100,000 SF.'

In view of this estimate, a 2-dimensional mechanical analogue for phase oscillations was constructed, using a quartz pendulum in vacuum, with electrodes to provide electrostatic forces for simulating the effects of the magneticfields[25]. Later, a second analogue model was made, using electrons 'suspended' in electric and magnetic fields [26]. It was also reported that a program for computing orbits to take account of all known systematic

Accelerator designs and major improvements

493

errors in the magnet (fringing fields, eddy current and saturation effects) was run on the NPL computer in England^, although the accuracy of this report is questioned by Mervyn Hine. CERN was due to get its own computer for these purposes in 1958, a Ferranti Mercury, but progress in the orbit computing programme was slow because of its late delivery^. In 1961 the computing power at CERN was greatly increased by the installation of an IBM 709, although the absence of a link between this and the Mercury caused problems atfirst"^.After these were solved, and the 709 replaced by a 7090, the availability of computing power was not a major problem for the machine designers, their increasingly complex programs being matched by the replacement of the 7090 by a CDC 6600 in 1965 and by the addition of a CDC 7600 in 1972, driven by the requirements of the physics analysis programs. Although outside the scope of this chapter, it should be mentioned that the CERN computer centre, with these and its subsequent IBM and Cray computers, pioneered many advances in computer networking, particularly over long distances, so that member state laboratories and universities could take part in the physics analysis programs. In fact CERN is now the centre of one of the most powerful networks in Europe. Machine design programs use two main principles, matrix matching and ray tracing. Each element of the machine can be represented by a transfer matrix and the earlier programs performed the transformations and matching needed to obtain a closed orbit round the proposed machine. The second type, which needs much greater computing power, traces a sufficient number of individual particles round many orbits of the machine to obtain some idea of the possible instabilities that may take effect and their resultant limitations on intensity in the beam. Most of the computer programs involved in this work are the result of studies at many laboratories. Someone writes a program to solve a particular problem, someone else takes it and extends it to cover other cases, a third adds extra facilities and so on. After a while it is often difficult to say who made the major contribution. At CERN a program, later called AGS, was written for the early design of the ISR by van der Meer and later extended by Keil and others [27]. It was also used for the SPS design, together with a program called FOCPAR, and for the early LEP work. The later versions of LEP were worked out using a new set of design programs called MAD (Methodical Accelerator Design). This was developed in the late 1970s with the aim of providing a standard input description for the various accelerator components. Existing programs used many different formats and if one wished to check the accuracy of one's program by comparison with the results from someone else's, the input data usually had to be reworked. Programs from other laboratories were gradually incorporated into MAD, so that it could handle most problems [28]. Computer programs are also used in the design of the individual components of an accelerator, such as magnetic devices and RF cavities. There is not space to go into these here, but the reader can get some idea of the extent of these from the proceedings of a conference [29]. Although becoming more and more sophisticated, these theoretical design procedures may not take into account all factors that affect the trajectories of the particles in a given Notes: p. 552

494

The Development of Accelerator Art and Expertise at CERN: 1960-1980

machine and it is necessary to carry out experiments on existing machines and compare them with the theoretical predictions to check the vaUdity of the theories. These experiments require the development of new and more sensitive beam instrumentation and this subject is discussed later. However, sometimes the problems are so new that it is necessary to build special apparatus to obtain experimental results. Thus, when the idea of using a Fixed Field Alternating Gradient (FFAG) structure was being considered for the next CERN machine after the PS, a 100 MeV electron model was designed and construction started. When the FFAG scheme was abandoned in favour of exploring the possibility of building intersecting storage rings for the PS [7], there were a number of problems, such as possible instabiHties in coasting beams and unexpected effects in 'stacking', i.e., the addition of further injected pulses of protons to the circulating beam. It was decided to build an electron analogue to investigate these problems. This analogue consisted of a storage ring, about 8 m in diameter, into which could be injected 2 MeV electrons from a Van de Graaff accelerator (Fig. 11.7). At this energy and radius, synchrotron radiation from the electrons is negligible, so they behaved in the same way as high energy protons. This equipment was called CESAR (Cern Electron Storage and Accumulation Ring) and various experiments were carried out to find the best methods of capture, stacking and the avoidance of instabilities and other means of beam loss [31, 32]. CESAR also allowed experience to be gained in producing a very high vacuum in a large system. Before this work was completed instabilities had been observed in the electron storage ring at Stanford, raising further doubts. These were allayed by an experiment in which a beam of protons was stored in the PS for several minutes [30]. The experimental approach was also taken when the effectiveness of beam 'cooHng' was in question for the proton-antiproton coUision proposal. To test this the ICE experiment, described in Section 11.3, was performed. The theory and construction of accelerators is not normally included in physics or engineering degree courses. In 1983 CERN decided to make up for this deficiency by following the example of the succesful CERN Schools of Physics and Computing and instituting a series of CERN Accelerator Schools (CAS). Each year a number of two week courses are held at different locations, mainly in the member states, covering all aspects of the design of accelerators and their technical equipment. Reprints of the lectures given at these schools are issued as CERN reports, and form an important contribution to the literature on the design of accelerators and their component parts. 11.2.3 IMPROVEMENT PROGRAMMES All the accelerators at CERN are continuously subject to minor modifications and improvements to provide better or different beams to the experimenters, but most have also had major improvement programmes to meet new demands. Such plans were drawn up for both the SC and the PS (called the CPS in some references) at around the same time.

Fig. 11.7 Layout of the CESAR experiment (CERN Yellow Report 64-19. Diagram SIS/R/6449, p. 40).

496

The Development of Accelerator Art and Expertise at CERN: 1960-1980

11.2.3.1 SC improvement Taking the SC first, a programme called SCIP was initiated in 1968 to produce a significant increase in the average intensity of the extracted beam. The main items involved were a completely new RF system, using a rotating capacitor instead of the tuning fork, so that the shape of the frequency change during the cycle could be altered from the sine wave imposed by the tuning fork. This allowed a more rapid acceleration and so a higher repetition rate. A new ion source and beam extraction system completed the major changes. The progress and difficulties experienced in this programme are given in detail by Hansen (this volume). 11.2.3.2 PS improvement The improvement programme for the PS was much more ambitious. Although the PS was currently running at more than ten times the original specified intensity, there were demands for still higher intensity. The programme was divided into two parts; the first involved a new main magnet power supply, additional RF equipment and extra cooling, to enable the repetition frequency to be doubled, and the second was the increase of injection energy to overcome space-charge limitations [33]. As the injected current is increased, space-charge causes the beam to become larger. Although the orbit correction systems had allowed a much larger beam to be accelerated in the PS than had originally been expected, the limit had now been reached at the injection energy of 50 MeV. The only way to increase the intensity further was to increase the injection energy, which would reduce the effect of space-charge on the beam size. A number of possibilities were explored, from an injector linac of 200 MeV to various schemes to boost the beam from the present 50 MeV Unac to a higher energy. Finally, it was decided that the most effective would be an 800 MeV Booster consisting of four separate rings, one above the other, so that the beam from the linac could fill each in turn and then, after acceleration and reduction in beam size, the four beams could be extracted sequentially, merged together and injected into the PS [34]. The construction of this was approved and a new SI (Synchrotron Injector) Division was set up at the beginning of 1968 to build this Booster. After transfer of some personnel, the new SI Division soon got under way and progressed rapidly with the design. The new power supply was installed in the PS and brought into operation in 1968 and work started on a 3 MeV model for the first part of a possible new linac^. Prototype magnets were deHvered the following year and most orders placed^. By the end of 1970, the civil engineering work was nearly finished and the majority of the components ordered or delivered. Installation started in 1971 and was completed in 1972. The Booster first operated in May 1972 and was approaching its design requirements at the end of the year, when the SI Division was dissolved and the Booster became the responsibiHty of what was now the MPS Division. Monoturn injection into the four rings presented no problems and filling with 100% efficiency became a well established procedure. Multiturn injection caused a few difficulties, but sufficient intensity could be built up

Accelerator designs and major improvements

497

on one ring to show that space charge problems should be manageable at the design intensity of 2.5 x 10^^ protons per pulse per ring^. An intensity from the PS of 5 x 10^^ pps was delivered regularly for a neutrino experiment the following year, thus meeting the intermediate stage target value [35]. As for the PS itself, although there were only two major changes as part of this improvement programme - the new power supply and additions to the RF system nevertheless so many individual components had been exchanged for new and improved ones over the years that it was remarked in 1972 that the only original parts now remaining were the main magnet and the linac structure. Plans for the replacement of even the latter were being considered^. The original 50 MeV linac had reached the practical limit of routine development and in order to meet the increasing demand of the ISR and the future SPS it would have been necessary either to rebuild it completely or build a new one. On the basis that to rebuild the existing one would cause an unacceptable interruption of the physics programme, and would not cost much less than building a new one, the construction of a new 50 MeV linac was authorised in October 1973^. This time it was designed and built by CERN instead of adopting an existing design, as was the case for the original linac. It was not until 1978 that this was completed, the first beam being accelerated to 50 MeV in September of that year. A month later the design intensity of 150 mA was reached, three times the normal output of the old one^^. Another important development of the PS was its multipulsing capability. The original scheme allowed sharing of a PS pulse between different users, in various ratios which could change between pulses. The requirements increased when the PS started supplying beams to the ISR and SPS when both the energy and intensity had to change from pulse to pulse. Extreme complexity was required for the p-pbar programme where the PS equipment had to go through a series of operations as comphcated as any ballet, but to nanosecond precision. The control system was evolved so that one operator could tune up a beam for one user at the same time as a second was working on another beam, without interference. A typical sequence of pulses supplied by the PS in 1982 is shown in Fig. 11.8.

26GeV/c

26 GeV/c

lOGeV/c

Double-batch transfer to SPS atlOGeV/c

East Hall (24 GeV/c) orISR(26GeV/c)

p production forAA(26GeV/c)

ISR(26GeV/c) or East Hall (24 GeV/c)

Tests for LEAR

Fig. 11.8 A typical example of a repetitive sequences of cycles (supercycle) used to supply the numerous PS customers in 1982 (CERN Annual Report, 1982, p. 86). Notes: p. 552

498

The Development of Accelerator Art and Expertise at CERN: 1960-1980

Deuterons and helium nuclei (alpha particles) had been accelerated in the old linac since 1974 and now, with the new linac taking over for protons, the old one was available for experiments to improve the alpha particle beam needed for an ISR experiment^ ^ Later, heavier nuclei were accelerated, initially oxygen O^"^ in 1986 followed by sulphur S^^"^ in 1987. These were injected into the PS and SPS, providing the highest energy heavy ions at that time. Thus the PS ended up becoming the most versatile high energy accelerator in the world, accelerating protons, antiprotons, electrons, positrons and a whole range of heavier ions. A report in 1983 gave a Ust of 19 different combinations of beams and particles the PS was supplying, or would supply in the future [36]. 11.23.3 ISR improvement Although the ISR did not have a formal improvement programme there were substantial modifications made to the rings during their lifetime. The most important of these was to the vacuum system, after the onset of the 'pressure bumps' which occured once the stored current exceeded a few amperes. This necessitated a revised bake-out schedule, glow discharge cleaning and the addition of a large number of sublimation pumps, as described by Russo (this volume). As this required major work on the vacuum chambers, it was carried out a sector at a time in the scheduled shut-downs. Thus, over the years, as more and more sectors were treated, the maximum stored current increased until it reached about 60 amperes and the average pressure was below 10"^^ Torr. Another major addition to the ISR was the superconducting low-beta section installed in 1981, which increased the luminosity at that intersection by a factor of 6.5 to above 10^^cm~^s"^ (see Sect. 11.5.1). 11.2.3.4 SPS improvement Despite the SPS soon reaching the design intensity, more was wanted. The first stage was to hold the magnetic field at the injection energy long enough for two batches of protons to be injected from the PS. Although this caused some beam loss at first, this was soon minimised. This was followed, less than a year after the first operation, by the instigation of an improvement programme to increase the SPS intensity to at least 3 x 10^^ protons per pulse. This involved the construction of a new inflector to allow up to five batches to be injected from the PS, taking advantage of the shortened PS cycle. To cope with the increased beam current, the RF power was doubled ^^ and later it was decided to add two 800 MHz cavities for Landau damping, to suppress the 628 MHz instabiUty which had been observed, and to fit stronger multipole magnets^^. Subsequent improvements to the SPS were mainly connected with the p-pbar programme (Sect. 11.3) and the decision to use the PS and SPS as injectors for LEP instead of building a separate injector synchrotron.

The proton-antiproton collider (p-pbar)

499

11.3 The proton-antiproton collider (p-pbar) One of the most exciting innovations at CERN was the proton-antiproton coUider. The origins of this proposal are discussed elsewhere in this volume, but some of the more technical developments will be gone into here. The idea of colliding particles of opposite charges in the same ring to obtain a greater release of energy in the centre of mass was first put forward by Wideroe in 1943. At that time he was thinking of the proton and the negative hydrogen ion. It was nearly twenty years later, in 1960, that this idea was taken up again, by Bruno Touschek at the Laboratori Nazionale di Frascati, this time using a particle and its anti-particle, and coUiding electrons and positrons. This led to the construction of the first electron/positron storage ring ADA [37]. This was followed by another, higher energy, machine ADONE at Frascati, as well as others in France, the USA, Germany and the USSR. A beam of positrons can be obtained by bombarding a heavy target with high energy electrons and using strong magnetic fields and rapid acceleration to reduce the radial excursion of a cone of positrons emerging from the target. If this beam is now injected into a storage ring, the high energy positrons emit synchrotron radiation which damps down their oscillations, so the size of the beam shrinks. Further injections can build up an intense circulating beam of positrons, to coUide with a beam of electrons injected in the opposite direction. Similarly, antiprotons can be obtained by bombarding a heavy target with high energy protons, but here the similarity ends. The yield is very much smaller - about one antiproton for every thousand 25 GeV protons incident on the target. Due to the greater mass of the antiproton compared with the electron, neither focussing nor acceleration are as effective in reducing the size of the beam and so only about one in every thousand antiprotons produced can be formed into a beam suitable for injection into a storage ring, following which there is negUgible synchrotron radiation to damp down the oscillations. Despite this, the possibility of storing antiprotons was mentioned in the early proposals for proton storage rings for the CERN PS [7]. A scheme using 400 GeV protons from the SPS to produce 28 GeV antiprotons to inject into the ISR was later worked out. The expected intensity was too low, however, to be of sufficient interest for the estimated cost of about 25 MSF [38]. 11.3.1 COOLING The first serious proposal to build a proton-antiproton collider was made by G.I. Budker in 1966. He suggested the use of electron 'cooling' to reduce the antiproton beam size and allow more intense beams to be built up. The idea was to coast a beam of electrons, travelling at the same velocity and so at a much lower energy, together with the beam of antiprotons. Then if the electrons have small transverse velocities, a 'cool' beam, the interaction between the two beams could result in the transfer of transverse momentum from the antiproton beam to the electron beam, thus cooUng the former [39]. Notes: pp. 552 ff.

500

The Development of Accelerator Art and Expertise at CERN: 1960-1980

Although Budker is generally credited with this idea, G.K. O'Neill claimed to have proposed it some years earUer and to have given it the name 'electron cooling', a claim that Budker did not contest. An experiment to demonstrate the effect was carried out at Novosibirsk [40] and work on the coUider started, although it was never finished. In 1968, Simon van der Meer at CERN came up with an idea which he originally called 'stochastic damping' and which he thought might be applicable to reducing the betatron oscillations of beams of protons in the ISR. However, when he worked out the magnitude of the effect he decided it was not of great interest and so did not pubHsh anything about it until pressed to do so four years later by his colleagues [41]. It became generally known as 'stochastic cooling'. The idea was that, although Liouville's theorem states that the emittance of a beam (the product of its divergence and radial extent at any point) cannot be reduced by external fields, this can apparently be circumvented for beams made up of a finite number of particles. For such a beam of charged particles oscillating in a magnetic field, there must be a statistical variation of the position of the centre of charge along the beam, so that, if this variation could be detected, it would be possible, with a suitable feedback system, to reduce the ampHtude of the oscillations. The impetus for pressing van der Meer to publish his idea came from the development of the so-called Schottky scan (by analogy with Schottky noise in a thermionic valve) which showed that the statistical variations of beam centroid position could be detected (see Section 4). The type of feed-back system needed is shown in Fig. 11.9. The transverse position of the centre of charge of the beam is detected at one point in the ring, the resultant signal ampUfied and used to provide a transverse kick at a position (n + 1/4) betatron wavelengths downstream to reduce the oscillation. These signals can take a 'short-cut' across

transverse pick-up

transverse kicker

Fig. 11.9 Simplified diagram showing transverse cooling (Report CERN/PS/84-32 (AA)).

The proton-antiproton collider (p-pbar)

501

the ring, which allows the transmission delays to be compensated for, so that the kicker works on the same portion of the beam that produced the signal. The pick-ups, amplifiers and kickers should have a very high frequency response, in the gigahertz range, so that portions of the beam as short as possible are sampled and fed back. The requirements for the feedback system were worked out [42] and it was shown that they were just within the capabilities of existing ultra-high frequency RF amplifiers. Following this, a practical test was proposed and carried out on one ring of the ISR in October 1974, when the vertical beam size was repeatedly reduced by a few percent when the system was turned on, and allowed to increase when it was turned off [43]. The beam size is also affected by the spread of momenta of the particles in the beam and a similar damping scheme was evolved by Thorndahl. Here the deviation from the reference orbit was measured by picking up signals and passing them through 'notch' filters which give zero response at the revolution frequency of the central momentum but give signals of opposite sign for higher or lower momenta. These can be used to accelerate or decelerate the sample to reduce the deviation [44] (see Fig. 11.10). 11.3.2 RUBBIA'S PROPOSAL With these two possible means of reducing the size of an antiproton beam so that successive pulses could be stacked and the intensity built up, it was not long before further ideas for proton-antiproton colUders followed Budker's original proposal. The first one published [45], proposed the use of 100 GeV protons from the Fermilab machine to produce 3.5 GeV antiprotons which would be stored and cooled in a small ring until sufficient intensity was built up. They would then be extracted and injected into the main ring, where they would be accelerated, together with a counter-rotating beam of protons, to produce coUisions at a total centre-of-mass energy of about 500 GeV. The possibilities longitudinal pick-up

longitudinal kic)(er

Fig. 11.10 Simplified diagram showing momentum cooling (Report CERN/PS/84-32 (AA)).

502

The Development of Accelerator Art and Expertise at CERN: 1960-1980

of using either electron or stochastic cooUng were mentioned, but no details were worked out. Rubbia did not succeed in persuading Fermilab to take up this idea, as they were fully engaged in a project to add a superconducting ring to their machine. He had better luck at CERN, where the possibilities were recognised by the physicists and a second proposal worked out, though it was also realised that there might be unknown difficulties. During 1976, working parties examined the possible schemes and the physics potential, as a result of which Adams set up two groups, one to construct a ring to carry out experiments in both electron and stochastic cooUng (ICE - Initial Cooling Experiment), and the other to look into the requirements to provide a p-pbar (proton-antiproton) colliding facility in the SPS. The cooling ring was built up rapidly, using a set of magnets that had originally been part of the muon storage ring for the (g-2) experiment, which had just ended. This storage ring owed more to accelerator technology than most experiments, consisting of a ring of 40 magnets with a uniform field, weak focussing of the muons being provided by electrostatic quadrupoles. A pion beam was injected and the pions decayed to muons in the ring. These continued to circulate during their lifetime while measurements were made. The magnetic field round the ring had to be kept uniform to extraordinarily tight tolerances [46]. The magnets from the (g-2) experiment were fitted with modified pole pieces to give alternating gradient focussing and assembled into a rounded square with four bending quadrants and four long straight sections to give room for the different types of cooling equipment (see Fig. 11.11). It was completed in under a year. The first tests showed momentum cooling in December 1977 and simultaneous cooling in all three planes was achieved in 1978 [48]. Figure 11.12 shows Schottky scans taken before and after momentum cooling in ICE. As the beam is cooled, the signal narrows and comes to a peak. The original idea was to cool the medium energy (3.5 GeV/c) protons stochastically and then to decelerate them to 100 MeV kinetic energy when they would be cooled further with electron cooling, as this is only effective at relatively low energies. However, the test on ICE showed that stochastic cooling alone would provide sufficient increase in phase-space density during the cycle time of the PS (which was to provide the antiprotons for stacking in an accumulation ring). The additional electron cooUng could thus be dispensed with, bringing a welcome simplification to the proposed scheme [47]. The experiments on electron cooling lagged behind those on stochastic cooling since the equipment for it took longer to prepare. Although no longer required for the proposed p-pbar facility, important information was obtained in the comparison of experimental and theoretical results that was to be of value for use in LEAR (see below) Up to this time, there was no information on the lifetime of antiprotons beyond some hundreds of microseconds, and so antiprotons were injected into the ICE ring and stored. The results gave a lower limit to their Hfetime of 1700 hours [48].

Fig. 11.11 Layout of the Initial Cooling Experiment (ICE) ring (CERN Annual Report, 1977, p. 49).

504

The Development of Accelerator Art and Expertise at CERN: 1960-1980

Fig. 11.12 Schottky scan of momentum distribution before and after cooling in ICE (CERN Annual Report, 1978, p. 17).

11.3.3 THE DEFINITIVE DESIGN The original proposal called for 26 GeV/c protons from the PS to be directed onto a target and the antiprotons produced to be focussed and directed into a storage and cooling ring. This was to have a very wide aperture operating at a fixed field corresponding to a nominal momentum of 3.5 GeV/c. Each injected pulse would undergo a rapid cooling to reduce its momentum spread (precooling). It would then be deposited by an RF system at the top of a stack which had a slightly lower momentum than the injected beam. The stack would be cooled continuously, both longitudinally and transversely, so the particles would slowly migrate to the bottom of the stack, where finally a beam of sufficient density would be formed. The RF system would then capture a fraction of the stack and accelerate it to the extraction orbit, when it would be extracted and injected into the SPS. PS type cavities would be added to accelerate the antiprotons in the SPS to 18 GeV/c whereupon the existing RF system would take over to accelerate them, together with protons injected from the PS, to the storage energy of 270 GeV/c [47]. It was later decided that the risk of losses involved in injecting into the SPS at as low an energy as 3.5 GeV/c was great enough to warrant returning the antiprotons to the PS to be accelerated to 26 GeV/c before transferring them to the SPS. In that way, the problems of the SPS were eased at the expense of one more complication in the choreography of the PS. This led to the arrangement shown in Fig. 11.13, which also allowed for the injection of antiprotons into the ISR. This was done once the project was completed, allowing comparisons between p-p and p-pbar reactions at that energy level [49]. The final scheme thus comprised several parts: modifications to the PS, the antiproton target, the Antiproton Accumulator (AA), modifications to the SPS and the various beam

The proton-antiproton collider (p-pbar)

V-^

SPS

\ .

V

^ ^ s , ^ p26-*270Gev/c

\ ^

\

> ^

XP^^*""

V

\

^

>^^^^^^K^

p26—270Gev/c

rv60-—•^''^

kk-^-^ilfx \

^^^^OV

r^° 1

^lp26Gev/c

// "^"^^"^X^(^^

x:^s^^^^^^^-—::=-rn

100 metres

'

505

TT?/ " " ^ S V ^

\

pO —26Gev/c

PS

b

i

1

Fig. 11.13 The p-p bar project. The Antiproton Accumulator (AA) is in the centre with its return path to the PS. New tunnels TT70 and TT6 allow injection of antiprotons into the SPS and ISR respectively (CERN Courier March 1980, p. 18).

lines and tunnels. This work was shared out between the divisions most concerned, so as to put the maximum number of personnel on the design and construction. In short, once it had been decided to go ahead with the project, there was considerable pressure to complete it as soon as possible. The proposed AA was only a quarter of the circumference of the PS and since the maximum number of antiprotons was needed from each pulse, the protons in the PS had to be concentrated into one quarter of its circumference. This was done by combining the beams from the four Booster rings in pairs, thus injecting two sets offivedouble intensity bunches into the PS where they were accelerated to 26 GeV. By RF manipulations one set of bunches was then accelerated slightly and the other decelerated until the two sets of bunches merged, at which point they were extracted and directed onto the antiproton target. This target presented a number of problems. The beam from the PS had to be focussed into as small a spot as possible, but the target had to be long enough for most of the protons to interact. This led to a target a few mm diameter and about 10 cm long. Tungsten was originally proposed but calculations of the thermal shock when over 10^^ protons hit it caused some doubts, although it was used for the first successful tests. Later

506

The Development of Accelerator Art and Expertise at CERN: 1960-1980

targets used a number of pieces of copper, mounted in a graphite sleeve to conduct the heat away [50]. For focussing the antiprotons from this target a magnetic horn was used, a modification of an idea put forward for focussing the parent beam in a neutrino experiment [51]. An intense pulse of current passing along the horn provides a strong focussing field on any particles that stray outside it. Antiprotons of about 3.5 GeV/c, the peak of the spectrum with 26 GeV/c incident protons, were then selected and directed into the AA ring. The intense radiation produced in the target area required heavy shielding and remote actuators to change the target, but the momentum selection of the antiprotons kept the radiation in the AA to a much lower level. Even with the magnetic horn and subsequent quadrupole focussing, the antiproton beam size was large and, to contain this and the stored stack, the AA had to have a vacuum chamber which was as wide as 70 cm in some places and as high as 20 cm in others. A separated function system was used but, to leave as much space as possible round the ring for the cooling systems, etc., no separate multipoles were used. All the necessary corrections were provided by suitably shaping the ends of the magnet poles [52]. Some of these wide aperture magnets were so short that it was said that they were just two end-effects joined together! A layout of the ring is shown in Fig. 11.14. It was necessary to have a kicker magnet in the AA ring to deflect the incoming beam onto the right path, but the stray field from this magnet could affect the stored beam. Thus it was necessary to insert a shield in the form of a shutter between the kicker magnet and the stored beam (see Fig. 11.15) during injection and then remove it to allow the newly injected beam to be added to the stack after precooling. The moving shutter mechanism, actuated through bellows in a huge bakable ultra-high vacuum tank was one of the most challenging engineering problems in the construction of the AA. The precooling must reduce the momentum spread by a factor of eight in the two seconds between pulses from the PS. It is carried out in momentum phase-space because this can work faster, but it involves an appreciable transfer of energy to the beam, requiring the use of a kicker in the form of a ferrite cored transformer. One leg of the yoke has accordingly also to be moved at the end of the precooling period, to allow the beam to pass over to the stack. The stack itself is cooled in all three dimensions by two different systems, a stack tail cooling to merge the deposited beam with the stack, and stack cooling gradually to increase the density at the core of the stack. The three systems are as shown in Fig. 11.16. The progress of the cooling sequence is shown in Fig. 11.17. When sufficient antiprotons have been accumulated in the dense core, they are extracted and directed along a beam line that turns them through more than 180° to join the beamline which was used to supply protons to the ISR. Going in the opposite direction, the antiprotons can be injected into the PS without changing the polarity of the magnetic field. Acceleration from 3.5 to 26 GeV in the PS provided no serious problems, but it was then necessary to compress the bunches just before extraction, so that they would fit in the SPS 200 MHz buckets. The PS also had to provide 25 GeV/c protons to inject into the SPS in the normal direction.

I

I

I

---

-

.-

F~P. 11.14 Layout of the Antiproton Accumulator (Report CERN/PS/AA 78-3).

- - Q

508

The Development of Accelerator Art and Expertise at CERN: 1960-1980

Shutter

Ferrite

Fig. 11.15 Injection kicker for the AA (Report CERN/PS/AA 78-3 (modified for Physics of Particle Accelerators, AIP Conference Proceedings 153, New York, 1987) (article by E.N.J. Wilson).

The most significant modification needed to the SPS was the provision of the two gigantic underground experimental areas, the first for the UAl experiment where the W and Z^ werefirstdetected and the second for the UA2 experiment. The site for thefirstwas chosen at one of the access areas where the SPS was nearest the surface, so that the 'cut and fill' method could be used (Fig. 11.18), but the second had to be at a deeper point where tunnelling was necessary. There were also considerable modifications needed to the accelerator. The vacuum had to be improved by the fitting of additional pumps and low-beta insertions had to be made in the lattice at the two experimental areas [53]. 11.3.4 THE PROJECT APPROVED The first design for the AA was published in January 1978 [47] and the project was approved in July 1978. By now, CERN had very experienced teams of accelerator designers and builders, and the work proceeded at a great pace. By the end of 1979 the building for the AA was complete and components were arriving, though there was some delay in the delivery of magnets, due to a protracted industrial dispute at the firm supplying them^"*. However, all was complete for the first tests to be carried out on 3 July 1980, when a beam of 3.5 GeV/c protons from the PS was injected and circulated for a few

The proton-antiproton collider (p-pbar)

509

PRECOOLING

-'-^-

STACK TAIL COOLING

•-^.

STACK CORE COOLING

-^ Fig. 11.16 The different cooling systems in the AA (CERN/PS/84-32/AA).

hours. Since the SPS was shut down for the major modifications described above, the available running time for most of the rest of the year was taken with detailed tests, still using protons, to determine the characteristics of the machine, and stacking and cooling was carried out. In the last running period, antiprotons were stacked and injected into the PS'^ When the SPS was able to operate again, 10 antiprotons were injected into it. Notes: p. 553

510

The Development of Accelerator Art and Expertise at CERN:

1960-1980

The first pulse is injected into the vacuum chambec

Precooling is applied.

The pulse is moved into the stack position.

The second pulse is injected 2.2 seconds later.

c

]

The second pulse is stacked after being precooled.

150 pulses later, the stack intensity is 10^ antiprotons.

After 3 hours, a dense core is forming in the stack.

r„

c

> ]

-^fter 120 hours the core contains enough antiprotons to be ejected. 7/76 remaining antiprotons are used to start the next core.

Fig. 11.17 The sequence of operations in the AA. Achievements with Antimatter (Geneva: CERN PubUcation, p. 16).

The proton-antiproton collider (p-pbar)

511

:^^^i#-

Fig. 11.18 Excavation for the UAl experiment in the SPS tunnel (CERN Annual Report, 1979, p. 13).

together with 5 x 10^^ protons, accelerated and collided at 270 GeV, on 10 July 1981^^. Not long after, 10^^ antiprotons per day were being accumulated. In view of the availabihty of beams of antiprotons, a proposal was approved in May 1980 for the construction of a Low Energy Antiproton Ring (LEAR) to carry out experiments on antiprotons decelerated in the PS to 600 MeV/c and injected into a new small ring, where they could be stored and a large number of possibilities explored [54] (see Fig. 11.19). They could be decelerated further, cooled with stochastic and electron coohng systems, and spilled out very slowly to experiments, using stochastic extraction [55]. The successful completion of this project opened a new field at CERN to a different range of experiments and experimenters. Following the discovery of the intermediate bosons, there was pressure for a greater luminosity in the SPS coUider, which would require considerably more antiprotons. Since the AA was in effect two machines in one, it was shown that separating the processes of precoohng and stacking would give a greater yield. Taking into account the recent knowledge in the field of beam manipulation and cooling, and taking advantage of a hquid Uthium lens for focussing the antiprotons first developed in the USSR [56], it was estimated that a factor often improvement in the antiproton yield could be obtained [57]. The Notes: p. 553

512

The Development of Accelerator Art and Expertise at CERN: 1960-1980

I I I I I I I I I I I )

Fig. 11.19 The layout of LEAR alongside the PS (Proc. 11th. Int. Conf. on High Energy Accels., CERN 1980, p. 819).

proposed new precooling ring was called the Antiproton Collector (ACOL), and it could be fitted round the outside of the AA, in the same building, as shown in Fig. 11.20. This project was approved and and came into operation at the end of 1987. 11.4 Beam instrumentation and its use 11.4.1 THE NEEDS The most significant advances in accelerator design would not have been possible without corresponding improvements in beam instrumentation. Without knowing what is happening in an accelerator no reasonable plans can be made to improve it, so different types of instrumentation have been evolved over the years to satisfy ever more stringent requirements.

I

1

I

Beam instrumentation and its use

I

.---.-.-.

I.

3

Fig. 11.20 The new ACOL ring around the old AA (CERN/PS/84-32 (AA)).

513

514

The Development of Accelerator Art and Expertise at CERN: 1960-1980

It is interesting to note that John Adams, just after the first successful run of the PS, wrote in the first quarterly report on the operation of the PS: Thus the situation in December 1959 was that the synchrotron had worked successfully up to its design energy, and already beyond its design current, but with its builders and operators in a state of almost complete ignorance on all the details of what was happening at all stages of the acceleration process.

This rather exaggerated the state of their ignorance and soon, with improved instrumentation, understanding of the operation of the accelerator proceeded rapidly and it was not long before the design intensity was exceeded by a factor of ten. The basic instruments of an accelerator are the current monitors and the beam position sensors, the first to show the number of particles circulating in the machine (current equals the number of singly charged particles passing per second) and the second to show the position of the centroid of charge of the beam at a given position. Knowing the position of this round the machine enables the operators to apply suitable combinations of dipole fields to minimise the departure of the mean orbit from the centre of the vacuum chamber and so allow the maximum size of beam to be accelerated. Amongst the things that made the rapid improvement of the PS intensity possible was the installation of new beam position indicators with an accuracy of down to 0.1 mm and new pick-ups with bandwidths up to 430 MHz, which enabled the accurate shape of single bunches to be determined^^. The next most important thing to determine is the betatron oscillation frequency, Q. This is the number of periods of the transverse oscillations in the focussing fields round the machine in both the horizontal and vertical planes. If it becomes an integer or a ratio of integers in either plane, any minor disturbances of the beam can build up to a major disruption. In an ideal machine, oscillations in the two planes are disconnected, but in practice there is usually some coupling, which extends the possibiHties for unstable resonances considerably. Figure 11.21 shows the possible resonances in the Qr/Qv plane in a typical accelerator. A working point has to be chosen which avoids the main resonances. Particles of different momenta perform slightly different orbits in a ring, the variation of path length with energy being called the 'chromaticity'. Stability requires the chromaticity to remain positive in both planes and the working point becomes a working line in the Qh/ Qv plane. At high beam currents, space-charge forces also come into effect. An extreme example was the ISR, where there was both a large momentum spread and a very large current. One of the limitations on stored current was found to be due to the change in Q due to space charge. This led to a violation of the stabiHty criterion in parts of the beam although it was satisfied for the beam as a whole. A part of the solution was to move the working line progressively, as the current was accumulated, to so-called 'prestressed' lines, which ensured positive chromaticity in all parts of the beam and at the same time avoided all resonances below the fifth-order during stacking and below eighth-order in the final storage condition [58] (see Fig. 11.22).

Beam instrumentation and its use 27.5

515

0.6 0.66 0.75

(7\ s Working points

Fig. 11.21 QH versus Qv plot showing resonance lines and possible working points (CERN Yellow Report 85-19, p. 90).

In the earlier days, the measurement of the betatron frequency was made by giving a short portion of the beam a kick, first in one plane and then in the other and measuring the frequency of the resulting oscillations. With the development of the Schottky scan, as described below, the measurement of the betatron frequency became possible without disturbing the beam. In rings with intense beam currents, other effects come into play, particularly when the beam is bunched, as is the case for most accelerators. Some can be predicted, such as those due to the beam induced currents in the vacuum chamber walls. These produce fields that may react back on the beam and cause instabilities. For example the 'head-tail' instability. Notes: p. 553

516

The Development of Accelerator Art and Expertise at CERN: 1960-1980

8.58 H

8.66

^

8.68

Fig. 11.22 The family of 'prestressed' working lines used for the ISR (CERN Annual Report, 1973, p. 108).

experienced in the PS and Booster, is caused by the fields set up by the head of the bunch affecting the tail of the same bunch. Figure 11.23 shows the theoretical prediction and practical observation of this type of effect. One cure for this type of'coherent' instability is to add octupole fields to provide a spread of betatron frequencies - an example of what is known as Landau damping. Often instabilities are first found experimentally and theoretical explanations have to be found before cures can be tried out. With increasing beam currents more and more possibilities for instabilities, both coherent and incoherent, come into play. We will not go into these beyond remarking that CERN has made significant contributions to the theoretical understanding and practical control of many types of instabilities, using schemes which included the application of multipoles, RF manipulations and feed-back systems. The importance of the work carried out on the ISR cannot be over stressed. As was remarked in the Annual Report for 1978, 'Mention should be made of one field in which the ISR have been a pioneer, i.e. the development and application of very refined diagnostic techniques to measure 'on line' the most intimate properties of the circulating beams; one can then devise and apply remedies and corrections, so preventing the onset of destructive beam instabilities. In fact, at such extreme values of beam densities space charge phenomena are dominating; their precise effects, very little understood only a decade ago, have become a subject of daily appUcation to the accelerator speciaUsts.'

Beam instrumentation and its use

517

Rev 0

REV 2

REV H

B RE:V5

MDDE 0

MODE 0

MDDE I

MODE 1

MDDE 2

MODE 2

Fig. 11.23 (a) Head-tail instability modes as predicted by theory, (b) These modes observed in the booster ring (CERN Annual Report, 1973, p. 90).

An idea of the activity in this field can be obtained from the presentation of no less than 17 papers on various aspects of beam behaviour and instabiUties by CERN authors at the 11th International Conference on High Energy Accelerators in 1980.

518

The Development of Accelerator Art and Expertise at CERN: 1960-1980

11.4.2 THE INSTRUMENTS This is another field where the cross-fertiUzation between laboratories results in continual refinement of the various forms of beam instrumentation. For example, most forms of beam position indicator follow one or two basic principles, but there is a great variety of different implementations, according to particular requirements. A good review of the wholefieldof beam instrumentation has been given by Koziol [59]. Here we will just give a few examples of new types of devices that have been developed at CERN. The most well known of these is the so-called Schottky scan. Schottky showed that the 'noise' in vacuum tubes is caused by a statistical variation in the cathode current due to the finite number of electrons involved. A statistical variation in the circulating current in the ISR was first detected in 1972, when a spectrum analyser was connected to a wide-band beam pick-up in a search for microwave instabiUties. The spectrum of the 'noise' showed the spread of rotational frequencies, and thus the spread of momentum, in the beam. Such a scan, taken in the ICE ring, has already been shown (Fig. 11.12). Similarly, if a differential pick-up is used, signals from the betatron oscillations can be observed on the spectrum analyser. These not only give a measure of the spread of betatron frequencies but can also show up the effect of passing through resonances on these frequencies. Figure 11.24 shows such a scan where the ISR beam is passing through fifth-order resonances and the improvement when these are avoided. This Schottky scan is now an important procedure used in all modem accelerators [60]. Another new concept was the 'beam transfer function' by analogy with the transfer function used in servo design. By perturbing the beam at one point and observing the response at another, stability diagrams can be built up. The availability of spectrum analysers incorporating fast Fourier transform circuitry enabled these transfer functions to be measured, using 'white noise', with negligible effects on the beam [61]. Many of the methods of measuring the transverse dimensions of a beam result in its partial or complete destruction, but a method of doing this without effect on the beam was developed at CERN in this period. This was the Ionization Beam Scanner (IBS) developed at the PS. It made use of the electrons produced by ionization of the residual gas in the vacuum chamber by the proton beam. The number of electrons liberated per unit volume in the beam is proportional to the proton density and so if the spatial distribution of these electrons can be measured, it will give a picture of the beam size and shape. This was done by using electric and magnetic fields. The electric field is scanned across the beam and when the equipotential line passes through the beam, the electrons from that region are constrained by the magnetic field to follow trajectories that take them into an electron multiplier to provide the output signal as shown in Fig. 11.25. This is used to provide a 'staircase' display, as shown in Fig. 11.26, where the variations in size and position of the proton beam during a complete cycle are shown [62, B32]. In the case of the ISR the residual gas pressure was too low for this device to work, so the 'sodium curtain' monitor was developed. A beam of sodium gas, wider than the beam but only 1 mm thick, was projected at supersonic speed across the vacuum chamber at an

519

Beam instrumentation and its use

Fig. 11.24

Schottky scans showing (a) fifth order resonances and (b) improved conditions with no resonances below eight order (CERN Annual Report, 1973, p. 107).

angle of 45 ° from a boiler into a receiver on the other side. The electrons liberated from the sodium by the beam were attracted by a high electric field to a scintillator screen where they were viewed by a television camera^^. Another requirement for the ISR was to get an accurate measurement of the rate of beam loss. This meant measuring very small changes in a beam current of several amperes. A new type of DC current transformer was developed that avoided the problems of drift that caused existing types to be unsuitable [63]. In high energy electron machines, beam profiles can be obtained by examination of the synchrotron radiation produced in the visible region from a bending magnet. It was not expected that such a system could be used for a proton accelerator at the energy of the

1-30v|^-30V

1

/

+0-5 kV

/

+ 30V| ^^-30v

/ - 2 - 5 kV

+ikv£

\ 1

1

• 30V W - 3 0 V

I

h2kV

y

•VSkV

\

l-5kV

\

|-»-2kV

-IkV

/

1

Fig. 11.25 Ionization Beam Scanner. Scanning through the beam by changing the electrostatic potentials (CERN Courier, Sept. 1973, p. 260). Notes: p. 553

520

The Development of Accelerator Art and Expertise at CERN: 1960-1980 •

Injection

Transition

Internal target 11 10% at 19 GeV/o

Fast ejection 58 at 24 GeV/c Two

bunches

Two

bunches

Slow ejection 62 at 24 GeV/c (55%) Internal target 8 at 24 GeV/c (25%) Fig. 11.26 Staircase plot of beam position and size in the PS using the IBS (CERN Courier, Sept. 1973, p. 261).

Accelerator components

521

SPS, since the calculated radiation in the main magnetic field is very small and of too low a quantum energy to be visible. However, it was realised that at the end of a magnet, where the field was changing rapidly, the situation was different and visible radiation might be expected [64]. Tests showed this to be true, and a profile monitor using synchrotron fight was installed at the SPS, giving results as shown in Fig. 11.27. Later an 'undulator', consisting of a series of transverse magnetic fields of alternating polarity, was installed to aUow observation at lower intensities when the SPS was used as a proton-antiproton collider [65]. These are just a few examples of the very considerable advances in beam instrumentation that have been carried out at CERN.

11.5 Accelerator components There have been so many developments and improvements in the components for accelerators carried out at CERN that it has been difficult to choose which to include in this chapter. A selection has been made of the major components, but it must not be forgotten that behind the reafisation of these developments are a whole range of improvements in design and manufacturing techniques and in services such as computing and electronics which are not included here.

Fig. 11.27 The horizontal distribution of the proton beam in the SPS from measurement of the synchrotron light (CERN Annual Report, 1979, p. 136).

522

The Development of Accelerator Art and Expertise at CERN: 1960-1980

11.5.1 MAGNETS 11.5.1.1 Iron-cored magnets We have already described the shuffling of the laminations for the PS magnets to obtain a more uniform coersive force between magnet blocks, a practice that was adopted for most subsequent machines worldwide. It was also the first machine where the laminations were stuck together with an epoxy glue rather than being welded together or held with tiebolts, although these had to be added later, when the epoxy suffered radiation damage and the end laminations started to move. These were combined-function magnets (each performing both bending and focussing functions). The same type of magnet was adopted for the ISR but the methods of design, construction and measurement were further refined. The first major new development was introduced in the construction of the PS Booster. The four identical rings were accommodated in a single magnet structure. The separatedfunction scheme was used, with triplet focussing for the first time, so it was necessary to build sets of magnets with four stacked dipoles and others with four stacked quadrupoles, where each of the four had to have identical characteristics [34] (see Fig. 11.28). So far, all the CERN machine dipoles had been of the ' C type, with the coils clear of the aperture, which allowed some access to the removable vacuum chamber. This type was also originally proposed for the 300 GeV machine. With the change to a separate-function design dipoles of the modified 'H' type, in which the vacuum chamber is sandwiched inside the core between the coils, were adopted as providing an appreciably cheaper solution. The magnet cores, the coils and the vacuum chambers were produced in industry and they were assembled and the two halves of the magnet cores welded together at CERN. A crosssection of one type of dipole is shown in Fig. 11.29. The magnet measuring equipment, used to ensure that the finished magnets were within tolerance, was computerised for the first time. In January 1975, after about 250 dipoles had been manufactured and about 100 installed in the tunnel, a routine check revealed that some of the latter were showing a low resistance between the epoxy and glass fibre insulated coils and earth, leading to potential breakdown. A detailed investigation showed that an unauthorised cleaning fluid, phosphoric acid, had been used by one of the dipole manufacturers when the coil ends had been brazed. Some of the glass fibres were hollow, allowing the phosphoric acid to find a way through the insulation and so providing the low resistance path. The fault was found in time for all the suspect magnets to be rebuilt without delaying completion of the machine. The first proposal for LEP incorporated an unusual type of dipole. Because of the very large radius needed to keep synchrotron radiation within bounds, the peak magnetic field required is quite low and it was suggested that this could be provided by two large shaped conductors, with an outer steel shell [66]. However, when the first detailed design was carried out [21], conventional ' C type laminated cores were proposed, but with just four long heavy-current busbars instead of the usual coils. In the next design it was proposed that, since the iron in a conventional laminated core would be a very long way from saturation, only about a third of the laminations were needed, if these could be spaced

Accelerator components

523

Fig. 11.28 Four-way bending magnets and quadmpoles for the Booster (CERN Annual Report, 1968).

uniformly [67]. This was done by punching indentations in the laminations so that when they were stacked together the indentations spaced them apart. The gaps were then filled with cement mortar to provide mechanical rigidity (see Fig. 11.30). These became known as concrete magnets and experiments were carried out to find the best methods of construction and curing of the mortar to produce consistent and stable magnets. This led to a detailed specification for their manufacture, which was successfully carried out by two different firms. Cement mortar is much cheaper than steel, so there was an appreciable saving in the cost of the magnets. In addition to the main magnets discussed above, all the machines require many other magnets, such as sextupoles, octupoles, correction dipoles and, in some cases, poleface windings to provide the 'fine tuning' and to combat the onset of instabihties. Often great ingenuity has had to be exercised to fit such elements into the machine lattice.

800

524

r I I

I

I

!

DIPOJLE B 2 I

Fig. 11.29 One type of 'H' dipole for the SPS (CERN/1050, p. 45).

The Development of Accelerator Art and Expertise at CERN: 1960-1980

1

Accelerator components

Fig. 11.30

525

Concrete dipole magnet cores for LEP (Diagram CERN/ISR-LEP/79-33).

11.5.1.2 Superconducting magnets It has been pointed out by Kjell Johnsen that major developments in the accelerator field are of two types, those that require the use of existing technology to implement a new principle and those that require new technology. The time scales are quite different as can be seen from two examples. Within a short time after the alternating-gradient focussing principle had been pubUshed, machines were being built and worked successfully. Superconducting magnets for synchrotrons required new technology which seemed to be always just on the horizon but took many years to become a practical possibiUty. That certain materials can become superconducting when cooled to a low enough temperature has been known for a great number of years. However, it was not until it was shown that some alloys of niobium could remain superconducting when subjected to a high magnetic field that it became interesting to build superconducting magnets to overcome the limitation of iron magnets to a maximum field of about 2 Tesla. It was the experimental physicists, who wanted constant magnetic fields over large areas without the enormous power consumption necessary for conventional magnets, who first exploited superconductivity in high energy physics. There were major though not insuperable pro-

526

The Development of Accelerator Art and Expertise at CERN: 1960-1980

blems with making big DC superconducting magnets, but the situation was quite different for synchrotrons. There the magnets had to be pulsed, and with the conductors then available eddy currents could cause them to 'quench' and become no longer superconducting. The Rutherford Laboratory developed a conductor in which thousands of thin strands of superconductor were embedded in a copper matrix, and this seemed so promising that, even before the SPS was approved, some pressure was exerted to redesign it to use superconducting magnets. This was one of the reasons why Adams proposed the 'missing magnet' design. However, even in 1971, a member of the Rutherford staff was reporting that: Work on superconducting magnets has now been in progress for over ten years; the problems of producing dc fields up to, say 60-70 kG are reasonably understood, and from a purely technical view point it would be relatively straight-forward to extend the technology to allow the magnet field to be cycled between zero and maximum with a few seconds rise time. However, the objective is not only to be able to produce a high field pulsed synchrotron magnet, but to do so with an accuracy, reliability and overall cost/GeV comparable with or better than the conventional 10-20 kO magnet systems [68].

The first application of superconductivity to the CERN accelerators was the design and production of the low-beta quadrupoles for the ISR. The fact that these were not pulsed simplified the design, but it was still necessary to provide thefieldquality and a mechanical design to withstand the enormous forces produced by the high field [69]. These were the first superconducting magnets to be used in routine operation in any accelerator. While following the progress of the Tevatron proposal at Fermilab, work on superconducting magnets at CERN was carried on at a low level until the proposal to put a hadron collider (LHC) in the LEP tunnel came to the fore. Although outside the timeframe of this chapter, it is worth noting that subsequent progress at CERN has been considerable. Following an eariier proposal [69a], prototypes of a novel 'two way' magnet have been designed and constructed. Each magnet contains two beam tubes with opposite magnetic polarities in a single magnet [70] (see Fig. 11.31). Thus half the number of magnets is needed for the two contra-rotating beams of protons, compared with coUiders such as the SSC machine which was to be built in the USA, and which had separate sets of magnets for the two beams. To gain the maximum energy within the restraints of the LEP tunnel, a much higher magnetic field is specified, 10 Tesla, necessitating cooHng the magnets to 1.8 Kelvin (degrees absolute) instead of the more usual 4.2 K. A collaboration between CERN and an Austrian firm resulted in the manufacture of a magnet that reached 9.5 T in 1989, then a world record^^. Subsequently, models of the twin-bore magnets have been manufactured in industry and have reached the required field of about 10 T.

Accelerator components

527

Fig. 11.31 Superconducting double-bore dipole for LHC (CERN Yellow Report 91-03, p. 75).

11.5.2 MAGNET POWER SUPPLIES At the time of construction of the PS it was customary to use rotating generator sets to power magnets. The main magnet power supply for a synchrotron normally used a motoralternator set fitted with a heavy flywheel, to minimise the pulse loading on the mains supply, and mercury arc rectifiers to provide the unidirectional current for the magnets [62, XIO]. However, the constantly reversing stresses, which the motor-alternator manufacturers do not normally have to deal with, have caused failures both at CERN^^ and at other laboratories [71] causing extensive shut-downs. In 1968, when the new power supply for the PS was installed, it was also a rotating machine, as that still seemed the best Notes: p. 553

528

The Development of Accelerator Art and Expertise at CERN: 1960-1980

solution. This was despite the fact that most of the motor-generator power supplies for the auxiliary and beam-line magnets, where the load was relatively constant, were being replaced by static power suppUes. However, the mercury arc rectifiers were replaced later by thyristors, which resulted in a substantial saving in power^^ The problem of pulsing did not occur for the ISR, and static power supplies could be used for the main magnet power supplies, since the magnetic field required was steady, or only ramped at a very slow rate. When the SPS was being designed it was realised that to provide the total power swing of 230 MW required at the magnet terminals was a serious problem, and the design of suitable rotating machinery would, if practicable, result in very considerable expense. However, there was another possibility. Since the PS days the national electricity distribution grids had been constantly extended and upgraded. It was suggested that they might be able to accept such pulsed loads, without producing unacceptable voltage and phase transients, as long as a compensator was fitted to reduce the large reactive power swing [72]. At the time when the location of the 300 GeV machine had not been decided and a British site was on offer, the Central Electricity Generating Board (CEGB) was persuaded to allow the temporary direct connection of the synchrotron Nimrod to the local grid towards the end of 1967, for tests to measure the disturbance caused. This was found to be less than expected. This was followed by overtures to the Electricite de France (EDF) to cooperate with the CEGB in carrying out an experiment in 1968 using the DC cable under the Channel. This was normally used to transfer power either way between the two countries, depending on which had a surplus. This link was programmed to transfer a 160 MW square wave every 4 seconds from the British to the French system [73]. The voltage and phase was monitored at many points in the two grid systems, and the disturbance was found to be sufficiently low that, when the CERN site was chosen, the EDF was able to agree that the SPS magnets could be powered directly via a special 380 kV line from Genissiat, about 33 km from CERN, which was a strong point of their system, provided that the necessary reactive compensator was installed, and despite this being the largest pulsed load on the European network. The design of this system has been described by Bayard [74]. Meanwhile, it had been agreed that the much smaller pulse load for the PS Booster could be drawn from the local Swiss distribution system after tests involving a partial excitation of the PS directly from the supply. The reactive compensator rating was doubled later, to enable the cycle time to be halved^^. In general the power supplies components were either standard manufacturer's items or were developed by the manufacturers for CERN. An example of the latter is the saturable reactor for the SPS compensator, which was the largest that had been made up to that time. However, the industrial standards of stability were often inadequate and CERN had to devise methods of making improvements. The first of these was the design of an electronic filter to reduce the ripple on the PS main magnet power supply by a factor of 100, thus minimising the ripple on the beams produced from the targets^l

Accelerator components

529

The ISR called for even greater precision in setting and stability. After close collaboration between the power supply manufacturers and CERN, tests on the main magnet supplies showed that a very low level of ripple had been achieved (less than 100 mV in 1800 V) and the auxiliary power supplies came up to similar standards^"^. To obtain the precision required it was necessary to develop a true 16-bit DAC (Digital to Analogue Converter), as nothing with this precision was available commercially [62, ElO]. After the initial operation, the sequencing of the power supplies was gradually taken over by the control computer, to allow the automatic co-ordination of the changes required during the beam manipulations [75]. In the case of the SPS, the main power supply consisted of 12 independent converter units for the dipoles and two for the quadrupoles, distributed round the ring at the access points. Since the magnets and quadrupoles were powered separately, it was essential to keep the currents exactly in step to keep to a given working point, despite changes in temperature, etc. in the various components. This was done by generating control waveforms for the converters in a computer. A program running continuously compared the current waveform with that which was desired every few milliseconds, calculated the changes necessary in the control waveform to minimise the difference and then updated the control waveform table for the next pulse [76]. The increase in maximum energy to 450 GeV (500 GeV with reduced duty cycle) and the demands of the p-pbar operation and injection for LEP required additions and modifications [77]. 11.5.3 RADIO-FREQUENCY SYSTEMS The radio-frequency (RF) system of an accelerator is an important component that has to meet many, often conflicting, requirements. It not only has to provide the fields for accelerating the bunches of particles and maintaining them in the phase space area known as 'buckets', but it also has to provide the means for shaping and displacing bunches to avoid instabiUties, which often requires the addition of RF systems at difierent frequencies from the main one used for acceleration. Here we can only deal with developments in the main RF systems, but the reader can get an idea of the complexity of the subject from a review of the RF manipulations needed for the p-pbar colUder [78]. For the PS, the RF system had to provide 100 keV per turn at a frequency which varied from 2 to 10 MHz during the acceleration cycle. This was provided by 16 cavities which were loaded with ferrite. The effective inductance of the ferrite was changed by an applied magnetic field to keep the cavities in tune as the frequency changed. This required 14 tons of ferrite, the largest amount produced in Europe up to that time^^. However, 5/6 of the RF power was lost in the ferrite. Thus for the improvement programme, instead of doubling the system to cater for the increase rate of rise of energy, which would not have been possible for lack of free space, it was decided to keep the same rate of rise for the first 80 ms, after which the frequency swing was much smaller. The extra accelerating field was provided by running nearer the peak and adding a fixed tune second harmonic cavity system, which took up much less space [33]. With the ever Notes: p. 553

530

The Development of Accelerator Art and Expertise at CERN: 1960-1980

increasing demand for greater intensity, the original RF cavities were progressively replaced by more powerful ones^^. In the case of the ISR, it might be thought that the RF problems were simple, but this was not so. Although only needing to provide a small accelerating field for manipulating the stored bunches into the required orbits, it had to do so in the presence of a large circulating current of protons. To produce the required voltage with a reasonable RF power level required the system to have a high shunt impedance, while to avoid interaction with the stored beam required a very low one. The problem was solved by the application of very strong negative feed-back. Another problem was that the circumference of the ISR was 1.5 times that of PS. With one turn extraction from the PS only 20 of the 30 RF buckets would be filled and the stack would be diluted by empty buckets passing through. This problem was solved by suppressing the RF cycles when no bunches were passing by providing a chopped sine wave, the so-called missing bucket scheme [79]. With pressure from the experimenters to increase the energy of the ISR beams from the injection value of 26 GeV/c to the maximum the magnet system would allow, 31.4 GeV/c, an attempt was made to rebunch the stored beam and accelerate it. However, the RF power available was only sufficient for beam currents up to 1 Ampere and so another method was tried, called phase displacement acceleration. In this process, empty RF buckets are moved through the stack from higher to lower momentum which results in a shift in the stacked beam towards higher momentum. By repeating this many times, the whole stack can gradually be brought up to the maximum energy [80]. When the design for a 300 GeV synchrotron was being worked out, the frequency change required during acceleration was only about 0.5% due to the high injection energy (originally 8 GeV), and so it was proposed that a fixed-tune system should be used [81]. It was demonstrated that a system could be made with sufficient bandwidth, and that a travelling-wave structure was superior to a standing-wave structure for this purpose, requiring less RF power for the same accelerating field. When the SPS was built it was fitted with such a travelling-wave system, operating at 200 MHz. Another innovation at that time was aimed at the booster synchrotron that would have been needed if the 300 GeV machine had been built on another site. This was a method of tuning a cavity mechanically without the losses involved in using ferrite. The tuning was obtained by the movement of a Hghtweight piston which was driven by a moving-coil system similar to that used in loudspeakers. A servo system driving the coil kept the cavity in tune as the frequency varied. A model was tested for 10,000 hours at 50 Hz without failure [82]. The original SPS RF installation was doubled for the intensity improvement programme and two 800 MHz cavities were added for Landau damping of instabilities on the flat top. Arrangements were also made to reverse the flow of power in one of the 200 MHz systems in preparation for p-pbar operation^^. Later, for accelerating leptons to feed LEP, a set of specially developed 200 MHz standing wave cavities were also added to the SPS. When it came to LEP, the importance and the cost of the RF system increased considerably compared with earlier machines, due to the large energy losses due to synchrotron radiation that has to be replaced. For example, in the 'Pink Book' [23] design, the

Accelerator components

531

RF system had to supply 1480 MeV per turn at maximum energy to make up for losses. Since the large diameter and small number of bunches meant that there would be about 25 microseconds between the arrival of each bunch at an RF station, an ingenious scheme was devised in which the power was transferred between bunches from the accelerating cavity, which of necessity has high losses, to a very low loss cavity and back again, in time for the next bunch [83] (see Fig. 11.32). This considerably reduced the RF power required, but it still totalled 96 MW for full energy operation. From the earliest designs it had been proposed that, if satisfactory superconducting cavities could be fitted, the top energy could be increased substantially. However, although work had been going on to develop such RF cavities in a number of laboratories for some years, none had demonstrated the ability to produce consistent results on the large scale that would be necessary for LEP. CERN had supported work going on at the KfK Laboratory at Karlsruhe, both on the superconducting RF separator mentioned below, and on a single cavity to be inserted into the DESY storage ring DORIS to investigate the effects of higher-mode excitation, electron bombardment and synchrotron radiation on the cavity^^. Work was begun at CERN on this subject in 1979 and from the start emphasis was placed on the development of cavity diagnostics, including precise temperature and X-

Fig. 11.32 Combination of accelerating and low-loss storage cavity for LEP (CERN/ISR/LEP 79-33). Notes: p. 553

532

The Development of Accelerator Art and Expertise at CERN: 1960-1980

ray mapping, to determine the source of the defects that caused inconsistent performance between supposedly identical niobium cavities [84] (see Fig. 11.33). The single cell cavity model was followed by a four cell model, and extensive studies were made of the surface and bulk material properties of niobium^^. A five cavity model made at CERN operated for two months in the e^e" coUider PETRA at DESY with no untoward effects showing up^^ (see Fig. 11.34). At the same time, work was going on to determine whether, instead of making the cavities out of sheet niobium, copper cavities with an internal coating of niobium could be used. These would not only be less costly, but the increased thermal conductivity of the copper could reduce the effects of 'hot spots' causing breakdown. After having tried a number of processes, the technique of sputtering proved to be the most successful, and a satisfactory cavity using this was made in 1983^^ The necessary manu-

Fig. 11.33 (a) Superconducting test cavity with diagnostic scanner, (b) Plot showing where losses are concentrated (CERN Courier, May 1982, pp. 137, 138).

Accelerator components

533

EQCC = 3 . I 2

MV/m

2000 h

1000 h

150

200

cm.

Fig. 11.33b

Fig. 11.34 The Superconducting 5-cell cavity unit built at CERN and installed in PETRA (CERN Courier, May 1983, p. 129).

Notes: p. 553

534

The Development of Accelerator Art and Expertise at CERN: 1960-1980

facturing information for this has been transferred to industry and, after the first twenty niobium cavities for the update of LEP (LEP 200) have been completed, the firm making them will manufacture the remainder using niobium coated copper. Another application for RF was in particle separators for beamlines. The principle is shown in Fig. 11.35. Particles in a narrow momentum band have velocities which differ mainly according to their rest masses and in a beam line this difference of velocity results in differences in transit time. Two RF cavities with fields that provide a transverse deflection are spaced such a distance apart, with a focusing lens system between, that if two different particles, such as pions and kaons, arrive at the peak of the deflecting field, they will be deflected equally. However, due to the different transit times, they will arrive at different phases at the second deflecting system and the initial deflection will be increased or cancelled out, thus separating the particles. This is one of the ideas that originated elsewhere, being suggested by Panofsky during a visit to CERN in 1959. It was improved at CERN [85] and then implemented for the first time [86], coming into operation in 1964^^. The improved version, which used three RF cavities to improve theflexibility,was first operated in 1967 and produced a separated beam of antiprotons at 12 GeV/c for the CERN 2 m bubble chamber [87]. This was then the highest energy separated beam anywhere. A similar one was made for use at the 70 GeV synchrotron at Serpukhov [88], following the agreement between CERN and IHEP (Sect. 5.5). By 1977 an RF separator

r. K

^\ 2n

1 — momentum analysed beam; 2 -- lens system;

'2r

3 •— beam stopper.

Fig. 11.35 Basic principle of a RF separator (Int. Conf. on High Energy Accels., Dubna, 1963).

Accelerator components

535

was providing beams at up to 110 GeV/c for BEBC (see Pestre, this volume) and a superconducting version, giving up to 37 GeV/c beams with a much longer duty cycle, and built as a joint project with KfK Karlsruhe, was operating with the Omega spectrometer^^. 11.5.4 VACUUM SYSTEMS When the PS was built it used what was then the standard way of building a vacuum system: stainless steel tubes with elastomer joints, evacuated by oil diffusion pumps backed by rotary pumps. It was satisfactory for the required degree of vacuum (about 10"^ torr), and only gave trouble later when the elastomer seals suffered from radiation damage. A new type of pump, the getter-ion, was considered and a sample obtained from the USA as no European manufacturer seemed interested, but there seem to have been difficulties with it and the decision was made to stay with the diffusion pumps^"^. After many years of operation, the system was progressively modified to have all-metal seals and the diffusion pumps were changed to getter-ion ones to reduce maintenance and provide a lower working pressure [89]. The first significant contribution CERN made to this subject was the work done on the vacuum system for CESAR, where a pressure less than 10"^ torr was required for the stored electron beam to have a usable lifetime. After initial tests at a somewhat higher pressure [90], the goal was reached after a further bake-out [32]. The experience gained in the CESAR experiment was put to good use in the design and construction of the ISR. Although small ultra-high vacuum systems were common, a system of this size brought a large number of new problems. A report which described the treatments and procedures used stated: 'When we started to build the ISR, we specified an average pressure of 10~^ torr for the main reason that we simply did not dare to specify a lower value in view of the enormous length and complexity of the system' [91]. As we have seen elsewhere (Russo, this volume), although they managed to improve this figure by a factor often for the early operation, it was not sufficiently low to obviate loss of beam due to an unexpected cause. The getter-ion pumps were supplemented by titanium sublimation pumps, which were already being used in the intersection areas to lower the local pressure for the experiments, the bake-out temperature was raised from 200° to 300 °C, and glow discharge cleaning was applied to all critical components. Eventually, pressures in the region of a few times 10~^^ torr were achieved. The world's largest ultra-high vacuum system also required new developments and improvements in vacuum gauges. The vacuum system components used in the ISR, such as the different types of vacuum pumps, were mostly standard components very carefully selected, but some modifications were called for, in which the manufacturers cooperated willingly. No-one could supply suitable large bore vacuum valves bakeable to 300 °C to isolate the sectors of the ring and so these, together with other types of valves, were designed by CERN [62, VIO & V12]. Another difficulty resulted from the experimenters at the ISR calUng for less and less metal between the colliding proton beams and their experiments. Thinner and thinner and more and more complicated intersection vacuum chambers had to be made, an example being Notes: p. 553

536

The Development of Accelerator Art and Expertise at CERN:

1960-1980

shown in Fig. 11.36. Later, titanium was used instead of stainless steel to reduce the interaction length^^. Innovations in mechanical design and methods of forming and welding thin sheets resulted from this work. The SPS required no special vacuum developments, as the original vacuum requirements were much less severe than for the ISR, but the same high standards were imposed on the design and construction of the vacuum system to provide the maximum reliabihty in such a large system. This came in good stead when the p-pbar project was instigated. The basic vacuum system, with the addition of a large number of sputter ion and titanium sublimation pumps, proved adequate to give the much lower pressure required. In contrast, new developments were required for the LEP vacuum system. The gas desorption by synchrotron radiation required a high pumping speed and the cross-section of the vacuum chanber was small, so some distributed pumping was needed. In earlier lepton machines this had been provided by having distributed ion pumps in an extension to the vacuum chamber, using the main dipole magnets to provide the magnetic field needed for the pumps, instead of the separate magnets used with lumped pumps. There

Fig. 11.36 Complicated intersection vacuum chamber for the ISR. The stainless steel is only 0.3 mm thick (CERN Annual Report, 1979, p. 115).

537

Accelerator components

were difficulties in using this scheme at LEP, due to the very low magnetic field at injection, but it was shown that this difficulty could be overcome by the use of larger cells than usual in the distributed ion pumps. However, this solution was not entirely satisfactory and when the idea of using a non-evaporative getter (NIG) was put forward in 1980 it was greeted with enthusiasm. The NIG consists of a strip of constantan coated with an alloy of zirconium, aluminium and titanium which, when heated and allowed to cool, absorbs gases Hke a sponge [92]. It is normally used in small pieces to maintain a good vacuum in electronic valves. An ItaUan firm had a world monopoly in the supply of this material and it co-operated in supplying sufficient material for tests, which included the manufacture of a vacuum chamber to be inserted into the e^e~ coUider PETRA at DESY, which was installed early in 1981. It operated satisfactorily and the decision was taken to adopt the NIG for LEP instead of the distributed ion pumps^^. Figure 11.37 is a cross-section of the LEP vacuum chamber, showing the NIG pump in a channel alongside and in communication with the beam channel. The NIG is activated by passing a current along the constantan strip, raising it to about 700 °C for the initial activation and, once the surface is covered with adsorbed molecules, regenerating it by heating to 400 °C^^. Subsequent satisfactory operation of LEP justified the decision to use this new type of pump. Cryopumping, the adsorption of gasses onto a surface below their condensation temperature, had been used locally on a small scale in the ISR to reduce the pressure, but this will provide a major part of the pumping speed in the proposed LHC to be installed in the LEP tunnel. Since the magnets will be of the 'cold bore' type, with the vacuum chamber at the same temperature, 1.7 °K, all gases would condense on the surface of the vacuum

-VACUUM CHAMBER -LEAD SHIELDING

COOLIHG CHANNELS

PUMPING HOLES GETTER PUMP

GETTER SUPPORT/ CERAMIC

Fig. 11.37 Section of the LEP vacuum chamber, showing the position of NEG pump. The lead coating is to reduce the external synchrotron radiation (CERN Yellow Report 89-05, p. 234). Notes: p. 553

538

The Development of Accelerator Art and Expertise at CERN: 1960-1980

chamber. However, once there is more than a mono-molecular layer on the surface, synchrotron radiation from the beam could cause the condensed gases to be liberated from the surface. A solution to this problem using a perforated screen at a slightly higher temperature inside the vacuum chamber has been proposed [70]. 11.5.5 BEAM EXTRACTION At the time the PS was built, it was normal to insert targets into the vacuum chamber and spill the beam progressively onto the target to produce beams of scattered protons or secondary particles [92a]. This has many disadvantages, both due to the high level of radiation produced in the machine, and from the point of view of experimental utilisation. Therefore, soon after the start of operation of the PS, eifort was put into schemes for ejecting the proton beam from the machine. This can be carried out in two main ways, known as fast and slow ejection in the early days, though the term 'extraction' is now more frequently used and we will use it here. 11.5.5.1 Fast extraction Fast extraction, the removal of a complete bunch or bunches from the machine, is easier in concept, although it presents serious technological problems. A high pulsed magnetic field is applied to the beam by means of a kicker magnet, causing one or more bunches, up to the whole beam, according to the pulse length, to be deflected into one or more septum magnets which then bend it out of the machine. Because of the difficulties of producing the very short duration, high pulsed, fields over a large area, the first PS installation took advantage of the shrinking of the size of the beam as it is accelerated to insert a magnet with a small aperture, normally out of the beam, horizontally into the beam just before extraction. Similarly, the septum magnet was moved, this time vertically, into position once the beam reached full energy [93]. The system came into operation in May 1963^^ and it was later found possible to add a fixed septum magnet in a short straight section to give a second extracted beam in July 1965. Later, as techniques for generating high power fast pulses progressed, the possibiHties were explored of building a kicker magnet with an aperture large enough to contain the full beam at injection so that it could be left in place the whole time. Tests were successful and an extraction system using a Full Aperture Kicker (FAC) became operational in 1969^^. A similar system was used to provide beams for the ISR when it started up in 1971. Later, improved versions of the FAC were developed and installed to take the load off* the plunging kickers'*^. High energy physics in Europe being relatively remote from the 'cold war', an agreement was signed between CERN and the Institute for High Energy Physics (IHEP) at the Serpukhov laboratory in the USSR in July 1967. It arranged for CERN to build and install a fast extraction system and an RF separator at the 75 GeV proton synchrotron being constructed there and which came into operation later that same year. In exchange,

Accelerator components

539

physicists from CERN and its member states would be allowed to mount experiments on what was then the highest energy machine in the world'^\ Agreement on the design, which now included the ability to serve up to three 'shots' per cycle into any of three extraction channels, was obtained by early 1969 and the rest of that year was spent in building and testing prototypes for the various pieces of equipment needed"^^. The system is described in [94]. Parts started arriving from manufacturers in 1970 and assembly was complete for testing at CERN by autumn 1971. After these tests proved satisfactory, the components were shipped to Russia towards the end of the year, assembled and installed by CERN personnel and the system provided the first extracted beam in February 1972. The RF separator (see Sect. 5.3) was installed in April and produced kaon beams at up to 32 GeV/c with 98% purity'^l 11.5.5.2 Slow extraction Slow extraction called for a small portion of the circulating beam to be peeled off every revolution for a time as long as 100 ms. The problem was how to do this without disturbing the rest of the circulating beam. It was proposed to apply a locaHsed quadrupole field to bring the circulating beam near an integer resonance, tending to build up betatron oscillations [95]. By adding a sextupole field, the particles on the outside would be brought closer to the resonance, and build up their oscillations most rapidly, until the amplitude gain in one revolution was sufficient to jump into a septum magnet assembly which would bend them out of the machine. After suitable magnets had been installed in the PS, a slow extracted beam was first brought out in August 1963 [96]. Some particles are lost in the septum of the septum magnet, which has to be sufficiently thick to carry the large current needed, and in 1969 work started on the development of an electrostatic deflector where the septum can be much thinner [97]. After some difficulties with high-voltage breakdown in the presence of a proton beam, the problems were solved and an electrostatic septum was used for the PS slow extracted beam in 1970^. It was later found that using the one-third integer resonance gave a more controllable slow spill and it was successfully used for the first time in the extraction system for feeding beams to the new West Experimental Hall"^^. 11.5.5.3 Further developments When it was decided to use the PS as injector for the SPS, a modified form of fast extraction, called continuous transfer, was devised to compensate for the difference in circumference between the two machines. This used an electrostatic septum and two kicker magnets driven by a 'staircase' pulse generator to peel off* one eleventh of the PS beam every revolution for eleven turns, and to fill one turn of the SPS [98]. The extraction systems for the SPS extended the experience obtained at the PS and used the same basic principles, but the higher energy brought more difficult technological problems. To obtain the necessary deflection of the protons being spilt out to cross a Notes: p. 553

540

The Development of Accelerator Art and Expertise at CERN:

1960-1980

magnetic septum, the electrostatic septum had to be 12 m long, made up of 4 units of 3 m each, yet it had to be ahgned to a fraction of a mm. It would have been diJB&cult to prevent buckUng in such a long strip of foil, which had previously been used, so the septum was provided by an array of closely spaced molybdenum wires, 0.15 mm diameter. These were tensioned by springs which kept them straight and retracted any broken wires out of the beam area (see Fig. 11.38). This was followed by two stages of magnetic septa and, according to the use of sextupoles and or kickers, three modes of extraction could be provided; fast extraction (3 to 23 microseconds), slow resonant extraction (0.5 to 2 seconds), using the half-integral mode, or fast resonant extraction (up to 3 milliseconds) [99]. As mentioned earlier, a form of 'stochastic' extraction was devised for LEAR, where spill times longer than 10 seconds were needed. The implementation of these various extraction systems required considerable developments in the various components. These included kicker magnets with very fast risetimes and septum magnets with ever greater current density in thinner septa [100], as well as high-power short pulse generators [101]. The latter required CERN developments in

Fig. 11.38 The SPS electrostatic septum, (a) One of the 3 m units, (b) Close-up showing the tensioning springs (CERN Annual Report, 1973, pp. 175, 176).

Accelerator components

541

Fig. 11.38b

triggered spark-gaps and the application of high-power hydrogen thyratrons when these became available. 11.5.6 CONTROL SYSTEMS In their original form, the control systems for both the SC and the PS were built up out of standard analogue and logic control components that were then commercially available. A number of problems had to be solved, mainly concerned with the distances signals had to be carried, and with the complexity of the personnel access and radiation safety systems. In the early 1960s, small computers began to become affordable and proposals were made for their use in accelerator control. Most of the early applications were limited to

542

The Development of Accelerator Art and Expertise at CERN: 1960-1980

data recording and multiplexing. A pioneer in this field was the Los Alamos Laboratory, where plans for the first complete computer control of an accelerator, the projected proton Unac LAMPF, were put forward in 1965. The PS ordered its first computer, an IBM 1800, in 1967, 'intended as a help to the operator and [which] then should offset the growing complexity of their work'"^^. In view of the present progress in this field, it is interesting that it was thought sufficiently important to note that the memory of this computer had been increased to 16 K words in 1968"^^. In the following years the 1800 took on more and more duties and was enlarged further. A minicomputer was added to carry out function generation and then some minicomputer display units to act as main operator consoles, supplemented by 'Midi' and mobile 'Mini' consoles for the Booster and local applications [102]. Going back to when the ISR were being constructed, planning for computer control of it was not started until 1967, about the time the excavation of the tunnel started. It was planned as a compliment to the manual control facilities, to be installed in parallel and used whenever its performance was superior. This was because it was feared that the ISR might require a long and arduous commissioning period and the computer system could not be allowed to present its own commissioning problems at the same time. It was decided to use a single control computer of reasonably high power and twin Ferranti Argus 500 computers were ordered in 1968 and delivered the following year, one for control and the other for program development [75]. In the absence of any higher level language, the applications programs at first were written in Assembly Language. However, in 1972 a real-time control language, CORAL 66, which had been developed for the British military services, became available and this was adopted for all subsequent programming"^^. A number of automatic control sequences were set up, which soon became vital for the achievement of the higher proton currents [104]. The ISR was a pioneer in using the then new electronic crate system CAMAC for control purposes. The next control development at CERN was the system for the SPS which incorporated a number of innovations. These included the first true distributed multi-computer control system, where any action could be carried out from any part of the system, the first multicomputer operating system, the first large scale use of an interpretive language for the applications programs, the introduction of the Data Module for isolating the appHcations programmer from the hardware details, and the provision of simple-to-program colour graphical and other interfaces to the operator [105, 106]. In the early 1970s, when the SPS design was being considered, computers had been appHed to control problems in a number of accelerator laboratories, but mostly in a piecemeal fashion. Where more than one computer was involved, these either performed independent control on different parts of the accelerator, or were organized in a master/ slave relationship. During the construction of what was then the world's largest accelerator, which later became the Tevatron, R.R. Wilson had decided to let each hardware group build its own control system, giving it some space in the control room for the initial running. He hoped to integrate them into a comprehensive machine control system later, a process which was to take several years.

543

Accelerator components

In the case of the SPS, due to the large size of the ring, with its six access shafts and equipment buildings, and the need to carry out commissioning locally, it was essential to have the computer system distributed round the accelerator. Each computer had to be able to operate autonomously. Thus, instead of having the distributed computers subservient to a single large central computer, as would be the normal practice for such a system, it was necessary to connect them to a network that would allow any two computers to communicate without the intervention of a third. Such a network is now called a Local Area Network (LAN), but no such system existed at the time. Even Ethernet, which was then the only standard proposed and still in its gestation stage, would not have satisfied all the requirements. A packet-switching network was designed specially for this appHcation, a specification drawn up and a contract entered into with a French firm for its implementation. A diagram of the complete system as planned in 1973 is shown in Fig. 11.39. It was later extended to cover the experimental areas. Another important decision was to use interpreted rather than compiled applications programs. This was because it was realised that the provision of adequate appUcations programs for the operation of the SPS would involve a very large effort in a relatively short time. To avoid having to employ a large number of programmers and follow the usual pattern of the equipment experts having to write detailed specifications for them to

<;=;^

< ; ^

CONSOLE

CONSOLE

<;=;=^ CONSOLE

DISPLAY

ALARM

SERVICE

LIBRARY

MESSAGE TRANSFER SYSTEM

INJECTION

POWER SUPPLY

NORTH

EXTRACTION

QP1

GP2

GP80

GP81

GP3

NORTH

EXPERIMENTAL

WEST

RADIO

EXTRACTION

FREQUENCY

GP4

GP6

GPS

GP61

WEST EXKRIMENTAL

Fig. 11.39 The SPS control computer system as planned in 1973. It was subsequently expanded to cover the experimental areas. GP = General Purpose computer in each auxiliary building (CERN Yellow Report 78-09,p. 7). Notes: p. 553

544

The Development of Accelerator Art and Expertise at CERN: 1960-1980

turn into code, debug it and then modify it as the experts changed their specification, it was thought essential to make provision for the accelerator experts to be able to write most of the applications programs themselves, in a simple-to-use and safe environment. This can be provided by the use of an interpreter, which is a program which executes instructions in a high-level language directly, rather than compiling them and then executing the resultant machine code. Since no interpreter for a multi-computer system was available, a new one was written and called NODAL [107]. This was the first true multi-computer operating system, and it was subsequently adapted for use at a number of other laboratories including DESY, RHEL, KEK, JET and ELETTRA. Another innovation was the introduction of the 'Data Module'. Until then, in most accelerator control systems using computers, the applications programmer was expected to incorporate direct references to individual hardware interface devices into his programs and carry out any necessary conversions. If there were any changes to the interface subsequently, this might involve changes to many programs, with the risk of introducing errors. A data module dealt with all the low level interaction needed for the control of a given type of equipment, such as the power supplies, taking into account any variations between different types. The applications programs could then call the data module, only having to give the name of the power supply, the action to be carried out and any values in engineering units. If there were any changes to the interface, or modifications to the power supply, only the data module had to be modified, leaving the application programs unchanged. This was the first example of what is now called object-oriented programming. Other special developments carried out for the SPS controls include a special multiplex system to interface to remote equipment and a raster-scan colour graphics system which allowed computer generated displays, detailed diagrams and television pictures to be incorporated in a common manner and allowed operator interaction by means of 'touch buttons' and track balls. Meanwhile, the PS controls group had been considering ways of overcoming the ever increasing demands on their existing system. A number of DEC PDP-11 mini-computers had been acquired and added to the system for special purposes, and it was decided to standardize on this make. A proposal for a new system was made in 1974. However, after the successful working of the SPS control system, using European rather than American computers, the PS was pressed by the CERN management to adopt the same system. This was resisted, on the basis that being built for a slow-cycling accelerator, it would not cope with the fast cycling and pulse-to-pulse modulation of the PS. So, after some tests, the PS controls group devised a suitable scheme, using NORD computers and the message transfer system and adopting and extending extending many of the SPS developments, data modules, NODAL, etc. The pulse-to-pulse modulation difficulties were overcome by the incorporation of microprocessors in the serial CAM AC units used as the interface to the equipment [108]. This project was authorized in 1976 and the first set of computers with the message transfer system was installed in the first half of 1977. The biggest problem was how to change over from the old system to the new with the least possible disturbance of routine operation, coupled with the fact that the huge volume of applications programs

Accelerator components

545

built up over the previous ten years would have to be adapted to the new system as well as all the interfaces changed"*^. Very careful planning, together with the adoption of formal programming procedures and rigorous off-line testing, enabled the progressive change over of the different machine systems to be carried out in the period 1980 to 1984 in the normal scheduled PS shutdowns [109]. Work on a possible control system for LEP had been going on in the ISR Division for some time before the project was approved and the teams to build it could be formed. One of the main differences in concept from previous systems came from the microprocessor revolution. Instead of a controls system entirely provided by a controls group, the equipment groups were independently working on incorporating microprocessors in their equipment to carry out many of the control processes, and so reducing the requirements on the control system. A number of other ideas were discussed and proposals made. One of these was for the use of the standard long-distance telephone technique of time-divisionmultiplexing (TDM) to overcome the difficulties of fast data transmission over the distances involved in going round the LEP tunnel [103]. Going a Httle beyond the period of this chapter, the decision was taken later to merge the SPS and LEP control systems and to control LEP from the existing SPS control room^^. This led to the need to interface the hardware groups' different local control systems to the main control network. The SPS message transfer system was not suitable for such a large extension and so, after a successful collaboration with IBM to test their proposed new token-passing Local Area Network (LAN) in an accelerator environment, it was adapted to use the previously proposed TDM to overcome its limitations on transmission distance. Another development for this system was the proposed use of multiple microprocessors in a standard crate system (VME) to replace the minicomputers previously used as local control processors. This was to obviate the difficulties previously experienced when a manufacturer replaces its minicomputer or its software by something new which is not always compatible with the old. This was started as a CERN development but, as described in Section 11.6.1, difficulties with an outside contractor meant that it was not available in time and so a makeshift solution had to be adopted, using personal computers. 11.5.7 ALIGNING THE MACHINES The theoretical design for the PS showed how critical was the placing and alignment of the magnets, and the precautions taken in the design and construction of the foundation system to minimise their movement have been described. However, a measurement system is required to make the original positioning and to check it later and this is where the survey team comes in. At the time of building the PS, geodesy relied essentially on angle measurement using a theodoUte. In the pre-computer age, the geodetic reference figure had to be simple, to allow the necessary computations to be carried out on mechanical calculators, leading to the octagon chosen for the PS. The accuracy required was greater than for normal inNotes: p. 553

546

The Development of Accelerator Art and Expertise at CERN: 1960-1980

dustrial applications and enquiries showed that no firm was interested in making a higher precision theodoUte^^ There were also problems with temperature variations in the radial tunnels, which could introduce errors up to a mm. Therefore, since distance measurements with invar wire in a tunnel are ten times more accurate than angle measurements over the larger distances, wherever possible all angle measurements were eliminated in favour of trilateral distance measurements, using invar wires [110]. Since the wires cannot be stretched sufficiently to eliminate the catenary without permanent deformation, accurate tension must be maintained in the wires, both when calibrating and using for measurement, so as to keep the catenary constant. On longer wires, 1 g variation of tension can make 10 microns difference in the measurement. The standard method of applying the tension at that time was to run the wire over a pulley, with a weight on the end. The survey group developed a system using knife-edge bearings instead of pulleys which eliminated the friction of the pulley bearings and improved the accuracy. This was given the name Distinvar and consisted of a balance beam, precision screw and measuring head. They also developed an 'electric eye' for theodoUtes^^. Some time later, the Distinvar was automated. The screw was driven by a servo motor which made the adjustment until the beam was balanced. A read-out then gave the difference between the wire length and the distance between the two points up to ±12 mm. This readout could be displayed locally or sent to a computer. This allowed measurements to be taken in areas where the radiation level was high [111]. A further development followed, giving full automation by the addition of a microprocessor to the unit, which speeded up measurements and increased the accuracy. In a test involving over 2000 measurements, the results showed a standard deviation of 2.6 microns [112]. The Distinvar has also been used not only by a number of other accelerator laboratories, but also in quite different fields [110]. With the coming of the SPS, a number of new problems arose. Access to the tunnel would only be possible via the six access shafts and the first task was to erect monuments over the site from which the positions of the shafts and their relation with the PS could be determined. The distances between the monuments were measured using a tellurometer, a microwave device that measures phase differences in a reflected wave. The main problem was to guide the tunnelling machine round each arc of the tunnel, with only the starting point fixed and the destination 1.2 km away. This was solved by the use of a gyrotheodolite, a device that provides an indication of direction relative to the rotation of the earth. Such an instrument is not easy to use and many surveyors had been discouraged, but the survey group introduced some improvements and developed an automatic measuring system which printed the transit times on tape. This was set up every 32 m and used to set the laser beam that was used to guide the tunnelling machine. This was so successful that the average error at the end of a sector was only about 20 mm after 1.2 km of boring. Once the tunnel was finished the basic network of monuments was built, using the invar wire system to set up a series of braced quadrilaterals. The nylon wire method normally

Relations with industry

547

used to measure off-sets to position the components proved unreliable due to air currents in the tunnel and so a laser automatic offset device was developed [113]. Later a Terrameter was obtained for long distance measurements and used for the basic layout for the monuments for LEP. This device uses lasers instead of microwaves and by using two lasers of different frequencies, it can compensate for changes in the propagation conditions over the measurement path. 11.6 Relations with industry 11.6.1 MUTUAL ADVANTAGE Throughout its life, CERN has placed requirements on industry to develop or produce devices that have stretched their abilities to the utmost. This has been to the advantage of both CERN and the industries concerned. An assessment of how much industry gained from this was made in 1975 [114] in which 127 firms cooperated by supplying figures on how much additional business they estimated they had gained as the result of a contract with CERN and what cost savings they had made due to the introduction of techniques developed by CERN. The total utiUty reported by a firm was compared with the total sales to CERN and the resulting utility/sales ratio was taken as a measure of the degree to which CERN had been useful to that firm. The average value of this ratio, over all products, was just over five. Although here has been some criticism of the way this assesment was carried out, and of the figures arrived at, nevertheless it showed that in most cases firms had gained considerably by their association with CERN. This was aided by CERN's policy of not taking out patents on its inventions. This assesment exercise was repeated about ten years later [115]. The number of firms giving estimates of increased sales and cost savings as a result of CERN contracts was increased to 160. In this survey, the overall utility/sales ratio came out to be 3.5. It was noted that CERN's purchases had stimulated technological improvements in fields which are not related to high energy and nuclear physics, such as solar energy, the electrical industry, railways, computers and telecommunications. A good example of the way in which a contract with CERN can turn out to be of great benefit to a firm is that of the control minicomputers for the SPS. A detailed specification of the requirements for the computers together with the necessary basic software was sent out to a large number of firms in Europe with a request for tenders. Although there were several offers of suitable hardware, none of the main estabUshed computer manufacturers could offer the software specified. The only offer that satisfied all the requirements came from a small firm, Norsk Data, who had developed an operating system for providing the automation of some systems on board ships. The subsequent order from CERN was the largest they had had at that time, leading them to expand and to set up an office near CERN. Other laboratories followed CERN's lead and so the firm grew and prospered, at Notes: p. 553

548

The Development of Accelerator Art and Expertise at CERN: 1960-1980

least for a while, before it decided to compete and ran into difficulties. A study was also made in 1987 of the ways accelerators and detectors found applications such actual and potential benefit were quoted

against the established firms in other fields in which technology developed in building in other fields and numerous examples of [116].

11.6.2 WORKING WITH INDUSTRY For a large proportion of the new developments at CERN, prototypes have been made inhouse, tested, and any necessary modifications carried out before engaging a firm to manufacture the quantities required. The 'know-how' resulting from the prototype work is passed on to the firm. In order to stimulate this type of cooperation with industry, a conference and technology exhibition was held at CERN in April 1974. Attended by about 250 representatives from European industry and member states, it aimed to show the advances that had been made in many fields by CERN personnel that could be of more general interest [62]. The interaction between industry and CERN during the development and construction of some of the large accelerator projects was described [117]. Some 270 exhibits were distributed round the two CERN sites, covering a wide variety of subjects, including beam instrumentation, cryogenics and superconductivity, data processing, electronics, magnets and power supplies, photography and optics, vacuum, workshop techniques and the large installations. The reaction from industry was positive, and there was a good follow-up from firms wanting further information. Recent examples of the successful transfer of technology to industry have been the superconducting cavities for the extension to LEP energy (LEP 200) and the superconducting magnets for the LHC, in both cases involving, or leading to, very valuable contracts. 11.6.3 DEVELOPMENT IN INDUSTRY Throughout its history there has been pressure from the delegates of the member states for CERN to do less development 'inhouse' and to farm more out to member state firms. Such 'contracted out' development has often worked well when the items to be developed are not too different from a firm's normal products and the firm can see some sales for the product outside CERN, or where large follow-up contracts from CERN depend on the development. Apart from these cases, experience has shown that contractual time scales for outside developments cannot be relied upon. Therefore, if a particular development is vital to the CERN programme, it is preferable to carry it out at CERN, where the personnel have more than just the contract price to spur them on. The delays with the tuning fork RF system for the SC have been described by Mersits in chapter 4 of the second volume of this history [118] and the troubles with the rotating condenser system to replace it are explained by Hansen in this volume.

Relations with industry

549

A further example which shows some of the pitfalls of an outside development contract seems worth giving in some detail. This was the contract for the multi-microprocessor local process control (PCA) units to be used for the LEP control system, to replace proprietary mini-computers previously used for this purpose (Sect. 5.6). The development of these units was being carried out at CERN and considerable progress had been made, including the construction of prototypes, when the pressure on the CERN management to place outside development contracts was very strong. They decided that the PCA was a suitable subject and insisted that both the development and the supply of the PCAs should be put out to tender to a single firm, rather than let CERN carry out the development and then go out to tender for the construction of the individual modules, which had been the original intention. In the latter case, the design would have been CERN's property and the construction might have been shared between a number of firms. To obtain a reaction from industry, an outline specification was sent out to 166 firms in all the member states, asking whether they would be interested in bidding for such a development. 25 firms showed some interest, but only 7 of these met the requirements laid down in the specification. The next stage was to produce a very detailed specification for a tendering exercise with these seven firms. Only two firms submitted tenders that came anywhere near the specification and even these proposals departed in many respects from the CERN concept. A contract was awarded in December 1985 to the firm that made the better proposal (document CERN/FC/2902). This was a small subsidiary of a large conglomerate, and after some delays of a non-technical nature, the contract was signed in July 1986. Since the delivery of the first modules was due one year after the signing of the contract, the policy of going to a commercial firm for the PCA had already resulted in a delay of about a year and a half in the development, compared with the original planning for the LEP control system. There were major differences between what was originally conceived for the PCAs and the DLX modules and their software that the firm had offered, since they proposed to make use of the development work they had already started with a view to military contracts. Although violating some of the CERN design concepts, these could have provided the faciUties needed for the LEP control system if they had been available on time. The first sign of trouble was when the time-scale started to slip back. The first two modules, due in July 1987, were first re-scheduled for October and then for April 1988. It appeared that there had been some reorganization within the conglomerate, and the firm with which CERN had placed the contract had been moved to a different part of the structure. The Hkelihood of miHtary sales of the DLX had receded and none of the original staff* with which CERN had negotiated the contract were still working on it. With no confidence that the contract could be completed without further delays, CERN was forced to cancel it. The delays in the development and supply of the DLX systems had made it necessary to build up some substitutes to cater for the injection tests planned for the summer of 1988. These were called 'mini-PCAs', made up from IBM PC/AT computers, CERN-built VME modules and special software written by CERN. These assemblies only provided a subset

550

The Development of Accelerator Art and Expertise at CERN: 1960-1980

of the PCAs' facilities, but with the cancellation of the DLX contract the only possibility of meeting the time scale for the start up of LEP was to develop these further as a somewhat unsatisfactory substitute for the original concept. 11.6.4 DOES CERN DEMAND TOO MUCH? It has often been said in the community without that CERN does everything in a goldplated way; that the machines are over-engineered and too expensive, and the demands made on manufacturers are unnecessarily severe. When this accusation was made about the PS, Mervyn Hine strongly defended the CERN position in a report he gave to a conference in 1961. 'A great deal of caution was used in the early days of the project, because the machine was of a new type, and was being built very largely by people who had had no previous experience with accelerator construction. The values of important parameters such as vacuum chamber aperture or permissible magnet-field fluctuations were so specified that even in very unlucky cases the machine would still probably work; and, if possible, correcting devices were built in so that the errors could be cancelled out if they were, in fact, found to be objectionable [119].'

These safety factors, particularly the vacuum chamber size, were vital factors in allowing the intensity to be increased by a factor of ten from the design value of 10^^ protons per pulse a few months after the initial operation and again by a factor of more than ten after the improvement programme some years later. They also enabled the machine to accelerate heavy ions, antiprotons, electrons and positrons. Later on, during the construction of the ISR, the engineering of the vacuum system was criticised. E. Fischer admitted that: 'During the design and construction of the vacuum system of ISR we have been extremely pessimistic - and we often felt bad about it. We have installed more pumping speed than necessary. We have reduced the gas desorption much more than in principle necessary. We have insisted on the possibility of 300 °C bake-out against the resistance of the designers of other equipment - when it had seemed that 200 °C was enough. When choosing between competingfirmswe have never accepted an offer, unless it was within our very tough technical specification. We have given the successful tenderers a bad time during the acceptance tests of all components.' *We had to be pessimistic because we were - and still are - so ignorant about many things: after all, ours are the first proton storage rings ever built in the world and it was difficult to predict what would happen when a high energy proton beam of many amps intensity circulates in an ultra-high vacuum system.' The first operating experiences have shown that our pessimism has almost compensated our ignorance. Perhaps we should have been still a bit more pessimistic - or a bit less ignorant [91].'

elations with industry 551 This was before the circulating proton current had reached a level high enough to cause the pressure bumps which necessitated even more pumping speed and the higher bakeout temperature. Another aspect of the safety factors built into the CERN machines, wherever there are any doubts as to whether existing theory is accurate enough and takes all effects into account, is their impact on reliability and adaptability. The main purpose of building an accelerator is to provide beams of particles for the users. If a machine can be commissioned in a short time and operated regularly according to schedule, as has been the case at CERN, physicists will be getting better value for money than with a cheaper machine that is often breaking down. In addition, the margins built into most designs have also enabled new demands, not envisaged when the machines have been designed, to be met by minor modifications, rather than needing a major redesign. It has been this 'over engineering' and attention to detail that has enabled the present complex of accelerators at CERN, shown in Fig. 11.40, to be built up and operated reliably. Each machine is dependent on one or more others. In this build-up the earHer

CERN ACCELERATOR COMPLEX

¥-¥^

ILIL

LEAR

Fig. 11.40 The CERN accelerator complex (CERN Slide, DI 8-7-91).

m

552

The Development of Accelerator Art and Expertise at CERN: 1960-1980

machines have generally had to provide a performance exceeding their original specifications. By contrast, when R.R. Wilson took over the building of the 200/400 GeV accelerator at the National Accelerator Laboratory in the USA, he set out to build it cheaper than any one else could do. In pursuit of this aim he cut the safety factor on the insulation for the magnet coils, with the unfortunate result that many of them failed after installation in the damp tunnel and, for the first year or so of operation, the machine had to be stopped frequently for one or more failed magnets to be replaced in the tunnel. When CERN also had trouble with the same type of magnets during the building of the SPS, it was first blamed on CERN having copied the Americans, but in this case it was not due to any design fault; it was due to the use by one of the manufacturers of an unauthorized cleaning fluid which, after a time, formed a conducting path through the glass fibre insulation^^. This was detected early enough by the CERN practice of not just testing items when they are supplied, but also carrying out repeated testing at and after installation. Thus the offending magnets could be removed from the tunnel and reworked without causing any delay in the completion of the installation. This is not the only case that could be quoted in which machines in other laboratories have taken a long time to commission because the specifications on the components have not been tight enough, but perhaps it serves as an illustration. 11.7 Concluding remark It is hoped that the above review will have given the reader some feeling, not only of the considerable extent of the developments made at CERN in the accelerator field during the period under review, but also of the way in which many of these have come about as the result of enthusiastic co-operation between people of different discipHnes within the organisation. One person may have an idea, but it takes many to put it into practice. Notes 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

See document CERN/869, 30 May 1969. CERN, Annual Report, 1957, p. 24. CERN, Annual Report, 1958, p. 26. CERN, Annual Report, 1960, p. 60. CERN, Annual Report, 1968, p. 99. CERN, Annual Report, 1969, p. 88. CERN, Annual Report, 1972, p. 89. CERN, Annual Report, 1972, p. 88. CERN, Annual Report, 1973, p. 95. CERN, Annual Report, 1978, p. 103. CERN, Annual Report, 1980, p. 15.

References 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53.

553

CERN, Annual Report, 1977, p. 127. CERN, Annual Report, 1978, p. 131. CERN, Annual Report, 1979, p. 104. CERN, Annual Report, 1980, p. 86. CERN, Annual Report, 1981, p. 112. CERN, Annual Report, 1961, p. 28. CERN Courier, Nov. 1970. CERN Courier, Sept. 1989. CERN, Annual Report, 1960, p. 35 and 1966, p. 85. CERN, Annual Report, 1979, p. 100. CERN, Annual Report, 1979, p. 99. CERN, Annual Report, 1962, p. 35. CERN, Annual Report, 1970, p. 102. CERN, Annual Report, 1955, p. 14. CERN Courier, Nov. 1972. CERN, Annual Report, 1980. CERN/SPC/444, Annex I, 4/9/79. CERN, Annual Report, 1980, p. 116. CERN, Annual Report, 1983, p. 61. CERN, Annual Report, 1983, p. 61. CERN, Annual Report, 1964, p. 115. CERN, Annual Report, 1977, p. 84. CERN, Annual Report, 1955, p. 25 and 1957, p. 33. CERN, Annual Report, 1976, p. 106. CERN, Annual Report, 1981, p. 110. CERN Yellow Report 85-19. CERN, Annual Report, 1963, p. 117. CERN, Annual Report, 1969, p. 94. CERN, Annual Report, 1973, p. 94. CERN, Annual Report, 1967, p. 17. CERN, Annual Report, 1969, p. 36. CERN, Annual Report, 1972, p. 96. CERN Courier, Nov. 1970. CERN, Annual Report, 1972, p. 86. CERN, Annual Report, 1966, p. 87. CERN, Annual Report, 1968, p. 96. CERN, Annual Report, 1972, p. 116. CERN, Annual Report, 1977, p. 101. CERN, Annual Report, 1982, p. 131. CERN, Annual Report, 1955, p. 24. CERN, Annual Report, 1957, p. 33. CERN, Annual Report, 1975, p. 162.

References [1] E.D. Courant, M.S. Livingston and H.S. Snyder, The strong-focussing synchrotron — a new high energy accelerator.' Phys. Rev. 88 (1952) 1190-1196.

Notes: p. 553

554

The Development

of Accelerator

Art and Expertise

at CERN:

1960-1980

[2] J.B. Adams, M.G.N. Hine and J.D. Lawson, 'Effect of magnet inhomogeneities on the strong-focussing synchrotron,' Nature, 171 (1953) 926-927. [3] J.B. Adams, 'Odd Dahl and the Machine at CERN', Festskrift til Odd Dahl (A.S. John Griegs Boktrykkeri, Bergen 1968). [4] J.B. Adams, Progress Report, 1 May-31 October 1956, CERN/179(A), p. 8-. [5] J. Adams, 'The design of the foundations for the magnet of the CERN altermating gradient Proton Synchrotron', CERN 56-21, Oct. 1956. [6] M.H. Blewett, 'Ten Years Ago .. some personal reminiscences', CERN Courier, Vol. 9, No. 11, Nov. 1969. [7] H.G. Hereward, K. Johnsen, A. Schoch, C.J. Zilverschoon, 'Feasibility of Storage rings for the CERN Proton Synchrotron', 1961 Int. Conf. on High Energy Accelerators, Brookhaven National Laboratory, USAEC, 1962. [8] 'Report on the design study of a 300 GeV proton synchrotron by the CERN study group on new accelerators', CERN AR/Int. SG/64-15 (1964). [9] J.B. Adams and E.N.J. Wilson, 'Design studies for a large proton synchrotron and its laboratory', CERN 70-6, 1970. a) C. Zilverschoon, 'Site Requirement for a 300 GeV Proton Synchrotron', CERN Report AR/Int. SG/ 62.1. [10] M. Goldsmith and E. Shaw, 'Europe's Giant Accelerator' (Taylor & Francis, London 1977). [11] E. Keil, 'Machine Geometries fitting into the ISR Tunnel', CERN ISR-TH/72-20, Geneva, 1972. [12] B.G. Pope (ed), 'Summary on Workshop on future ISR Physics', CERN/ISRC/76-32, Geneva, 1976. [13] SCISR Study Group, 'Superconducting Conversion of the Intersecting Storage Rings', CERN 77-20, Geneva, 1977. [14] B. Autin, D. Blechschmidt, A.A. Garren, K. Johnsen, E. Keil, B.W. Montague, J.-C. Schnuriger, C. Zettler and B.W. Zotter, '400 GeV Large Storage Rings with Conventional Magnets', CERN/ISR-LTD/75^5 (1975). [15] L. Camilleri (ed), 'The Physics Interests of a 10 TeV Proton Synchrotron, 400 x 400 GeV Proton Storage Rings and Electron-Proton Storage Rings', CERN 76-12 (1976) Sect. 2.1. [16] D. Blechschmidt, M.H. Blewett, K. Hiibner, A.M. Hutton, K. Johnsen, E. Keil, B.W. Montague, L. Rosegotti, J.-C. Schnuriger, C. Zettler and B.W. Zotter, 'Studies of 400 GeV Superconducting Storage Rings', CERN 77-21, 1977. [17] MISR Study Group, 'The Merging of the Intersecting Storage Rings for a 60 GeV Collider with the 400 GeV Proton Synchrotron', CERN 78-01, Geneva, 1978. [18] R. BilHnge, H.F. Hoffmann, A. Hoffmann, K. Hiibner, A. Hutton, K. Johnsen, E. Jones, B.W. Montague, B.H. Wiik and C. Zettler, 'An e-p faciUty in the SPS', CERN ISR-ES^E-GS/76-50. [19] J. ElHs, B.H. Wiik and K. Hubner (eds), 'CHEEP, an e-p FaciHty in the SPS', CERN 78-02, 1978. [20] J.R.J .Bennett, R. Billinge, M.H. Blewett, P. Brabham, A. Carne, D.A. Gray, M.R. Harold, H.F. Hoffmann, A. Hutton, K. Johnsen, E. Jones, E. Keil, S. Klemperer, J.R. Maidment, G.H. Rees, B. Richter, F. Sacherer, W. Schnell, T. Suzuki, A. Verdier and E.N.J. Wilson, 'Design Concept for a 100 GeV e+e~ Storage Ring', CERN 77-14, 1977. [21] The LEP Study Group, 'Design Study of a 15 to 100 GeV e^e" Colliding Beam Machine (LEP)', CERN/ ISR-LEP/78-17, Geneva, 1978. [22] 'Proceedings of the LEP Summer Study', Les Houches Sept. 10-22 1978, CERN 79-01. [23] The LEP Study Group, 'Design Study of a 22 to 130 GeV e"'e" Colliding Beam Machine (LEP)', CERN/ ISR-LEP/79-33, Geneva, 1979. [24] A. Hutton, 'Present Status of the LEP Project', Proc. 11th. Int. Conf. on High-Energy Accelerators, CERN, 1980. [25] M. Barbier and A. Schoch, 'Study of two-dimentional non-linear oscillations by means of an electromechanical analogue model', CERN 58-5, April 1958.

References

555

[26] M. Barbier, 'Etude des oscillations non lineaires a I'aide d'un modele analogique a cage d'electrons', CERN 61-3, August 1961. [27] E. Keil, Y. Marti, B. Montague and A. Sudboe, T h e ISR computer program for synchrotron design, orbit analysis and insertion matching', CERN 75-13, 1975. [28] F.C. Iselin, 'The MAD program, reference manual', CERN LEP-TH/85-15, 1985. [29] W. Busse and R. Zelazny (eds.), 'Computing in Accelerator Design and Operation', Lecture Notes in Physics, 215 (Springer-Verlag, BerUn, 1983). [30] Y. Baconnier, B. de Raad and Ch. Steinbach, 'Experiments on Beam Survival and non-linear Resonances in the CERN PS', Proc. V Int. Conf. on High Energy accelerators. Frascati 1965. [31] A Bruckner, K. Hubner, E. Jones, H. Koziol, L. Magnani and H. Pentz, 'Some recent experiments with CESAR', Proc. Int. Symp. on electron and positron storage rings, Saclay 1966, p. Ill-1-1. Presses Universitaires de France. 1967 (Atom. Energ. 22 (1967)). [32] K. Hubner, E. Jones, H. Koziol, L. Magnani, M.J. Pentz and A. Rugiero, 'Recent Expriments with the CERN Electron Storage and Accumulation Ring', Proc. Sixth Int. Conf. on High-Energy Accelerators, Cambridge, Mass. 1967. [33] P.H. Standley, 'The CPS Improvement Programme', Proc. V Int. Conf. on High Energy Accelerators', Frascati 1965, CNEN, Roma, 1966. [34] C. Bovet and K.H. Reich, 'A Four-ring Vertically Stacked 800 MeV Booster Injector for the CERN Proton Synchrotron', Proc. Sixth Int. Conf. on High Energy Accelerators, MIT, Cambridge, Mass. 1967. [35] K.H. Reich (Rapporteur), 'The CERN PS Booster: Design expectation confronted with reahty, two years after start-up', Proc. IXth Int. Conf. on High Energy Accelerators, SLAC, Stamford, May 1974. [36] The PS staff represented by R. BiUinge, 'The CERB PS complex: a multi-purpose particle source', Proc. 12th. Int. Conf. on High Energy Accelerators, Fermilab, Aug. 1983. [37] C. Bernardini, U. Bizzari, G.F. Corazza, G. Ghigo, R. QuerzoH and E. Touschek, 'A 250-MeV electronpositron storage ring: the 'A d A", 1961 Int. Conf. on High Energy Accelerators, Brookhaven, 1961. [38] K. Hubner, K. Johnsen and G. Kantardjian, 'The feasibiUty of Antiprotons in the ISR', CERN/ISR-LTD/ 75-45, 1975. Revised version in CERN 76-12. [39] G.I. Budker, Proc. Int. Symp. on electron and positron storage rings, Saclay 1966, p. II-l-l. Presses Universitaires de France, 1967. (Atom. Energ. 22 (1967)). [40] G.I. Budker, N.S. Dikansky, V.I. Kudelainen, I.N. Meshkov, V.V. Parchomchuk, D.V. Pestrikov, A.N. Skrinsky and B.N. Sukhina, 'Experimental studies of electron cooling'. Part. Ace. 7 (1976) 197-211. [41] S. van der Meer, 'Stochastic damping of betatron oscillations in the ISR', Internal Report CERN/ISR-PO/ 72-31, CERN, Geneva, August 1972. [42] W. Schnell, 'About the FeasibiUty of Stochastic Damping in the ISR', CERN-ISR-RF/72-46, Geneva, 1972. [43] P. Bramham, G. Carron, H.G. Hereward, K. Hubner, W. Schnell and L. Thorndahl, 'Stochastic CooUng of a Stored Proton Beam', Nuclear Instruments and Methods, 125 (1975) 201-2. [44] G. Carron and L. Thorndahl, 'Stochastic Cooling of Momentum Spread by Filter Techniques', C E R N ISR-RF/78-12, 1978. [45] C. Rubbia, P. Mclntyre and D. CHne, 'Producing Massive Neutral Intermediate Vector Bosons with Existing Accelerators', Proc. Int. Neutrino Conf., Aachen (1976). [46] F.J.M. Farley and E. Picasso, 'The muon g-2 experiments', CERN/LEP-DI/89-42, Aug. 1989. [47] 'Design Study of a proton-antiproton colliding beam facility', CERN/PS/AA 78-3, 1978. [48] F. Krienen, 'Initial Cooling Experiments (ICE) at CERN', Proc 11th Int. Conf. on High Energy Accelerators, CERN, Geneva, 1980. [49] P.J. Bryant, 'Antiprotons in the ISR', IEEE Trans. Nucl. Sci., NS-30, Aug. 1983. [50] E.J.N. Wilson, 'Antiproton Production and Accumulation', AIP Conf. Proc. 153, Vol. 2, American Institute of Physics, New York, 1987.

556

The Development of Accelerator Art and Expertise at CERN: 1960-1980

[51] S. van der Meer, 'A directive device for charged particles and its use in an enhanced neutrino beam', CERN 61-7, 1961. [52] B. Autin, A. Bellanger, R. Billinge, R. Brown, CD. Johnson, E. Jones, R. Sherwood and H.H .Umstatter, *Multipole Fields in the Antiproton Accumulator Magnet System', IEEE Proc. Nucl. Sci. NS-26, 1979. [53] P.E. Faugeras, A. Faugier and A. Hilaire, The Low Beta Insertions in the SPS and their chromaticity correction', Proc. 11th Int. Conf. on High Energy Accelerators, CERN, Geneva 1980. [54] P.Lefevre, D. Muhl and G. Plass, *The CERN Low Energy Antiproton Ring (LEAR) Project', Proc. 11th Int. Conf. on High Energy Accelerators, CERN, Geneva, 1980. [55] R. Cappi, W.E.K. Hardt and CH.P. Steinbach, 'Ultraslow Extraction with good duty factor', Proc. 11th. Int. Conf. on High energy Accelerators, CERN, Geneva, 1980. [56] B.F. Bayonov, A.D. Chemyakin, V.N. Karasyuc, G.I. Silvestrov, T.A. Vsevolozhskaya, V.G. Volohov and G.S. Willwald, The antiproton target on the basis of Hthium lenses', Proc. 11th. Int. Conf. on High Energy Accelerators, CERN, Geneva, 1980. [57] E.J.N. Wilson (ed), 'Design Study of an Antiproton Collector for the Antiproton Accumulator (ACOL)', CERN 83-10, Oct. 1983. [58] P.J. Bryant, 'Dynamic compensation during stacking of the de-tuning caused by space charge effects', Proc. IXth Int. Conf. on High Energy Accelerators, SLAC, Stamford, lUPAP, 1974. [59] H. Koziol, 'Beam Diagnostics', CERN 89-05. [60] J. Borer, P. Bramham, H.G. Hereward, K. Hiibner, W. Schnell and L. Thomdahl, 'Non-destructive Diagnosis of coasting beams with Schottky noise', Proc. IXth Int. Conf. on High Energy Accelerators, SLAC, Stanford, 1974. [61] J. Borer, G. Guignard, A. Hofmann, E. Peschardt, F. Sacherer and B. Zotter, 'Information from beam response to longitudinal and transverse excitation', IEEE Trans. Nuc. Sci., NS-26, June 1979. [62] 'Meeting on Technology arising from High-energy Physics', CERN, Geneva. CERN 74-9, Pt. 1 Presentations, Pt. 2 Technical notes, 1974. [63] K. Unser, 'A toroidal DC beam current transformer with high resolution', IEEE Trans. Nuc. Sci., NS-28, June 1981. [64] R. Bossart, J. Bosser, L. Bumod, E. D'Amigo, G. FerioH, J. Mann and F. Meot, 'Proton beam profile monitor using synchrotron light', Proc. 11th Int. Conf. on High Energy Accelerators, CERN, Geneva, 1980. [65] J. Bosser, L. Bumod, R. Coisson, E. D'Amico, G. Farioli, J. Mann and F. Meot, 'Single bunch profile measurement using sychrotron Hght from an undulator', IEEE Trans. Nucl. Sci., NS-30, Aug. 1983. [66] R. BiUinge, P. Brabham, H.F. Hoffmann, A.M. Hutton, K. Johnsen, E. Jones, E. Keil, B. Richter, W. Schnell, A. Verdier and E.J.N. Wilson, 'Design concept for a 100 GeV e'^e" storage ring', IEEE Trans. Nucl. Sci., NS-24, June 1977. [67] J.P. Gourber and L. Resegotti, 'Implications of the lowfieldlevels of the LEP magnets', IEEE Trans. Nuc. Sci. NS^26, 1979, 3185. [68] P.F. Smith, 'Superconducting Synchrotron Magnets — Present Status', Proc. 8th Int. Conf. on HighEnergy Accelerators, CERN, Geneva, 1971. [69] J. Billan, K.N. Henrichsen, H. Laeger, Ph. Lebrun, R. Perin, S. Pitchier, P. Pugin, L. Resegotti, P. Rhomig, T. Tortschanoff, A. Verdier, L. Walckiers and R. Wolf, 'A superconducting high-luminosity insertion in the Intersecting Storage Rings', IEEE Trans. Nuclear Science, NS-26 June 1979. a) J.P. Blewett, '200 GeV Intersecting Storage Accelerators', Proc. 8th Int. Conf. on High Energy Accelerators, CERN, 1971. [70] The LHC Study Group, 'Design Study of the Large Hadron Collider (LHC)', CERN 91-03, Geneva, 1991. [71] H.C. Brooks and A.B.D. Reed, 'The failure of Nimrod main magnet power supply alternators', lEE Trans. 1967, NS-114, p. 517. [72] J.A. Fox, 'Static power supplies for large pulsed magnets', Proc. 2nd Int. Conf. on Magnet Technology, Oxford 1967.

References

557

[73] M.G. Dwek, M.N. Eggleton and J.A. Fox, 'Direct supply of a large pulsed load from the e.v.h. transmission network', Proc. lEE, 117, No. 5, May 1970. [74] O. Bayard, T h e supply of the 148 MW pulsed power to the CERN SPS and the associated mains voltage stabilization and filtering', IEEE Trans. Nucl. Sci., NS-26, June 1979. [75] P. Wolstenholme, T h e impact of computer control on the performance of the CERN Intersecting Storage Rings', Proc. IXth. Int. Conf. on High Energy Accelererators, Stanford, lUPAP, May 1979. [76] H.K. Kuhn and J-D. Pahud, T h e control systems for the CERN Super Proton Synchrotron ring power supplies', IEEE Trans, on Nucl. Sci., NS-28, No. 3, June 1981. [77] J-D. Pahud, T h e various system aspects of the main power supply of the CERN-SPS', CERN 90-07. [78] D. Boussard, 'RF for the CERN proton-antiproton coUider', AIP Conf. Proc. 153, Vol. 2, American Institute of Physics, New York, 1987. [79] W. Schnell, 'Stacking with missing buckets, another way of gaining the ISR/CPS circumference factor', CERN ISR-RF/66-34. Nov. 1966. (Also: W. Schnell, 'Stacking in proton storage rings with missing buckets', Proc. Sixth Int. Conf. on High-Energy Accelerators, Cambridge, Mass. 1967). [80] K.N. Henrichsen and M.J. de Jong, 'Acceleration by phase displacement in the ISR', Proc. IXth Int. Conf. on High Energy Accelerators, SLAC, Stanford, lUPAP, 1974. [81] W. Schnell, 'A wide band travelUng wave accelerating method for a 300 GeV Proton Synchrotron', Proc. V Int. Conf. on High Energy Accelerators, Frascati, 1965. [82] W. Schnell and C. Zettler, 'Results on High-Power Models of Mechanically Tuned Cavities for Fast-cycling Booster Synchrotrons', Proc. Sixth Int. Conf. on High-Energy Accelerators, Cambridge, Mass. 1967. [83] W. Schnell, 'Modulated Cavities', CERN-ISR-LTD/76-8, CERN Feb. 1976. [84] Ph. Bernard, G. Cavallari, E. Chiaveri, E. Haebel, H. Heinrichs, H. Lengeler, E. Picasso and V. PicciareUi, 'First results on a superconducting RF-test cavity for LEP', Proc. 11th Int. Conf. on High-Energy Accelerators, CERN, Geneva, 1980. [85] W. Schnell, 'Discussion of a Radio Frequency Particle Separator for the CERN Proton Synchrotron', CERN 61-5, 1961. [86] M. Bell, P. Bramham, R.D. Fortune, E. Keil and B.W. Montague, 'RF Particle Separators', Proc. Int. Conf. on High Energy Accelerators, Dubna, USSR, 1963. [87] P. Bernard, P. Lazeyras, H. Lengeler and V. Vaghin, 'The New Three Cavity RF-Separator of CERN', Proc. Sixth Int. Conf. on High Energy Accelerators, Cambridge, Mass. 1967. [88] N .Galjaev, V. Kotov, A. Samoilov, V. Vaghin, P. Bernard, D. Lazard, P. Lazeyras and H. Lengeler, 'The High Energy Separated Beam and the R F Separator for IHEP (Serpukhov)', Proc. VII Int. Conf. on HighEnergy Accelerators, Yerevan, 1970. [89] The CPS Staff, 'The CPS Improvement 1965-1973; an assessment', Proc. IXth Int. Conf. on High Energy Accelerators, SLAC, Stamford, lUPAP, 1974. [90] S. Hansen, E. Jones, H. Koziol and M.J. Pentz, 'Some results of Stacking Experiments with the CERN Electron Storage and Accumulation Ring (CESAR)', CERN 65-8, Feb. 1965. [91] E. Fischer, 'Two Kilometers at 10~^^ torr. The CERN Intersecting storage rings for Protons', V-th International Vacuum Conference, Boston, Mass. October 1971. Also CERN-ISR-VA/71-55. [92] B. Ferrario, L. Rosai and P. della Porta, 'Distributed pumping by non-evaporative getters in particle accelerators', IEEE Trans, on Nucl. Sci., NS-28, No. 3, June 1981. a) H. Fischer and W. Richter, 'Production of Secondary Beams at the CERN Proton Synchrotron' Proc. 1961 Int. Conf. on High-Energy Accelerators, Brookhaven, USAEC, 1961. [93] R. BertoUoto, H. van Breugel, L. Caris, E. Consigny, H. Hijkhuisen, J. Goni, J.J. Hirsbrunner, B. Kuiper, S. Milner, S. Pichler and G. Plass, 'The Fast Ejection System of the CERN 25 GeV Proton Synchrotron', Proc. Int. Conf. on High Energy Accelerators, Dubna, USSR, 1963. [94] R. Bossart, H.V. Breugel, S. Herin, J. Cuperus, H. Dijkhuizen, F. Fabiani, G. Indreas, P. Innocenti, I. Kamber, B. Kuiper, J. Leroux, A. Messina, S. Milner, J. Nuttall, P. Riboni, H. Reige, and I. Ijspert, 'The

558

[95] [96] [97] [98] [99] [100] [101] [102] [103] [104]

[105] [106] [107] [108]

[109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119]

The Development

of Accelerator

Art and Expertise

at CERN:

1960-1980

Fast Ejection Equipment for the Serpukhov 70 GeV Proton Synchrotron', Proc. 8th. Int. Conf. on HighEnergy Accelerators. CERN 1971. H.G. Hereward, 'The Possibility of Resonant extraction from the CPS', CERN AR. Int. GS/61-5, Dec. 1961. C. Bovet, G.R. Lambertson and K.H. Reich, 'Measurements on Slow Beam-Ejection from the CPS', CERN 64^25, June 1964. J. Bleeker, C. Germain, M. Thivent and R. Tinguely, 'Development of an Electrostatic Septum for the Slow Ejection of the CPS', Proc. 8th. Int. Conf. on High-Energy Accelerators, CERN 1971. D.C. Fiander, D. Grier, K.D. Matzmacher and P. Pierce, 'A modulated fast bump for the CPS continuous transfer', IEEE Trans. Nucl. Sci., NS-24, June 1977. Y. Baconnier, P. Faugeras, H.K. Kissler, B. de Raad and W. Scandale, 'Extraction from the CERN SPS', IEEE Trans. Nuc. Sci., NS^24, No. 3, June 1977. W.C. Middlekoop, 'Magnetic and electrostatic deflecting devices'. Meeting on Technology arising from High-Energy Physics, CERN 74^9, 1974. D.C. Fiander, D. Grier, K.D. Matzmacher and P. Pierce, 'High-voltage pulse generators for kicker magnet excitation', CERN/MPS/SR 73-6, 1973. B.E. Carpenter, 'Experience with Interactive Control Software at the CERN Proton Synchrotron', Conf. on Software for Control, lEE Conference Publication No. 102, London, 1973. P. Wolstenholme, 'An integrated Digital Communications system for LEP, CERN/LEP Note. 196, Nov. 1979. J. Gamble, J.Y. Hemmery, D. Kemp, R. Keyser, J.P. Koutchouk, P. Martucci, L. Tausch and L. Yos, 'Towards full automation of accelerators through computer control', Proc. 11th Int. Conf. on High Energy Acclerators, CERN, Geneva, 1980. M.C. Crowley-Milling, 'The Design of the Control System for the SPS', CERN 75-20. M.C. Crowley-Milling, 'Experience with the Control System for the SPS', CERN 78-09. M.C. Crowley-Milling and G.C. Shering, 'The NODAL system for the SPS', CERN 78-07, Sept. 1978. B.E. Carpenter, A. Daneels and F. Perriolat, 'The planned replacement of a functioning control system on the CERN 28 GeV accelerator', 3rd. Int. Conf. Trends in On-line Computer Control Systems, lEE Conf. Pub. No. 172, London, 1979. B.E Carpenter, R. Caillaiu, G. Cousinier and W. Renner, 'System software of the CERN Proton Synchrotron control system', CERN 84^16, 20 Dec. 1984. J. Gervaise, 'High-precision survey and alignment techniques in accelerator construction'. Meeting on Technology arising from High-energy Physics, CERN 74-9, June 1974. J. Gervaise, 'Automatic measuring device', Proc. Sixth Int. Conf.on High-Energy Accelerators, Cambridge, Mass. 1967. G. Bain, C. Bore, W. Coosemand, J. Dupont, J.-P. Farbre, R. Gavaggio and F. Peron, 'Automatisation par Micro-ordinateur d'Instrument Geodesique de Measure de Distance: le Distinvar', CERN 84-07, 1984. J. Gervaise, 'Geodesy and Metrology at CERN: a source of economy for the SPS programme', CERN 7619, 1976. H. Schmied, 'A Study of Economic Utility resulting from CERN Contracts', CERN 75-5, Geneva, 1975. M. Bianchi-Streit, N. Blackburne, R. Budde, H. Reitz, B. Sagnall, H. Schmied and B. Schorr, 'Economic utility resulting from CERN contracts (Second study)', CERN 84-14, 1984. O. Barbalat, 'Advanced technology and applications arising from particle physics', CERN 87-10. C.J. Zilverschoon, 'Some aspects of the realization of High Energy Projects in CERN', CERN 74-9. U. Mersits, in A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN, Volume II (North Holland, Amsterdam, 1990). M.G.N. Hine and P. Germain, 'Performance of the CERN Proton Synchrotron', 1961 Int. Conf. on High Energy Accelerators, Brookhaven National Laboratory, USAEC, 1962.

CHAPTER 12

The Development of Electronic Position Detectors at CERN (1964^1ate 1970s) Ivana GAMBARO

Contents 12.1 12.2 12.3 12.4

Introduction Early spark chambers Film-less spark chamber techniques The multiwire proportional chamber 12.4.1 Mechanical structure and electrostatic forces 12.4.2 Gas mixture 12.4.3 Electronics 12.4.4 Applications of the MWPCs 12.4.4.1 The CERN-Heidelberg spectrometer 12.4.4.2 The chambers of the Spht Field Magnet detector 12.4.5 The MWPC as an investigation tool: the centre-of-gravity method 12.5 The multiwire drift chamber or drift chamber 12.5.1 The first chambers 12.5.2 Mechanical construction and associated electronics 12.5.3 High accuracy drift chambers 12.5.4 The time projection chamber 12.6 The multistep avalanche chamber (MSC) 12.7 Concluding remark Notes References

559

561 563 566 569 572 574 575 580 580 584 588 589 591 593 594 598 600 604 606 613

For Luca Preface In the 1960s the advent of new accelerators opened up new areas for high-energy physics (HEP) experiments, new detection techniques were developed and the old ones underwent substantial improvements. More and more complex events produced by interactions at higher and higher energies were registered by track devices that can be roughly divided in two groups: visual and electronic, or bubble chambers and spark chambers, later followed by more sophisticated devices. The first electronic chambers used at CERN were spark chambers whose basic element is a pair of metal plates to which a high tension pulse is applied. The earUest versions used photographic recording. From the early 1960s onwards these detectors have played an essential role in high-energy physics, allowing important discoveries such as that of the muon neutrinos identified by L. Lederman, J. Steinberger and M. Schwartz at Brookhaven in 1962. This class of devices was extensively used in many experiments at CERN as well as in other laboratories thanks to its attractive features e.g. triggerability and a short recovery time, that allowed a good data-taking speed. However the photographic films employed to stock information soon set a limit to their statistical accuracy. A few years later, in 1968, G. Charpak, Nobel prize for physics in 1992, developed at CERN a more versatile electronic device: the multiwire proportional chamber (MWPC), a powerful new tool in experimental particle physics. Subsequently a rich variety of electronic detectors has been conceived and developed: drift chambers, time projection chambers (TPCs), multistep avalanche chambers (MSCs), etc. Through the seventies and later in the eighties they have become standard instruments in high-energy physics, their appUcations ranging from simple counters to mammoth detectors. In this chapter I concentrate my study on the development of electronic position detectors from the mid-sixties until the late seventies to which CERN scientists made significant contributions either in terms of small and sophisticated prototypes or in terms of huge multi-purpose detectors^ After a brief historical introduction the main steps in the development of wire chambers will be analyzed beginning with the first sonic spark chambers and wire spark chambers. Then MWPCs, drift chambers, with some variants Uke the MSCs or the TPCs, will be treated. I will discuss the characteristics of the gaseous ionization detectors together with their advantages and weaknesses and the main technical problems connected with their construction e.g.: the choice of the gas mixture, of the geometry etc., stressing the role played by improvements in electronics. Electronic detectors have played an essential role in the first large facilities designed for use with colliding beams, like the Split Field Magnet (SFM) detector system at the CERN Intersecting Storage Rings (ISR). Their use in such large spectrometers has stimulated a major 560

Introduction

561

development effort to solve the complex technical problems encountered, thus allowing a wide exploitation of this technique. Both aspects will be discussed. Describing the main developments of this class of detectors due to CERN scientists I have been forced, by the limited time and space at my disposal, to omit many contributions and not to discuss important applications in big experimental facilities developed in the late seventies, e.g. the large mass detectors for high-statistics neutrino physics for the experiments WAl, or the European Muon Collaboration (EMC) experimental set up, etc., together with mixed detection systems like the European Hybrid Spectrometer. I have concentrated on the first experimental applications of large chambers as in the spectrometer built by the CERN-Heidelberg collaboration in 1969-70 or in the SFM detector system that became operational in 1973, because from the point of view of the development of the technique, they have played a fundamental role. A number of problems with the mechanics, the gas mixture, and the electronics of the chambers emerged during the construction and were solved by the CERN groups. In the field of electronic detectors which covers a multitude of devices I have limited my study to the development of gaseous ionization detectors, my choice being motivated by the key function assumed by them during the seventies in the deep transformation from the old physics to the new, or in other words from the hadron resonances and soft scattering experiments to ones based on the quark-gauge theory picture of elementary particles. As in many other high-energy physics research centers, at CERN, from the late seventies onwards, another class of electronic detectors allowing the measurement of energy flux, namely calorimeters, was extensively used together with MWPCs or drift chambers to equip large detection systems. This technique was exploited in the large mass detectors for high-statistics neutrino physics installed in 1977-78 at the CERN SPS, but its advantages over conventional electronic detectors have become particularly attractive with the advent of colliding beam machines and the construction of A% detection systems to surround the interaction regions. At CERN such detection systems were installed in the early 1980s (UAl, a well known highly sophisticated faciUty of this kind, went into operation in 1982 at the pp collider and provided outstanding experimental results thanks in part to this new electronic detection method). Since progress in detection techniques during the eighties is not included in this survey, this class of devices will not be analyzed in the following pages^.

12.1 Introduction In the 1960s the most widely used track devices in high-energy physics experiments were bubble chambers and spark chambers. These two groups of instruments belong to two different experimental traditions that can be traced back to the beginning of the century: the tradition of image-producing instruments initiated by the Wilson cloud chamber and the tradition of logic devices inaugurated by the Geiger-Miiller counter. Continuity of Notes: p. 606

562

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

skills and technology, of personnel, and of the experimental evidence shown by the detector chosen, characterize both traditions. Both kinds of detectors have advantages and weaknesses. A bubble chamber gives a detailed and complete picture of an event, and a physicist can go back and study a photograph in search of crucial features of a process that happened years ago. However, it has a long sensitive time (or memory) and a long recovery time. A spark chamber, on the other hand, provides a partial, or rather a sampled description of an interaction between elementary particles, and only interesting events are recorded by means of a photographic film or a computer. However its 'memory' is 1000 times shorter and, if digitized, data taking can be automatized by means of a computer online^. From the beginning electronic detectors had features that became more and more appealing as the research in high-energy physics moved from large cross section events to the rare processes and from lower to higher energies. Their triggerability, their high repetition rate and the possibiUty of using a computer on-Une played a major role. In fact in hadron-hadron interactions at proton machines such as those at CERN, low cross section phenomena were usually submerged in a sea of soft-scattering background, and most of the analysis of track data produced by bubble chambers consisted in separating events of interest from uninteresting background. Electronic detectors allowed one to minimize the problem of separating the wheat from the chaff because they could be triggered by external counters (spark chambers), or could be self-triggering (MWPCs) and therefore record only interesting events. Bubble chambers had the advantage of giving a good vertex detection, but this feature became less appealing to physicists than triggerability when they began to concentrate their research on rare events or on inclusive cross sections. Experiments on rare processes require ample statistics, and the high repetition rates shown by electronic devices became increasingly necessary from the mid-1960s onwards. A comparison between typical values of the repetition rate for bubble chambers and electronic detectors is interesting (see also Table 12.1): bubble chambers 1/sec wire spark chambers 100/sec MWPCs lOVsec Moreover the higher energies that became available at the end of the seventies called for detection equipment able to measure the high momenta of the particles produced. This would have required bubble chambers with a tremendously intense magnetic field or with a weaker field but with huge dimensions, and in both cases serious technical complications prevented their construction. Electronic devices, by contrast, were less problematic, even if they still left open the question of vertex detection. As for the use of computers on-line, a turning point was the informal meeting organized in March 1964 jointly by the Data Handling Division and the Nuclear Physics Division of CERN. Its purpose was to discuss the new film-less spark chamber techniques and associated computer use, and to get a clearer idea about the direction in which CERN should proceed. This meeting, being the first that dealt exclusively with chambers with

Early spark chambers

563

automatized data-taking using small computers on line, drew the physicists' attention to the new possibiUties opening up in experimental high energy physics. 'A higher degree of automation of the experiment', the possibility of changing some parts during the running of the experiment itself, the possibility of discriminating between uninteresting and interesting events and the widening of the 'range of questions which can be put to the nature of physics', were singled out by the almost 200 physicists attending the meeting as the most promising features. Twenty five years later the widespread use of computers on-line together with their essential role in most experiments has exceeded every expectation. The main steps in the development of electronic track detectors will be discussed in the following pages beginning with the first film-less spark chambers developed at CERN in early 1960s, through the multiwire proportional chambers and the drift chambers, ending with the multistep avalanche chambers and the time projection chambers. CERN has made significant contributions to all of these developments.

12.2 Early spark chambers The use of particle detectors based in one form or another on the energy lost by ionization by a charged particle as it traverses the device has characterized detection techniques in the field of subatomic physics from the start. In a large class of instruments the detecting material is a gas where the charged particle forms electron-ion pairs along its path. By collecting the free charges that are thus created, it is possible to obtain an electrical pulse signaling the passage of the charged particle. This principle informed the apparatus used as early as 1908 by Lord E. Rutherford and H. Geiger for 'counting' the number of a particles emitted per second by a given quantity of a radioactive substance"^. The simplest type of gaseous detector consists of a cylindrical chamber with a wire stretched along its centre. The chamber walls act as the negative electrode, and the positive voltage is applied to the central electrode. Under the influence of the electric field, the electrons are collected at the centre while the positive ions move towards the walls. As the magnitude of the applied voltage is increased, the different regimes depicted in Fig. 12.1 are encountered. At low voltages we have an ionization-chamber region in which the charge collected at the anode is just the number of electrons produced by the ionizing particle. Then, when the proportional threshold is reached, electrons acquire sufficient energy to cause secondary ionization, consequently high gains are reached - up to 10^ but the size of the output pulse still depends on the number of primary electrons. A saturation region follows where the high output pulses do not depend on the ionization source (typical working region of the so-called magic gas). Finally, at higher voltages the Geiger region is reached, in which the discharge is self-sustaining and the output pulses all have the same size regardless of the number of primary electrons. The great advantage of operating in this region is the very large output pulse, so that operation of a Geiger-Miiller counter is simple and reliable. Notes: p. 606

564

The Development of Electronic Position Detectors at CERN 10"-

T

T

(1964-late

1970s)

Geiger-MUIIer \ counter i

Region of limited proportionolity^ I

^Recombination f before collection

Ulonuatfon nr. ctiomber

.llO*

V^250

500 Voltoge, volts

1000

Fig. 12.1 Gain-voltage characteristics for a proportional counter, showing the different regions of operation (Ref. [148].

In 1928 H. Geiger and W. Miiller improved the technique and developed the counter bearing their names, and able to detect even a couple of ions produced in its volume. During the thirties new geometries were investigated. In 1933 the first parallel-plate ionization chamber was built operating in the proportional region^. Fifteen years later J.W. Keuffel developed the parallel-plate spark counter with the fastest response then available. It was little but a variation on the Geiger-Miiller geometry. However its rise time was 10 nanoseconds, and 0.15 nsec were achieved in the following years, while the discharge of a Geiger-Miiller counter could take tenths of a microsecond to develop^. The next step involved converting the device from a counter into a track-locating detector by using a photographic recording. The first observation that the discharge between parallel plates was located along the path of the ionizing particle (due to Keuffel), and later the first photographs of a spark discharge published by F. Bella and C. Franzinetti, allowed one to localize the discharge to within one cubic mm. Some years later, in 1957, at a conference held in Padova a young physicist from the Nuclear Chemistry Laboratory at the College de France, G. Charpak, showed that it was possible to obtain sparks following exactly the trajectories of the incoming particles. This led to an offer for a good job at a new international laboratory named CERN, with some consequences for the subsequent

Early spark chambers

565

part of our story^. Initially these results had little impact on high-energy physicists and it was only at the end of the fifties that their interest was awakened. In 1957 T.E. Cranshaw and J.F. DeBeer introduced the technique of pulsing the high voltage, leaving a small clearing potential on the plates between pulses in order to remove old ions. Two years before, in 1955, two itaUan physicists, M. Conversi and A. Gozzini at the University of Pisa, had developed the neon-tube hodoscope, later named the 'flash chamber', a detector in which the discharge was localized in an array of small glass tubes filled with neon. They showed that their apparatus, triggered by counter coincidences, could detect single- and double-track cosmic ray events. As in Italy, by the mid-50s there were no accelerators in Japan competitive with the British or the American ones then available, and cosmic ray physics was the only way to participate in particle physics. Early in 1956 the cosmic-ray division of the Institute of Nuclear Studies in Tokyo decided to begin a new programme of experiments on extensive air showers and asked S. Fukui, a research associate at the University of Osaka, to build a neon hodoscope. Immediately he started to work with S. Miyamoto on the Italian neon-filled device, and within three years they ended up with a new kind of track detector, the first example of a properly operating sp»ark chamber which could produce clear pictures of particle tracks. The 'discharge chamber', as the two Japanese physicists christened the new-born apparatus, when filled with a noble gas, operated as a track-delineating device, where the discharge followed the path of the charged particle, rather than as a track-sampling device. It thus provided a projection of the particle track on the plane of the plates^. With this crucial contribution by Fukui and Miyamoto the spark chamber became a precious instrument for high-energy physics, and the number of groups working on or with the device began to grow at an explosive rate^. In its standard form the spark chamber is made of a set of parallel metallic plates inserted in a volume filled with a noble gas at normal pressure, typically a heUum-neon mixture. The plates are connected, in alternating order, to a pulsed high-voltage supply or to ground. This detector is a passive instrument because it is necessary to know that a particle is traversing it. Information is provided by coincidence or anti-coincidence counters which are the control system of the chamber. This system controls a high voltage pulse and then triggers the chamber. The electric field between the plates is of such a strength (E > 10 kV/cm) that, at the place of initial ionization, avalanches and streamers are formed. The two ends of this plasma channel advance quickly (v = 10^ cm/sec) towards the anode and the cathode running parallel to the electric field lines, and reach both electrodes in about 10 nsec. A current, i.e. a spark, will subsequently pass between themi^ Triggerability together with the short memory time of this device were a definite advantage in comparison with the bubble chamber technique, at least for some areas in elementary particle physics. A bubble chamber can at the most record up to 20 particles during every expansion cycle, whereas the particle flux traversing a spark chamber can be 10^/sec, allowing an accurate selection of the interesting events. Moreover the longer occupation time of a bubble chamber (or in other words the fact that any additional event Notes: pp. 606 ff.

566

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

within this time interval will not be recorded as a distinct new event) prevented its use with high fluxes, and required complex methods physically to separate different particle beams. These difficulties could be avoided with a spark chamber on condition that particles could be identified through a specific counter system. Finally, at least until the late 1960s, the ease of construction and the relatively low cost of spark chambers allowed scientists to build chambers conceived for a single experiment in a short time, whereas the construction of a bubble chamber usually required complex planning and several years of work. From the early 1960s onwards interest in spark chambers triggered wide improvements in the technique. A good detection efficiency was rapidly reached: 100% for single tracks, and more than 95% for four tracks. In 1962, at the Argonne National Laboratory, A. Roberts and co-workers showed that a spark chamber could be used with a magnetic field to determine the momentum and the sign of an incoming particle. Later in the same year at Brookhaven, Lederman, Steinberger and Schwartz demonstrated the existence of two neutrinos by means of a set of spark chambers coupled with heavy aluminium plates^ ^. Another interesting feature of this detector is the fact that a photograph of an event taken in a spark chamber contains less information than a bubble chamber cliche. This constituted an advantage because it implied a faster analysis of the photographs by coordinate measuring automatic systems Uke H.P.D. or Luciole that could perform the operation in a few seconds^^. Later, from the mid-sixties onwards, spark chambers too, in their classical version with photographic film recording, began to lose ground in favour of systems which completely automated data taking and processing by means of computers on-Hne (like the wire spark chamber)^^. This was probably the most important improvement in spark chamber technique. It was not only a question of making the data taking procedure faster, easier and more reliable. It also meant that one was able to transmit directly information to a computer and consequently that one had the possibihty of both recording only selected events (thus saving off*-line computer-time), and of monitoring, controlling and in some cases modifying the operation of the detector system during the running of the experiment itself. This feature has been, together with the good operation of electronic detectors in high particle fluxes, the chief factor accounting for the success of wires over bubbles.

12.3 Film-less spark chamber techniques As we have mentioned, in March 1964 an informal meeting was organized jointly by the Data Handling Division and the Nuclear Physics Division of CERN. Originally planned as a small colloquium for 20 persons with the purpose of discussing the new film-less spark chamber techniques and associated computer use, and for defining the policy which CERN should follow, the meeting attracted more than 200 physicists from several European and American laboratories. This was indicative of the growing interest in these techniques inside the high-energy physics community. P. Preiswerk, head of the NP division, ascribed this interest to the possibility of 'a higher degree of automation of the experiments' and

Film-less spark chamber techniques

567

consequently of the widening in the 'range of questions which can be put to the nature of physics'. Furthermore 'learning faster about what he is wondering about in nature [...] with computers-on-line the physicist will receive certain answers during the running of the experiment in the experimental halls', and so he will be 'able to act and to put new questions on the ground of this information during the running of the experiment'^'^. New film-less techniques had already been proposed at the International Conference on Instrumentation for High-Energy Physics held at CERN in July 1962, but the results from the first experimental set-ups using digitized spark chambers together with small computers on-Hne, were discussed at this meeting^^. The most important methods analyzed can be classified into three main groups: the acoustic system, the vidicon system and the wire system^^. With the acoustic (or sonic) method detection is achieved through a microphone that indicates the arrival of a sound wave produced by the spark in a narrow gap spark chamber. Besides the advantage of operating reliably in a magnetic field, however, the acoustic spark chamber showed a number of problems connected with the fact that the velocity of the pressure wave is not exactly constant - it depends on the specific gas used, and is a function of the temperature and of the distance the wave has already travelled. But the major disadvantage encountered was the limited number of simultaneous sparks the chamber could record: eight microphones were necessary for recording only two sparks. This has been the chief factor compromising the success of this detector. Nevertheless it has been to the sonic spark chamber's credit that it inaugurated the 'missing mass' technique with the CERN missing mass spectrometer. Between 1964 and 1966, Bogdan Maglic and his team used it to investigate the mass spectrum of the unstable particle X " in the reaction TT" + p ^> p + X~, measuring the angle of the final state proton. Acoustic spark chambers and scintillation counter hodoscopes connected on-Hne to the CERN Mercury computer allowed physicists to acquire ample statistics thus demonstrating the value of a completely automated data taking system^^. The vidicon system was the only film-less method that used the optical emission of sparks. It usually consisted of a vidicon television-camera tube with associated electronic circuits able to read the spark positions directly onto a magnetic tape recorder or to store the digitized information temporarily in a magnetic core buffer. This method had some disadvantages since the standard tubes could not be as sensitive as film to faint sparks, and, moreover, vidicons seemed to be affected by variations of temperature and even by weak magnetic fields. Since they depended on technical developments in the television industry, their prospects were strictly connected to improvements in the sensitivity of the tubes^^. Another method proposed to combine the spark chamber with the computer was the digitized spark chamber. In a narrow-gap spark chamber parallel metallic plates are substituted by planes of parallel wires and therefore the currents created by the spark are forced to follow the wires it touches. By means of these currents it is possible to localize the spark and then the path of the particle. The link with the computer can be obtained with several methods, the most common being the magnetic core read-out and the magnetostrictive read-out. In the first, a tiny ferrite core is threaded by each wire and when a Notes: p. 607

568

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

current pulse passes, the magnetization of the core is driven from one stable state to the other. Conventional computer electronics then reads the state of the cores. With the magnetostrictive read-out, cores are substituted by a magnetostrictive ribbon which lies at right angles over the wires but separated from them by very thin melinex tape. When a spark current flows along a wire and passes close to the ribbon its field creates a magnetostrictive pulse that travels in both directions along the ribbon and is detected by tiny pick-up coils mounted at each end. Either of the two timing measurements indicates the position of the sparking wire. The main problems arose for both methods when they were used in magnetic fields (magnetic core read-out usually required an awkward amount of magnetic shielding, while in the magnetostrictive read-out strong magnetic fields could reduce the pulse amplitude by about 50% endangering considerably time measurements). Other difficulties were encountered: the problem of spark current overshoot with ferrite core recording and, with the magnetostrictive method, the reduced intensity of the magnetostrictive pulse, barely above the noise level when there were many simultaneous sparks^^. Another method for determining the position of a spark along a wire was proposed by Charpak, and was based on the relative magnitudes of the two currents that diverged from the spark^^. In practice the three systems (except the magnetostrictive method) all suffered from rather serious problems of stereo ambiguity in the case of multiple sparks, and sometimes it was not even possible to tell whether there was more than one spark. 'In looking at the future, - said M.G.N. Hine, director of the Data Handhng Division, in his concluding remarks at the end of the meeting - 'I do not put my money on the acoustic chamber, I think it is too like the bubble chamber in having a 19th century steamage feel about it [...] I would also vote against any photographic system or any vidicon system mainly because I think the difficulty of actually optically looking into a spark chamber is going to become more and more of a nuisance as time goes on'. A few other possibilities were left: the magnetostriction wire which seemed to solve rather directly the otherwise serious problem of stereo ambiguity with multiple sparks, and the current distribution method proposed by Charpak, which seemed to have the greatest technical attractiveness and the minimum number of serious difficulties^^ Besides these problems other general subjects connected with the use of computers onHne stimulated the debate, involving some of the speakers in semantic disputes over: what is a computer? what is to be regarded as on-line use? or how much use should be made of a computer? As R.H. Miller remarked 'the computer could be used to facilitate calculations to be made during the experiment; or, if it is to be part of the data-logging system, it could simply provide a buffer storage to smooth out tape unit use; it could multiplex the output to several tape units; or it could carry the reduction all the way to the final numerical results before producing any output. Between these, there is almost a continuum of possibiHties'. On the other hand Miller underUned that not all experiments were suitable for on-line computer use. When many similar events were expected the experiment could benefit from an on-line computer, but when the event sought was particularly rare or unusually difficult to analyse some caution was necessary: 'if a computer is used along with

The multiwire proportional chamber

569

automatic data transcription, there is a danger of missing discoveries because one has not been clever enough a priori to write a programme to handle that kind of event, and the programme may throw it out [...] Unexpected discoveries may be very difficult to pursue, and may require planning a new experiment'^^. Fifteen years later the theoretical framework in which detectors and experiments will be planned and made will show deep differences. The geometry of detectors will be chosen in order to avoid the detection of undesired events and sophisticated electronic triggers will become an imperative in order to reject the vast majority of events, processing only the rarest ones^^. Other questions about whether a special purpose or a general purpose computer should be used for on-line applications were discussed, and there were of course supporters for both approaches. Hine underlined the advantages of having a general purpose computer on-line, advantages associated with the ability 'to alter the discrimination logic in an experiment by changing programmes rather than by having to modify the hardware', but difficulties could be encountered due to the lack of man-power and money. Nevertheless Hine seemed to be optimistic because the manpower aspects were turning out to be less serious than expected, and as for the money this was not a new problem since there was and there is 'a rather general rule: in physics with big machines you cannot afford to be poor. Bernard Shaw said 'poverty is the worst of crimes' and he would have been a very good high-energy physicist with that philosophy''^^.

12.4 The multiwire proportional chamber Rapid progress in particle physics depends on the increasing intensity and energy of the accelerator sources as well as on the continuing evolution of its detection techniques. The two essential features of a detector are its spatial resolution and its time resolution. Spatial resolution denotes the ability to localize the position of a particle in space in order to associate two or more tracks with a particular event, while by time resolution is meant the ability to localize the passage of a particle in time. While a bubble chamber records all tracks entering during its sensitive time (a few milliseconds), a spark chamber remembers events for 1 /xsec, a time interval associated with the longevity and the mobility of free electrons in gases. A related property is the recovery time, namely the minimum time interval between events which can be separately recorded. This feature of the detector affects the repetition rate that in late sixties was about 1/sec for bubble chambers and about 100/sec for wire spark chambers (see Table 12.1). At CERN Charpak and his team applied the well known technique of proportional counters to overcome these problems, and thanks to modern solid state electronics they demonstrated that it was possible to build wire chambers where each wire acted as an independent detector equipped with a separate amplifier and pulse shaper. Whereas the space resolution achieved with the first chambers was similar to that in wire spark chambers, the time resolution and the recovery time were substantially better. The first multiwire proportional chambers made in 1968 showed: Notes: p. 607

570

The Development

of Electronic Position Detectors at CERN

(1964-late

1970s)

Table 12.1 Particle detectors in HEP (from Charpak [43]). Visual Detectors

Space Resolution

Time Resolution

Repetition Rate

Cloud chamber Photographic emulsion Bubble chamber Spark chamber Streamer chamber

0.3 mm 1 /^m 70 //m - 1 mm 0.2 mm - 1 mm 0.2 mm - 1 mm

1/10 s 1 ms 1 lis 1 us

1/mn continuous 1/s 10/s 10/s

1 cm 1 cm

1 /zs 1 /zs 1 ns 1 ^s 20 ns 5 ns

lOVs lO^/s lO^s 100/s 10Vs/cm2 10Vs/cm2

00

Digitized Detectors Geiger counter Proportional counter Scintillation counter Automatized spark chamber MWPC Drift chamber

0.2 mm 0.2 mm 0.05 mm - 0.5 mm

- time resolution below 0.4 ^sec - counting rates of the order of 2.5 • 10^/sec per wire^^. The maximum counting rate was limited by the available electronic circuitry and locally by the space charge created by positive ions. This new detection method had immense potential. Both space and time properties could be improved to such an extent that 'it might well herald a new revolution in detection techniques'^^. Furthermore the MWPC did not need to be triggered by auxiHary counters, because the chamber was always sensitive and was self-triggering, or, in other words, the selection could be made by means of the electronic readout itself. The price to pay for these attractive features was the circuitry, which was complex and expensive. Every chamber required for each wire an amplifier and a fixed delay - in order to amplify the signals and to have time to do fast logic and select particular events - and a memory with a gate in front of it to accept or reject events and then to store the interesting ones. When Charpak first proposed the MWPC at an international conference in September 1968, the necessity of using hundreds or even thousands of electronic channels caused considerable scepticism among the physicists present at the meeting^^. Let's analyze the properties of this detector. A multiwire proportional chamber is usually made of uniformly spaced thin anode wires sandwiched between two cathode planes (cathodes may consist of either uniform conducting foils or of wire grids. Fig. 12.2a). The first chambers built at CERN had this typical structure: distance between the wires = 1 mm, cathode-anode distance = 8 mm, wire diameter = 20 /xm. The distribution of equipotential lines shows that there are three distinct regions of electrical field (Fig. 12.2b): thefieldis uniform in the region A, far from the anode wires; between the wires, in the region C, there is a weak field, and close to the wires (region B) thefieldis stronger, as in an ordinary cylindrical counter. If a particle ionizes the filling gas the

The multiwire proportional chamber

571

Cathode planes can also consist, of wires

Cathode planes

|||[||||[|[|i|||||||i||||i|| 05 0.6 0.7

| | ^ ^ | W "Hlffl 1 1 1 LmM^^^^^^ lillii lllllll 1 ^f 1 1 1

V

0.80 035 090

m

|/|imj|

' 1 j(i||n mf^

P 1 ^1 l l j 1 | |l 11 l l j l

iiiiiiiiiiiiniiiiiiiitiiiiiiiiiiiiiiii

" j||||||li||||l||l|||||N

11IP 1 jl Ijl ||l 1 1 1 |j || llll III 1 i l l ill 1 j jll 1 111 1 1 I'M jl 1 1 1 1 ll 1 Jl lljl 1 1 1 || Ijl 1 llj ij 1 11 II 1ill II ll ll ||| II 1 ll i| lllj 1 1 1 ll 1 11 lllljllllllillll iiijiiiiiiiiijjijiiiiijiiiiiijiin^ liliiil llllllll |||||l|||: Fig. 12.2a,b a) Structure of a multiwire proportional chamber (Charpak and Sauli [57]); b) Equipotential lines in a multiwire chamber with one displaced wire (Charpak & Sauli [57]).

electrons produced drift in the uniform field till the closest wire where they produce avalanches. And since the avalanches develop only within a radial distance of the order of the wire diameter, the amplification properties on each wire are the same as those of a single proportional counter^^. Notes: pp. 607 ff.

572

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

The key feature of a wire proportional chamber is that if a negative pulse is created on a wire by the avalanches, then positive pulses are obtained simultaneously on the neighbouring wires. And this is true for any spacing between the wires. Moreover the pulses are fast-rising: rise-times of the order of 10 nsec have been observed at the beginning of the pulse, which then slows down and lasts for a few microseconds. With ampUfiers sensitive to the negative polarity of the pulse - in the first chambers amplifiers with an input impedance of about 10 KQ and a simple three transistor design with a gain of 200 were used - the wires act as independent proportional counters with a sensitive volume limited to half the distance between two wires^^. Simple electrostatics calculations show that the collection of electrons does not usually give rise to a detectable pulse, and it is the motion of the cloud of positive ions left that, migrating towards the cathode, is responsible for pulses. Actually it took some time to understand the exact distribution of induced charges in space and time over the electrodes in a given detector geometry, but these first studies were sufiicient to allow a first exploitation of this technique for medium and large size chambers as is shown in the following paragraphs. 12.4.1 MECHANICAL STRUCTURE AND ELECTROSTATIC FORCES Multiwire chambers are delicate instruments: large quantities of fragile wires are stretched to the limits of tensile strength in very high electrostatic fields, and are submitted to constant bombardment by intense ionizing radiation. Consequently a number of problems with the mechanical structure arose during the construction at CERN of the first very large chambers. The main problem is to support a succession of foils or wire planes constituting the electrodes while respecting the mechanical and electrical tolerances, and making the whole structure gas tight. The mechanical frame has several functions: -

it fixes the electrodes; it provides the necessary mechanical strength to withstand the resultant stress; it encloses the gas volume; it makes it possible to supply electric power and gas for the chamber, and to extract the signals.

The most common techniques are two. Both were developed at CERN, by the group of Steinberger for the experiments on CP violation (the CERN-Heidelberg collaboration^^) and by the group of A. Minten and G. Charpak - the so called SFM group - during the preparation of the detector system to be used with the CERN Split Field Magnet facility. The first one uses a set of self-supporting insulating frames of extruded or machined fiber-glass, one per electrode. The chamber is mounted glueing together the required number of frames and is kept gas-tight by O-rings embedded in them. The wire electrodes are soldered on printed circuits which are an integral part of the frames. Chambers of this kind have been used in the CERN-Heidelberg spectrometer and as prototypes for the SFM faciUty^^ The second method is based on the use of metallized self-supporting

573

The multiwire proportional chamber

honeycomb or expanded polyurethane planes that are both the cathode planes and the support of the chamber. This technique was used for the chambers that in 1973 went into operation at the SFM, and is particularly suited when the available detection area is limited, as in the case of a spectrometer magnet, because the ratio between the active area and the total surface is more favourable than in the previous method. This advantage is, however, balanced by an increase of the chamber thickness in the active area^^. Another major mechanical problem encountered by the two CERN groups in the construction of large MWPCs was due to the dependence of the gain on mechanical tolerances and on the electrostatic forces acting between wires. The gain of a chamber at a given voltage depends on the electric field in the multiplication region (the region B in Fig. 12.2b), and the field can change along a wire or from wire to wire depending on mechanical variations or on small displacements of the wires from the wire plane^^. But the most serious mechanical difficulties in large size chambers arise from the electrostatic forces which occur in the chambers in two ways: as a repulsive force between adjacent wires of the same potential, and as an attractive force between the anode and the cathode planes. Wires stretched loosely are displaced from the neutral plane because of the repulsive force, and the new equilibrium then established has all wires alternatively displaced up and down (see Fig. 12.3). By stretching the wires - made almost exclusively in gold-plated tungsten due to its favourable strength properties - one can ensure their stable position in the neutral plane, but for long wires, indispensable in the case of large chambers, the required tension reaches a high value which the wire cannot withstand. In this case a 0.1 mm displacement of a wire in the wire plane implies a 8% change in the charge of the two closest wires giving a 100% gain variation at gains around 10^. This results in vibrations, discharges and sparking, even at normal working voltages. It is therefore necessary to clamp the wire at shorter intervals. Several solutions were developed using insulated wires or conductive strips put close to the anode wires and raised to a potential able to restore the field and consequently the efficiency of the chamber. Two of the most popular methods were developed in the early seventies at CERN by the two above mentioned groups and later by S. Majewski and F. SauU^^.

) *

Fig. 12.3 Electrostatic instability in multiwire proportional chambers. The wires are shown alternatively displaced by a quantity d from the central plane (Sauli [148]). Notes: p. 608

574

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

Finally, it is generally found that a careful cleaning of the chamber before putting it together is one of the fundamental prerequisites for proper functioning, since during operation the noise level of the chamber greatly depends on the dirt adhering to the surfaces. Usually the dirt is removed from the printed circuit boards and from the electrodes by washing them with a solvent like liquid freon spray. Just how important is the cleanliness of a wire detector is clear from the accident with the vacuum system of the UAl detector which took place in 1982. The currents of the compressed air system of the central detector were inadvertently reversed, and dust was picked up and blown onto the wires. The result was the delay of the first run of the experiment from the spring to the fall of 1982. The central detector had to be disassembled and cleaned, causing - according to some accounts - great resentment in the UA2 group, which was ready to run and could not get beam time because both experiments had to be run together^^. While the mechanics of the chambers, as we have seen, caused some headaches for CERN scientists, the most fundamental limitations in chamber operation were connected with the physical and chemical constraints in gas amplification. 12.4.2 GAS MIXTURE In the early years of chamber construction, in order to keep down the electronics cost and complexity, a minimum gain was required from the circuitry, and the gas gain was pushed as high as possible. Charpak and his group concentrated their efforts on selecting a gas giving the maximum amplification, and they found that ordinary argon, bubbling through n-pentane or heptane cooled at 0° C gave satisfactory results, at least with their small prototype. Argon, being a noble gas, has zero electron affinity and therefore allows a high degree of multiplication, while the organic vapour quenches the discharge i.e. neutralizes the positive ions and prevents electrons being ejected from the cathode. Later the problem of the gas turned out to be one of the most ticklish problems for gaseous detectors. The composition of the gas can be determined with respect to several, very often contradictory conditions, and in the majority of cases one has to rely on empirical knowledge. For instance, in seven articles selected at random, nineteen components are mentioned^^. Studies by the SFM group indicated that a good performance could be obtained with isobutane mixed with argon. If freon-13 Bl (CFsBr) was added multiplications of the order of 10^ were obtained without entering into Geiger operation. Since normally, in a conventional proportional counter, the avalanche is limited when the positive ion-space charge reduces the field at the wire, the authors speculated that negative freon ions and isobutane, neutralizing the effect of space charge, allow the multiplication to continue and quench the photons sufficiently to prevent Geiger action. The magic recipe recommended by the SFM group was (by volume): 0.5% freon-13 Bl (CFsBr) 24.5% isobutane (iso C4H10) 75% argon.

The multiwire proportional chamber

575

Moreover electronegative gases, and specifically those that have been halogenated, reduce the sensitive region of a MWPC to narrow cyUnders around the wires. This allows one to handle tracks that are strongly inclined to the plane of the wires with satisfactory results (instead of getting pulses on, say, five wires, only one gives an output)^^. During the construction of large chambers a complex problem soon emerged: isobutane polymerizes, and the secondary products contaminate the electrodes. In addition the use of magic gas quickened the deterioration with time of the chamber, or accelerated its death in case of very strong irradiation, because of the very high gas amplification factors that could be obtained. By 1971 further studies showed that the addition of special agents Hke methylaP^, or the use of quenching gases which did not polymerize and had ionization potentials below that of isobutane (10.6 eV) could improve the performance of the chamber. The problem, however, is still open since the contamination is strongly catalyzed by fluorine compounds and the mechanism of the chemical reaction is not fully understood. The higher the rate of the incident beam, the faster will be the ageing of the chamber due to the polymerization, so that the life-time of the chambers was and is still a serious problem in case of high particle rate. These difficulties have been partially solved by progress in electronics that has made available circuitry with high sensitivity thus allowing a low gain in the gas mixture with enormous practical advantages for the chamber operation^^. 12.4.3 ELECTRONICS The most interesting characteristic of electronic detectors is the possibility of selecting out particular events from background and/or other competing reactions which occur simultaneously, and recording only the events satisfying specific criteria. The electronic logic required for this selection is called the trigger in current nuclear and high-energy physics parlance. In spark chambers the control system is generally formed by a set of coincidence or anti-coincidence counters, while in the MWPCs the selection is obtained by means of sophisticated electronics which elaborates the signal from the anode wire according to criteria fixed in advance. This is why the MWPC is called self-triggering. Today the increased signal processing power per read-out channel allows many HEP experiments to use several different triggers and to record more than one type of reaction at the same time. Moreover this readout method can considerably increase the data acquisition speed: pulse electronics can operate orders of magnitude faster than film transport systems used in the case of optical recording. Almost every group working with proportional chambers has developed its own electronic circuitry that can solve the specific requirements of its experiment. Problems connected with the electronics can thus be very different depending on the kind of experiment one is doing. When the MWPCs were first used major problems were the cost of the circuitry and the space taken by the read-out electronics. Another was the noise that could interfere with chamber operation. All of these have been partly or totally solved by recent progress in electronics. Figure 12. 4(a) shows a typical single-wire electronic channel where Notes: p. 608

576

The Development of Electronic Position Detectors at CERN (1964-late 1970s) Discriminator Amplifier

Write gate

Read gate Memory

Delay

""TMJTDTlKtlF" t Fast out

Write

DC out

Read Coord. 6 bit

Oi*Or

Or

Amp

a-a

Memory 256xA

FADC

2L

(6 bit )

Memory -OrC?r

Ql*C?r o

X

(6

Disc

Memory

bit)

T I

Inter- I

18 >|

Memory

l('?'°b!r)l=q _ f

Clock 31-25

MHz

dE/dx 6 bit (compressed)

8

FADC

I

fTTTTTTr Address counter

I

Time 10 bit, UUnnss)

rp I

i J ^

Fig. 12.4a,b Schematic comparison of track chamber signal-processing electronics, (a) Typical electronics chain for an MWPC. After amplification, the signal is discriminated, shaped to a logical level and then delayed. Events considered interesting by fast trigger electronics are selected by means of a logic gate, stored in memory elements, and finally read out in a sequential way into a computer (Sauli [148]). (b) Signal processing in continuously sensitive tracking devices. Controlled drift of electrons from an ionization track produces avalanches at a sense wire. The charge diffuses to the ends of the resistive sense wire (QL, QR) in the ratio of the distances of impact point to the ends of the wire. The signals are amplified by low-noise preamplifiers and every 30 nsec the pulse height is sampled, digitized and recorded. This processing chain allows the measurement of unambiguous three-dimensional space points with a resolution of « 0.20 x 10 x 10 mm^ and simultaneous ionization measurement (Fabjan & Fischer [80]).

the signal coming from the anode wire is amplified, discriminated, shaped to a logical level and then delayed. The delay element can be active or passive and by means of a logical gate allows the selection of the events that are considered interesting by fast trigger electronics. The signals that pass the 'exam' are then stored in the memory elements (one per wire) and successively read out to a computer. As I mentioned before this way of

The multiwire proportional chamber

577

triggering the detector is completely different to that in spark chambers and is particularly suited for modern particle physics experiments which are highly selective. The properties of the chambers can be exploited to the fullest extent if there are available as many channels as there are the wires, and it was this that led initially to the high cost of the electronic circuitry. The Omega Spectrometer in its first version (operational in 1972) was equipped with optical spark chambers for this reason (in late 1969 it cost up to 40 SF for each wire in a MWPC, and 10^ wires had been foreseen by the Omega project working group)"^^. The same problem emerged during the discussions preceding the construction of the SFM, when Steinberger presented a proposal for a 10^-wire detector equipped with large size Charpak chambers. F. Krienen and A. Minten commented on the high price and complexity. Counting only the price of the components the cost was around 40 SF, though the overall cost was closer to 100 SF per wire"*^. To decrease these costs several alternatives to the single-wire electronic channels were developed based on delay line read-outs or on analogic methods'*^. Decisive progress was made when nuclear electronics was largely standardized into a modular form and when integrated circuits became available at low cost. Standardization of logic signal levels and data processing protocols has been very important for the industrial support of electronic instrumentation. Circuits for the basic processing functions (e.g. amplification, discrimination, etc.) built into separate electronic modules of standard mechanical and electrical specifications could then be interconnected as desired. These systems (Nuclear Instrument Module or NIM and CAM AC, introduced by 1967 and 1970 respectively, see Table 12.2) turned out to be extremely advantageous as they allowed the design of many different systems using the same set of modules, with a consequent massive price reduction. The revolution in miniaturization heralded by integrated circuits had an even stronger impact on experimental particle physics. In 1964, the year of the meeting on filmless spark chamber techniques, the average price of an integrated circuit performing simple functions was $19, while by 1972 it had already decreased to $1. By 1971, 6000 component equivalents were put on a chip about 6 mm square"^^. A few years later the metal oxide semiconductor (MOS) integrated circuit, allowing intense integration, became the cheapest form of integrated circuitry and LSI (Large Scale Integration) the most exhaustive exploitation of that form"^. Electronics miniaturization has made possible the production at low cost and reduced bulk of circuits performing very complex functions, and it has made wire chambers highly competitive in comparison with other detection methods. Figures 4(a) and 4(b) allow a comparison between a typical electronic chain for an MWPC used in the early seventies and a more sophisticated read-out technique later employed in large facilities and characterized by an increased signal processing power per read-out channel. Progress in electronics for particle physics is illustrated by Table 12.2. The credit for the first large chamber readout using integrated circuits has to be ascribed to a co-operation between the CERN-Heidelberg group working on the spectrometer for CP violation experiments (see Section 12.4.4.1), and a group at Columbia University (N.Y.). To give the reader an idea of electronic circuitry considered at the time to be highly Notes: pp. 608 ff.

578

The Development

of Electronic

Position

Detectors

at CERN

(1964-late

1970s)

Table 12.2 Electronics for particle physics (Fabjan & Fischer [80]) Item

Approximate year of introduction

Characteristics and comments

NIM electronics (Nuclear Instrumentation Modules)

1967

Signal processing with standardized modular instruments; modularity allows repeated use for different experimental configurations; standardizations permit interchangeability, external serviceability and international industrial support.

CAMAC

^1970

Extends the NIM concept to computer-oriented modular data acquisition systems; TTL-oriented signal levels; MHz signal transfer; subsequently becomes widely used in industry for process control.

Custom-integrated circuits

1971

First attempts to have MWPC electronics in medium-scale integration, Concept becomes viable for experiments with ^ 10^ identical circuits per customer.

CAMAC-compatible ADC

1972

Packaging density of ADC has increased by several hundred during period 1970-1979. Price decreased approximately by same factor.

Low-noise chargesensitive preamplifiers

1974

State-of-the-art analogue instrumentation techniques successfully adapted to high-energy physics; basis for instrumentation of ion- and low-gas-gain proportional chamber.

Programmable pre-processors

-^1977

Logic decisions, too complex for conventional logic modular instrumentation, conferred to specially built programmable processor; speed of computation versus ease of programmation controversy.

CAMAC replacement

^1978

Start of discussions: new system (*Fast Bus') oriented towards high-speed data transfer for 'fast' processing, based on ECL technology.

CCD, flash encoders

1978

Charge-coupled devices or flash encoders permit 'continuous' (up to 100 MHz sampling rate at present) digitisation of detector signals; allows track chamber construction with ^^.l mm^ granularity for information read-out.

sophisticated, I report some properties of this MWPC readout system developed in 1970. The system, a 5000 wire proportional chamber readout system, was designed to take advantage of the high counting rate capability of the MWPCs, and to minimize background counts by achieving a very small practical resolving time. The most appealing features of this electronics, which was based on Motorola MECL II integrated circuits, and which required a significant developmental effort were:

The multiwire proportional chamber

579

- low wire signal thresholds (a few hundred microvolts); - a trigger from each chamber to eliminate the need for other counters and thus to preserve the low mass of the spectrometer; - decision logic that allowed one to send only interesting data to the computer; - low decision deadtime (200 nsec); - fast readout time of 200 nsec per track"^^. In the fall of the same year, 1970, the SFM group made a comprehensive survey of the electronics available, identifying as crucial points, besides the cost, the reduction of the space taken by the circuitry and the optimization of read-out speed. Three integration techniques were available: 1) MOS (field effect), 2) TTL (transistor-transistor logic) and 3) ECL (emitter coupled logic); 1, 2, 3 was the order of increasing speed, while 3, 2, 1 was the order of increasing possibility of large-scale integration. For every single-wire electronic channel, integration of the full chain in two parts not necessarily in the same technique was considered, and the cost estimate was about 30 SF per wire, definitely lower than two years before^^. Another prominent feature exhibited by highly sophisticated electronic circuits in detection systems is correlated with data acquisition. As anticipated by many participants in the film-less spark chamber technique meeting held at CERN in March 1964 the problem of data taking and processing soon became extremely important in experimental highenergy physics. Modern particle physics experiments are highly selective: interesting events are often characterized by small interaction cross sections and submerged by a large background coming from more probable interactions which have to be rejected. By means of the technology available by the end of the seventies the rate with which events could be transmitted and stored on magnetic tapes was about 10-100 per second, while already in 1968 the first multiwire proportional chamber showed counting rates of the order of 2.5 • 10^/sec per wire"^^. Practical limitations in data transmission thus imposed and still impose today a high selectivity, which was required also by the cost and the availability of off*-line analysis (in the late seventies the fastest existing machines needed from 0.1 up to 10 seconds per event to treat the data obtained by complex detector systems). By the early 1970s, when the computers ran slower, it was already clear that 'the handUng of the data [would] probably represent a very severe bottle-neck' in the following years, and that the demand for 'fast decision making devices directly linked to the detectors' was even more urgent, as H. Schopper and K. Winter underlined in a note to M.G.N. Hine in February 1971^^. This chapter deals above all with the development of electronic detectors, mainly wire chambers, and therefore I will not deal with the exceptional evolution in the field of data selection, of monitoring and of control in large detector systems, that was achieved in the seventies. However I would Uke to emphasize that in this period, for the first time, a hierarchy of different fast decision levels in the data treatment with increasing selectivity and complexity became feasible for the physicist. This was made possible by the widespread availabiUty of cheap and constantly improving integrated circuits, by the advent of fast analogue-to-digital converters (ADC), and time-to-digital converters (TDC), and, in Notes: p. 609

580

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

the late seventies, by the development of microprocessor systems. In addition microprocessor systems have allowed a better exploitation of existing detection techniques. From 1977-78 onwards the increasing need for pre-processing work on the data due to the massive use of calorimeters, to the introduction of pictorial drift chambers and later of time projection chambers, has become imperative. The central detector of UAl experiment produced approximatively 3 • 10^ words of 16 bits for each single event. And every TPC, for instance, needs sampling of thousands of analogue signals at a rate of one sample every 100 nsec for each signal, thus producing so many data words that it is absolutely impossible to record them without efficient data compression. In cases Uke these many microprocessors working simultaneously on parallel streams of data, have become the only solution able to digest all these data in a reasonable time^^. 12.4.4 APPLICATIONS OF THE MWPCs The first MWPCs - outside laboratory development - were built at CERN in 1968 by G. Amato and G. Petrucci for a beam profile analysing system. The apparatus, whose main purpose was to speed up the tuning procedure of high-energy secondary beams, consisted of two small MWPCs (100 mm x 100 mm, 32 wires each), wire pulse amplifiers (one channel for each wire), a channel analyser, a channel scanning system, and an oscilloscope. Low-cost amplifiers were adopted in this case. Each unit consisted of a threestage d.c. coupled amplifier, with a transistor sequence PNP-NPN-PNP to compensate for the temperature drift. The maximum acceptable rate, limited by the electronic circuitry was about 50,000 particles/sec/wire. These chambers, in conjunction with a simple data handling system, provided an immediate and complete description of all the interesting beam parameters (beam emittance, energy spectrum, etc.)^^. MWPCs were later used in several experiments. In 1969 a system of seven small chambers (useful area 18 cm x 18 cm) was developed by the CERN-EPF-Imperial College-Milan collaboration for a diffraction dissociation experiment on the CERN PS. The chambers were used to define momentum, angle and position of the incoming beam of n~. An efficiency in excess of 99% was achieved with a total time resolution of 150 nsec, while the total recovery time (or dead time) was determined by the amplifier and was less than 0.3 //sec per wire. Results like these together with work in progress in other laboratories led Lederman to assert 'that proportional chambers are one of the most exciting new detectors to appear in some time [...] and even if only part of the projections are realized, physics will have a powerful and versatile new 'microscope'^^' 12.4.4.1 The CERN-Heidelberg

spectrometer

Despite the optimistic assertion by Lederman, scientists very soon reaHzed that 'the construction of large (more than 50 cm x 50 cm) MWPCs is no trivial problem!'^^. They could be used in sophisticated experiments, but a number of difficulties - absent in the case of small chambers - were connected with their construction. For instance when high

The multiwire proportional chamber

581

sensitivity amplifiers are employed (say sensitive to signal of 0.3 mV), long wires can act as good antennas! The first large area multiwire proportional chambers were built at CERN by the CERN-Heidelberg collaboration (spokesman Steinberger) for a spectrometer designed principally to detect the charged decay mode of the neutral kaon in the momentum interval 5-12 GeV/c, for a decay path of ~ 25 Ks Hfetimes, at a maximum data taking rate. The apparatus, proposed in 1969, consisted of a decay region followed by a spectrometer, a trigger plane and a muon detector. The installation of the beam and detector was finished in early 1971 and 'was clearly a multiple success' since the data taking 'rates were at least two orders of magnitude greater than previously possible' - the group underlined in a memorandum to the members of the Electronic Experiment Committee (EEC) - 'and we claim some credit for the fact that we recognized the power of the MWPC and demonstrated this power in an experiment'^^. Some more details on this detector can illustrate more clearly the problems encountered with the construction of large chambers. The spectrometer, the most important element of the apparatus, had three large multiwire proportional chamber planes (270 cm x 90 cm) equipped with both vertical and horizontal signal wires - gold plated tungsten wires 20 /im in diameter and spaced 2 mm apart - and a wide gap bending magnet. Between the second and the third wire plane a threshold Cerenkov counter could label electrons, while a muon hodoscope had two counter planes and a 3.2 m concrete absorber to identify muons (Fig. 12.5 shows the apparatus up-graded in 1972 with a fourth chamber, the first one from the left). The spectrometer was designed in such a way as to maximize the data acquisition rate, minimize the amount of matter in the path of the particles, and keep the momentum resolution and geometrical detection efliciency at a predetermined level - the resolution in momentum was ~ d=l%, and ~ ±0.5 mrad in angle. The first attempt to build a large chamber was something of a failure because of the displacements of the wires due to the electrostatic forces (Fig. 12.3). A number of different materials and mechanical arrangements were thus tried to support the long wires. In the end fine nylon wires - 20 )um diameter - were used whose effect on the efficiency of the chamber was limited to a small insensitive area (a hole 0.5 mm wide). Other mechanical problems were related to the tension of the wires which was 50 g for the signal wires, and 110 g for the copper-beryllium wires - 50 /xm in diameter and spaced 1 mm apart constituting the high-voltage planes. The tension had to be uniform and this represented a severe technical problem together with the fragility of the wires. Moreover the reinforced plastic frames were not sufficiently rigid to support the wire tension, so that in each chamber nine of them were attached to a single rigid metal frame in the following order: 1) 2) 3) 4) 5)

a mylar window with gas inlet and outlet; high-voltage wires; vertical signal wires; high-voltage wires; clearing-field wires to clean out ions and electrons; Notes: p. 609

Fig. 12.5 Magnetic spectrometer for detecting two charged decay products of neutral K mesons, side view (upper) and top view (lower). The spectrometer, consisting of a magnet and four MWPCs, each equipped with a horizontal and a vertical signal wire plane, measures the momenta of the two charged particles; the Cerenkov counter identifies electrons from K t + n*e% decay and the muon hodoscopes detect muons from K t + nip% decay (Gjesdal et al. [99]).

$. R

The multiwire proportional chamber

583

Fig. 12.6 Exploded view of a 2-coordinate multiwire chamber showing the number and the complexity of the required parts (SauU [148]).

6) 7) 8) 9)

high-voltage wires; horizontal signal wires; high-voltage wires; a mylar window.

This hst reveals the complexity of these chambers which required an adequate mechanical design and considerable patience and skill in assembly. Figure 12.6 shows an exploded view of a similar chamber. The gas filling chosen was 65% argon and 35% isobutane. The electrical characteristics of the chambers were: 1) 2) 3) 4)

efficiency > 99.5%; time resolution: 30 nsec; essentially no dead time (< 1 jusec per wire); read-out time of the entire event information into a buffer: 200 nsec.

The important innovation was obviously the introduction of MWPCs that allowed a higher rate of data acquisition in comparison with spark chambers (that meant 5000 K decay events per second of 'beam on' time, to be compared to 50 events for spark chambers), the elimination of some counter planes usually necessary in the triggering of spark chambers, and the possibility of a preliminary decision from the trigger counter information before storage (the time required to accept or reject an event was ^ 200 nsec). Besides the delicate and complex mechanical construction, the price to be paid for these

584

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

improvements was sophisticated electronic circuits capable of maintaining the intrinsic time resolution of the chambers. These required a significant developmental effort as I remarked in the previous section^"^. The spectrometer became operational in spring 1971 and was used for more than three years with the proton beam of the CERN PS. Several experiments on CP phenomenology were performed by means of this facihty up-graded with a fourth chamber (see Fig. 12.5), 5 10^ disintegrations were recorded and analysed, and important results were obtained on the K L - K S mass difference (short-lived and long-lived neutral K mesons), on the Ks Ufetime, on the phase 0+_ relative to the decays KL -^ n^n~ and Ks —> 7i"^7c~, and on the charge asymmetry ^L in semileptonic decays^^. Experience drawn from these first large chambers proved to be extremely useful for the construction of the chambers of the Split Field Magnet detector system. 12.4.4.2 The chambers of the Split Field Magnet detector The Split Field Magnet detector was the only major facility built in anticipation of the start up of the Intersecting Storage Rings. Like every spectrometer it consisted of a magnet and a detection system. Its construction was accepted at the beginning of 1969 and the first events were registered in August 1973. Several difficulties had to be worked out before its completion. The efficient use of the limited experimental space at the ISR, the reliability required from an apparatus working in an inaccessible environment, the necessity of adding experiment-dependent devices, such as Cerenkov counters and ionization detectors, and of connecting them to the trigger logic and the interfaces, were major challenges to the SFM working group (see also Russo, this volume. Chapter 4). Between March and November 1968 three alternative proposals were made for an ISR general purpose detector at intersection 4, showing differences both in the structure of the magnetic field, and in the kind of electronic detectors employed. In March 1969, after a year of discussion on the different magnet systems, a simpHfied version of Steinberger's proposal was accepted since it seemed to assure the best analysis of the secondaries both in the forward and in the backward hemisphere. The magnet would have two arms of oppositefield,each about 5 m long, 1 m high, and 2 m wide, with an increase in width to 3 m towards the centre. Later this field configuration turned out to be inappropriate for the study of processes characterized by large transverse momentum. In fact three years later, in 1972, anomalously huge hadron yields at large transverse momentum were discovered at the intersections 1 and 2 of the ISR (experiments 102, 103, and 203)^^. These results inaugurated a new tradition of hard-scattering experiments aimed at the detailed investigation of these phenomena and which demonstrated in the following years the jet structure of large px processes. 'The SFM was practically blind in the most interesting region, around 90°' because of its field configuration. Since its inception its exploitation has required a long and patient effort at both the hardware and software levels to make the SFM a powerful, though not

The multiwire proportional chamber

585

ideal, instrument to satisfy the requirements of the new physics^^. At the same time, from the point of view of the development of electronic detectors, the SFM has played a unique role. Indeed, in its final layout it was equipped with a 70 000-wire detector. This meant that a large number of problems with the mechanics, the gas mixture, and the electronics of the chambers had been solved which had never been encountered before with small devices. In 1969 the use of MWPCs was strongly supported by Steinberger in the committees and in the meetings of the working groups at the time when the largest operational chambers were 18 cm x 18 cm^^. Later, after 1970, the largest detector using MWPCs and from which the SFM working group could obtain suggestions and expertise, was the spectrometer built by the CERN-Heidelberg collaboration, which was equipped with three chambers and a 5000 wire proportional chamber readout system (see section 12.4.4.1). By contrast, the SFM detector system in its first version, almost completed by October 1974, included twenty four chambers in the forward detector, each consisting of two wire planes, and eight chambers in the central detector, of which two had nine, two had ten, and four had three wire planes: in total about 70 000 wires (Fig. 12.7)^^. As for the data readout the chambers were self-triggering and a rate of 50 000 triggers per second could be obtained. Decisions for trigger acceptance were made at two levels. At the first there were fast decision making circuits using pulses coming from blocks of wires. Thereafter experiment dependent additional hardware (fast auxiliary detectors such as scintillation counters and Cerenkov counters) could also be involved in the decision making. If the product of a collision was of interest, a 100 nsec gate was opened and the signal was allowed through

central

forward detector

beam 2

lower pole piece vacuum chamber

INSIDE OF ISR

Fig. 12.7 Arrangement of MWPCs in the gap of the SFM (CERN Annual Report 1977, p.34). Notes: p. 609

586

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

into a memory later read by a computer. This meant that something Uke 100 000 circuits were involved^^. To achieve this formidable task several groups had to work in parallel following a well arranged schedule. One group from the ISR Division (directed by L. Resegotti) was engaged in the construction of the magnet system - consisting of a main magnet and four compensator magnets-. Another one (directed by E. Jones) investigated the possible types of vacuum chambers (in order to obtain a high transparency for secondary particles in the SFM region the ISR vacuum tube had to meet specific requirements). Finally Charpak and Minten were charged by the ISR Committee to study a preliminary plan for the detectors to be put in the gap^^. In the first discussions, back in 1968, several detector arrangements were presented: small gap optical chambers, MWPCs, and streamer chambers. Soon after the decision to build the so-called SpUt Field Magnet was taken the choice was limited to spark chambers plus a vidicon system, or to a system consisting of large MWPCs. The first proposal, put forward by Krienen, had the advantage of a relatively low cost, while the MWPCs, proposed by Charpak and Steinberger, despite the higher cost, worked better in high magnetic fields and had a very short sensitive time. However, since only small-sized units had been used till then, the second proposal required further study in order to determine its relative merits with respect to the more classical types of detectors^^. The developmental effort required was substantial and demanded a considerable deployment of personnel and money. For 1969 funds came directly from the budgets of the Track Chamber Division and the Nuclear Physics Division, subsequently from the ISR Department. For the triennium 1970-1972 the budget required by the SFM group including the computer, was 8.2 million SF and as for the personnel for the year 1970 only, a request for eight posts was made. In total the construction of the spectrometer cost about 23 milHon SF^^ Between February and August 1970 the choice of the detection technique was directed definitively on the MWPCs, thanks to the work of the SFM group. It had built and tested a large prototype chamber (active area: 44 cm x 161 cm, 1400 wires), had explored systematically the proportional chamber properties, had investigated a new gas mixture (argon + isobutane + freon-13 Bl), allowing multiplications of the order of 10^ without entering into Geiger operation, and had developed specific electronic circuitry. By the end of August it was decided to build a 'zero series' consisting of 4 chambers with active dimensions 38 cm x 153 cm, and 5000 wire electronics, that had to be operational during the year 1971; and to develop a research program to investigate new construction methods to reduce dead regions due to chamber frames, and to set up the integration of the wire electronics for the full system. The time schedule foresaw the installation of the final layout of the chambers by the end of 1972^^. In April 1971 the detector layout included a central detector for large-angle particles (initially four chambers were proposed, later eight were installed), and two forward detectors for particles with momentum in the beam direction (24 chambers). The standard size for the MWPCs was 100 cm x 200 cm. Every chamber had to have 1) a ratio of

The multiwire proportional chamber

587

sensitive area/total area close to unity to avoid a dead region, and 2) a long as possible lifetime in a radiative environment. These difficulties were later solved by building a new almost frameless, self supporting chamber, and by the addition of methylal or propylalcohol to the magic gas to delay the deterioration of the chamber^^. In March of the following year Minten reported to the ISR Committee that there were still technical problems with the design of the 'close-packed' chambers of the central detector and that the schedule was somewhat uncertain, but that they could be ready early in 1973, while the 24 chambers for the forward detectors should have been ready for tests by the end of 1972. He was too optimistic: a few months later difficulties with the electronics resulted in a redesign and caused a further delay. Consequently it was necessary to wait until August 1973 for the first 'forward chambers' to be installed in the gap of the magnet which had been carried from the assembly hall to the intersection region 1-4 at the ISR two months before. In the fall of 1973 the first experiments began to run at the SFM, though the equipment for the apparatus was completed only two years later^^. By October 1973 the 'forward chambers' installed were working well, but the two arms of the SFM still lacked six chambers, while the only one, out of the eight foreseen, built and installed in the central detector seemed to be very sensitive to various types of noise in the vicinity^^. One year later, in the fall of 1974, the central detector was equipped with five more chambers, and finally in the spring of 1975 the last 'central chamber' became operational. In the meantime the SFM group had undergone several changes. Early in 1973 Charpak, one of the main supporters of the spectrometer, and his nearest coworkers, left the group and its endless problems to go back to laboratory work on prototypes, still giving, however, advice now and then on how to solve the problems raised by the chambers' installation in the SFM^^ By 1976 a programme of improvements to the SFM started to facilitate the detection of tracks in complex events by means of new chambers with eight wire planes which replaced some with only two planes. Particles in the central region were identified with six Cerenkov counters and some hodoscopes to measure the time-of-flight, whose installation was completed by July 1977^^. Nevertheless the number of physicists working in the experimental areas of the ISR and in particular at the SFM was decreasing sharply, not only because of the difficulties of experimenting with a detector system ill-adapted to the new requirements of HEP research - 'the SFM was practically blind in the most interesting region, around 90°' as I mentioned before - but also because of the appealing opportunities offered by the new machine, the Super Proton Synchrotron (SPS), which went into operation in June 1976. In September 1978 P.G. Innocenti, SFM co-ordinator, wrote to the Director General L. Van Hove stressing that the gravity of the situation should not be underestimated, and calhng for energetic action. 'If one lets the number of users decrease further, a threshold of no return may be crossed. [.,.] and the further reduction of ISR physics represented by an eventual SFM stop, may open the way to a sneaking question, whether ISR operation is justified at all for so few users'. An entire chapter in this volume (by Arturo Russo) is devoted to the history of the CERN ISR, and I refer to it for a detailed analysis. Here it is enough to recall that the ISR survived and the SFM with them. Notes: pp. 609 ff.

588

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

Indeed in the last period of activity (1978-1983) there was even an increase in the number of users who were able to maintain a very active and interesting programme^^. 12.4.5 THE MWPC AS AN INVESTIGATION TOOL: THE CENTRE-OF-GRAVITY METHOD As I mentioned in Sect. 12.4, the motion of the ions liberated in the avalanches created in an MWPC controls all the important information that can be extracted from a chamber. In the ten years that followed the publication of the first article on the MWPC a lot of work has been done in this domain, and several contributions are due to Charpak and his team both in the determination of the limiting factors in the accuracy of position measurements with MWPCs, and in the study of the mechanism of pulse formation in the chambers. Rather early - in 1973 - it was realized that the induced charge distribution reflects the original position of the localized ionization between wires^^ Then in 1977-79 Charpak and his group improved the so-called method of localization by centre of gravity of the induced pulses (or method of centroids). In the most interesting experiments made by the group a chamber of the type illustrated in Figs. 12.8(a) and 12.8(b) was used. The gold-

a)

V* V—K V-^^ V—'^ ^—'

b) b

!i Fig. 12.8a,b Principle of operation of an MWPC with cathode-induced pulse read-out. The centre-of-gravity of the measured induced pulses represents the two-dimensional coordinates of the initial avalanche (Charpak and SauU [54]).

The multiwire drift chamber or drift chamber

589

plated tungsten anode wires, as usual, were 2 mm apart and had a diameter of 10 /xm, while the cathode planes were made of 50 /zm diameter wires, 500 /zm apart, connected in a group of six wires (a strip). In one cathode plane the wires were parallel to the anode wires; in the other they were orthogonal. A coUimated soft x-ray source was employed as a radiation source at different positions in the chamber filled with xenon + isobutane + methylal mixture. By recording the charge profile of the pulses induced in cathode strips by an avalanche occurring near an anode wire, and computing the centre of the distribution, significant progress was made in the position resolution. A mean position accuracy of (Ty « 35 /xm was obtained along the anode wires' direction (y in Fig. 12.8a) while in the orthogonal direction (x in Fig. 12.8a) CTX « 150 imv. The major difficulty with this method was its high cost due to the mechanical construction and to the use of analog to digital converters (ADCs) where the pulses from the amplifiers were fed before their being sent to a computer. Only the dramatic decrease in the cost of electronic components performing fast complex computations has allowed its exploitation in the eighties^^. Besides biomedical applications this localization method has been used in conjunction with drift time measurement in the time projection chamber (TPC), the most sophisticated of the current ionization detectors^^.

12.5 The multiwire drift chamber or drift chamber In parallel to the proportional chambers another detector related to them was developed: the multiwire drift chamber or drift chamber. The essential idea here is that the time lag between the production of electrons in a medium by ionizing collisions and the appearance of the pulse at a wire of the chamber can be used to measure the position of the initial electrons, and therefore to detect the ionizing track (see Fig. 12.9). In 1969 Lederman, impressed by the potential resolving power of this new detector, gave, as a reasonable prediction, 60 /xm for its accuracy, and after a few years of exploitation of this technique it was possible to assert that drift chambers had reached a level where no other localization detector or read-out method could compete in price and performance. The increased accuracy and the lower costs enabled one to avoid using MWPCs in most cases. At CERN several prototypes were developed, while the first operational drift chamber is due to A. Walenta (I. Physikalisches Institut of the University of Heidelberg)^"^. Later large planar drift chambers were built to equip magnetic spectrometers or huge detectors, as in the case of the CERN experiment WAl on high energy neutrino interactions. Moreover by drifting the electrons along well defined Unes of force it was possible to match many geometrical situations, this being possibly the most interesting application of the drift chamber principle of operation. In fact during the seventies in Europe and in the USA, investigations were carried out in this field which showed the interesting potentialities offered by large drift volumes, particularly the possibility of measuring both the threedimensional position of electrons liberated in the gaseous volume and the energy loss along a track'^^. These studies resulted in the construction of several central tracking Notes: p. 610

590

The Development of Electronic Position Detectors at CERN

(1964-late

1970s)

Particle trajectory

^

^

^

^ A J Anode

^ ^ j •^-f ^ /

/

^

^

^

-'Electrons ^ ^ / drifting XX Cathode to anode O ^ -35kV

^ ^ ^ J^/^ ^ ^ ^. •1 7kV

-05

-1

-2 /

-2-5

-3I
Field-shaping wires

Fig. 12.9 A drift chamber with a shaped or 'tailored' field where electrons drift to the anode in a region of constant field gradient so that the drift distance is directly proportional to the drift time (Charpak & South worth [52]).

detectors for storage ring experiments coupled with magnetic fields with cylindrical symmetry. Figure 12.10 shows four different types of cylindrical wire chambers with different geometries^^: a cylindrical drift chamber with open cell geometry, like the TASSO chamber for PETRA at the DESY Laboratory (Fig. 12.10b); a jet or pictorial drift chamber, like JADE, again for PETRA, the Axial Field Spectrometer (AFS) for the CERN ISR and UAl for the CERN pp (Fig. 12.10c)^^ and a time projection chamber, like the detector for the PEP4 experiment at the Stanford Linear Accelerator Center (SLAC), and the central detectors of DELPHI and ALEPH for the CERN Large Electron-Positron colHder (LEP) (Fig. 12.10d)^^. All of these have been used in the most modern collider machines since the late seventies and beyond, and they have been successfully coupled to new and sophisticated instruments like the electromagnetic or hadron calorimeters. These various types of cylindrical drift chambers have become basic instruments of the so-called new physics tradition. It is not possible here to cover the multitude of different planar or volumetric chambers that arose in the seventies, however, even if I limited myself to the ones built at CERN. Hence only a few examples will be treated to illustrate the principles of operation of this kind of chamber, the technical problems encountered and the most important contributions to this technique made by CERN groups, together with some developments in the technique of drift chambers that in the late seventies and early eighties have been applied in volumetric chambers to reach a three-dimensional read-out of particle tracks. The most typical technical problems raised by this kind of detector were connected: 1) with the mechanics of the chambers as for the MWPCs, though to a lesser extent;

The multiwire drift chamber or drift chamber

591

Beam pipe

Fig. 12.10 Four different types of cylindrical wire chambers: (a) proportional chamber; (b) cylindrical drift chamber; (c) jet drift chamber; (d) time projection chamber (Kleinknecht [113]).

2) with the necessity of having a constant and well known drift velocity and a reduced electron diffusion, difficulties partially solved by the choice of the gas; 3) with the influence of external magnetic fields. I shall describe in the following pages if and how these difficulties have been solved, underlining specific contributions by CERN scientists and particularly by Charpak's group. 12.5.1 THE FIRST CHAMBERS Although the concept had been advanced by Charpak and co-workers in 1968, together with the results from the first MWPC, and the first small chambers had been constructed already in 1968-69 at CERN by the same group, at Heidelberg by Walenta and at Saclay Notes: p. 610

592

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

by J. Saudinos in 1970, general acceptance among high energy physicists waited on the reports of pioneering groups with operating experienced^. In May 1973 at the 5th International Conference on Instrumentation for HEP held in Frascati, interesting results were discussed by groups from CERN, Heidelberg, Saclay and the large size chambers of Harvard were presented (up to 4 m x 4 m). From then on the prospects for this new device were excellent^^. Here I will describe schematically the early prototypes and the first operational chambers used in experiments. The first studies exploiting the drift time for a coordinate measurement were presented by Charpak together with the multiwire proportional chamber at the congress held in the Chateau of Versailles in September 1968. In the basic chamber a 3 cm long drift space was added to a proportional counter with a wire mesh with 90% transparency separating the two regions. The 200 V tension applied to the drift region allowed the ionization electrons to drift onto the sense (or anode) wire where they could be detected. A system of three chambers was used. The time lag was measured and then converted by means of a time-toamplitude converter, enabling one to detect the position of a particles with a space resolution of the order of 100 /im^^ However, if a large detection surface was required - as in the case of most high energy physics experiments - this structure implied large working voltages and long drift times^^. Hence other structures were investigated. Some months later, for the first time, the word 'drift chamber' appeared in a contribution by the group of Charpak to an international seminar on film-less chambers held at Dubna in April 1969. This time a 3 cm long drift space was added to a MWPC (12 cm x 12 cm) and separated from it by the usual grid with 90% transparency. Electrons drifted under the influence of the electric field, were detected by the multiwire chamber, and the time taken to cross the drift space was used to give a measurement of the position of the incoming beam - auxiliary scintillation counters defining the beam and providing the zero of time TQ-. One of the major problems emerged immediately: the main contribution to the width of the resolution, hence a limitation in accuracy, was due to the diffusion of the electrons in their flight^^. Obviously a linear space-time relationship would be preferable, which meant a uniform electric field. The use of an MWPC coupled with a drift space thus raised problems due to a strong non-linearity in the low field region between the anode wires (region C in Fig. 12.2b). By 1970 the first operational chamber made its appearance. Built by Walenta at Heidelberg this chamber had a different structure. To avoid a zero-field region the anode wires (or counting wires) were alternated with thick field-shaping potential wires electrically connected to the cathode plane which reinforced the electric field in the critical region (see Fig. 12.11). Moreover the so-called left-right ambiguity did not show thanks to the splitting of the counting wire in two wires 1 mm apart^"^. In August 1971 a CERN-Heidelberg collaboration (I. Physikalisches Institut of the University of Heidelberg) started data-taking for an experiment on K-meson decays using for the first time large drift chambers (active area > Im^). The magnetic spectrometer was equipped with seven drift chambers of the Walenta type with a location accuracy a = 0.35 mm. Their use was particularly suitable since the particle flux and the trigger rate were high: in a burst of 0.3 sec the chambers were irradiated with 2 • 10^ particles (i.e. a

593

The multiwire drift chamber or drift chamber ]

I 1

A,.2.

\p •

,A,-i .< "*

1 1 1

1/ Vl-I

V

cathode

.'^i>.|A*^ --V,1 /

-i

*|*

.^ •>•;

••*

A*2.Ao yi*2

"^

cof/)oc/e

Fig. 12.11 Principle of the multiwire drift chamber. Ai: anode wires, T: particle track, Vi: drift spaces, x: measured coordinate. The drift path is indicated by the dashed arrows (Walenta [166]).

rate of 6 • 10^ particles/sec) and the trigger rate was 100 per burst. Preliminary results were presented at the 17th International Conference on High Energy Physics held at Chicago in 1972, while a more complete report was pubUshed in 1975^^. Building chambers with wires longer than 1 m the CERN-Heidelberg group realized that electrostatic problems were less serious than in the case of an MWPC: counting wire pairs were in stable equilibrium, only the individual wires of each pair repelling each other (see Fig. 12.11). For that reason further potential wires (P') were inserted between the wires Ai and Ai+i of each pair to compensate forces electrostatically. In this multiwire structure, however, a long time is necessary to collect at the anode all the electrons produced by an ionizing particle and consequently multitrack capability per wire is not possible. Moreover to maintain an almost radially symmetric drift field the ratio between the gap length and the wire spacing had to be close to unity, and that meant, for typical wire spacings (5-10 cm), thick chambers and consequently a reduced packaging density. In the same years Charpak's group investigated other geometries to solve this problem. Figure 12.12 shows the structure of a cell of a drift chamber built by the CERN group where the two sets of parallel cathode wires are connected to uniformly decreasing potentials - starting from ground in front of the anode - and the two field wires reinforce the field in the transition region to the adjacent cells. In 1972-74 Charpak and co-workers constructed several chambers with this structure and with sizes ranging from a few cm^ to 50 cm X 50 cm, the most interesting feature being the adjustable electric field suitable for the detection of high-energy charged particles in strong magnetic fields^^. Subsequently other planar chambers have been developed at CERN and in other laboratories having additional field-shaping wires or flat electrodes replacing them, but in general their structures were similar or intermediate between the ones described^^. 12.5.2 MECHANICAL CONSTRUCTION AND ASSOCIATED ELECTRONICS As for the mechanics connected with the construction of drift chambers, in general the same techniques developed for the MWPCs were employed, except for the high accuracy drift chambers where more care had to be taken in positioning the wires, and on the Notes: p. 611

594

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

Screening

Cathode drift wires

electrodes

Field wire - HV I

7

Anodic

wire

couple

•»• HV 2

Fig. 12.12 Cross section of a drift-chamber module, in the plane perpendicular to the wires. A set of parallel cathode wires are connected to a regularly decreasing potential, from zero (in front of the anode) to the value -HVl at each end of the drift cell. This produces a uniform-field region. The sharpness of the transition from one cell to the next is reinforced by thefieldwire, at potential -HVl. The single anode wire is replaced by a couple of 20 iim wires, 100 ^m apart, to resolve the right-left ambiguity. The gap is 2 x 3 mm^ and the cell width 50 mm. To avoid interactions between adjacent modules, a thin aluminium foil has been added on each side of the cathode planes, at 3 mm, and is maintained at ground potential. The over-all width of each module is 12 mm (Breskin et al. [24]).

mechanical tolerances. The usual problems of wire instabilities are shown by the cathode wire planes in structures, Uke the one depicted in Fig. 12.12. To avoid them gap-restoring strips (see Sect. 12.4.1) are inserted between the cathodes and the screening electrodes, however with less problems than in the case of an MWPC since the strips are outside the drift volume and therefore do not affect the performance of the chamber. The read-out electronics, on the contrary, shows differences in comparison with the one used in MWPCs. In fact drift chambers need very fast electronics to give their best performance. The signal has to be amplified and shaped at frequencies higher than in an MWPC, and to measure the time of drift one has to use time-to-digital converters with a channel resolution of about 1 nsec for high accuracy. For instance, in the case of a typical drift velocity, i.e. 4 cm//isec, over a length of 1 cm, the electron diffusion width is about 100 /xm which corresponds to a time spread of 2.5 nsec. To take advantage of this intrinsic accuracy a counting frequency of about 400 MHz is necessary. On the other hand a drift chamber has fewer wires to be handled, and that was and is its strength in comparison with the MWPC. Over the years several specific circuits have been developed for drift chambers by CERN scientists, thanks also to recent progress in electronics that has substantially decreased costs and technical difficulties related to the construction of the early chambers^^.

12.5.3 HIGH ACCURACY DRIFT CHAMBERS The accuracy that can be obtained in a drift chamber depends mainly on the knowledge of the space-time relationship and of the diffusion properties of electrons in gases, and therefore on the choice of the gaseous mixture.

The multiwire drift chamber or drift chamber

595

In general the drift velocity of electrons is a function of the electric field, and variations in its value can result in a complicated space-time relationship. However in some gaseous mixtures the velocity approaches a constant value for moderately large fields. For example in a 70%-30% mixture of argon-isobutane the velocity is roughly constant at fields exceeding 1 kV/cm and if the structure of a chamber is designed to avoid regions where the field is lower than this value, a good accuracy can be achieved. Small additions of other substances can improve the performance of the detector. In constructing drift chambers the choice of the drift velocity is also influenced by several other factors, namely the length of the drift path, the intensity of particles crossing the chamber and the speed of the recording electronics^^. But the choice of the mixture has another effect on the accuracy of a chamber. In fact, during the drift in the electric field, electrons diffuse following a Gaussian distribution, and the standard deviation of space diffusion depends on the electric field and on the gas^^. A good choice would be carbon dioxide thanks to its very low diffusion coefficient. However its use is not possible because of the poor quenching properties of this gas in proportional counters, and usually argon-isobutane mixtures are preferred. A lot of research work has been done in this field resulting in several sets of measurements for different drift chamber structures filled with different gas mixtures. This has resulted in a good knowledge both of the space-time relationship and the diffusion of electrons in flight^^. Major contributions to the optimization of the working parameters in the drift chambers are due to the group of Charpak and to the group at Heidelberg (mainly J. Heintze and A. Walenta) that in the late 1970s developed a jet chamber system (JADE) for PETRA experiments^^. In 1972-74 the CERN group made a systematic study of the drift properties in gases and developed an adjustable electric field drift chamber (AFDC), whose principle of construction is shown in Fig. 12.12. To understand better the properties of the chamber in view of possible large scale applications Charpak and coworkers studied the modifications of the drift velocity and direction induced by variations of the electric field, of temperature and of gas composition, and concluded that 1) for a mixture corresponding to about 3 1 % isobutane the drift velocity is constant for electric fields over several hundred volts around 1 KV/cm - the finally adopted gas mixture had 67.2% argon, 30.3% isobutane and 2.5% methylal - 2) to maintain an accuracy of 100 /xm it is possible to tolerate over-all temperature variations of about 14° C and 3) the gas mixture has to be stabilized to ±1.5% in the isobutane content. If the AFDC was operated under conditions where the electric field saturated the drift velocity, an accuracy of about 60 jum was reached over drift regions of 25 mm, a very linear space-time correlation was obtained for perpendicular tracks, and inclined tracks showed only simple geometrical distortion of linearity^^. But the most interesting feature of this chamber was that the same results could be obtained in a wide range of external magnetic fields when properly tilting the electric field equipotentials. Very frequently detection chambers have to be placed in magnetic fields, and it is obvious that in a drift chamber any component of a magnetic field perpendicular to the drift line can influence the drift of the electrons. The effect is even bigger when the field is parallel to the wires. In Notes: p. 611

596

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

the case of a uniform magnetic field the CERN group proposed a radical solution to this problem. By using separate voltage distributions on the two multiwire cathodes, the electric field direction can be tilted in order to provide a force to compensate for the Lorentz displacement. The tilting angle a necessary to obUge the electrons to drift parallel to the cathode planes, can easily be obtained. For instance in a drift chamber module like the one shown in Figure 12.12, if the voltages applied to the cathode wires are chosen so as to tilt the equipotentials by about 50°, it is possible to drift electrons properly towards the sense wire in a magnetic field of 18 kG perpendicular to the drawing. With this method a 100% efficiency was achieved over the whole drift length^"^. At the Wire Chamber Conference held in Vienna in February 1978 several contributions dealt with this type of high accuracy detector. The Omicron spectrometer at the CERN 600 MeV Syncrocyclotron (SC) was equipped with a set of AFDCs giving a good space resolution, 150±30//m, in a 1 T magnetic field. At the CERN ISR (intersection 1) a system of cylindrical drift chambers with field-shaped drift cells for operation in a 1.5 T magnetic field were developed to study high mass electron pairs and large transverse momentum hadronic phenomena (exp. 108), and satisfactory results were reported by the CERN-Columbia-Oxford-Rockefeller collaboration^^. Another major step in the improvement of the performance of a planar drift chamber was the possibility of determining the second coordinate simultaneously by measuring the position of the avalanche along the sense wire. Even a rough location was desirable because it could eliminate ambiguities created by multiple tracks. Several approaches were proposed, most of them by the Charpak group, and some were applied in the late seventies in the volumetric drift chambers of the central detectors of the axial field spectrometer (AFS) at the ISR and of the UAl at the pp, and in the time projection chambers. Again the prolific group of Charpak showed its ingenuity in obtaining as much information as possible from avalanches in gaseous media^^. A first approach, the current division method, was proposed by Charpak as early as 1963 and discussed in the 1964 meeting on film-less spark chamber techniques and associated computer use (see Sect. 12.3 in this chapter). Originally this method was based on the relative magnitudes of the two discharge currents that diverge from the spark towards the two earthed ends of a wire, and that are divided according to the path lengths. Ten years later G. Charpak, F. Sauli and W. Duinker applied this method to the discharge currents that flow from the avalanche along a sense wire in a proportional chamber, and discussed the results in the same article in which they proposed the AFDC. This preliminary research, together with the results of another CERN group, showed that accuracies of the order of 1 cm could be obtained in chambers of 1 m length^'^. Later improvements of this technique were applied to the measurement of the third coordinate in central track detectors like JADE, AFS, and UAl (see Fig. 12.4(b) and Table 12.3)^^ In 1973 difficulties encountered in the first applications of this technique stimulated Charpak and his CERN group to investigate another approach based on delay lines parallel to the sense wire and that could be either placed in the cathode or used between two sense wires. Accuracies between 2 and 3 mm were obtained along the wire in a drift

597

The multiwire drift chamber or drift chamber Table 12.3 Central track detectors (from Kleinknecht [113]).

Max. track length

Name

Radial L (cm)

Axial z (cm)

TASSO CELLO CLEO Mark II JADE

85 53 75 104 57

330 220 190

AFS

Flux density B(T)

No. of measured points

Gas pres- No. of sure signal (bar) wires

Spatial resolution (7(r,^)

(^z

(/zm)

(mm) 3^ 0.44 5(0.25) 4 16

15 12 17 16 48

1 1 1 1 4

2340 5432

234

0.5 1.3 0.5(1.5) 0.4 0.45

1536

200 170 250 200 180

60

128

0.5

42

1

3400

200

UAI

112

250

0.7

-100

1

6100

TPC

75

100

1.5

186

10

drift: ch. div. <200

TRIUMF

54

69

0.9

12

1

2232 +13824 144 (600) + 630

Method of z measure ment

calc.

meas. 1.7

4° stereo cathodes

charge division 17 charge division 250 )um charge 8-25 mm division 0.2 drift (0.6)

Momentum resolution olP" [(GeV/c)-^%]

5 1.9 2.2

1.0

drift

chamber of 150 cm length^^. The construction of cyUndrical chambers was a rather formidable problem in the mid-seventies and this method has been widely used to measure the coordinate parallel to the generatrix in the cyUndrical geometry of a volumetric chamber^^^. One of the first applications of this technique has been the above mentioned system of cylindrical drift chambers with field-shaped drift cells at intersection 1 of the CERN ISR (exp. 108) constructed by the CERN-Columbia-Oxford-Rockefeller collaboration^^^ A third method developed by the same group around this time was based on the measurement of the centre of gravity of the pulses induced on the cathode strips (see Fig. 12.8a and Sect. 12.4.5). This one has also found an important application in cylindrical wire chambers and in particular in the TPC principle of operation. All this research work on high accuracy chambers, either multiwire proportional or drift, has been stimulated by the fact that in the 1970s new accelerators made higher and higher energies available, while the magnetic bending powers that could be used in the analyzing spectrometers were and are limited. Hence an increase in the spatial resolution of the detectors employed began to be a must. Better accuracies being not only a question of improving the read-out electronics and the general mechanical tolerances, new research was carried out on the many processes involved in the generation of the physical position message in a gas detector. As we have seen new methods of localization were then proposed and tested on planar chambers, which later proved to be extremely useful in Notes: pp. 611 ff.

598

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

building volumetric chambers^^^. Consequently detectors with cylindrical geometry particularly suited to the colliding beam machines, and to the new trends in experimental high-energy physics requiring 47rdetectors, could be constructed only at the end of the seventies because at the beginning of the decade the techniques required to reconstruct three-dimensional tracks were not available^^^. What is more, once the scientists had investigated the new methods, they had to build small cylindrical prototypes to study their properties, and then to construct the detector itself. The whole process could mean years of work^^. If we look at the ISR physics in the seventies it emerges that, after an encouraging start (1971-74), a rather difficult period ensued (1974—77). Instrumentation at the intersections turned out to be quite inadequate to meet the new requirements of HEP, and ISR physicists realized that they should have been far more ambitious with detectors^^^. This survey on the developments in high accuracy read-out for drift chambers suggests that this insufficient experimental preparation in the field of 47i detector systems was due, at least in part, to the lack of techniques of basic importance in the construction of such detectors, techniques that, at the level of laboratory prototypes, were developed only by the midseventies. Consequently, concerning the CERN ISR, the answer, in terms of huge multipurpose detector systems, to the questions raised in 1972 by the discovery of an anomalously high production of hadrons at large PT, could only come in 1979, when a superb new detector for high-pj jet physics - the Axial Field Spectrometer (AFS) (experiment 807) - was installed at intersection 8^^^. 12.5.4 THE TIME PROJECTION CHAMBER From the early seventies large detectors using electronic circuits have undergone major changes, and have become more and more complex. Basically they can be classified into three main groups: a) Magnetic spectrometers for fixed target experiments formed by magnets, MWPCs, drift chambers, Cerenkov counters, scintillator counters, calorimeters etc. A first example is the spectrometer of the CERN-Heidelberg collaboration (see section 12.4.4.1). A later one is the experimental facility for experiment NA2 (European Muon Collaboration or EMC), showing a much more sophisticated structure^^^. b) Large mass detectors for high-statistics neutrino physics like the one for experiment WAl of the CERN-Dortmund-Heidelberg-Saclay collaboration that employed large area drift chambers coupled with calorimeters^^^. c) An detectors for colUding beam machines, inaugurated by the Mark I detector that in 1974 discovered the J/psi particle at the SPEAR ring (Stanford). A later example is DELPHI, a huge multipurpose experimental facility at the CERN LEP^^^. A main component of several An detectors is the time projection chamber developed at Berkeley by D.R. Nygren and co-workers in the seventies. The proposal to investigate the feasibiUty of this novel concept in particle detection goes back to 1974, a small prototype

The multiwire drift chamber or drift chamber

599

chamber went into operation only in 1978, while the new facility for PEP based on this detector became operational by the mid-eighties^^^. Hence the wide exploitation of this technique belongs to the 1980s and the 1990s rather than to the period we are analyzing. However the TPC - also called the 'electronic bubble chamber' - is the most sophisticated of the current ionization detectors making use of ideas from both the MWPC and the drift chamber. I shall describe briefly its basic structure and how the principles of operation of proportional chambers are applied in this detector. The structure of the detector, positioned so that its centre is at the intersection point, is shown in Fig. 12.13. The sensitive volume of the chamber, filled with an argon-methane mixture at a gas pressure of about 10 bar, is kept completely free from anode or potential wires^^^ Particles emanating from the centre produce electrons which drift, under the influence of both the electric and the magnetic field, towards the endcaps where they are detected by the anode wires as in an MWPC. The magnetic field confines the electrons to helical trajectories about the drift direction, thus solving the otherwise serious problem caused by diffusion along the relatively long distance - both the diameter and the length can be as large as 2 m. One coordinate of the space point projected onto the endcap plane is given by the firing anode wire, while the second is obtained from the signals induced on the row of cathode pads along the anode wire. Using the centre-of-gravity method this gives the position of the avalanche along the firing wire. The third coordinate (z) is obtained by measuring the drift time along the cylinder axis. This technique gives many Endcap Wires

Endcap Wires Negative High Voltage Electrode

-Beann Pipe

-192 dE/dx Wires per Sector 12 Spacial Wires per Sector

Fig. 12.13 The TPC structure (Nygren [132]). Notes: p. 612

600

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

space points for each track and thus allows a full reconstruction of the particle trajectory with a precision of GJ. « 200 jum and a spatial resolution of 180 /xm in the (r,0)-plane. It is worth remarking that, essential to the formulation of the time projection chamber concept, has been the research carried out in 1973 by Charpak and Sauli. Particularly important was their discovery that the positive signals induced on all electrodes near a proportional avalanche preserve most of the information of the track, and their centre-ofgravity method developed on this basis^^^. Moreover since the charge collected at the endcaps is proportional to the energy loss of the particle, the signal amplitudes also give information on dE/dx of the particle. This information, coupled with the momentum of the particle, allows the identification of the particle itself. Similar methods have been developed for other cylindrical drift chambers Uke ISIS for the European Hybrid Spectrometer at the CERN SPS. In his first proposals Nygren foresaw 14000 channels to store the ampUtude and timing information picked up by the anode wires and the pads, and to each of them a 'charge coupled device' (CCD) - a new electronic device - was connected. The CCD is an analog shift register capable of storing associated time and pulse-height information. Pattern recognition and track finding are accordingly considerably simplified in comparison with cylindrical chambers with uncorrelated coordinate information. This is the main innovation of this detector, together with the choice of an electric field parallel to the magnetic one. At the CERN electron-positron colliding storage ring LEP, TPCs have been built as central track detectors for the experiments DELPHI and ALEPH. They incorporate improvements to this technique thanks to further investigations performed on test detectors^ ^^

12.6 The multistep avalanche chamber (MSC) The MSC constitutes an improvement of the parallel plate avalanche chamber, and was originally developed by the CERN group in 1978 to allow a gated operation of proportional chambers, and to overcome the limitation, due to space charge, in the detection efficiency of an MWPC in high particlefluxes^^'*. In fact experiments have been limited by the properties of this detector in terms of accuracy and rate capability**^. An example is given by the discovery of the upsilon particle, when a primary beam less intense than the available one had to be used in order to match the maximum tolerable rate shown by the MWPCs employed* *^ By separating the overall gain into two amplification elements, each below the critical value for secondary effects to appear, Charpak and Sauli obtained multiplication factors above 10^ with high resolution, thus implying for the multistep avalanche chamber (MSC) the possibility of detecting single electrons and of good performance with particle fluxes orders of magnitude more intense than in usual wire chambers. The idea is to keep the gas amplification low in the first volume of the chamber, and to finally admit, for high-gain

The multistep avalanche chamber (MSC)

601

amplification, only the small fraction of events that are interesting for the specific experiment and which are selected by an external trigger. The principle of operation is illustrated in Fig. 12.14(a). Electrons produced in the upper part of the chamber are multiplied by a factor Mi in the preamplifying gap Ai, then drift under the influence of an electric field to the grid G which, pulsed by the trigger, acts as a gate controlling their transfer to the ampHfying element A2 of gain M2. Typically a total gain of Mi x M2 « 10^-10^ can be obtained. The first results were proposed in June 1978 by Charpak and SauH, thanks also to the pioneering work of S. Majewski in Warsaw^^'^. In the years 1978-79 many different construction schemes (gated or not) have been implemented by the CERN group as shown in Figs. 12.14(b,c,d). Electrons multiplied in the first gap can be transferred to an MWPC (Fig. 12.14b), to a second parallel plate amplifying gap (Fig. 12.14c), to an MWPC through an electronic gate which admits only selected tracks (Fig. 12.14d), to a spark chamber and even to a streamer chamber^^^. Rather early, by mid-1978, Charpak and SauU realized - thanks also to the investigations made of the photo-ionization process in gases by Seguinot and Ypsilantis - that by simply adding a proper window to this chamber, transparent to the external beams of vacuum ultraviolet (VUV) photons capable of ionizing a photoionizable vapour filling the chamber, they had available a good imaging VUV detector that could be used to identify particles by Cerenkov Hght imaging^ ^^. The chamber operating with a photosensitive gas Uke triethylamine (TEA) or tetrakis(dimethylamino)ethylene (TMAE) - which allow the production of photoelectrons in the upper region - coupled to a radiator (solid, liquid or gaseous) and equipped with suitable optics, constitutes a ring imaging Cerenkov detector or RICH, a counter that allows the identification of particles via the Cerenkov effect^^^. To understand better the specificity of RICH counters let me briefly summarize some basic characteristics of Cerenkov counters. Charged particles traversing a transparent medium with index of refraction n and with a velocity v > c/n radiate Cerenkov effect photons at an angle 9 given by: 0 = cos-i(nj8)-\j8>n-i where j8 = v/c. From the 1950s this dependence of the emission angle of Cerenkov radiation on particle velocity has been exploited by particle physicists in the form of Cerenkov counters. This family of detectors provides the most accurate measurements of particle velocities, information that, coupled with measurements of the momenta, allows particle identification. Different devices belong to this family: the threshold Cerenkov counter, detecting particles whose velocity exceed a certain value, the differential Cerenkov counter, sensitive to the radiation emitted between 0 and {0 + A0), the Differential Isochronous Self CoUimating (DISC) counter, that constitutes an improvement of the differential counter of which it corrects the optical and chromatic aberrations, and finally the Ring Imaging Cerenkov (RICH) counter, conceived for measuring, with large acceptance, the Cerenkov angle of each photon detected. Both DISC and RICH have been developed Notes: p. 612

Y m

5.

P

Fig. 12.14 (a) Principle of the gated multistep detector: electrons liberated by an ionizing event in A1 are amplified by a factor MI and transferred to A2 (gain Mz) under the control of the gate G (Charpak & Sauli [56]). Several kinds of MSCs have been developed by Charpak and his team: (b) a PreAmplification and Transfer (PAT) element followed by a conventional MWPC. A conversion and drift (C&D) space could be added for X-ray detection. This structure has been used by A. Breskin, G. Charpak, S. Majewski, G. Melchart, G. Petersen and F. Sauli, mainly to study the preamplification factors and the energy and position resolutions both for X-rays and charged particles. (c) Two parallel-plate elements, with a transfer of charge from PA1 to PA2; good energy and time resolutions have been obtained using this configuration. (d) A gated MSC where a pair of closely spaced electrodes (G in the figure) control the transmission of electrons from the PAT element to the MWPC (Breskin et al. [25]).

2

n 2 I

F 2

$

L

The multistep avalanche chamber (MSC)

603

by CERN scientists. The first was devised by R. Meunier in 1962, and the second was proposed in 1977 by T. Ypsilantis and J. Seguinot^^^ While the differential Cerenkov counters can only be used for particles parallel to the optical axis of the detector, a velocity measurement for diverging particles from an interaction region requires a different approach. Seguinot and Ypsilantis in 1977 proposed a new idea. They showed that the admixture of a photosensitive gas molecule (benzene) into a gas-filled MWPC allowed it to be used as an efficient single photon detector when one of its cathode surfaces was replaced by a wire mesh with a UV transparent window. The positional sensitivity of this device could permit single photoelectrons to be imaged. Figure 12.15 shows the proposed principle for a RICH detector. It consists of a spherical mirror of radius R whose centre is the source of secondary particles, and a spherical detector surface at radius (1/2)R with the Cerenkov radiating medium between (1/2)R and R. The ring image has a radius r = f0 at the detector surface, f = (1/2)R being the focal length. The critical point of such a RICH counter is the development of photoionization detectors. The first images were obtained at CERN by G. Charpak, S. Majewski, G. Melchart, F. Sauli and T. Ypsilantis using a multiple avalanche chamber (MSC) with triethylamine (TEA) as photosensitive gas^^^. After 1980 the technique was extensively developed. Applications of the multistep to the Cerenkov ring imaging technique were

Particle 1

Target

Particle 2 Detector radius RI2 Mirror radius R

Fig. 12.15 Schematic representation of a ring imaging Cerenkov counter with large phase acceptance (Seguinot & Ypsilantis [153]). Notes: p. 612

604

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

made in the eighties. In 1981-83 the group of Charpak, as a participant in a collaboration CERN-Saclay-Stony Brook, built a large counter based on the MSC, TEA as filling gas and CaFi for the windows. The detector, the first one of this kind effectively employed in an experiment, has allowed hadron identification at the experiment E605 at Fermilab^^^. Subsequently several very large detectors based on a long drift time projection chamber coupled to an MWPC single electron detector, with tetrakis(dimethylamino)ethylene (TMAE) as photoionizing gas and quartz windows, have been developed at CERN (for DELPHI) and at Stanford (for the SLAC Linear Collider Detector or SLD) with up to 30 m^ of detector surface^^"*. Applications of this detector have been foreseen for the next generation of colliding beam machines: LHC at CERN and the now cancelled SSC in the USA. 12.7 Concluding remark In this chapter on electronic particle detectors at CERN I have limited my analysis to the gaseous ionization detectors and to their development, giving only a little information about their use in huge detector facilities. I have omitted the treatment of streamer chambers, scintillation counters, calorimeters, transition radiation detectors, etc. My choice has been motivated by the fact that in the late sixties and through the seventies the most innovative contribution due to CERN scientists has been the wire chamber and its numerous progeny. This is definitely the factor that has most revolutionized the experimental approach to high energies in the period 1965-1980. Consequently my aim has not been to review thoroughly the whole field of electronic detectors, but to suggest a guiding thread linking the first sonic spark chamber of Maglic at the CERN missing-mass spectrometer with the latest electronic chambers like the TPC for DELPHI at the CERN LEP. The main aspects of this technique here outlined suggest those factors which have been prominent in the development of gaseous ionization detectors and in their success in the high-energy physicists community, namely: their being self-triggering and the use of the computer on-line, their short recovery time and the trend towards experiments characterized by high accuracy measurements on rare events where the use of high rate detectors was a must, the advent of integrated circuits and the massive reduction in cost and bulk of electronic circuitry during the seventies, the need for large sensitive volumes in neutrino physics and the possibility of building huge detector systems equipped with tens and even hundreds of thousands of sensitive wires (Gargamelle, the heaviest bubble chamber, had a volume of few m^ i.e. 100 times smaller than WAl), and finally the use of large chambers in experimental facilities by physicists that 'recognized the power of the MWPC and demonstrated this power in an experiment' since only the use in an experiment can fully illustrate the potentiaHties of a detector prototype^^^. Finally, besides long wires, small circuits and powerful computers, let me add a few words about the men, since most of the progress achieved in this field was due to the competence, the talent and the determination of Charpak and his coworkers, who, over the years, have put a wide range

Concluding remark

605

of prototypes at the experimental physicists' disposal. From his early studies in the mid1950s on the sparking process itself till his most recent contributions in the field of position-sensitive detectors, Charpak has proposed a variety of original methods which have found, or are beginning to find, applications not only in experimental high energy physics, but also in many fields that are remote from this discipUne such as astrophysics, nuclear medicine or molecular biology. Gaseous detectors are used in j8-chromatography, thermal neutron imaging, X-ray imaging, proton radiography and low-energy gamma-ray imaging thanks also to his pioneering work in these appUed fields. Charpak was awarded the Nobel prize for physics in 1992 for his invention and development of particle detectors and, in particular, the multiwire proportional chamber. Clearly CERN physicists and engineers have contributed with outstanding results both to the development and improvement of other detection techniques, and to the construction of many large detector systems, equipped with different kinds of wire chambers, developing specific techniques to solve specific problems^^^. An historical survey outlining the prominent traits of experimental high-energy physics in the 1980s would see some mammoth detector systems equipped with cylindrical drift chambers and large calorimeters - merely referred to in this chapter - playing a major role. I could by no means analyze all of them here with the care they deserve. Among the wire chamber applications in large facilities, however, I would like to recall the hybrid systems, where wire chambers have been employed to rejuvenate bubble chamber technique. Several hybrid systems have made use of either planar or volumetric wire chambers coupled to bubble chambers either huge or small with different aims. In the last years of the decade hybrid detectors became very appealing since they could combine the unique features of the bubble chamber as a vertex detector with the versatility of electronic chambers in selecting rare events. A main example at CERN is the Big European Bubble Chamber (BEBC) and its External Muon Identifier (EMI), a 150 m^ multiwire proportional chamber system placed behind it to identify muons originating from neutrino or hadron interactions, that went into operation in 1977. Later, in the 1980s, another proportional chamber arrangement, the Internal Picket Fence (IPF) was installed between the magnet and BEBC to improve its performance^^^. Another example is the European Hybrid Spectrometer (EHS), partly operational in 1979 and completed by 1981. At the heart of this faciUty was a rapid cycling bubble chamber (at the beginning the Rapid Cycling Bubble Chamber RCBC, and later a smaller one the LExan Bubble Chamber, LEBC) surrounded by a variety of different devices providing a trigger so that only the interesting events were selected for recording on film. There were magnets, MWPCs, drift chambers, siUca-aerogel Cerenkov detectors, etc., the most interesting element being a pictorial drift chamber, ISIS (an acronym for Identification of Secondaries by Ionization SampHng), the first ever developed, and able to identify particles emerging from the bubble chamber by measuring the ionization density along the particle tracks. The EHS was proposed in 1974 - before the so-called November Revolution - to improve bubble-chamber measurements of high-energy soft multiparticle interactions. In 1979 this system, or at least the parts by then available, was used to investigate charm particle production and decay properties under the pressure of new Notes: pp. 612 ff.

606

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

theoretical and experimental results in the field, and proved to be a unique tool to investigate particles with lifetimes greater than 5 • 10~^^ sec thanks to the spatial resolution achieved with LEBC (of the order of 30-40 /im). In the second half of the 1970s it was commonly said that the bubble chamber was dead, and the excellent results provided by this facihty made some physicists assert in 1981 that small rapid cycHng high resolution bubble chambers were 'the best device for the study of short lifetime particles produced with small cross sections and [that] the future [was] indeed an exciting one'^^^. A late, though prolific marriage between bubbles and wires then, before the bubble chamber definitively left its place at the forefront of experimental high-energy physics in the early 1980s, as electronic detectors began to provide computer-constructed images with such a good spatial resolution as to allow the merging of the logic tradition with the imageproducing one^^^.

Notes 1. Apart from conference proceedings, articles, and books, a collection of minutes of the meetings of the Intersection Storage Rings Committee and the Scientific Policy Committee were used for this chapter, together with summaries of the Omega Project Working Group meetings and memoranda from CERN physicists to the Committees. Further information was derived from the CERN Annual Reports and the CERN Courier. During this study I profited from several interviews and discussions with CERN physicists: W. Bartl, W. Blum, G. Charpak, H. Leutz, L. Montanet, D.O. Morrison, F. Sauli, J. Seguinot, J. Steinberger, U. Trevisan, H. Wahl, K. Winter, T. Ypsilantis, and by a bibHography provided by C.W. Fabjan and H. Schopper. I am also indebted to Prof. G. Salvini (Accademia Nazionale dei Lincei and Rome University) and to Prof. F. Sebastiani (Rome University) for helpful comments and suggestions. I would particulariy like to thank Dr. F. Sauli for his constant and invaluable support throughout this study and the writing of this paper. I would also Hke to thank Dr. G. Charpak for his attentive reading of an earlier version of this text. This research has been supported by the Italian Istituto Nazionale di Fisica Nucleare. 2. By the mid-1970s studies on large-pr hadron production in hadronic interactions and observations of jet events in e"''e~ annihilation stimulated experimenters to conceive detection systems surrounding the interaction regions in the colliding beam machines as completely as possible. Layers of detectors to catch every particle which emerged were built. These so-called 4n detection systems usually included charged particle tracking chambers (MWPCs, drift chambers or TPCs), detectors to identify particles using Cherenkov radiation, and finally, to measure the energy flux, thick, highly instrumented blocks of material (electromagnetic and hadron calorimeters) in which electromagnetic and hadronic particles cascaded and converted their energy into ionization. As for the history of this technique it is worth recalling that both the first calorimeters and the first large-scale detectors of this type were developed for cosmic ray physics, respectively by the mid-1950s and the mid-1960s (see Pugh et al. [138a], and Murzin [131a]. For the first pioneering appHcations of this technique to high energy physics at CERN see Engler et al. [79a] (H. Schopper, letter to the author, 25 May 1991). 3. Galison [89], [91]. 4. Rutherford & Geiger [144], p. 141. 5. Zipprich [169]. 6. Brown & Evans [27], Damy de Souza Santos & Wataghin [73], Gisolf [98], Roberts [141].

Notes

607

7. Bella and Franzinetti [11], [12], Charpak [31], [31a], and [63a], Keuffel [110]. Also Charpak, private communication. 8. Conversi [68a], Conversi & Gozzini [68], Cranshaw & DeBeer [69], Fukui [88a], Fukui & Miyamoto [88]. As for the accelerators in operation before 1956, and capable of producing at least n mesons, see Amaldi [4b]. 9. On the history of early spark chamber technique see GaHson [89]. 10. Krienen [115], Rice Evans [139], sections 1.4, 3.1 and 3.2. 11. Danby et al. [72], Davis [75], Krienen [115]. During the 1960s CERN developed a neutrino physics programme in competition with the one at Brookhaven. The choice of the detector technique played a major role in allowing the American team 'to win the race'. In volume II of the history of CERN Mersits proposed the following interpretation: '[by early 1960s at CERN] the spark chamber technique was still regarded as too unreliable, too little experience had been gained with it, and there was unfortunately also not enough confidence in the know-how of CERN staff in this field' (U. Mersits, 'The construction of the 28 GeV Proton Synchrotron and the first six years of its scientific exploitation' in Hermann et al. [105], p. 231). On the neutrino programme at CERN ibidem pp. 215-234. 12. See Hermann et al. [105], chapter 9. 13. In a narrow-gap spark chamber parallel metaUic plates can be substituted by planes of parallel wires. When a spark occurs the current is localized in one or two wires of each plane, and two wire planes mounted orthogonally will give both the x and the y coordinates. 14. Preiswerk [138]. 15. CERN Courier, 2, September 1962; Nuclear Instruments and Methods 20, 1963. 16. Many of these film-less techniques were developed at CERN: the television method (Gelernter [93]), the core read-out method (Krienen [114]), the current division (Charpak et al. [33]), and the delay-Hne methods (Charpak [32]). Others were developed in other laboratories. The magnetostrictive method, for instance, which became very popular in wire spark chambers, was created in Berkeley at the Lawrence Berkeley Laboratory (Perez-Mendez & Pfab [135]), as was the acoustic one (MagUc & Kirsten [121]). 17. The existence of a discrete mass manifests itself as a peak in the angular distribution of protons of all momenta in a given momentum band. However, some experimental results produced by means of this spectrometer were not confirmed experimentally using other methods. See U. Mersits, 'The construction of the 28 GeV Proton Synchrotron and the first six years of its scientific exploitation' in Hermann et al. [105], pp. 204-205. See also Crozon [70] pp. 250-251, and on the sonic spark chambers Maglic & Kirsten [121], Blieden et al. [14], Lillethun & Zanella [119], Krienen [115] p. 9, Rice Evans [139] pp. 137-140, and the Sessions III and IV of the Spark Chamber Meeting [156]. 18. Later a plumbicon television camera system (where the substance of the photoconductive surface in the television camera is different from the one employed in the vidicon system) worked at the CERN Omega Spectrometer. See Garvey [92]; Session I in Spark Chamber Meeting [156], pp. 57-110; Rice Evans [139] pp. 140-145. 19. See Session II in the Spark Chamber Meeting [156], GianneUi [97], Rice Evans [139] pp. 145-158 and Krienen [115]. 20. Charpak et al. [33], Charpak et al. [34]. 21. Hine[106]. 22. Miller [129] and 'General discussion on on-line computer use' in Spark Chamber Meeting [156], pp. 299312. 23. On the changes in the experimental high energy physics practice see Pickering [137] chapter 12. 24. Hine [106]. 25. Charpak et al. [35] p. 268. 26. Lederman[116]p. 102. 27. I refer to the International Symposium on Nuclear Electronics, Versailles September 1968 [161]. Charpak [36]; Charpak [50], p. 140.

Notes: p. 613

608

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

28. In a typical chamber with an applied voltage of 4000 V, the field at the wire can reach 2.2 • 10^ V/cm. As in a cylindrical counter, in an MWPC we find a variety of ampUfication processes: an avalanche size proportional to the number of initial electrons for low gains, an amplification saturated by space charge effects for high gains, and a propagation by secondary photons for gases with low quenching properties leading either to a Geiger-type propagation along the wires or to a streamer mode followed by a spark. 29. Charpak et al. [35], Charpak [39], Charpak [53]. 30. This collaboration included physicists from the Institut fur Hochenergiephysik of Heidelberg University. Since other groups from Heidelberg participated in collaborations with CERN, from now on by the CERN-Heidelberg collaboration I shall mean the above mentioned one. Otherwise I shall specify the Heidelberg institute involved. 31. Charpak et al. [41], Schilly et al. [152]. 32. SauH [148], Boucher et al. [19]. 33. Increasing the voltage V above the threshold value Vj (see Fig. 12.1) the gain M depends exponentially on the charge per unit length Q = CV. Consequently the gain change is approximately given by the following equation: (AM)/M = lnM(AQ)/Q. The effect on Q due to a uniform change in the wire radius and in the gap can be appreciable. With typical diameter variations around 1% in 20 /im wires a 3% change in gain is reached, while a 0.1 mm difference in the gap length causes a gain variation of 15% (SauH [148], pp. 54-56). 34. Trippe [158], Dieperink et al. [78], Kleinknecht et al. [111], Charpak et al. [41], Majewski & SauH [122], SauH [148]. 35. H. Hoffmann, interviewed by J. Krige, CERN, 23 May 1990. A detailed account of this postponement and related problems is given in Taubes [157], Chap. 6. 36. Veress & Montvai [160], p. 78. 37. Boucher et al. [17] pp. 156-157. 38. Gas mixture investigated by the SFM working group to avoid time degeneracy of the chambers, Charpak et al. [42]. 39. Boucher et al. [17]; Charpak et al. [42]; Veress & Montvai [160]; Fabjan & Fischer [80]; SauH, interview in his office, CERN, 28 March 1990. 40. By 1973 a plumbicon television camera system similar to the vidicon television-camera tube with associated electronic circuits was operational at the CERN Omega Spectrometer (see Sect. 12.3). 41. Summaries of the Omega Project Working Group meetings, 12 August, 17 September and 23 October 1968, NP Omega M 49/51 p. 2 (NP-25/22868); Omega meeting, 17 December 1969, (A 10-0-01/20589). Actually there were several reasons for the choice of optical chambers, amongst others the fact that the conventional wire chamber readout techniques (ferrite core, and magnetostrictive) were not suitable for operating in the high and non-homogeneous magnetic field of the spectrometer (Physics with the Omega Spectrometer, Notes from a meeting held at Cosener's House, 19-20 June 1970, p. 36, NP-27/22870). For SFM see Winter [168] p. 8. Other information kindly provided by G. Charpak (letter to the author, 17 June 1991). 42. Since the first appearance of the MWPC several methods to reduce substantially the number of amplifiers required for the readout have been discussed. In 1968 Charpak's group proposed three methods similar to the principles put forward in the mid-1960s to automatize the spark chamber readout. In the first the plane of wires is built as a lumped delay line and the difference in the arrival time of the pulse at the two ends of the line determines the position of the active wire. In the second method the wires are connected to a resistive attenuator network and the ratio between the pulse heights at the two ends localizes the active wire. In the third technique the wires are connected in different subgroups by transformer coupling. All these methods showed serious limitations when there was simultaneous counting by the wires or if an unfavourable signal-to-noise ratio characterized the amplifiers (Charpak et al. [37]).

Notes

609

43. Braun & MacDonald [21], chapter VIII. 44. The degree of integration is measured in bits or gates (a circuit which fills a logic function) per chip, and LSI refers to chips containing more than one hundred gates per chip. 45. Cunitz et al. [71]. 46. W. Beusch, 'Multiwire proportional counters for Omega', 20 November 1970, pp. 7-9 (NP-27/22870), where the author quotes a survey by the SFM group. Moreover, close contacts between CERN and industries were established which resulted in the development of specific circuitry, as in the case of an eight channel integrated circuit based on CMOS technology developed in the early seventies by a French firm (EFCIS, Grenoble) at the suggestion of Charpak. However the first prototypes of this candidate for the SFM's electronic circuitry came too late to be used in the spectrometer (Sauli, interview in his office, CERN 16 December 1991). 47. Charpak et al. [35], p. 268; Fabjan & Fisher [80]. 48. Charpak et al. [35] p. 268, Fabjan & Fischer [80] pp. 1046-1052. Memorandum to the Director General M.G.N. Hine from H. Schopper and K. Winter, 23 February 1971 (DIR-ADM-NP-01/ 20275). 49. Verkerk [159] p. 395-396. 50. Amato & Petrucci [6], CERN Rapport Annuel 1968 p. 32. 51. CERN Rapport Annuel 1969, p. 34, Bemporad et al. [13], Lederman [116]. 52. Beusch, 'Multiwire proportional counters for Omega', 20 November 1970, p. 9 (NP-27/22870). 53. Memorandum from CERN-Heidelberg group to members of the EEC, 5 January 1972 (MGNH-31/ 22031). 54. Dieperink et al. [78], Kleinknecht et al. [Ill], Dieperink et al. [79], Schilly et al. [152], Cunitz et al. [71]. 55. Gjesdal et al. [99], Geweniger et al. [94], Geweniger et al. [95], Geweniger et al. [96], Kleinknecht [112], CERN Rapport Annuel 1970, pp. 32-33 and 1974 pp. 30-31. 56. Alper et al. [4a], Banner et al. [10], Biisser et al. [28]. For a review on this subject see Darriulat [74]. As for the denotation of the experiments usually adopted, the three digit numbers stand for the ISR experiment number and the first digit refers to the intersection region. 57. Jacob [108] pp. 33-35, Pickering [137] pp. 150-152 and pp. 360-364, CERN Rapport Annuel 1977, p. 20. Quotation from Jacob [108] p. 35. 58. I refer to the chambers developed by the CERN-EPF-Imperial College-Milan collaboration for a diffraction dissociation experiment on the CERN PS. 59. To have an idea of the technological effort required it is worth noting that the wires were made of 20 //m diameter gold-plated tungsten, spaced 2 mm apart, and this distance had to be kept constant to about 100 ^m accuracy (Charpak [50], pp. 140-141). 60. For more details on the data processing see Charpak & Southworth [52] p. 7 and the Technology Notes in Meeting on Technology [125] vol. 2 particularly the Note D47. 61. See CERN Annual Report 1969, pp.20-21; minutes of the third meeting of the ISRC held on 18-19 March 1969 (CERN/ISRC/69-21); minutes of the fourth meeting of the ISRC held on 22-23 April 1969 (CERN/ ISRC/69-33) both in MGNH-33/22033; draft minutes of the fifty-sixth meeting of the Scientific PoHcy Committee (SPC) held on 11 November 1969 (CERN/SPC/284/Draft); and Memorandum to F. Bonaudi, G. Cocconi, K. Johnsen, C. Peyrou, H. Schopper, J. Steinberger, Seer. ISRC, from Charpak and Minten, 2 July 1970 (CERN Archives Box K642). 62. The three proposals were put forward by Krienen, Steinberger and Hyams (see Winter [168]). Minutes of the fifth meeting of the ISRC held on 20-21 May 1969 (CERN/ISRC/69-35) in MGNH-33/22033. Minutes of the sixth meeting of the ISRC held on 3 ^ June 1969 (CERN/ISRC/69^0) in NP-64/22907. Memorandum to Cocconi et al. from Charpak and Minten, 12 May 1969; Memorandum to European HEP Groups from Charpak and Minten, 27 May 1969; Memorandum to those interested from Charpak and Minten, 27 May 1969, Memorandum to SFM Working Group from Charpak and Minten, 3 February 1970, all in CERN Archives Box K642.

610

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

63. Memorandum from C. Peyrou to B. Gregory, Director General, 8 October 1969 (A08-03/20580); Memorandum from the SFM Detector Group to J. Steinberger, 31 August 1970, p. 3 (CERN Archives Box K642); CERN Rapport Annuel 1977, p. 20. 64. Memorandum to F. Bonaudi, G. Cocconi, K. Johnsen, C. Peyrou, H. Schopper, J. Steinberger, Seer. ISRC, from Charpak and Minten, 2 July 1970, SauU report on MWPCs p. 2 (CERN Archives Box K642); Memorandum from the SFM Detector Group to J. Steinberger, 31 August 1970 (CERN Archives Box K642). 65. Minten [130], p. 14. The prototype and the 'zero series' of four chambers were built using the same method as for the chambers made by the CERN-Heidelberg collaboration to investigate CP violation phenomelogy (Schilly et al. [152]; Charpak et al. [41]). This new almost frameless construction method was specifically developed for the final layout of the SFM detector system (Boucher et al. [19]). As for the improvement of the gas mixture see Charpak et al. [42]. However experiments were performed at intersection 4 even before the spectrometer became fully operational as in the case of experiment R402 devoted to the quark search. This experiment, by a CERN-Munich collaboration, ran in 1971-72 and profited from the above mentioned 'zero series' of MWPCs (Bott-Bodenhausen et al. [16]). 66. CERN Rapport Annuel 1973, pp. 117-119. The construction of the 'forward' detector chambers is described in Boucher et al. [19]; see also Charpak [44], Boucher et al. [18] on the detector system, and Fischer et al. [85] on the gas mixture. 67. The problem of the sensitivity against external noise had already occurred with the 'forward' chambers. See Boucher et al. [19] p. 243. 68. Minutes of the twenty-seventh meeting of the ISRC held on 21 March 1972 (CERN/ISRC/72-8); minutes of the thirty-first meeting of the ISRC held on 23 August 1972 (CERN/ISRC/72-25); minutes of the thirtythird meeting of the ISRC held on 15 November 1972 (CERN/ISRC/72-33) all in NP-69/22912. Minutes of the forty-first meeting of the ISRC held on 16 October 1973 (CERN/ISRC/73-31); minutes of the fiftysecond meeting of the ISRC held on 23 October 1974 (CERN/ISRC/74-52) all in NP-64/ 22907. CERN Annual Report 1975 p. 119. Charpak, interview in his office, CERN, 13 September 1990. Among the first results of his going back to work on small prototypes was a series of articles on the properties of induced charge distribution in the avalanche process, see paragraph 12.4.5. 69. CERN Rapport Annuel 1976, p. 70; CERN Rapport Annuel 1977, pp. 77-78. 70. Memorandum of P.G. Innocenti to DG, L. Van Hove, 27 September 1978, in DGR-LVH-37/21300; Jacob [108] pp. 33-37, p. 58 and Fig. 2.2 at p. 36 showing the number of physicists working on approved experiments at the ISR for each year from 1971 to 1983. After a fine start - a maximum was reached in 1974 with more than 300 physicists involved in research at the ISR -, the number dropped to about 150 in 1978, and finally rose to 250 in the years 1981-1983. 71. Charpak & Sauli [45], Charpak & Sauli [46], Charpak & Sauh [49]. 72. Charpak [53] pp. 4 ^ ; Charpak et al. [54]; Charpak & SauH [62] pp. 304^310; Charpak & SauH [57], pp. 408411; Charpak etal. [58]. 73. See Sauh [150] p. 307; Kleinknecht [113] chapter 3; Leo [117] chapter 6. 74. Walenta [164]. 75. However problems with drift chambers can arise with high particle rates, since its principles of operation imply a lower repetition rate in comparison with the MWPCs. In this case the use of MWPCs is preferable. Lederman [116], Charpak [51]. 76. Heintze [103]; Kleinknecht [113], chapter 3. 77. The first pictorial drift chamber was ISIS, an external particle identifier for a rapid cycling bubble chamber developed for the CERN European Hybrid Spectrometer. Proposed in 1974 ISIS (an acronym for Identification of Secondaries by Ionization Sampling) went into operation in late 1979 (Allison et al. [4]). 78. Actually the TPC, developed by D.R. Nygren at Berkeley, constitutes a novel concept in particle detection in comparison with other cylindrical chambers. It makes use of an electric field parallel to the magnetic one, and of a new electronic element: the charge coupled device (CCD), an analog shift register capable of

Notes

79. 80.

81. 82.

83.

84.

85.

86. 87. 88. 89. 90. 91. 92. 93.

94. 95. 96.

611

storing associated time and pulse-height information. Pattern recognition and track finding are simpHfied considerably in comparison with cyHndrical chambers with uncorrelated coordinate information. Since it is the most sophisticated of the current ionization detectors, making use of ideas from both the MWPC and the drift chamber, it will be described in the section devoted to the drift chambers. Charpak et al. [35], Charpak [38], Walenta [164], Walenta [165] and Saudinos [145]. Frascati meeting [87]. For the CERN results see Charpak [44]; for the Heidelberg chambers see Walenta [167], for the Saclay large drift length chambers see Saudinos [146] and Saudinos et al. [147]; for the Harvard very large proportional drift chambers see Cheng et al. [64] and Cheng et al. [65]. Charpak [36] p. 1.15-1.16; Charpak [38] p. C2.93. Nevertheless chambers of this kind with drift length up to 50 cm have been used successfully in the 1 GeV spectrometer at Saturne, built at Saclay. With 800 V/cm of drift field, a pure methane filling, and a drift velocity of 10 cm/^usec, accuracies of about 1 mm were obtained (Saudinos [145], Chaminade et al. [30], Saudinos [146] and Saudinos et al. [147]). Bressani et al. [26]; this study was reported in a wider context in Charpak et al. [40] pp. 25-28. The contribution by T. Bressani, G. Charpak, D. Rahm and C. Zupancic to the 1969 Dubna Conference, published in the proceedings mainly written in Russian, and difficult to find, has been kindly pointed out to me by Prof. Walter Blum (interview in his office, CERN, 11 September 1990). Walenta et al. [165]; Rice-Evans [139] chapter 10; Sauli [148] pp. 74^77. In some configurations it is impossible to distinguish between particles passing to the left and to the right of a sensing (or counting) wire, hence the so-called left-right ambiguity. In his chamber Walenta solved this problem by splitting the counting wire into two wires 1 mm apart. Later another potential wire was inserted between the two wires to solve electrostatic problems (Walenta [166]). In 1973, to work out the ambiguity during event reconstruction, the CERN group proposed another method that uses three equal chambers with parallel wires stacked so that the central one has the wires displaced by half a wire distance with respect to the other two. Charpak et al. [47], Breskin et al. [23], Breskin et al. [24]. Altogether the chambers were in operation during about 1500 hr, from August 1971 till May 1972 and were irradiated with 10^^ particles i.e. 2 • 10^ per cm^. See CERN Rapport Annuel 1971, p. 41, and 1972 p. 37 and p. 49. The construction and the properties of the chambers are described in Walenta [166], while a wider report on the measurement of the (K+ -^ e''"v)/(K+ -^ //+v) branching ratio, can be found in Heard et al. [102]. Charpak et al. [47], Breskin et al. [23], Breskin et al. [24]. Marel et al. [123] dealing with a system of 14 m^ hexagonal planar drift chambers designed for the neutrino experiment WAl; Atac & Taylor [9]. Among the first circuits developed I can mention the ones due to C. Rubbia and to H. Verweij. See Rubbia [142], Rubbia [143], Verweij [162], Verweij [163]. See also on this subject Rice Evans [139] and Sauli [148]. Sauli [148] pp. 22-29 and Fig. 30 at p. 27. SauU [148] pp. 30-31 and Fig. 35 at p. 30. See SauU [148]. On the electron drift in gases an important contribution is due to V. Palladino and B. Sadoulet from the Lawrence Berkeley Laboratory (Palladino & Sadoulet, [134]). The results of the Heidelberg group are reviewed in Heintze [103]. Chambers of this kind have been used for the first time at Fermilab in 1975-76 for a K-e elastic scattering experiment with a high energy kaon beam (Filatova et al. [84]). Others, built around 1975, are still in use at CERN in test setups as monitors, showing the extraordinary longevity of this kind of instrumentation (Sauli, interview in his office, CERN 16 December 1991). Charpak et al. [47], Breskin et al. [23], Breskin et al. [24]. The Proceedings of the Conference were published in the vol. 156 of Nuclear Instruments and Methods. The detector systems quoted are described in Chiavassa et al. [66], and Camilleri et al. [29]. For the current division method see Charpak et al. [33] and Foeth et al. [86]; for the method of the centre of gravity see Sect. 12.4.5 in this chapter; the use of the delay lines has been proposed in Charpak [44].

612

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

97. Charpak et al. [47] and Foeth et al. [86]. 98. Results of early tests performed, using this technique, with a small prototype of the cylindrical drift chamber vertex detector of the AFS are reported in Fabjan et al. [81]. 99. Charpak et al. [48], Breskin et al. [22], Breskin [23]. On the delay line method a lot of work has been done at the Lawrence Berkeley Laboratory by the group of Perez-Mendez, above all on MWPCs for biomedical appHcations. See for instance Perez-Mendez [136]. 100. Breskin et al. [22] p. 5. 101. Camilleri et al. [29]. 102. A first scheme for a three-dimensional digitized chamber incorporating many new features that had been observed in proportional chambers, was suggested by Charpak in 1970. Charpak et al. [40]. 103. The problem of reconstructing events with a complex geometry was usually partially solved by placing many independent planes of MWPCs or drift chambers along the trajectory of the tracks. 104. Sauli [149], SauH [151]. 105. Darriulat [74] pp. 163-166; Jacob [108] pp. 33-35; Pickering [137] pp. 359-364. 106. Albrow et al. [2]; Gordon et al. [101]. 107. The facility went into operation at the CERN SPS in August 1978 (see CERN Rapport Annuel 1978, pp. 32-34). 108. Detector system operational from December 1976 to December 1983. 109. Amaldi[5]. 110. PEP stands for Positron-Electron Project, an electron-positron coUiding beam machine built at SLAC thanks to a collaboration between Stanford and the Lawrence Berkeley Laboratory (LBL). As for the principles of operation of a TPC and its developments see Nygren [132], Marx & Nygren [124] and Nygren [133]. The performance of the prototype is described in Fancher et al. [82]. 111. Actually the only chamber filled with gas at high pressure has been that at Berkeley. Other TPCs later developed employ gas at atmospheric pressure because of the technical difficulties raised by the first prototypes. 112. Charpak & Sauli [46]. See also Sect. 12.4.5. 113. Heintze [103], Marx & Nygren [124], ALEPH [3], Kleinknecht [113], Leo [117]. 114. Sauli [150], Charpak & Sauli [62]. 115. In much the same way as the gas gain saturates with space charge created by the avalanches in the chamber gap, the chamber efficiency decreases if the rate of incident particles becomes too high (Breskin et al. [24]). 116. Herb et al. [104]. 117. Sauli, interview in his office, CERN 16 December 1991. 118. Charpak et al. [55], Charpak & Sauli [56], Breskin et al. [25], Charpak [60], Charpak [61], Charpak & Sauli [62], Charpak [63]. 119. Charpak & Sauli [56], Charpak [60]. Two years before, in 1976, at CERN, Seguinot and Ypsilantis had investigated the photo-ionization process in gases and shown that single UV photon pulse counting in MWPCs was possible (Seguinot & Ypsilantis [153]). In the same article they had presented an appHcation of this technique in detecting the Cerenkov ring image. 120. TEA photoionization potential is 7.5 eV, while that of TMAE is lower: 5.4 eV. Therefore TMAE allows the use of quartz windows, transparent for photons below 8 eV, and this constitutes a substantial improvement because quartz windows are more resistant and cheaper than CaF2 windows used with TEA. 121. The first RICH was actually proposed by Roberts, but the first practical RICH detector is due to Ypsilantis and Seguinot (Roberts [140], Seguinot & Ypsilantis [153]). As for DISC see Meunier et al. [126] and Meunier et al. [127]. For a general review on Cerenkov counters see Litt & Meunier [120], Seguinot [154] and Seguinot & Ypsilantis [155]. 122. Charpak et al. [59]. 123. Charpak [60], Glass et al. [100], SauH [150] pp. 338-347.

References

613

124. As for DELPHI at the CERN LEP, see DELPHI [76]. Detectors of this kind have been constructed at the CERN SPS too to equip the up-graded Omega spectrometer, see Apsimon et al. [7]. As for Stanford see Ashford et al. [8] which reports on a Cerenkov Ring Imaging Detector (GRID) - substantially similar to the RICH device except for the acronym - conceived for the SLD, a second generation detector system at the SLAC Linear CoUider (SLC) designed to study Z^ decays, and incorporating several state-of-the-art detectors with uniform response over nearly 47t steradians. 125. Quotation from the Memorandimi of the CERN-Heidelberg group to members of the EEC, 5 January 1972 (MGNH-31/22031). Charpak, interview in his office, CERN 13 September 1990. Steinberger, interview in his office, CERN 17 April 1991. 126. As for other detection methods here it suffices to recall the key contributions to the development of calorimeters and transition radiation detectors. Through the eighties calorimeters, either electromagnetic or hadronic, have become more and more attractive for high-energy physics, thanks to their abiHty to measure neutral particles, otherwise difficult to be detected, to the extraordinary short time scale on which the signal from these detectors is formed, andfinallythanks to their very accurate measurements - more precise than with magnetic methods - performed at the increased energies of modem accelerators. A survey devoted to them certainly should include as major examples the calorimeters for high-statistics high-energy neutrino physics (experiment WAl of the CERN-Dortmund-Heidelberg-Saclay or CDHS collaboration) and for the study of neutral current neutrino interactions with nucleons (experiment WAl8 of the CERN-Hamburg-Amsterdam-Rome-Moscow or CHARM collaboration), both developed at the CERN SPS. It should also include the already mentioned Axial Field Spectrometer equipped with a hadron calorimeter to study large transverse momentum phenomena at intersection 8 of the CERN ISR (experiment 807). For the CDHS collaboration see Holder et al. [107], for the CHARM collaboration see Diddens et al. [77]. And for the experiment 807 of the BNL-CERN-Copenhagen-Lund-Rutherford-Tel Aviv collaboration see Botner et al. [15]. For developments in the field of transition radiation (TR) detectors I would certainly quote the pioneering work of C.W. Fabjan, W. WiUis and co-workers and their large TR detector developed in 197677 for the identification of electrons with momentum above 1.5 GeV/c at intersection 8 of the ISR (exp. 806 of the BNL-CERN-Syracuse-Yale collaboration). See Cobb et al. [67], Fabjan & Fischer [80], and Kleinknecht [113] pp. 136-139. 127. The IPF was installed in April 1981, tested in May and put into operation in August of the same year (CERN Annual Report 1981, p. 56). See also Brand et al. [20]. 128. L. Montanet, interview in his office, CERN 15 April 1991. H. Leutz, interview in his office CERN 20 March 1991. On the EHS see Aguilar-Benitez et al. [1], on charm physics with LEBC see Montanet & Reucroft [131]. 129. A peculiarity of the image-producing tradition is the production, as experimental demonstration, of fine detailed photographs of individual events, while the attempt to provide large amount data and then a large number of selected events is a typical aspect of the electronic tradition. In the early 1980s electronic detection techniques and highly sophisticated computers exhibited images of events reconstructed electronically with such a high spatial resolution as to allow counter physicists to search for 'golden events'. Galison [90] chapter 5.

References [1] M. Aguilar-Benitez, The European Hybrid Spectrometer', Nuclear Instruments and Methods A258, 1987, pp. 26-50. [2] M.G. Albrow, C.W. Fabjan and M. Jacob, Selected Topics in ISR Physics, CERN Yellow Report 82-11, 15 November 1982. [3] ALEPH Collaboration (Bari-Beijing-CERN-Clermont Ferrand-Copenhagen-Demokritos-DortmundEcole Polytechnique-Edinburgh-Frascati-Glasgow-Heidelberg-Imperial College-Lancaster-Marseille-

614

[4]

[5] [6] [7]

[8]

[9] [10]

[11] [12] [13] [14]

[15]

[16]

[17] [18]

[19]

The Development of Electronic Position Detectors at CERN (1964-late 1970s) MPI Munchen-Orsay-Pisa-Rutherford Laboratory-Saclay-Sheffield-Siegen-Trieste-Westfield CollegeWisconsin) Technical Report 1983 for CERN-Lep Committee. W.W.M. Allison, C.B. Brooks, J.N. Bunch, J.H. Cobb, J.L. Lloyd and R.W. Fleming, T h e Identification of Secondary Particles by lonisation Sampling (ISIS)', Nuclear Instruments and Methods 119, 1974, pp. 499-507. a] B. Alper, H. Boggild, G. Jarlskog, G. Lynch, J.M. Weiss, P. Booth, L.J. Carroll, J.N. Jackson, M. Prentice, G. von Dardel, L. Jonsson, G. Damgaard, K.H. Hansen, E. Lohse, F. Bulos, L. Leistam, A. Klovning, E. Lillethun, B. Duff, F. Heymann and D. Quarrie, 'Production of High Transverse Momentum Particles in p-p CoUisions in the Central Region at the CERN ISR', Physics Letters 44B, 1973, pp. 521-526. b] E. Amaldi, T h e History of CERN during the Early 1950s', in ref. [27a], 508-518. U. Amaldi, An Experimentalist's Overview of the Parallel Development of Accelerators and Detectors, CERN-EP/88-11, 26 January 1988. G. Amato and G. Petrucci, A Beam-Profile Analyser Using Proportional Wire Chamber, CERN Yellow Report 68-33, 6 August 1968. R.J. Apsimon, P.S. Flower, K.A. Freeston, G.D. Hallewell, J.A.G. Morris, J.V. Morris, C.N. Paterson, P.H. Sharp, C.N. Uden, M. Davenport and J. Fades, T h e Recent Operational Performance of the CERN OMEGA Ring Imaging Cerenkov Detector', IEEE Transactions on Nuclear Science 33, 1986, p. 122-131. V. Ashford, T. Bienz, F. Bird, G. Hallewell, D. Leith, D. McShurley, A. Nuttall, B. Ratcliff, R. Reif, D. Schultz, S. Shapiro, T. Shimomura, N. Toge, S. Williams, D. Bauer, D. Caldwell, A. Lu, S. Yellin, M. Cavalli-Sforza, D. Coyne, R. Johnson, B. Meadows and M. Nussbaum, 'Development of the Cerenkov Ring Imaging Detector for the SLD', IEEE Transactions on Nuclear Science 33, 1986 p. 113-121. M. Atac and W.E. Taylor, 'The Development of a New Drift Chamber with a New Gas Mixture', Nuclear Instruments and Methods 120, 1974, pp. 147-151. M. Banner, J.L. Hamel, J.P. Pansart, A.V. Stirling, J. Teiger, H. Zaccone, J. Zsembery, G. Bassampierre, M. Croissiaux, J. Gresser, R. Morand, M. Riedinger and M. Schneegans, 'Large Tranverse Momentum Particle Production at 90° in pp Collisions at the ISR', Physics Letters 44B, 1973, 537-540. F. Bella and C. Franzinetti, 'On the Theory of the Spark Counter', Nuovo Cimento 10,1953, pp. 1335-1337. F. Bella and C. Franzinetti, 'Spark Counters', Nuovo Cimento 10, 1953, pp. 1461-1479. C. Bemporad, W. Beusch, A.C. Melissinos and E. SchuUer, 'Performance of a System of Proportional Wire Chambers', Nuclear Instruments and Methods 80, 1970, pp. 205-212. H. Blieden, D. Freytag, F. Iselin, F. Lefebvres, B. Maglic, H. Slettenhaar, S. Almeida and A. Lang, 'System Consisting of Sonic Spark Chambers, Time-of-Flight and Pulse-Height Counters (Missing-Mass Spectrometer) with On-Line Computer', in ref. [156], pp. 49-56. O. Botner, S. Dagan, C.W. Fabjan, H. Gordon, P. Jeffreys, G. Kesseler, W. Molzon, Y. Oren, L. Rosselet, R. Schindler, S.D. Smith, J. van der Lans, C.J. Wang, W.J. WiUis, W. Witzeling, and C. Woody, 'The AFS Hadron Calorimeter at the CERN ISR', IEEE Transactions on Nuclear Science 28, 1981, pp. 510-513. M. Bott-Bodenhausen, D.O. Caldwell, C.W. Fabjan, C.R. Gruhn, L.S. Peak, L.S. Rochester, F. Sauli, U. Stieriin, R. Tirler, B. Winstein and D. Zahniser, 'A Search for Quarks at the Intersection Storage Rings', Physics Letters 40B, 1972, pp. 693-698. R. Boucher, G. Charpak, Z. Dimcovski, G. Fischer, F. SauH, G. Coignet and G. Flugge, 'Investigation of Some Properties of MWPCs', Nuclear Instruments and Methods 88, 1970, pp. 149-161. R. Boucher, G. Charpak, E. Chesi, L. Dumps, H.G. Fischer, H.J. Hilke, P.G. Innocenti, G. Maurin, A. Minten, L. Naumann, F. Piuz, J.C. Santiard and O. Ullaland, 'A System of Proportional Chambers with 50000 Wires', in ref. [87], pp. 280-283. R. Boucher, G. Charpak, E. Chesi, L. Dumps, H.G. Fischer, H.J. Hilke, P.G. Innocenti, G. Maurin, A. Minten, L. Naimiann, F. Piuz, J.C. Santiard and O. Ullaland, 'Proportional Chambers for a 50 000-Wire Detector', Nuclear Instruments and Methods 115, 1974, pp. 235-244.

References

615

[20] C. Brand, R.C.A. Brown, E. Chesi, H. Foeth, A. Gilgrass, H.J. Hilke, D. Jacobs, P. Lazeyras and Y. Sacquin, 'Development of a 150 m^ Proportional Chamber System with a 1 MiUion Bit Buffer', Nuclear Instruments and Methods 136, 1976, pp. 485-495. [21] E. Braun and S. MacDonald, Revolution in Miniature (Cambridge: Cambridge University Press, 1978). [22] A. Breskin, G. Charpak, F. Sauli and J.C. Santiard, T w o Dimensional Drift Chambers', Nuclear Instruments and Methods 119, 1974, pp. 1-5. [23] A. Breskin, G. Charpak, B. Gabioud, F. SauH, N. Trautner, W. Duinker, G. Schultz, 'Further Results on the Operation of High-Accuracy Drift Chambers', Nuclear Instruments and Methods 119, 1974, pp. 9-28. [24] A. Breskin, G. Charpak, F. Sauli, M. Atkinson and G. Schultz, 'Recent Observations and Measurements with High-Accuracy Drift Chambers', Nuclear Instruments and Methods 124, 1975, pp. 189-214. [25] A. Breskin, G. Charpak, S. Majewski, G. Melchart, G. Petersen and F. Sauli, 'The Multistep Avalanche Chamber: a New Family of Fast, High-Rate Particle Detectors', Nuclear Instruments and Methods 161, 1979, pp. 19-34. [26] T. Bressani, G. Charpak, D. Rahm and C. Zupancic, 'Track Localization by Means of a Drift Chamber', International Seminar on Filmless Spark and Streamer Chambers, Dubna, 15-18 April 1969, pp. 275-280. [27] S.C. Brown and R.D. Evans, 'Discharge Counters of Unconventional Geometry', Physical Review 55, 1939, pp. 1133-1134. a] L.M. Brown, M. Dresden and L. Hoddeson, Pions to Quarks-Particle Physics in the 1950s (Cambridge: Cambridge University Press, 1989). [28] F.W. Biisser, L. Camilleri, L. DiLella, G. Gladding, A. Placci, B.G. Pope, A.M. Smith, J.K. Yoh, E. Zavattini, B.J. Blumenfeld, L.M. Lederman, R.L. Cool, J. Litt and S.L. Segler, 'Observation of TT^ Mesons With Large Transverse Momentum in High Energy pp ColHsions', Physics Letters 46B, 1973, pp. 471-476. [29] L. Camilleri, C. del Papa, L. Di Leila, F. Doughty, R. Harfield, C.J. Onions, B.G. Pope, S.H. Pordes, J. Singh, A.M. Smith, H. Wind, B.J. Blumenfeld, R.J. HoUebeek, H. Cunitz, L.M. Lederman, D. Levinthal, W. Sippach, R.A. Vidal, A.L.S. Angelis, L. Lyons, N. Phinney, A.M. Segar, J.S. Wallace-Hadrill, T.O. White, T.J. Chapin, R.L. Coll, Z. Dimcovski, A.F. Rothenberg, M.J. Tannenbaum, 'A System of Cylindrical Drift Chambers in a Superconducting Solenoid', Nuclear Instruments and Methods 156, 1978, pp. 275-282. [30] R. Chaminade, J.C. Duchazeaubeneix, S.M. Fontaine, D. Garetta, C. Laspalles, J. Saudinos and M. Van den Bosche, Note CEA-N-1522, CEE Saclay (1971) p. 160. [31] G. Charpak, 'Principes et essais preliminaires d'un nouveau detecteur permettant de photographier la trajectoire de particules ionisantes dans un gaz'. Journal de Physique 18, 1957, pp. 589-592. a] G.Charpak, 'Principe d'un detecteur de temps d'efficacite tres court, permettant de photographier la trajectoire de particules ionisantes dans un gaz', in ref. [132a], XVII.11-XVII.15. [32] G. Charpak, 'Location of the Position of a Spark in a Spark Chamber', Nuclear Instruments and Methods 15, 1962, pp. 318-322. [33] G. Charpak, J. Favier, L. Massonet, 'A New Method for Determining the Position of a Spark in a Spark Chamber by Measurement of Currents', Nuclear Instruments and Methods 24, 1963, pp. 501-503. [34] G. Charpak, J. Favier, L. Massonet, 'Determination of the Position of Sparks by Means of Measurement of Currents', in ref. [156], pp. 333-335. [35] G. Charpak, R. Boucher, T. Bressani, J. Favier and C. Zupancic, 'The Use of Multiwire Proportional Counters to Select and Locahze Charged Particles', Nuclear Instruments and Methods 62,1968, pp. 262-268. [36] G. Charpak, 'Evolution des techniques de chambres a etincelles en 1968', in ref. [161], pp. 1.1-1.44. [37] G. Charpak, R. Boucher, T. Bressani, J. Favier and C. Zupancic, 'Some Read-out Methods for Proportional Multiwire Chambers', Nuclear Instruments and Methods 65, 1968, pp. 217-220. [38] G. Charpak, 'La detection des particules au moyen des decharges dans les gaz'. Journal de Physique CoUoque C2 30, 1969, pp. C2.86-C2.96. [39] G. Charpak, Evolution of the Automatic Spark Chambers', Annual Review of Nuclear Science 20, 1970, pp. 195-254.

616

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

[40] G. Charpak, D. Rahm and H. Steiner, 'Some Developments in the Operation of Multiwire Proportional Chambers', Nuclear Instruments and Methods 80, 1970, pp. 13-34. [41] G. Charpak, G. Fischer, A. Minten, L. Naumann, F. Sauh, G. Fliigge, Ch. Gottfried and R. Tirler, 'Some Features of Large Multiwire Proportional Chambers', Nuclear Instruments and Methods 97, 1971, pp. 377-388. [42] G. Charpak, H.G. Fischer, C.R. Gruhn, A. Minten, F. SauH, G. Plch, G. Fliigge, 'Time Degeneracy of MWPCs', Nuclear Instruments and Methods 99, 1972, pp. 279-284. [43] G. Charpak, 'L'evolution des detecteurs de particules en physique des hautes energies'. Journal de Physique colloque CIO, 1973, pp. 73-82. [44] G. Charpak, 'Wire Systems', in ref. [87], pp. 247-255. [45] G. Charpak and F. Sauli, High Accuracy, Two Dimensional Readout in MWPCs, CERN Yellow Report 73-^ (1973). [46] G. Charpak and F. Sauli, High Accuracy Measurements of the Center of Gravity of Avalanches in Proportional Chambers, CERN Yellow Report 73-11 (1973). [47] G. Charpak, F. Sauli and W. Duinker, 'High-Accuracy Drift Chambers and Their Use in Strong Magnetic Fields', Nuclear Instruments and Methods 108, 1973, pp. 413^26. [48] G. Charpak, F. SauH and J.C. Santiard, Two-Dimensional Drift Chambers, CERN NP Internal Report 73-16 (1973). [49] G. Charpak and F. Sauli, 'High-Accuracy, Two-Dimensional Read-Out in Multiwire Proportional Chambers', Nuclear Instruments and Methods 113, 1973, pp. 381-385. [50] G. Charpak, 'Particle Detectors' in ref. [125], vol. 1, pp. 129-145. [51] G. Charpak, 'Wire Chambers: a Review and Forecast', Comments on Nuclear and Particle Physics 6,1976, pp. 157-171. [52] G. Charpak and B. Southworth, 'New Particle Detectors - The Multiwire Proportional Chamber and the Drift Chamber', The Physics Teacher 15 (1), January 1977, p. 3-8. [53] G. Charpak, 'Multiwire and Drift Proportional Chambers', Physics Today 31 (10), October 1978. [54] G. Charpak, G. Petersen, A. Policarpo and F. Sauli, 'Progress in High Accuracy Proportional Chambers', Nuclear Instruments and Methods 148, 1978, pp. 471-482. [55] G. Charpak, G. Melchart, G. Petersen, F. Sauli, E. Bourdinaud, P. Blumenfeld, J.C. Duchazeaubeneix, A. Garin, S. Majewski, R. Walczak, New Approaches to High-Rate Particle Detectors, CERN Yellow Report 78-05, June 1978. [56] G. Charpak and F. Sauli, 'The Multistep Avalanche Chamber: a New High-Rate, High-Accuracy Gaseous Detector', Physics Letters 78B, 1978, pp. 523-528. [57] G. Charpak and F. SauH, 'MWPCs and Drift Chambers', Nuclear Instruments and Methods 162,1979, pp. 405-428. [58] G. Charpak, G. Melchart, G. Petersen and F. SauH, 'High Accuracy Localization of Minimum Ionizing Particles Using the Cathode-Induced Charge Centre-of-Gravity Read-Out', Nuclear Instruments and Methods 167, 1979, pp. 455^64. [59] G. Charpak, S. Majewski, G. Melchart, F. Sauli and T. Ypsilantis, 'Detection of Far-Ultraviolet Photons with the Multistep Avalanche Chamber. Application to Cerenkov Light Imaging and to Some Problems in High Energy Physics', Nuclear Instruments and Methods 164, 1979, pp. 419-433. [60] G. Charpak, 'Some Recent Trends in the Evolution of Gaseous Detector', Nuclear Instruments and Methods 196, 1982, pp. 11-19. [61] G. Charpak, 'Gaseous Detectors for Particle Physics: a Still Blooming Source of New Instruments', Nuclear Instruments and Methods 217, 1983, pp. 5-7. [62] G. Charpak and F. Sauli 'High Resolution Electronic Particle Detectors', Annual Review of Nuclear and Particle Science 34, 1984, pp. 285-349. [63] G. Charpak, 'Will Gaseous Detectors Survive the Rapid Progress in the Competing Techniques?', Nuclear Instruments and Methods A252, 1986, pp. 131-136.

References

[64] [65]

[66]

[67]

[68]

[69] [70] [71] [72]

[73] [74] [75] [76] [77]

[78] [79]

617

a] G. Charpak, Electronic Imaging of Ionizing Radiation with Limited Avalanches in Gases, CERN-PPE/ 93-25, 16 February 1993, Nobel Lecture given 10 December 1992 (to be published by Almqvist & Wiksell, Stockholm, for the Nobel Foundation). D.C. Cheng, W.A. Kozanecki, R.L. Piccioni, C. Rubbia, L.R. Sulak, HJ. Weedon and J. Whittaker, 'Very Large Proportional Drift Chambers with High Spatial and Time Resolution', in ref. [87], pp. 268-274. D.C. Cheng, W.A. Kozanecki, R.L. Piccioni, C. Rubbia, L.R. Sulak, H.J. Weedon and J. Whittaker, 'Very Large Proportional Drift Chambers with High Spatial and Time Resolution', Nuclear Instruments and Methods 117, 1974, pp. 157-169. E. Chiavassa, S. Costa, G. Dellacasa, M. GaUio, A. Musso, A. Panighini, T. Bressani, K. Bos, W. van Doesburg, A. Stanovnik and D. Vranic, 'Multiwire and Drift Chambers for the Omicron Spectrometer', Nuclear Instruments and Methods 156, 1978, pp. 187-198. J. Cobb, C.W. Fabjan, S. Iwata, C. Kourkoumelis, A.J. Lankford, G.C. Moneti, A. Nappi, R. Palmer, P. Rehak, W. Struczinski and W. WilUs, 'Transition Radiators for Electron Identification at the CERNISR', Nuclear Instruments and Methods 140, 1977, pp. 413^27. M.M. Conversi and A. Gozzini, 'The 'Hodoscope Chamber': a New Instrument for Nuclear Research', Nuovo Cimento 2, 1955, pp. 189-191. a] M. Conversi, 'The Development of the Flash and Spark Chambers in the 1950s', in CoUoque International sur I'Histoire de la Physique des Particules, Journal de Physique (CoUoque C8 Supplement) 43, fasc. 12, 1982, pp. 91-99. T.E. Cranshaw and J.F. DeBeer, 'A Triggered Spark Counter', Nuovo Cimento 5, 1957, pp. 1107-1116. M. Crozon, La matiere premiere (Paris: Seuil, 1987). H. Cunitz, W. Sippach, J.H. Dieperink, 'A 5000 Wire Proportional Chamber Readout System for a LargeAperture Magnet Spectrometer', Nuclear Instruments and Methods 91, 1971, pp. 211-220. G. Danby, J.-M.Gaillard, K. GouHanos, L.M. Lederman, N. Mistry, M. Schwartz and J. Steinberger, 'Observation of High-Energy Neutrino Reactions and the Existence of Two Kinds of Neutrinos', Physical Review Letters 9, 1962, pp. 36-44. M. Damy de Souza Santos e G. Wataghin, 'Sopra un nuovo tipo di contatore di corpuscoH', Nuovo Cimento 15, 1938, pp. 104-107. P. Darriulat, 'Large Transverse Momentum Hadronic Processes', Annual Review of Nuclear and Particle Science 30, 1980, pp. 159-210. D.G. Davis, 'La chambre a etincelles'. Endeavour 22, 1963, pp. 19-23. DELPHI Technical Proposal CERN/LEPC/1983/3 pp. 83-86. A.N. Diddens, M. Jonker, J. Panman, F. Udo, J.V. AUaby, U. Amaldi, G. Barbiellini, A. Baroncelli, V. Blobel, G. Cocconi, W. Flegel, W. Kozanecki, E. Longo, K.H. Mess, M. Metcalf, J. Meyer, R.S. Orr, F. Schneider, A.M. Wetherell, K. Winter, F.W. Btisser, P.D. Gall, H. Grote, P. Heine, B. Kroger, F. Niebergall, K.H. Ranitzsch, P. StaheUn, V. Gemanov, E. Grigoriev, V. Kaftanov, V. Khovansky, A. Rosanov, R. Biancastelli, B. Borgia, C. Bosio, A. Capone, F. Ferroni, P. Monacelli, F. de Notaristefani, P. Pistilli, C. Santoni and V. Valente, 'A Detector for Neutral-Current Interactions of High-Energy Neutrinos', Nuclear Instruments and Methods 178, 1980, pp. 27-48. J.H. Dieperink, K. Kleinknecht, P. Steflfen, J. Steinberger, T. Trippe, F. Vannucci, Construction Problems with Large Proportional Wire Chambers, CERN NP Internal Report 69-28, 1969. J.H. Dieperink, P. Steflfen, J. Steinberger, T. Trippe, F. Vannucci, H. Wahl, D. Zanello, H. Filthuth, K. Kleinknecht, V. Lixth, P. Mokry, H. Schneider, M. Vysocansky and G. Zech, 'A Large Multiwire Proportional Chamber Spectrometer', International Conference on Instrumentation for HEP, Dubna 1970, pp. 251-264. a] J. Engler, W. Flauger, G. Gibbard, F. Monnig, K. Runge, H. Schopper, 'A Total Absorption Spectrometer for Energy Measurements of High Energy Particles', Nuclear Instruments and Methods 106, 1973, pp. 189-200.

618

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

[80] C.W. Fabjan and H.G. Fischer, 'Particle Detectors', Reports on Progress in Physics 43, 1980, pp. 10031063. [81] C.W. Fabjan, J. Lindsay, F. Piiiz, F. Ranjard, E. Rosso, A. Rudge, S. Serednyakov, W.J. WiUis, H.B. Jensen and J.O. Petersen, 'A Drift Chamber Vertex Detector for Intersecting Storage Rings', Nuclear Instruments and Methods 156, 1978, pp. 267-274. [82] D. Fancher, H.J. Hilke, S. Loken, P. Martin, J.N. Marx, D.R. Nygren, P. Robrish, G. Shapiro, M. Urban, W. Wenzel, W. Gorn and J. Layter, 'Performance of a Time Projection Chamber', Nuclear Instruments and Methods 161, 1979, pp. 383-390. [83] T. Ferbel (editor). Techniques and Concepts of High Energy Physics II (New York: Plenum Press, 1983). [84] A.N. Filatova, T.S. Nigmanov, V.P. Pugachevich, V.D. Riabtsov, M.D. Shafranov, E.N. Tsyganov, D.V. Uralsky, A.S. Vodopianov, F. SauU, M. Atac, 'Study of Drift Chamber System for a K-e Scattering Experiment at the Fermi National Accelerator Laboratory', Nuclear Instruments and Methods 143,1977, pp. 17-28. [85] H.G. Fischer, H.J. Hilke, F. Piuz, and O. Ullaland, 'Investigations on the Operation of Large Proportional Wire Chambers', in ref. [87], pp. 275-279. [86] H. Foeth, R. Hammarstrom and C. Rubbia, 'On the Localization of the Position of the Particle Along the Wire of a Multiwire Proportional Chamber', Nuclear Instruments and Methods 109, 1973, pp. 521-524. [87] Proceedings of the 5th International Conference on Instrumentation for HEP, Frascati 8-12 May 1973, editor S. Stipcich (Frascati: CNEN, 1973). [88] S. Fukui and S. Miyamoto, 'A New Type of Particle Detector': the "Discharge Chamber", Nuovo Cimento 11, 1959, pp. 113-115. a] S. Fukui, 'Development of the Discharge (Spark) Chamber in Japan in the 1950s', in ref. [27a], pp. 252259. [89] P. GaUson, 'Bubbles, Sparks and the Post-War Laboratory', in ref. [27a], pp. 213-251. [90] P. Galison, How Experiments End (Chicago: University of Chicago Press, 1987). [91] P. Galison, Image and Logic, to be published. [92] J. Garvey, 'Television Cameras in High Energy Physics Experiments', in ref. [87], pp. 463^72. [93] H. Gelernter, 'The Automatic Collection and Reduction of Data for Nuclear Spark Chambers', Nuovo Cimento 22, 1961, pp. 631-642. [94] C. Geweniger, S. Gjesdal, T. Kamae, G. Presser, P. Steffen, J. Steinberger, F. Vannucci, H. Wahl, F. Eisele, H. Filthuth, K. Kleinknecht, V. Lixth and G. Zech, 'Measurement of the Charge Asymmetry in the Decays Kj^ ^ Tc^e^v and Kj^ ^ TT^/Z^^V'. Physics Letters 48B, 1974, pp. 483-486. [95] C. Geweniger, S. Gjesdal, G. Presser, P. Steflfen, J. Steinberger, F. Vannucci, H. Wahl, F. Eisele, H. Filthuth, K. Kleinknecht, V. Liith and G. Zech, 'A New Determination of the K^ —> TT+TC"', Physics Letters 48B, 1974, pp. 487^91. [96] C. Geweniger, S. Gjesdal, G. Presser, P. Steffen, J. Steinberger, F. Vannucci, H. Wahl, F. Eisele, K. Kleinknecht, V. Liith and G. Zech, 'Measurement of the Kaon Mass Difference mL - ms by the two Regenerator Methods', Physics Letters 52B, 1974, pp. 108-112. [97] G. Giannelli, 'A Magnetostriction Method for Spark Localization' in ref. [156], pp. 325-328. [98] J.H. Gisolf, 'The Counting of Electrons by Means of a Discharge Tube', Physika 4, 1937, pp. 69-70. [99] S. Gjesdal, G. Presser, P. Steffen, J. Steinberger, F. Vannucci, H. Wahl, H. Filthuth, K. Kleinknecht, V. Liith and G. Zech, 'Search for the Decay Ks -> 2//', Physics Letters 44B, 1973, pp. 217-220. [100] H. Glass, M. Adams, A. Bastin, G. Coutrakon, D. Jaffe, J. Kirz, R. McCarthy, J.R. Hubbard, Ph. Mangeot, J. MuUie, A. Peisert, J. Tichit, R. Boucher, G. Charpak, J.C. Santiard, F. Sauli, J. Crittenden, Y. Hsiung, D. Kaplan, C. Brown, S. Childress, D. Finley, A. Ito, A. Jonckheere, H. Jostlein, L. Lederman, R. Orava, S. Smith, K. Sugano, K. Ueno, A. Maki, Y. Hemmi, K. Miyake, T. Nakamura, N. Sasao, Y. Sakai, R. Gray, R. Plaag, J. Rothberg, J. Rutherfoord and K. Young, 'Construction and Operation of a Large Ring-Imaging Cerenkov Detector', IEEE Transactions on Nuclear Science 30, 1983, pp. 30-34.

References

619

[101] H. Gordon, R. Hogue, T. Killian, T. Ludlam, M. Winik, C. Woody, D. Burckhart, V. Burkert, O. Botner, D. Cockerill, W.M. Evans, C.W. Fabjan, T. Ferbel, P. Frandsen, A. Hallgren, B. Heck, M. Harris, J.H. Hilke, H. Hofmann, P. Jeffreys, G. Kantardjian, G. Kesseler, J. Lindsay, J.H. Lubatti, W. Molzon, B.S. Nielsen, P. Queru, L. Rosselet, E. Rosso, A. Rudge, R.H. Schindler, T. Taylor, J. van der Lans, D.W. Wang, C. Wang, W.J. Willis, W. Witzeling, H. Boggild, E. Dahl-Jensen, I. Dahsen, P. Dam, G. Damgaard, K.H. Hansen, J. Hooper, R. Moller, S.0. Nielsen, L.H. Olsen, B. Schistad, T. Akesson, S. Almehed, G. von Dardel, G. Jarlskog, B. Lorstad, A. Melin, U. Mjommark, A. Nilsson, M.G. Albrow, N.A. McCubbin, M.D. Gibson, J. Hiddleston, O. Benary, S. Dagan, D. Lissauer and Y. Oren, T h e Axial Field Spectrometer at the CERN ISR', Nuclear Instruments and Methods 196, 1982, pp. 303-313. [102] K.S. Heard, J. Heintze, G. Heinzelmann, P. Igo-Kemenes, W. Kalbreier, E. Mittag, H. Rieseberg, B. Schiirlein, H.W. Siebert, V. Soergel, K.P. Streit, A. Wagner and A.H. Walenta, *A Measurement of the (K+ -> e+v)/(K+ -> /x+v) Branching Ratio, Physics Letters 55B, 1975, pp. 327-330. [103] J. Heintze, *Drift Chambers and Recent Developments', Nuclear Instruments and Methods 156, 1978, pp. 227-244. [104] S.W. Herb, D.C. Hom, L.M. Lederman, J.C. Sens, H.D. Snyder, J.K. Yoh, J.A. Appel, B.C. Brown, C.N. Brown, W.R. Innes, K. Ueno, T. Yamanouchi, A.S. Ito, H. Jostlein, D.M. Kaplan and R.D. Kephart, 'Observation of a Dimuon Resonance at 9.5 GeV in 400-GeV Proton-Nucleus Collisions', Physical Review Letters 39, 1977, pp. 252-255. [105] A. Hermann, J. Krige, U. Mersits and D. Pestre, History of CERN, volume II. Building and Running the Laboratory, 1954-1965 (Amsterdam: North-Holland, 1990). [106] M.G.N. Hine, 'Concluding Remarks' in ref. [156], pp. 371-376. [107] M. Holder, J. Knobloch, G. Laverriere, J. May, H. Paar, P. Palazzi, F. Ranjard, P. Schilly, D. Schlatter, J. Steinberger, H. Suter, H. Wahl, E.G.H. WiUiams, F. Eisele, C. Geweniger, K. Kleinknecht, D. PoUmann, G. Spahn, H.J. Willutzki, W. Dorth, F. Dydak, V. Hepp, W. Heyde, K. Tittel, M. Vysocansky, J. Wotschack, P. Bloch, B. Devaux, M. Grimm, J. Maillard, Y. Malbequi, G. Marel, B. Peyaud, J. Rander, A. Savoy-Navarro, G. Tarte, R. Turlay, F.L. Navarria, 'A Detector for High-Energy Neutrino Interactions', Nuclear Instruments and Methods 148, 1978, pp. 235-249. [108] M. Jacob, 'The Role of the ISR in the Development of Particle Physics' in ref. [109], pp. 21-81. [109] M. Jacob and K. Johnsen, A Review of Accelerator and Particle Physics at the CERN Intersecting Storage Rings, CERN Yellow Report 84-13. [110] J.W. Keuffel, 'Parallel Plate Counters', Review of Scientific Instruments 20, 1949, pp. 202-208. [Ill] K. Kleinknecht, V. Liith, P. Steffen, F. Vannucci, H. Wahl and G. Zech, 'Some New Results on the Development of Support Lines for Large Proportional Wire Chambers, CERN Internal Report 70-18, 1970. [112] K. Kleinknecht, 'CP Violation and K^ Decays', Annual Review of Nuclear and Particle Science 26, 1976, pp. 1-50. [113] K. Kleinknecht, Detectors for Particle Radiation (Cambridge: Cambridge University Press, 1986). [114] F. Krienen, 'Digitized Spark Chambers', Nuclear Instruments and Methods 16, 1962, pp. 262-266. [115] F. Krienen, 'Les chambres a etincelles du Cern,' Industries Atomiques, No. 5/6, 1970, pp. 3-12. [116] L. Lederman, 'New Revolution in Particle Detection', Comments on Nuclear and Particle Physics 3, 1969, pp. 101-106. [117] W.R. Leo, Techniques for Nuclear and Particle Physics Experiments (Berlin: Springer Verlag, 1987). [118] J.W. Lillberg, 'A Time Projection Chamber Data Acquisition System', Nuclear Instruments and Methods A240, 1985, pp. 122-129. [119] E. Lillethun and P. Zanella, 'Description of the Mathematics Involved in the Reconstruction of Spark Position in an Acoustical Spark Chamber', in ref. [156], pp. 171-180. [120] J. Litt and R. Meunier, 'Cerenkov Counter Technique in High-Energy Physics', Annual Review of Nuclear and Particle Science 23, 1973, pp. 1-43.

620

The Development of Electronic Position Detectors at CERN (1964-late 1970s)

[121] B.C. Maglic and F.A. Kirsten, 'Acoustic Spark Chamber', Nuclear Instruments and Methods 17,1962, pp. 49-59. [122] S. Majewski and F. Sauli, Support Lines and Beam Killers for Large Size Multiwire Proportional Chambers, CERN NP Internal Report 75-14 (1975). [123] G. Marel, P. Bloch, S. Brehin, B. Devaux, A.M. Diamant-Berger, C. Leschevin, J. Maillard, Y. Malbequi, H. Martin, A. Patoux, J. Pelle, J. Plancoulaine, G. Tarte and R. Turlay, 'Large Planar Drift Chambers', Nuclear Instruments and Methods 141, 1977, pp. 43-56. [124] J.N. Marx and D.R. Nygren, T h e Time Projection Chamber', Physics Today 31 (10), October 1978. [125] Proceedings of the Meeting on Technology Arising from High-Energy Physics, 24-26 April 1974 (Geneva: CERN 74-09, 2 vols., 1974). a] International Conference on Mesons and Recently Discovered Particles and 43° Congresso Nazionale della Societa Italiana di Fisica, Padova-Venezia 22-28 September 1957 (Padova: Societa ItaHana di Fisica, 1958). [126] R. Meunier, J.P. Stroot, B. Leontic, A. Lunby, 'DISC: compteur Cerenkov a selection de vitesse'. Nuclear Instruments and Methods 17, 1962, pp. 1-19. [127] R. Meunier, J.P. Stroot, B. Leontic, A. Lunby and P. Duteil, 'Compteur DISC a radiateur Hquide' Nuclear Instruments and Methods 17, 1962, pp. 20-30. [128] Proceedings of the Topical Conference on the Application of Microprocessors to HEP Experiments, 3-6 May 1981 (Geneva: CERN 81-07, 1981). [129] R.H. Miller, 'Remarks on On-Line Computer Use' in ref. [156], pp. 279-281. [130] A. Minten, The Split Field Magnet Facility, CERN/ISRC/71-19, 27 April 1971. [131] L. Montanet and S. Reucroft, 'High Resolution Bubble Chambers and the Observation of Short-Lived Particles', Physics Reports 83 (1), 1982, pp. 61-83. a] V.S. Murzin, 'Principles and Application of the Ionization Calorimeter' in J.G. Wilson and LA. Wouthuysen (eds.). Progress in Elementary Particle and Cosmic Ray Physics (Amsterdam: North Holland, 1967), vol. 9, chap. IV, 245-303. [132] D.R. Nygren, LBL (spokesman). Proposal for a PEP Facihty Based on the Time Projection Chamber, LBL-UCLA-Yale-Riverside-Johns Hopkins, PEP Experiment No. 4, PUB-5012 (December 1976). [133] D.R. Nygren, 'Future Prospects of the TPC Idea', Physica Scripta 23, 1981, pp. 583-588. [134] V. Palladino and B. Sadoulet, 'Application of the Classical Theory of Electrons in Gases to Drift Chambers', Nuclear Instnmients and Methods 128, 1975 p. 323-335. [135] V. Perez-Mendez and J.M. Pfab, 'Magnetostrictive Readout for 'Wire Spark Chambers', Nuclear Instruments and Methods 33, 1965, pp. 141-146. [136] V. Perez-Mendez, 'The Application of High Energy Physics Techniques in Medical Research', IEEE Transactions on Nuclear Science 23, 1976, pp. 1334-1343. [137] A. Pickering, Constructing Quarks (Chicago: The University of Chicago Press, 1984). [138] P. Preiswerk, 'Introduction', in ref. [156], pp. 1-2. a] G.E. Pugh, D.H. Frisch and R. Gomez, 'Efficient, Fast, Energy Sensitive Gamma-Ray Counters for Use above 50 MeV, Review of Scientific Instruments 25, 1954, 1124^1126. [139] P. Rice Evans, Spark, Streamer, Proportional and Drift Chambers (London: The Richeheu Press, 1974). [140] A. Roberts, 'A New Type of Cerenkov Detector for the Accurate Measurement of Particle Velocity and Direction', Nuclear Instruments and Methods 9, 1960, pp. 55-66. [141] A. Roberts, 'Development of the Spark Chamber: a Review', Review of Scientific Instruments 32, 1961, pp. 482-485. [142] C. Rubbia, The Time Stretcher, a Device for the Measure of the Time of the Electron Drift in Proportional Chambers, CERN NP Internal Report 73-1, February 1973. [143] C. Rubbia, New Electronics for Drift Chambers, CERN NP Internal Report 75-10, 1975. [144] E. Rutherford and H. Geiger, 'An Electrical Method of Counting the Number of a-Particles from Radioactive Substances', Royal Society Proceedings 81, 1908, pp. 141-161.

References

621

[145] J. Saudinos, 'High Resolution Nuclear Spectroscopy with the Satume Cyclotron', Proceedings Topical Seminar on Interactions of Elementary Particles with Nuclei, Trieste September 1970 (INFN, Trieste). [146] J. Saudinos, 'Operation of Large Drift Length Chambers', in ref. [87], pp. 316-317. [147] J. Saudinos, J.C. Duchazeaubeneix, C. Laspalles et R. Chaminade, 'Localisation de particules par compteur a migration', Nuclear Instruments and Methods 111, 1973, pp. 77-81. [148] F. SauU, Principles of Operation of Multiwire Proportional and Drift Chambers, Cern 77-09, 3 May 1977. [149] F. Sauli, 'Limiting Accuracies in Multiwire Proportional and Drift Chambers', Nuclear Instruments and Methods 156, 1978, pp. 147-157. [150] F. Sauh, 'New Developments in Gaseous Detectors' in ref. [83], pp. 301-350. [151] F. Sauli, 'Le camere proporzionali multifili: un potente strumento per la ricerca applicata', II Nuovo Saggiatore 2, 1986, pp. 26-^2. [152] P. Schilly, P. Steffen, J. Steinberger, T. Trippe, F. Vannucci, H. Wahl, K. Kleinknecht and V. Liith, 'Construction and Performance of Large Multiwire Proportional Chambers', Nuclear Instrimients and Methods 91, 1971, pp. 221-230. [153] J. Seguinot and T, Ypsilantis, 'Photo-Ionization and Cerenkov Ring Imaging', Nuclear Instnmients and Methods 142, 1977, pp. 377-391. [154] J. Seguinot, Les compteurs Cerenkov: applications et limites pour I'identification des particules. Developpements et perspective, CERN-EP/89-92, LPC/89-25, Juillet 1989. [155] J. Seguinot and T. Ypsilantis, Ring Imaging Cerenkov Counters, CERN-LAA/PI/91-004, March 1991. [156] Proceedings of the Informal Meeting on Film-less Spark Chamber Techniques and Associated Computer Use, 3-6 March 1964 (Geneva: CERN 64^30, 1964). [157] G. Taubes, Nobel Dreams - Power, Deceit, and the Ultimate Experiment (New York: Random House, 1986). [158] T. Trippe, Minimimi Tension Requirement for Charpak Chamber Wires, CERN NP Internal Report 6918, 1969. [159] C. Verkerk, 'Concluding Remarks', in ref. [128], pp. 395-404. [160] I. Veress and A. Montvai, 'Survey on Multiwire Proportional Chambers', Proceedings of the Wire Chamber Conference, Vienna, 14-16 February 1978, Nuclear Instruments and Methods 156, 1978, pp. 73-80. [161] Proceedings of the International Symposium on Nuclear Electronics, Versailles, September 1968. [162] H. Verweji, 'Some Remarks on Electronics for Drift Chambers', in ref. [87], pp. 616-621. [163] H. Verweij, 'Electronics for Drift Chambers', IEEE Transactions on Nuclear Science 22,1975, pp. 437-440. [164] A.H. Walenta, Diplomarbeit (I.PhysikaHsches Institut of the University of Heidelberg, 1969). [165] A.H. Walenta, J. Hientze and B. Schurlein, 'The Multiwire Drift Chamber, a New Type of Proportional Wire Chamber', Nuclear Instruments and Methods 92, 1971, pp. 373-380. [166] A.H. Walenta, 'A System of Large Multiwire Drift Chambers', Nuclear Instruments and Methods 111, 1973, pp. 467-475. [167] A.H. Walenta, 'Operation and Further Development of Large Area Drift Chambers', m ref. [87], pp. 264267. [168] K. Winter, A Summary of Discussions on a Large Magnetic Analysis System of ISR Reactions, CERN NP Internal Report 69-2, 14 February 1969. [169] B. Zipprich, 'Uber einen Proportionalverstarker zum Nachweis einzelner Korpuskularteilchen' Zeitschrift fur Physik 85, 1933, pp. 592-617.

This Page Intentionally Left Blank

Name index Abragam, A. 196, 206, 289 Abrahamsen, E. 281 Abramowicz, H. 47(M71 Abrams, G.S. 162, 164^165, 168 Abrams, R. 166 Acad, C.R. 412 Achinstein, P. 272 Acker, H.L. 406 Adams, J.B. 8-10, 23, 27-28, 35, 79-96, 153, 173, 202-204, 220,225-226,228-231,233-237,243-250, 255, 375, 393-394, 446, 480-482, 502, 514, 526, 554 Adams, M. 618 Adelberger, E.G. 413 Adler, K. 281 Adler, S. 299-300,311 Aysto, J. 411 Aguilar-Benitez, M. 613 Aigrain, P. 95-96 Akesson, T. 619 Akulov, V.P. 318 Albajar, C. 469,472 Albright, C.H. 316, 325 Albrow, M.G. 156, 161, 164, 227-228, 246, 248, 334,411,613,619 Alessandrini, V. 321, 326 Alexander, G. 472 Alff-Steinberger, C. 472 AUaby, J.V. 89, 165, 615, 470 AUardyce, B.W. 407, 409, 412 AUasia, D. 470 Allen, R.C. 470 Allison, J. 205 Allison, W.W.M. 610, 613-614 Almen, O. 408 Almehed, S. 619 Almeida, S. 614 Almon, O. 403 Alper, B. 163-164, 609, 614 Alpsten, M. 409 Alstad, J. 409

Altarelli, G. 165, 293 AlthoflF, K.W. 473 Alvarez, L. 40, 254, 272 Alvarez Gaume, L.293 Amaldi E. 10, 69, 74-76, 81-82, 93-94, 96, 375, 607, 614 Amaldi, U. 156, 162, 165, 470, 612, 614, 617 Amarel, I. 411 Amati, D. 292-293, 303, 321, 324, 326 Amato, G. 580, 609, 614 Amendolia, S.R. 162, 165 Anderson, H.L. 406-407 Anderson, Ph. 309 Andersson, G. 335, 354, 358, 366, 385, 403, 406, 408^09,411 Angelini, C. 471 Angelis, A.L.S. 163, 165, 615 Ankenbrandt, C M . 243, 250 Antony, M. 154 Appel, J.A. 168, 619 Appelqvist 409 Apsimon, R.J. 612, 614 Armbruster, P. 338, 406 Armenise, N. 470 Armenteros, R. 54, 272 Arnison, G. 472 Asboe-Hansen, P. 412 Ascoli, R. 292 Ashford, V. 166, 612, 614 Ashkin, J. 341 Astbury, A. 246, 248, 472 Astner, G. 409 Atac, M. 618 Atkinson, M. 615 Aubert, B. 162, 167, 473 Aubert, J.J. 165 Audi, G. 411 Augustin, J.-E. 162, 164-165 Autin, B. 554, 556 Azvmaa, R.E. 412

623

624

Name index

Baader, R. 407 Backe, H. 349, 407-408 Backenstoss, G. 340-342, 344,346-347, 377, 403407, 469 Baconnier, Y. 555, 558 Bagnaia, P. 472 Bain, G. 558 Bakker, C.J. 7, 282 Baldinger, E. 341 Baldo-Ceolin, M. 429, 473 Baltay, C. 472 Banner, M. 163, 165-166, 227, 238, 248, 472, 609, 614 Bannier, J. 10, 72-73, 94, 109, 111, 157 Barbalat, O. 247,558 Barbaro-Galtieri, A. 472 Barbiellini, G. 617 Barbier, M. 554^555 Barbieri, R. 326 Bardakci, K. 321,326 Bardeen, W.A. 316, 325 Barish, B.C. 471 Baroncelli, A. 617 Barr, G.D. 472 Bartel, W. 165, 470, 606 Bassampierre, G. 165, 614 Bastin, A. 618 Battiston, M. 248 Bauer, D. 614 Baugh, D.J. 177, 202-203, 205 Bayard, O. 557 Bayonov, B.F. 556 Beck, E. 409 Becke, U. 165 Becker, S. 411 Beer, W. 407 Beger, H. 379, 410 Bell 298, 300, 436-437, 451 Bell J.S. 293, 297, 299, 307, 311, 324^325, 437, 469, 471^72 Bell, M. 557 Bella, F. 564, 606-607, 614 Bellanger, A. 556 Bellettini, G. 155, 164-165 Bellotti, E. 167 Bemporad, C. 609, 614 Benary, O. 619 Bendali, N. 412 Bengtsson, B. 409

Bennett, J.R.J. 554 Bennett, S. 466, 472-473 Benvenuti, A. 469, 471 Berge, P. 471 Bergstrom, I. 332, 377, 397-398, 403, 405 Berley D. 217 Berman, S.M. 163, 165 Bemabeu, J. 351 Bernard, B.S. 257 Bernard, P. 557 Bemardini, C. 555 Bemardini, G. 423, 469, 471 Bemas 354,357,383,404 Berastein, J. 451, 472 Berthelot, A. 43^5, 62, 180, 202 Bertholet, R. 410 Bertin, A. 242, 407 Bertocchi, L. 303, 324 BertoUoto, R. 557 Bertrand, G.H. 166-167 Beusch,W. 609,614 Beyer, H.J. 411 Biancastelli, R. 165, 617 Bianchi-Streit, M. 558 Bienlein, J.K. 471 Bienz, T. 614 Biggs, P.J. 165 Bilenky, S.M. 473 Billan, J. 556 Billinge, R. 233, 239-240, 242, 247-250, 554, 556 Binon, F. 407 Bird, F. 614 Bishop, G.R. 281 Bizzari, U. 555 Bjerge, T. 413 Bjorken, J.D. 138, 161, 165-166, 439, 471 Bjorastad, T. 411-412 Blackburae, N. 558 Blair, W. 196 Blanc-Lapierre, A. 93 Blankenbecler, R. 169 Blaser, J.P. 376, 393, 396, 409 Blechschmidt, D. 554 Bleeker, J. 558 Blewett, J.P. 556 Blewett, M.H. 159, 480, 554 Blieden, H. 607,614 Blobel, V. 617 Bloch, F. 7,289

Name index Bloch, P. 619-620 Block, M.M. 469, 471 Blomqvist, J. 351 Bloom, E.D. 161, 166 Blum, W. 606,611 Blume, S. 273 Blumenfeld, BJ. 165-166, 615 Blimienfeld, P. 616 Blythe, F. 404 Boal, D.H. 410 Bobyr, V. 407 Bock, R. 411 Bodek, A. 471 Boehm, F. 407 Boggild, H. 72, 164, 614 Bogh, E. 408 Bogoliubov 284 Bohr, Aa. 281, 283, 335, 336, 403, 406 Bohr, N. 161, 279-281, 294, 335-336, BoUen, G. 411 Bonaudi, F. 131, 156, 159, 212, 218, 220, 227-228, 231, 244^250, 273, 609-610 Bondorf, J.P. 410 Bonetti, S. 167 Bonn, J. 409 Booth, P. 164, 614 Borchert, G.L. 412 Bore, C. 558 Borer, J. 556 Borge, M.J.G. 412 Borgenthun, E. 409 Borgia, B. 617 Bos, K. 411,617 Boschitz, E.T. 378, 404 Bosio, C. 165, 617 Bossart, R. 556-557 Bosser, J. 556 Bossetti, P.C. 471 Botner, O. 613-614, 618-619 Bott-Bodenhausen, M. 469, 472, 610, 614 Botterill, D.R. 473 Bouchiat, C. 310-311, 313, 325 Bouchiat, M.A. 470 Boucher, R. 166, 608, 610, 614^15, 618 Bourdinau, E. 616 Bourquin, M. 473 Boussard, D. 557 Bovet, C. 555, 558 Bowcock, J. 292,303,324

Boyarsky, A.M. 164^165, 168 Boyer, M. 206 Bruckner, A. 555 Brabham, P. 243,554-557 Braccini, P.L. 165 Bradaschia, C. 165 Brand, C. 613-614 Brandt, R. 403 Braun, E. 609, 614 Braun-Mimzinger, P. 410 Bregman, M. 247 Brehin, S. 620 Breidenbach, M. 161, 164-166, 168 Breskin, A. 611-612,615 Bressani, T. 166,611,615,617 Breugel, H.V. 557 Brewer, J.H. 350, 408 Brianti, G. 9, 233, 357, 370, 403, 412 Briggs, D. 164-165 Brisson, V. 166-167 Brix, P. 341-342, 406 Brodsky, S. 169 Bromberg, C. 163, 166 Bromley, D.A. 381, 398-399, 405, 411 Brooks, C.B. 613-614 Bros, J. 302-303,324 Brostrom, K.J. 413 Brout, R. 309 Brown, B.C. 168, 619, 250 Brown, C. 618 Brown, C.N. 168 Brown, L.M. 272,615 Brown, R. 556 Brown, R.C.A. 614 Brown, S.C. 606, 615 Bryant, P.J. 555-556 Bucci, C. 350 Buchinger, F. 412 Bud, R. 273 Budde, R. 558 Budker, G.I. 215, 243, 499-501, 555 Budker, G.I. 243, 499, 555 Buenerd, M. 410 Biisser, F.W. 166, 609, 615, 617 Biittgenbach, S. 411^12 Bullock, F.W. 167 Bulos, F. 164-165, 168, 614 Bunch, J.H. 613^14 Buras, A.J. 317,325

625

626

Name index

Burckhart, D. 618-619 Burger, A. 272 Burger, J. 165 Burhop 63 Burkert, V. 618-619 Burkhardt, H. 469 Bumod, L. 556 Busse, W. 555 Cabibbo, N. 291-292, 296, 297, 324, 397, 472-473, 443, 46(M61, 467 Caesar 246 Cahn, R.N. 161, 166 Caianiello, E.R. 280-281 Caillaiu, R. 558 Caldwell, D.O. 614 Callan, C. 300 Camilleri, L. 156, 163-166, 227, 238, 248, 554, 611612, 615 Camplan, J. 359, 408 Capone, A. 617 Cappi, R. 556 Carboni, G. 407 Cans, L. 557 Carlen, L. 410 Carlson 301 Came, A. 554 Carpenter, B.E. 558 Carraz, L.C. 412 Carre, M. 411 Carroll, J.L. 164 Carroll, L.J. 614 Carron, G. 243, 555 Carter, A.L. 407 Carter, J.R. 470 Castaldi, R. 165 Cavallari, G. 557 Cavalli, D. 167 Cavalli-Sforza, M. 169, 614 Cavasinni, V. 165 Cemigoi, C. 340, 404 Cemy, J. 411 Cerri, C. 165 Cerulus, F. 292 Cheze, J.B. 166 Chaminade, R. 611, 615, 621 Chan, H.M. 326 Chanda, R. 406 Chapin, T.J. 165, 615 Charalambus, S. 406-407

Charpak, G. 133, 159-160, 166, 340, 388, 403, 455, 560, 564, 568, 570, 572, 574, 586-587, 591-593, 595-596, 600-618 Chaumont, J. 411 Chavanne, A. 10, 72, 82 Chen, M. 165 Cheng, D.C. 611,617 Chernyakin, A.D. 556 Chesi, E. 614 Chew, G. 301 Chiavassa, E. 611,617 Chiaveri, E. 557 Childress, S. 618 Chinowsky, W. 164^165, 168 ChoUet, J.C. 472 Chounet, L.M. 167, 466, 473 Christenson, J.H. 161, 166, 450, 469, 472 Citron, A. 95 CittoHn, S. 263 Cleymans, J. 325 Cline, D. 215, 217, 224^225, 230-231, 237, 240, 243-245, 250, 255, 420^21, 446, 469, 471, 555 Cnops, A.M. 167, 472 Cobb, J. 613,617 Cobb, J.H. 167 Cobb, J.L 613^14 Coc, A. 411 Cocconi, G. 128, 131, 159-160, 165, 188, 609-610, 617 Cockerill, D. 619 Cohen, Y. 35 Coignet, G. 614 Coisson, R. 556 Coll, R.L. 615 Collins, H.M. 93 Collins, P. 166 Collins, T.L. 243 Consigny, E. 557 Conta, C. 167, 169 Conversi, M.M. 565, 607, 617 Cool, R.L. 165-166, 615 Coosemand, W. 558 Corazza, G.F. 555 Coremans, G.H.B. 166 Cork, B. 202 Cornwall, J.M. 311 Coryell, C D . 334 Costa, G. 470 Costa, S. 617

Name index Courant, E.D. 553 Courant, H. 460 Cousinier, G. 558 Coutrakon, G. 618 Coward, D.H. 166 Cox, C.R. 407 Coyne, D. 614 Cozzens, S.E. 273 Craigie 162, 166 Cranshaw, T.E. 565, 607, 617 Crawford, E. 273 Cremmer, E. 314^315, 320, 322, 326 Crittenden, J. 618 Croissiaux, M. 165, 614 Cronin, J.W. 450-451, 454, 469, 472 Crowe, K.M. 350,407^08 Crowley-Milling, M.C. 37, 215, 233, 245, 247, 447, 558 Crozon, M. 161-162, 164, 166, 206, 607, 617 Cundy, D.C. 166-167, 470 Cunitz, H. 609,615,617 Cuperus, J. 557 Curci, G. 325 D'Amico, E. 556 D'Amigo, E. 556 D'Andrea 157 Dagan, S. 614, 619 Dahl, O. 480,554 Dahl-Jensen, E. 619 Dahsen, I. 619 Dakin, J.T. 165 Dallman, D. 24, 273 Daly, P.J. 412 Dam, P. 619 Damgaard, G. 164, 614, 619 Damy de Souza Santos, M. 617 Danby, G. 471,607,617 Daneels, A. 558 Daniel, H. 406-^07 Damulat, P. 156, 161, 163, 166, 210, 212, 237, 227, 238, 242, 248, 254, 272, 447-448, P. 469, 609, 612, 617 Daum, C. 406 Davenport, M. 614 Davies, J.A. 408 Davies, P. 274 Davis, D.G. 607, 617 de Benedetti, C. 206 de Benedetti, S. 341

627

de Bouard, X. 469 de Chambrier, G. 407 de Gaulle, Ch. 33-34 de Jong, M.J. 557 de Notaristefani, F. 617 deRaad, B. 234,555,558 de Raedt, J. 407 de Saint Simon, M. 411 de Wit, S.A. 406 deWitt, B.S. 310 de-Shalit, A. 331 deBeer, J.F. 565, 607, 617, Deden, H. 161, 166 Degrange, B. 167 Degrange, D. 166 Dekkers, D. 469 del Papa, C. 165, 615 della Negra, M. 257 della Porta, P. 557 Dellacasa, G. 617 Delznero, R. 166 Denegri, D. 469 Deponmiier, P. 469 Derrick, M. 167 de Rujula, A. 293 Deser, S. 319, 326 Dessagne, P. 412 d'Espagnat, B. 281, 289-293, 296, 324 deStaebler, H.H. 166 Detraz, C. 411-412 Deutsch, J.P. 349, 404, 408 Devaux, B. 619-620 di Leila, L. 145, 152, 156, 160-163, 166-167, 210211, 227, 238, 248, 447, 472, 615 Diakonou, M. 164, 167 Diamant-Berger, A.M. 620 Dick, L. 403 Diddens, A.N. 165, 613, 617 Dieperink, J.H. 472, 608-609, 617 Dijkhuizen, H. 557 Dikansky, N.S. 243, 555 Dimcovski, Z. 165, 614-615 Dixit, M.S. 407 Dobinson, R.W. 165 Domingo, J. 393-394, 407, 412 Donnachie, A. 177, 227 Dorenbosch, J. 470-471 Dorfan, D. 472 Dorth, W. 619

628

Name index

Doughty, F. 615 Dowell, J.D. 257 Drees, J. 166 Drell, S.D. 161, 167, 303 Drell-Yan 139-140 Dresden, M. 272, 615 Duchazeaubeneix, J.C. 615-616, 621 Duclos, J. 346, 407, 469, 473 Duff, B. 165, 614 Duinker, W. 596, 615-616 Dumps, L. 614 Duong, H.T. 411^12 Dupont, J. 558 Durant, J. 36 Duteil, P. 407,620 Dwek, M.G. 557 Dydak, F. 470,619 Dyson, F. 284 Dzierba, A. 166 Fades, J. 614 Ecklund, S. 250 Eggleton, M.N. 557 Eichten, T. 161, 167, 469, 471 Einstein, A. 307, 320 Eisele, F. 618-619 Eisenhandler, E. 272 Ekspong, G. 334, 404 Ekstrom, C. 386,411^12 Ellis, J. 163, 218, 293, 316-317, 320, 325-326, 554 Ellis, S.D. 167 Elsenhans, O. 407 Ely, R.P. 472 Endt, P.M. 403 Engfer, R. 342, 349, 406^08 Engler, J. 617 Englert, F. 309 Epherre, M. 411-412 Epherre-Rey-Campagnolle, M. 412 Epstein, H. 299, 302-303, 306, 324^325 Erdal, B.R. 409 Erhan, S. 166 Ericson, P. 334 Ericson, T. 293, 306, 325, 331-333, 343-344, 351, 354, 373, 403^06 Eriksen, E. 281 Esten, M.J. 167 Evans, L. 250 Evans, P.-R. 620 Evans, R. 607,611

Evans, R.D. 615 Evans, W.M. 619 Everhart, G. 165 Ewan, G.T. 412 Faberge, T. 294 Fabiani, F. 557 Fabjan, C.W. 161, 163, 167, 606, 608^14, 617-619 Faesler, A. 470 Faessler, M. 164, 167 Faissner, H. 44, 184, 203-204, 243, 429, 433, 469471 Falk-Vairant, P. 258, 410 Fallieros, St. 280-281 Fancher, D. 612, 618 Farbre, J.-P. 558 Farioli, G. 556 Farley, F.J.M. 555 Faugeras, P.E. 556, 558 Faugier, A. 556 Favier, J. 166, 615 Fayet, P. 319 Fazzini, T. 469 Feinberg, G. 472 Feldman, D. 292 Feldman, G.J. 164^165, 168 Fender, B.F.F. 206 Ferbel, T. 618-619 Ferger, F.A. 158, 233, 245, 247 Ferioli, G. 556 Fermi, E. 286 Ferrara, S. 293, 314, 318-320, 326 Ferrario, B. 557 Ferretti, B. 294 Ferroni, F. 617 Feynman, R.P. 138, 161-163, 167, 284, 288, 308, 310, 319, 439^W0, 471, 473 Fiander, D.C. 558 Fidecaro, G. 281, 469 Fidecaro, M. 403, 406, 409 Fiebig, A. 379, 404 Field, R.D. 163, 167 Fields, T. 167 Fierz, M. 292, 294 Filatova, A.N. 611,618 Filippas, T.A. 167 Filthuth, H. 44, 48, 58, 618 Finger, M. 409 Finley, D. 618 Finocchiaro, G. 165, 453

Name index Fiorentini, G. 408 Fiorini, E. 61, 167 Fischer, H.G. 608, 610, 613 Fischer, E. 158, 167, 550, 557 Fischer, G. 614^16 Fischer, G.E. 164^165 Fischer, H. 557 Fitch, V.L. 450-453, 469, 472 Fliigge, G. 614-616 Flauger, W. 617 Flegel, W. 617 Fleischmann 62 Floratos, E.G. 317, 325 Florent, R. 42, 45, 48, 58, 62, 64 Flower, P.S. 614 Flowers, Sir B. 78, 96, 375 Foa, L. 165 Foeth, H. 611-612,614,618 FogH, G.L. 470 Foldy, L. 403 Fontaine, S.M. 615 Forsling, W. 405 Fortune, R.D. 557 Foucher, R. 366,409,411 Fourier 302 Fowler, E.G. 167 Fox, G. 166 Fox, J.A. 556-557 Frangsmyr, T. 273 Frandsen, P. 619 Fransson, K. 407 Franzinetti, C. 41, 159, 167, 471, 564, 606-607, 614 Franzini, P. 453 FraternaU, M. 169 Frautschi, S. 301 Freeston, K.A. 614 French, B. 159-160, 167 Freytag, D. 614 Friedberg, C.E. 164^165, 168 Friedberg, R. 453,472 Friedman, D. 314 Friedman, J.I. 166-167, 439 Frisch,D.H. 620 Froman, P.O. 281 Froissart, M. 302 Fronsdal, C. 292 Fryberger, D. 164-165, 168 Fubini, S. 212, 218, 226-227, 244, 292, 293, 299, 303, 324

629

Fuchs 44 Fukui, S. 565, 607, 618 Funke, G.W. 73, 81-82, 86, 94-95 Furlan, G. 299,324 Furmanski, W. 317, 325 Gabathuler, E. 247. 396 Gabathuler, K. 407 Gabioud, B. 615 Galjaev, N. 557 Gaillard, J.M. 469, 473, 617 Gaillard, M.K. 316-317, 325 Galiana, R. 373, 410 Galison, P. 36, 38, 161, 168, 201, 253, 272-273, 420, 469, 606-607, 613, 618 Gall, P.D. 617 Gallio, M. 617 Gamba, A. 280-281 Gambaro, I. 160, 262, 455 Gamble, J. 558 Gandsman, J. 167 Garcia, A. 413 Garetta, D. 615 Gareyte, J. 250 Garin, A. 616 Garren, A.A. 554 Garron, J.P. 407 Garvey, J. 607, 618 Gastaldi, U. 246,407 Gastmans, R. 316, 325 Gavaggio, R. 558 GeflFen, D. 292 Geheniau, J. 177 Geiger, H. 564, 606, 620 Geiregat, D. 470-471 Gelbke, C.-K. 410 Gelemter, H. 607, 618 Gell-Mann, M. 287-288, 290, 298, 451, 460, 466, 472-473 Gemanov, V. 617 Gentner, W. 10, 82, 95, 335, 341, 354, 366, 376,403404, 406 Genuth, J. 272 Georgi, H. 313, 317, 428, 470 Gerard, J.M. 472 Germain, C. 473, 558 Geflfen, D. 292 Germain, P. 558 Gershtein, S.S. 288 Gervais, J.L. 158, 168, 314, 317, 558

630

Name index

Geweniger, C. 472, 609, 618-619 Ghigo, G. 555 Giacomelli, G. 162, 168 Giannelli, G. 607, 618 Giannini, R. 373 Gibbard, G. 617 Gibson, M.D. 619 Gilgrass, A. 614 Gillet, V. 405 Gilly, L. 407 Giovanetti, K.L. 407 Girardeau-Montaut, J.P. 407 Giromini, P. 165 Gisolf, J.H. 618 Gjesdal 609 Gjesdal, S. 609,618 Gladding, G. 166, 615 Glaser, D. 254 Glaser, V. 292-293, 302-303, 305-306, 324-325 Glashow, S.L. 162, 168, 209, 308-310, 313, 317, 418, 424, 428, 433, 443, 470-471 Glass, H. 612, 618 Gleditsch, E. 334 Gliozzi, F. 322, 326 Goddard, P. 321-322, 326 Goebel, CJ. 321 Goebel, K. 406 Goffee, R. 274 Goggi, G. 156, 163, 169 Goldberg, H. 166 Goldberger, M. 287, 297 Gol'fand, Yu.A. 317 Goldhaber, G. 140-141, 161, 164^166, 168, 288 Goldhagen, P. 165 Goldschmidt-Clermont, Y. 184, 190-191, 201, 203205, 272, 379, 413 Goldsmith, M. 95-96, 554 Goldstone, J. 297, 309, 322, 326 Gomez, R. 166, 620 Goni, J. 557 Gordon, H. 612, 614, 618-619 Gorini, G. 407 Gom, W. 618 Gorres, J. 407 Gottfried, Ch. 616 Gottfried, K. 403, 437, 471 Gottstein 62 Gouanere, M. 407 Goudsmit, P.F.A. 407

Goulianos, K. 617 Gourber, J.P. 246,556 Goure 62 Goward, F. 479 Gozzini, A. 565, 607, 617 Grannis, P. 165 Gray, D.A. 554 Gray, R. 618 Green, D. 165 Green, M. 315 Green, M.A. 244 Gregory, B. 7-10, 36, 41^2, 45-46, 48-64, 81-82, 88-89, 93-96, 116, 133, 157, 159-160, 172, 220, 333609-610 Gregory, J. 36 Grenacs, L. 408 Gresser, J. 165, 614 Grier, D. 558 Grigoriev, E. 617 Grimm, M. 619 Grimm, P. 410 Gross, D.J. 300, 312, 324, 440, 471 Grosse, E. 380, 410 Grosse, H. 317, 325 Grote, H. 617 Gruhn, C.R. 614, 616 Grunder, H. 240 Guerriero 61 Guet, C. 410 Guignard, G. 556 Guillemaud-Mueller, D. 412 Gunn, J.C. 177, 190, 193, 202-205 Gurr, H. 470 Gygax, F.N. 408 Haag, R. 280-281, 284, 288, 324 Haas, H. 412 Haebel, E. 557 Hagberg, E. 409,412 Hagebo, E. 360, 408^09, 411 Hagedorn R. 292-293, 293, 303, 325 Haggerty, H. 166 Hagstrom, W.O. 272, 274 Haguenauer, M. 166-167 Hahn, B. 375 Hahn, O. 334 Haidt, D. 166-167, 470 Haissinsky, J. 334 Haissinsky, M. 406 Hallewell, G.D. 614

Name index Hallgren, A. 619 Hallgren, B. 274 Hamel, J.L. 165-166 Hamilton, J.H. 388, 390,411 Hammarstrom , R. 618 Hampton, G.H. 49, 62-63, 82, 93-95, 108-109, 111, 157, 108-111, 157,205, 375 Handler, P. 184 Hannaway, O. 272 Hansen, K.H. 164, 614, 619 Hansen, P.G. 36-37, 334, 379, 381, 396, 404^12, 496 Hansen, S. 557 Hanson, G. 163-165, 168 Harari, H. 168 Hardt, W.E.K. 556 Hardy, J.C 391,412 Harfield, R. 615 Hargrove, C.K. 407 Harnel, J.L. 614 Harold, M.R. 554 Harris, M. 619 Hartill, D.L. 168 Harting, D. 176-177, 193, 201-203, 281 Hartman, G.C. 166 Hartmann, O. 350 Hasert, F.J. 166, 167 Hassam, T. 167 Haunschild, H.H. 82 Healey, P. 273 Heard, K.S. 611,619 Heck, B. 619 Hecken, R. 404 Heckwolf, H. 410 Hedin, B. 373, 406 Hegel, U. 406 Heine, P. 617 Heinemeier, J. 412 Heinrichs, H. 557 Heintze J. 461, 469, 473, 595, 610-612, 619 Heinzelmann, G. 619 Heisenberg, W. 44, 78, 286, 294^295 Hemmery, J.Y. 558 Hemmi, Y. 618 Henck, R. 409 Henley, E.M. 292 Henrichsen, K.N. 556-557 Hepp, K. 284 Hepp, V. 619

631

Herb, S.W. 162, 164, 168, 619 Hereward, H.G. 243, 554^556, 558 Herin, S. 557 Hermann, A. 35-36, 61-62, 64, 93-95, 168, 200, 205, 242-243, 272, 274, 405, 558, 607, 619 Herrlander, C.J. 405 Herrmann, G. 335, 360 Herz, A.J. 377, 403, 405^06, 410 Hesse, K. 407 Heusse, P. 167 Hevly, B. 36 Heyde, W. 619 Heymann, F.F. 159, 165, 614 Hicks, G.S. 166 Hiddleston, J. 619 Hientze, J. 621 Higgs, P. 309 Hijkhuisen, H. 557 Hilaire, A. 556 Hilke, H.J. 614, 618 Hilke, J.H. 619 Hill, C. 404 Hincks, E.P. 406-^07 Hine, M.G.N. 42, 61, 64, 94^95, 128, 158, 168, 177, 185-189, 202-205,493, 550, 554, 558, 568-569, 579, 607, 609, 619 Hirsbrunner, J.J. 557 Hirsch, R. 58 Hoddeson, L. 242-244, 272, 615 Hoglund, A. 409 Hofer, H. 375, 378, 404 Hoflf, P. 411 Hoffmann, A. 554, 556 Hoffmann, H. 262, 608 Hogaasen 194 Hogue, R. 618-619 Hohbach, R. 379, 404, 410 Holder, M. 205-206, 470-472, 613, 619 HoUebeek, R.J. 164^165, 615 Holmen, G. 411 Holton, G. 272 Hom, D.C. 168, 619 Hong-Mo, C. 321 Hood, D.W. 167 Hoogeweegen, C.E.I.M. 109 Hooper, J. 280-281, 619 Horn, D. 161, 168 Hornsh0j, P. 409, 412 Hsiung, Y. 618

632

Name index

Hubbard, J.R. 618 Ruber, G. 409,411-412 Huck, A. 412 Hudis, J. 409 Hiibner, K. 168, 242-243, 554^556 Htifner, J. 344, 407 Hugenholtz, N.M. 281 Hugon, L. 407 Huson, R. 239, 243-245, 250 Husson, J.P. 409 Hutton, A.M. 554, 556 Hyams, B. 160, 168, 469, 609 Igo-Kemenes, P. 619 Ijspert, I. 557 Iliopoulos, J. 162, 168, 209, 325-326, 424, 443, 470471 Indreas, G. 557 Ingram, C.H.Q. 407 Innes, W.R. 168, 619 Innocenti, P.G. 557, 587, 610, 614 lofTe, B.L. 310 Iselin, F.C. 555, 614 Ito, A.S. 168, 618-619 Iwata, S. 167, 617 Jackiw, R. 299-300, 311, 324 Jackson, J.N. 164, 614 Jacob, M. 35, 37, 151, 154, 156-157, 161-165, 168, 218,227,243,247,248,293,472, 609-610, 612-613, 619 Jacobs, D. 614 Jacobson, E. 281 Jacquinot, P. 411-412 Jaffe, D. 618 Jaffre, M. 166-167 Jahnke, U. 407 Jahnsen, T. 409 Jakobssson, B. 410 Jaksic, B. 292 James, F.A.J.L. 93,273 Jane, J.M.R. 472 Jankovc, Z. 280,-281 Jarlskog, C. 164, 316, 325, 614, 619 Jastrzebski, J. 409,411 Jauch, J.M. 292, 294 Jauneau, L. 167 Jean, M. 407 Jean-Marie, B. 164, 165, 168 Jeckelmann, B. 407 Jeffreys, P. 614, 619

Jenkins, D.A. 407 Jensen, H.B. 167, 167, 618 Jensen, J.H.D. 336 Jentschke, W. 9-10, 37,44,46-^9, 52, 55-56, 62, 64, 75, 95, 128, 159, 172, 178-179, 200, 202-204, 211, 225, 242, 245, 374, 376-377, 404, 431, 609-610, 617-618, 621 Jostlein, H. 168 Johansson 380, 410 Johnsen, K. 8, 24, 35, 37, 112, 114, 116-117, 120, 124^126,155,156,158-159,164,168-169,210, 211, 212, 242, 305, 525, 554^556, 609-610, 619 Johnson, A. 409,411 Johnson, C D . 556 Johnson, C.S. 406 Johnson, R. 614 Johnson, R.P. 243, 250 Johnston, R. 292 Jonckheere, A. 618 Jones, E. 554-557, 586 Jones, G. 407 Jones, T.W. 167 Jonker, M. 470^71, 617 Jonson, B. 381, 391, 396, 403^04, 409, 411-412 Jonsson, L. 164, 614 Jordan, B. 469 Jostlein, H. 618-619 Juhala, R. 166 Julia, B. 314 Julien, J. 410 Juncar, P. 411^12 Kabe, S. 167 Kadyk, J.A. 164^165, 168 Kaftanov, V. 617 Kalbreier, W. 619 Kallen, A.O.G. 281 Kamae, T. 618 Kamber, I. 557 Kanellopoulos, Th. 292, 306, 325 Kankeleit, E. 407^08 Kantardijan, G. 242, 555, 619 Kaplan, D.M. 168, 618-619 Kaplan, N. 272 Karasyuc, V.N. 556 Karlsson, E. 350, 408 Karvinen, A.O.T. 410 Kasha, H. 166 Kastler, A. 367 Kaufman, S.L. 388,411

Name index Keil, E. 169, 493, 554^557 Kemp, D. 558 Kemp, M.A.R. 205 Kendall, H.W. 161, 166-167, 439 Kephart, R.D. 168, 619 Kem, F. 411 Kesseler, G. 614, 619 Kessler, D. 407 KeuflFel, J.W. 564, 606-607, 619 Keyser, R. 558 Khovansky, V. 617 Kibble, T.W.B. 309 Kienle, P. 405 Killian, T. 618-619 Kim, J.E. 470 Kinoshita, T. 308 Kirk, W.T. 471 Kirsten, F.A. 607,619-620 Kirz, J. 618 Kislinger, M.B. 163, 167 Kissler, H.K. 558 Kistemaker, J. 403 Kjelberg, A. 335, 356, 360, 363, 403, 408^09 Klapisch, R. 334, 379, 396-398, 411^12 Klein, O. 308 Klein, W. 292 Kleinheinz, P. 412 Kleinknecht, K. 338, 469, 472-473, 608-610, 612613, 617-619, 621 Kleinpoppen, H. 411 Klemperer, S. 554 Klempt, W. 412 Klotz, G. 412 Klovning, A. 164, 614 Kluberg, L. 166-167 Kluge, HJ. 411 Knipper, A. 412 Knobloch,J. 619 Knop, G. 469 Kobayashi, M. 456, 461, 467, 472-473 Koch, H. 406-407 Koch, J. 408 Kopf, U. 409 Kofoed-Hansen, O. 334, 352-353, 373-374, 376, 404, 408, 410 Kogut, J. 161, 165, 169 Kohler, S. 292 Kopfermann, H. 341, 406 Kotov, V. 557

633

Kounnas, C. 320, 326 Kourkoumelis, C. 167, 617 Koutchouk, J.P. 558 Kowarski, L. 204, 272-273 Kozanecki, W.A. 617 Koziol, H. 518, 555-557 Kroger, B. 617 Kramers, H. 287 Kratz, K.-L. 412 Krenz, W. 166-167 Krienen, F. 160, 167, 555, 577, 607, 609 Krige, J. 35-36, 38, 61, 93-94, 156-160, 162-163, 168-169, 200, 205-206, 242, 274, 403-558, 608, 619 Kristiansson, P. 410 Kropac, W. 166 Kudelainen, V.I. 243, 555 Kiindig, W. 408 Kugler, E. 383-385, 411^12 Kugler, H. 409 Kugler, L. 409 Kuhn, H.K. 557 Kuhn, T.S. 162, 169 Kuiper, B. 557 Kummer, W. 82 Kurosawa 278 Kuti, J. 161, 169 Laeger, H. 556 Lagarrigue, A. 40-42, 4 4 ^ 5 , 51-52, 54, 61, 63, 421 Lagarrigue, P. 418 Lahanas, A.B. 326 Lamb, W.E. 283,411 Lambertson, G.R. 558 LandshoflF, P.V. 163, 168 Lang, A. 614 Langacker, P. 470 Langevin, M. 412 Lankford, A.J. 617 Lanske, D. 166 LapostoUe, P. 373, 403 Larsen, R.R. 164-165, 168 Larsson, P.O. 412 Laspalles, C. 615, 621 Laurelli, P. 165 Lautrup, B. 316, 325 Laverriere, G. 619 Lawson, J.D. 554 Layter, J. 618 Lazard, D. 557 Lazeyras, P. 557, 614

634

Name index

Le Bellac, M. 326 Lebrun, Ph. 556 Lederman, L.M. 139-141, 144-145, 152, 161-162, 165-169, 220, 23, 240, 243, 250, 433, 473, 560, 566, 580, 607, 609-610, 615-619 Lee, T.D. 288, 297, 302, 432, 453, 470, 472 Lee, W. 469 Lee, Y.Y. 165 Lefebvres, F. 614 Lefevre, P. 556 Lehmann, J. 408 Lehmann, P. 10 Lehr, G. 64 Leisi, H.J. 407 Leistam, L. 164, 614 Leith, D. 614 Lengeler, H. 557 Leo, W.R. 612, 619 Leong, J. 165 Leontic, B. 620 Leprince-Ringuet, L. 41-42, 289, 375 Leraie, J. 411 Leroux, J. 557 Leschevin, C. 620 Leutwyler, H. 325 Leutz, H. 613 Levaux, P. 10 Levin, D.N. 311 Levinthal, D.A. 165, 615 Levy-Mandel, R. 58, 61-63 Liberman, S. 411-412 Likhtman, E.P. 317-318 Lillberg, J.W. 619 Lillethun, E. 159, 164^165, 607, 614, 619 Limon, P.J. 166, 243 Lindahl, A. 409 Lindb'ick, S. 373 Lindenberger, K.H. 407 Lindhard, J. 408 Lindsay, J. 167, 618-619 Linglin, D. 257, 274 Link, R. 407^08 Linnemann, J.T. 165 Lipman 202, 205 Lipnik, P. 408 Lissauer, D. 167, 619 Litke, A.M. 164, 168 Litt, J. 612,615,619 Litt, L. 166

Livdahl, P. 243 Livingston, M.S. 553 Llewellyn-Smith, C. 300, 311,316, 427^28, 44a 441, 469-471 Lloyd J.N. 613-614 Lobachov 454 Locher, M.P. 351 Lorstad, B. 619 Lohrmann, E. 246 Lohse, E. 164, 614 Loiseaux, J.M. 410 Loken, S. 618 Longo, E. 617 Longuemare, C. 167 Lorenz, E. 166 Lovelace, C. 321-326 Lovseth, J. 436, 469, 471 Lu, A. 614 Lubatti, J.H. 619 Ludlam, T. 163, 167, 618-619 Luders, G. 281, 285, 288, 324 Liike, D. 168 Luth, V. 164-165, 168, 617-619, 621 Lulu, B.A. 164-165, 168 Lunby, A. 620 Lundquist, S. 405 Lurie, D. 292 Lutz, A.M. 167 Lynch, G. 164, 614 Lynch, H.L. 164^165, 168 Lynn, J.E. 403^04, 409 Lyon, D. 164^165 Lyons, L. 165, 615 Muhl, D. 556 Mac Donald, S. 609,614 Macq, P.C. 340, 349, 408 Madame Curie 334 Maglic, B.C. 567, 607, 614, 619-620 Magnani, L. 555 Magnus, P.V. 413 Maiani, L. 162, 310, 424, 443, 472, 615 Maidment, J.R. 554 Maier, M.R. 412 Maier-Leibnitz, H. 78 Maillard, J. 619-620 Majewski, S. 573, 601, 603, 608, 615-616, 620 Maki, A. 618 Malamud, E. 166 Malavard, L. 95

Name index Malbequi, Y. 619-620 Malcor, A. 63 Malmskog, S.G. 409 Mandelstam, S. 301, 303 Mandrillon, P. 410 Manfrass, K. 35 Mangeot, Ph. 618 Mann, J. 421, 556 Mannelli, I. 61, 167 Mansoulie, B. 472 Mantovani, G.C. 164, 169 Marciano, W. 169 Marel, G. 611,619-620 Margulies, S. 166 Marin, P.C. 159, 469 Marshak, R.E. 288, 473 Marti, Y. 555 Martin, A. 82, 157, 292-293, 301-303, 305, 317, 324^325 Martin, H. 620 Martin, P. 410, 618 Martucci, P. 558 Marx, J.N. 612,618,620 Maskawa, T. 456, 467, 461, 472-473 Massam, T. 164 Matthews 284 Matthiae, G. 165 Mattsson, S. 412 Matzmacher, K.D. 558 Maurel, M. 410 Maurin, G. 263, 614 May, J. 619 Mayer, M.G. 336 Mayer-Kuckuk, T. 325, 405 McCarthy, R. 618 McCorriston, T. 165 McCubbin, N.A. 619 Mclntyre, P. 215, 217, 243-244, 420, 446, 469, 471, 555 McKee, R.J. 407 McKenzie, J. 167 McLeod, D. 166 McShurley, D. 614 Meadows, B. 614 Medinnes, M. 166 Meier, P.P. 408 Melchart, G. 603, 615-616 Melin, A. 619 Melissinos, A.C. 614

635

Mellon, A.W. 201, 272 Melville, Sir Harry 110 Menzione, A. 165 Meot, F. 556 Mermod, R. 466, 469 Merrison, A.W. 469 Mersits, U. 35-37, 61, 93-94, 168, 200, 242, 272, 274, 329, 405-406, 558, 607, 619 Mes, H. 407 Meshkov, I.N. 243,555 Mess, K.H. 617 Messiah, A. 282, 557 Metag, V. 410 Metcalf, M. 617 Meunier, R. 407, 603, 612, 619-620 Meyer, J. 58, 63, 204, 617 Meyer, Ph. 292,311 MichaeUs, E.G. 340, 356, 370, 373-374, 376-378, 403-404,408^10 Michaelsen, R. 407-408 Michel, L. 280-281, 286, 289 Michette, A.G. 167 Middelkoop, W.C. 158, 558 Miller, G. 166 Miller, R.H. 568, 607, 620 Mills, F. 217, 244 Mills, R.L. 308 Milner, S. 557 Milsztajn, A. 471 Minten, A. 133, 159, 169, 572, 586-587, 577, 609610, 614^16, 620 Mistry, N. 617 Mittag, E. 619 Miyake, K. 618 Miyamoto, S. 565, 607, 618 Mjornmark, U. 619 Mo, L.W. 166 Monnig, F. 617 Mohr, P.J. 344, 407 Mohr, R. 363 Mokry, P. 617 M0ller, C. 280-281, 289, 294 Moliere, 6, 292 MoUer, R. 619 Moltz, D.M. 413 Molzon, W. 167, 614, 619 MonaceUi, P. 617 Moneti, G.C. 617 Montague, B.W. 156, 554-555, 557

636

Name index

Montanet, L. 606, 613 Month 217 Montvai, A. 608, 621 Moore, R.B. 411 Morand, R. 165, 614 Morehouse, C.C. 164, 165, 168 Morfin, J. 166-167 Mori, S. 166 Morpurgo, M. 167, 184, 203-204 Morris, J.A.G. 614 Morris, J.V. 614 Morrison, D.R.O. 260, 272-274, 606 Mottelson, B.R. 281, 283, 336, 338, 405-406 Mougey, J. 410 Mouzourakis, P. 167 Mueller, A.C 411^12 Munnich, F. 409 Mukhin, A. 469 Miiller, W.J.F. 410, 564 Munzenberg, G. 338, 406 MuUer, F. 163 MuUie, J. 618 Mulvey, J.H. 181, 201-203, 211-213, 242, 247, 250 Munday, G. 396, 412 Murzin, V.S. 606, 620 Musset, A. 418 Musset, P. 61, 161, 167, 169, 469-471 Musso, A. 617 Mustard, R. 165 Myatt, G. 167, 469 Myhrer, F. 351 Nakada, T. 407 Nakamura, K. 167 Nakamura, T. 618 Nambu, Y. 297,309,322 Nanopoulos, D.V. 316, 317, 320, 325-326 Nappi, A. 167, 617 Natali, S. 166-167 Nathan, O. 405 Naumann, R.A. 409 Navarria, F.L. 619 Ne'eman, Y. 290, 298, 460, 473 Negri, P. 61 Negus, PJ. 205 Neri, G. 407 Neugart, R. 411-^12 Neveu, A. 317, 321 Newman, C. 165 Nguyen-Khac, U. 167

Niebergall, F. 473,617 Nielsen 378,403 Nielsen, B.S. 619 Nielsen, H. 321 Nielsen, H.L. 409 Nielsen, K.O. 352, 354, 356, 358, 403, 408 Nielsen, O.B. 333, 357, 379, 403-404, 409-410, 412 Nielsen, S.0. 619 Nifenecker, H. 410 Nigmanov, T.S. 618 Nilsson 340 Nilsson, A. 407, 619 Nilsson, S. 336, 338, 404, 406, 412 Nishijima, K. 287 Nixon, R. 213 Noecker, M.C. 470 Noll, H. 410 Nonte, J. 272 Noren, B. 410 Noriin, L.-O. 350 Norton, A. 273 Norton, W.W. 272 Nussbaum, M. 614 Nuttall, A. 614 Nuttall, J. 557 Nygren, D.R. 598, 610, 612, 618, 620 Nyman, G. 412 O'Neill, G.K. 133, 160, 168, 500 Oades, G. 403 Ogloblin, A.A. 411 Ohm, H. 412 Olive, D. 321-322,326 Olsen, L.H. 619 Onions, CJ. 615 Orava, R. 618 Oren, Y. 614, 619 Orr, R.S. 617 Ortoli, F. 95 Oset, E. 351 Oskarsson, A. 410 Otten, E.W. 366, 375, 388, 404, 409, 412 Otto, Th. 411 Paar, H. 619 Pagels, H. 169 Pahud, J.-D. 557 Pais, A. 287, 290, 451, 466, 472 Palazzi, P. 619 Palladino,V. 611,620 Palmer, R.B. 167, 617

Name index Panighini, A. 617 Panman, J. 617 Pansart, J.P. 165-166, 614 Pappas, A.C. 332, 334-335, 354, 376, 403, 405-406, 409 Parasiuk 284 Parchomchuk, V.V. 243, 555 Pascal 63 Pascaud, C. 167 Paschos, E.A. 161, 166 Pastore, F. 156, 169 Paterson, C.N. 614 Paterson, J.M. 164-165, 168 Patoux, A. 620 Pattison, J.B.M. 166-167 Patzelt, P. 360, 408^09 Paul, H. 469 Paul, W. 44, 58, 77-78, 187, 197, 205-206, 308, 333, 403 Pauli, W 300 Peak, L.S. 614 Pearce, R.M. 407 Pedroni, E. 407 Peigneux, J.P. 407 Peisert, A. 618 Pelle, J. 620 Penionzhkevich, Yu.E. 411 Penney, R.W. 280 Pentz, H. 555 Pentz, M.J. 555, 557 Peoples Jr, J. 243, 272 Percival, P.W. 408 Perez-Mendez, V. 607, 612, 620 Perin, R. 556 Perkins, D.H. 64, 166-167, 436-^37, 440, 469, 471 Perl, M.L. 164^165, 168 Peron, F. 558 Perrin,F. 10, 4 1 - 42, 45-50, 52, 55-56, 58, 62, 69, 76, 81-82, 93, 125, 431 Perrin, P. 410 Perring, J.K. 472 Pemolat, F. 558 Peschardt, E. 556 Pesnelle, A. 411^12 Pestre, D. 35-37, 38, 61, 93-94, 156-157, 159, 161, 168-169,200-204,206,242-243,271-274, 309, 329, 341, 379, 405-406, 481-482, 558, 619 Pestrikov, D.V. 243, 555 Petermann, A. 284, 288,292-293, 324

637

Petersen, G. 615-616 Petersen, J.D. 167 Petersen, J.O. 618 Petieau, P. 167 Petitjean, C. 349, 407^08 Petronzio, R. 317, 325 Petrucci, G. 222, 231, 247, 580, 609, 614 Peuse, B. 412 Peyaud, B. 619 Peyrou, C. 42, 44, 47-48, 56, 58, 61-62, 64, 128, 159, 609-610 Pfab, J.M. 607,620 Phinney, N. 165, 615 Picard, J. 407 Picasso, E. 127, 218, 247, 159, 410, 555, 557 Picciarelli, V. 557 Piccioni, O. 287 Piccioni, R.L. 617 Pichler, S. 556-557 Pickering, A. 157, 161-162, 169, 607, 609, 612, 620 Picketty, C.A. 470 Pierce, P. 558 Pierre, F. 164^165, 168 Pillet, P. 411 Pillier, O. 407 Pinard, J. 411-412 Pine, J. 166 Pistilli, P. 617 Pitzurra, O. 407 Piuz, F. 167, 614, 618 Plaag, R. 618 Placci, A. 166, 407, 615 Plancoulaine, J. 620 Plass, G. 248,556-557 Plch, G. 616 Pleming, R.W. 613-614 Podolsky, B. 307 Poelz, G. 406-407 Poincare, H. 325 Polacco, E. 407 Policarpo, A. 616 Polikanov, S.M. 338 PoUmann, D. 619 Polyakov, A. 315 Pompidou, G. 86 Pope, B.G. 164^166, 218, 220-221, 244-245, 554, 615 Pordes, S.H. 165, 615 Potter, K. 156, 159-160

638

Name index

Povel, H.P. 407 Povh, B. 366,403 Powell, C.F. 95 Preiswerk, P. 188, 333, 356, 367, 405^06, 566, 607, 620 Prentice, M. 614 Prentki, J. 218, 272, 289-290, 292-293, 296-297, 310-311,316,324-325 Prescott, C.Z. 470 Presser, G. 618 Pugachevich, V.P. 618 Pugh, G.E. 338, 620 Pugin, P. 556 PuUia, A. 167 Pun, T.P. 168 Puppi, G. 81, 469, 471 Queru, P. 619 Quarrie, D. 165, 614 Querzoli, R. 555 Quinn, H. 317 Quitman, D. 406 Rabi, I.I. 127 Ragnarsson, I. 412 Rahm, D. 167,611,615 Rahmy, R. 156, 403 Raisbeck, G.M. 336, 406 Ramm, C. 52, 417, 482 Ramond, P. 317 Ramsay 454 Rander, J. 619 Ranft, J. 325 Ranitzsch, K.H. 617 Ranjard, F. 167, 618-619 Rapidis, P.A. 164-165, 168 Ratcliflf, B. 614 Rau, R. 243, 254 Ravn, H.L. 381, 383, 404, 409, 411^12 Rebbi, C. 322, 326 Reed, A.B.D. 556 Reeder, D.D. 244 Rees, G.H. 554 Regge, T. 301 Rehak, P. 167, 617 Reich, K.H. 555, 558 Reif, R. 614 Reige, H. 557 Reines, F. 470 Reithler, H. 243, 469, 471 Reitz, H. 558

Renner, B. 309 Renner, W. 558 Renuart, J. 407 Resegotti, L. 160, 556, 386 Resvanis, L.K. 167 Reucroft, S. 613, 620 Rho, M. 325 Rhoades, T.G. 165 Rhode, M. 165 Rhomig, P. 556 Riabtsov, V.D. 618 Riboni, P. 557 Richard-Serre, C. 412 Richter, A. 412 Richter, B. 140-141, 162, 164-165, 168-169, 211 212, 237, 239, 243, 443, 554, 556 Richter, D. 350 Richter, W. 557 Riedinger, M. 165, 614 Rieseberg, H. 469 Riisager, K. 403,412 Rimmer, E.M. 407 Rimoldi, A. 169 Rip, A. 273 Roberts, A. 202, 566, 612, 620 Robrish, P. 618 Rochester, L.S. 614 Rode, A. 407 Rosch, W. 410 Roglic, V. 280-281 Rohlf, J. 166 Rohlin, J. 407 Rohlin, S. 407 RoUier, M. 167 Rosanov, A. 617 Rose, S. 204 Rosen, N. 307 Rosenfeld 308, 319 Ross, D.A. 317, 325 Ross, J. 472 Rosselet, L. 619 Rossetti, C. 324 Rossetti, G. 299 Rossini, B. 169 Rosso, E. 167, 618-619 Roth, R. 472 Rothberg, J. 618 Rothenberg, A.F. 165-166, 615 Rousset, A. 37, 40, 61-62, 166-167, 418

Name index Rowe, E.M. 244 Rozental, S. 280-281, 282-283 Rubbia, C. 89, 136-137, 144, 150, 158, 161, 208, 211, 213, 215-218, 220-222, 224-225, 229-233, 236, 237-250, 254^255, 257,259, 266,273-274,420-421, 443,446-^7,449,452,456, 465, 569,471-473, 501, 555,611,617-618,620 Rubinstein, H. 305 Rudge, A. 167, 618-619 Rudstam, G. 321, 332, 335-336, 354, 360, 403, 406, 408-409 Riietschi, A. 407 Ruegg, H. 321, 326 Ruff, G.A. 411 Ruggiero, A.G. 158, 169, 240, 555 Runge, K. 617 Rusack, R.W. 165 Russo, A. 36-38, 158, 160, 162-163, 498, 535, 584, 587 Rutherford, E. 606, 620 Rutherford, Lord E. 563 Rutherford, J. 618 Ryde, H. 405 Ryuji 250 Sacherer, F. 554, 556 Sachrajda, C.T. 317, 325 Sacquin, Y. 614 Sacton, J. 166-167 Sadoulet, B. 164, 168, 218, 223, 231, 244, 247-248, 257,259,263,611,620 Sagnall, B. 558 Saint-Jalm, J.L. 412 Sakai, Y. 618 Sakata 298 Sakharov, A.D. 317 Sakita, B. 314, 317, 321 Salam, A. 144, 162, 209, 284, 290, 318, 324, 418, 433, 470 Salmeron, R. 202-203 Salvini, G. 176-177, 193-194, 202-203, 245, 259, 606 Salzman, F. 292, 303 Salzman, G. 292, 303 Samoilov, A. 557 Samuel, R.L. 158, 169 Sandvold, H. 206 Sanguinetti, G. 165 Santiard, J.C. 614^16, 618 Santoni, C. 617

639

Sasao, N. 618 Saudinos, J. 592,611,615,621 SauH, F. 573, 596, 600-601, 603, 606, 608-612, 614616, 618, 620-621 Sauvage, G. 473 Savard, G. 411 Savoy-Navarro, A. 619 Sawyer, R.F. 292 Scandale,W. 250,558 Scarf, F.C. 292 Scase, R. 274 Schiirlein, B. 619, 621 Schaffer, S. 93 Schardt, D. 412 Scharff-Hansen, P. 451 Scherk, J. 321-322, 326 Schilly, P. 608, 610, 619, 621 Schindler, R.H. 614,619 Schistad, B. 619 Schlatter, D. 619 Schlein, P. 166 Schmeissner 48, 58, 62 Schmied, H. 38, 558 Schmit, C. 407 Schmitt, H. 406-^07 Schneegans, M. 165, 614 Schneider, F. 617 Schneider, H. 617 Schnell, W. 123, 158, 169, 243, 554-557 Schneuwly, H. 407^08 Schnuriger, J.-C. 554 Schoch, A. 481, 554 Schopper, H. 155, 164, 196, 201, 204-206, 397, 404, 609-610, 617 Schorr, B. 558 Schottky 518 Schroder, A. 412 Schroder, W.U. 407^08 Schrodinger, E. 307 Schubert, K. 162, 165 SchuUer, A. 410 SchuUer, E. 614 Schult, O.W.B. 412 Schulte-Meermann, W. 63, 81, 108-109, 157 Schultz, D. 614 Schultz, G. 615 Schultze, K. 166-167, 469, 471 Schumann, M. 95 Schussler, F. 410

640

Name index

Schwaller, P. 407 Schwartz , M. 433, 453^54, 472, 560, 566, 617 Schwarz, J.H. 315, 317, 321 Schweikhard, I. 411 Schwinger, J. 284, 308-309, 418 Schwitters, R.F. 164^165, 168-169 Schwitz,W. 407 Scott, W.G. 167 Seaborg, G.T. 183 Sebastiani, F. 606 Segar, A.M. 165, 615 Seghal, L.M. 470 Segler, S.L. 166, 615 Seguinot, J. 601, 603, 606, 612, 621 Sens, J.C. 168, 331, 341-342, 351,403,405-406, 619 Serednjakov, S. 167, 618 Sessler, A. 243 Shabalin, E.P. 310 Shafranov, M.D. 618 Shakespeare, W. 99, 154^155 Shapin, S. 93 Shapiro, G. 618 Shapiro, S. 614 Sharp, P.H. 614 Shaw, B. 569 Shaw, E. 95-96, 554 Sheline, R.K. 338, 406, 412 Shering, G.C. 558 Sherr, R. 292 Sherwood, R. 556 Shimomura, T. 614 Shinn, T. 273 Shutt, R.P. 40 Sidenius, G. 409 Siebert, H.W. 619 Siegbahn, K. 403 Siffert, P. 409 Sigurgeirsson, T. 280-281 Sikkeland, T. 406 Silvestrov, G.I. 556 Singh, J. 615 Singh-Sidhu, J. 165 Sippach, W. 615,617 Sivers, D. 169 Skrinsky, A.N. 243, 555 Slettenhaar, H. 614 Sloan, T. 205 Smadja, G. 166 Smith, A.M. 165-166, 615

Smith, Ch.L. 324-325 Smith, P.P. 556 Smith, S.D. 614,618 Smoquina, G. 82, 95 Snow, G. 460 Snyder, H.S. 553 Sobel, H. 470 Soergel, V. 246, 334, 403-^04, 461, 469, 619 Sorlin, S. 273 Solomon, J. 166 Sona, P.G. 403 Southworth, B. 245, 250, 609, 616 Spahn, G. 619 Specht, H.J. 334, 399, 405 Speiser, D. 292 Spezewski, J.J. 411 Spighel, M. 407,612 Stachel, J. 410 Stadler, B. 406 Stahelin, P. 617 Stafford, G.H. 202-203, 205 Stampke, S. 166 Standley, P.H. 555 Stanek, R. 166 Stanghellini, A. 303, 324 Stanovnik, A. 617 Steams, M.B. 341, 406 Stefanini, A.M. 412 Steflfen, P. 617-619,621 Steinbach, Ch. 555-556 Steinberger, J. 133, 156, 160, 170, 297, 300, 324, 421,426,433,437,452,454-455,469,471, 560, 566, 581, 584^586, 606, 609-^10, 613, 617-619, 621 Stelzer, H. 410, 615 Stem, J. 311,325 Stiening, R. 243 Stierlin, U. 469,614 Stirling, A.V. 165, 614 Stoltenberg, G. 57, 86, 95 Stolzenberg, H. 411 Strassmann, F. 334 Strathdee, J. 318 Strauch, K. 169 Streit, K.P. 619 Stroke, H.H. 412 Strolin, P. 250 Stroot, J.P. 340, 375, 405, 407, 620 Stroynowski, R. 162-163, 167, 170 Stmczinski, W. 617

Name index Strutinsky, V.M. 332, 338 Stiickelberg, E. 284 Stumer, I. 167 Sudarshan, E.G. 288 Sudboe, A. 555 Sueh, S.Y.H. 473 Sugano, K. 618 Sukhina, B.N. 243, 555 Sulak, L.R., 244,617 Sundarshan, E.C.G. 473 Sundell, S. 359-360, 383, 404, 408, 411^12 Susini, A. 373 Susskind, L. 161, 169 Suter, H. 619 Sutherland, D. 299, 300, 324 Suzuki, T. 554 Swatez, G.M. 253, 272 Swiatecki, W. 332, 338 Symanzik 302 Talmi, I. 403 Tamvakis, K. 326 Tanenbaum, W.M. 164^165, 168 Tannenbaum, M.J. 165-166, 615 Tanner, N.W. 333, 404, 407 Tarte, G. 619-620 Taubes, G. 161, 163, 170, 209, 236, 242, 241, 243, 247-250, 274, 608, 621 Tauscher, L. 346 Taylor 439 Taylor 611 Taylor, M. 614 Taylor, R.E. 166 Taylor, T. 619 Teiger, J. 165-166, 614 Teillac, J. 69,403,411 Telegdi, V.L. 197, 241, 250, 341, 398 Teller, E. 183 Teng, L. 240 Tengblad, O. 413 Teucher 48, 58-59, 62, 64 Thatcher, M. 96 Thibault, C. 411^12 Thirion, J. 403 Thirring, W. 259,292,305 Thivent, M. 558 't Hooft, G. 310-311, 316, 325, 470 Thorn, C.B. 321-322, 326 Thorndahl, L. 501, 555 Thun, R. 165

641

Tibell, G. 410 Tichit, J. 618 Tidemand-Petersson, P. 412 Tiktopoulos, G. 311 Ting, S.C.C. 141, 151-152, 162, 165, 170, 237, 248 Tinguely, R. 473, 558 Tirler, R. 614^16 Tittel, K. 134, 619 Toge, N. 614 Tolhoek, H.A. 292 ToUestrup, A.V. 243,469 Tomonoga, Sin-Itiro, 284 Tonin, M. 303, 324 Torelli, G. 407-^08 Tortschanofr, T. 556 Touchard, F. 411^12 Tournier, M. 329 Touschek, B. 499 Touschek, E. 555 Trakkas, C. 167 Trautner, N. 615 Traweek, S. 272, 274 Treiman, S. 297 Trevisan, U. 606 Trilling, G.H. 164^165, 168 Trippe, T. 608, 617, 621 Trumpy B. 93 Tryeciah, W.S. 244 Tschalar, C. 412 Tsyganov, E.N. 618 Tunaal, T. 409 Turkot, F. 243 Turlay, R. 450, 466, 469, 472, 619-620 Tuyn, J. 358 Uden, C.N. 614 Udo, F. 617 Ueno, K. 168, 618-619 Ukawa, A. 308 UUaland, O. 614, 618 Umstatter, H.H. 556 Unser, K. 556 Uralsky, D.V. 618 Urban, M. 618 Vaghin, V. 557 Valdata, M. 165 Valente, V. 617 Valentine, J.M. 177 Valloton 95 van Breugel, H. 557

642

Name index

van den Bosche, M. 615 van der Lans, J. 614 van der Meer, S. 158, 170, 208, 215, 220-222, 230, 232-234, 239-240,237, 243-245,247, 266,269,418, 420, 447, 449, 469, 472, 493, 500, 555-556 van Doesburg, W. 617 van Doninck, W. 166-167 van Hove, L. 7-10, 27-28, 35, 37, 93, 95, 135, 158, 169,192,197, 205-206,218, 220,223,225, 228,231, 237, 241-246, 248-250, 255, 259, 273, 293-294, 303-304, 310, 325, 333, 393, 397, 399,403,405,446, 587, 610 van Kampen 287 van Nieuwenhuizen, P. 314, 320, 326 van Royen, R. 298, 324 Vannucci, F. 164-165, 168, 617-619, 621 Veltman, M. 220, 223, 225-226, 297, 299, 309-310, 316, 324^325, 436, 469, 471 Veneziano, G. 218, 293, 304^305, 320, 325 Venus, W. 166-167 Verdier, A. 554, 556 Veress, I. 608, 621 Verkerk, C 609,621 Vemon, W. 472 Verweij, H. 611,621 Vialle, J.L. 411-412 Vialle, J.P. 161, 167, 169, 469-471 Vidal, R.A. 165, 615 Vieira, DJ. 411 Vilain, P. 166-167 Villars 300 Virchaux, M. 471 Vitale, A. 242, 407 Vitak, B. 292 Vivargent, M. 194-195, 197, 206, 451^52, 465 Vodopianov, A.S. 618 Vodoz, J. 206 Vogt Nilsen, N. 372 Volkov, D.V. 318 Volohov, V.G. 556 von Dardel, G. 164, 192, 200-201, 205, 212, 243, 614, 619 von der Malsburg, Ch. 407 von Dincklage, R.-D. 412 von Gierke, G.O.J. 281 von Gunten, A.H. 407 von Heppe, H. 58 von Krogh, J. 166-167 von Neumann, J. 307

von Weizsacker 78 Vranic, D. 617 Vsevolozhskaya, T.A. 556 Vuilleumier, J. 407, 408 Vysocansky, M. 617, 619 Wachsmuth, H. 166-167 Wadden, J.S. 407 Wagner, A. 619 Wahl, H. 469,617-619,621 Walczak, R. 616 Walecka, J.D. 292,403 Walenta, A.H. 589, 591-592, 595, 610-611, 619, 621 Walker, E. 350 Walker, J.K. 214,243 Walker, R.L. 243 Walker, R.St.J. 109, 111, 157 Wallace-Hadrill, J.S. 165, 615 Walter 346 Walter, G. 412 Walter, H.K. 407-408 Wang, C.J. 614, 619 Wapstra, A.H. 411 Ward, J. 470 Wataghin, G 617 Watkins, P. 161, 170, 242, 272, 274 Watson, K.M. 286 Weedon, H.J. 617 Weerts, H. 166 Weilhammer, P. 202 Weinberg, A. 272 Weinberg, S. 144, 162, 209, 283, 299, 309-311, 317, 418, 433, 470 Weisberger, W. 299 Weise, W. 325, 343, 351, 406 Weiss, J.M. 164, 614 Weisskopf, V. 5, 8, 20, 42, 45-50, 52, 55, 61-62, 69, 93, 95-96, 127, 155, 156, 161, 169, 220, 298, 306, 324, 329, 331, 332, 335, 354, 373, 375, 377, 403, 405^06, 421, 431, 451, 459, 469, 472 Wendt, K. 412 Wess, J. 292, 300, 314, 318-319, 324^326 Westfall, C. 273 Wetherell, A.M. 165, 617 Whitaker, J.S. 164^165, 168 White, S.N. 166 White, T.O. 165, 615 Whittaker, J. 617 Wideroe, R. 499 Wien, K. 407

Name index Wigner, E.P. 285, 391 Wiik, B.H. 210-211, 226, 242, 246-247, 554 Wilczek, F. 170, 312 Wildermuth, K. 292, 306, 325 Wilkin, C. 351, 407 Wilkinson, Sir Geoffrey 335 Wilkinson, D.H. 84, 334, 374-375, 376-378, 379, 403, 409 Willems, J. 10, 81-82, 95 Williams, E.G.H. 619 Williams, S. 614 Willis, W. 161, 167, 210-211, 460, 473, 613-614, 617-619 Willitts, T.R. 469 Willutzki, H.J. 619 Willwald, G.S. 556 Wilsky, K. 409, 412 Wilson, E.J.N. 554^556 Wilson, R. 32, 75-78, 84, 87, 214, 217, 220-221, 239-240, 243-244, 247, 250, 268, 272-274, 481, 542, 552 Wind, H. 615 Wing, W.H. 388,411 Winik, M. 618-619 Winkelmann, F.C. 168 Winstein, B. 614 Winter, K. 38, 127, 131, 156, 159-161, 170, 426, 430, 451^52, 465, 469-473, 579, 606, 609, 617, 621 Winter, W. 244 Wiss, J. 164-165, 168 Witten, E. 320 Witzeling, W. 614,619 Wolf, R. 556 Wolfenstein, L. 325, 341, 453 Wolstenholme, P. 557-558 Woody, C. 614,618-619 Wotschack, J. 619 Wouthuysen, S.A. 10 Wu, S.L. 165, 470 Yamaguchi, Y. 292 Yamanouchi, T. 168, 619

643

Yan, T.M. 161, 167, 170 Yang, C.N. 288, 308-311, 316, 319, 432, 470 Yellin, S. 614 Yelton, J.M. 165 Yerwas, P. 469 Yiou, F. 336,406 Yoh, J.K. 166, 168, 615, 619 Yoshimura, M. 317 Young, K.K. 165, 618 Ypsilantis, T. 601, 603, 606, 612, 616, 621 Yukawa, H. 343 Yung, K. 166 Zaccone, H. 165 Zahniser, D. 614 Zanella, P. 607, 619 Zanello, D. 617 Zavattini, E. 166, 340, 346, 404, 407, 615 Zech, G. 617-619 Zehnder, A. 407-408 Zel'dovich, Y.B. 288 Zelazny, R. 555 Zeldes 386 Zerwas, P. 243, 471 Zettler, C. 554, 557 Zichichi, A. 151-152, 161, 163-164 Ziegert, W. 412 Zilverschoon, C.J. 554, 558 Zilverschoon, K. 409 Ziman, J. 273 Zimmermann 302 Ziock, K. 407 Zipprich, B. 606, 621 Zipse, J.E. 164^165 Zotter, B.W. 554, 556 Zsembery, J. 165, 614 zu Putlitz, G. 405 Zumino, B. 285, 293, 300, 311, 314, 316, 318-319, 324^326 Zupancic, C. 166, 611, 615 Zweig, G. 298,324 Zylberstejn, A. 166

Thematic subject index Abragam report 197-198 accelerators: In general accelerator metrology 118-119 and beam extraction techniques 20-22, 33-34, 482, 538-541 and beam instrumentation 123-124, 512-521 construction costs of 75-76 design 75-76, 83-84, 88-89, 91, 49(M94 focussing techniques 481, 492-494 geodesic alignment 545-547 magnet system 522-526 over-engineered 550-552 RF systems 529-535 as symbols of prestige and power 4 vacuum systems 124, 535-538 see also: CERN: Accelerator Research Division, Accelerator Schools Particular machines at CERN ACOL 504-513 CESAR 76, 121, 494, 535 CHEEP 210-211, 226-228, 239, 486 ISR: administration of 100, 102-107, 114-118, 124-132, 135, 150-151, 586 antiproton injection 229, 504 colliders and fixed target machines 98, 101-102, 135 and computers 124, 542 construction of 24, 112-119, 298 as developing cooling techniques for ppbar project 501 design of 98-109, 112-115, 129, 153, 481 and detectors 23-24, 135-137, 561, 584-589, 596, 598-599 difficulties of experimenting at 25, 98, 105-107, 129-132 and experimental conservatism 135-137, 150-152 experimental programme of 5, 15, 24-27, 35, 99, 105, 112, 127-132, 135 finances of 24, 107-112, 116-117, 393, 499 improvements to 24-25, 498 and international borders 107 low P insertion 24-25, 126, 526 luminosity of 23-25, 105, 126 magnets system 119-120, 522 and other CERN machines 15, 25-27, 66--69, 71, 121, 155-156, 497, 506 and participating labs 127, 145-154, 584-586, 598-599

644

Thematic subject index

645

and physics theory 99, 137-145, 151-152, 154^155 shut down of 25, 153-156 and Split Field Magnet 28, 31, 100, 104, 129, 132-134, 136, 147, 152, 188-189, 560, 572, 574, 577, 579, 584^588 stacking system 122-127, 530 user numbers at 26-27, 145 vacuum system 24, 121-122, 535, 550 LEAR 228-229, 334, 352, 502, 510 LEP: and computers 493, 545 design and construction of 489-490, 547 detectors 590 finances of 393, 398, 400, 489-492 magnets 522-3, 526 origins 4, 35, 144, 211-213, 227-228, 487-492 and other CERN machines 156, 393, 398, 400 research at 420, 430, 432 technology transfer 548-549 vacuum system 536-537 LHC 419, 526, 537, 604 MISR 484-485 PS: alignment of 545-546 beam extraction 20-22, 33, 538-539 beam instabiUty 515 beam intensity 19-20 beam system 21 booster 496-497, 516-522, 528 and computers 492-493, 544-545 construction of 117, 480, 527-528 experimental programme at 5-6, 19 finances 499 improvements to 19-20, 44, 112-114 as ISR injector 20, 104-106, 114, 118-120, 122-125 modified for ppbar 505 and other CERN machines 89-90, 351, 383, 496-498, 504-516 research at 5-6, 19, 21-22, 329, 336, 342, 352, 386, 418^20, 429, 460, 463 role in European physics 98-99 and stacking system 123, 529-530 storage rings 494 and strong focussing 479-480 versatiUty of 498 ppbar coUider at SPS: and CERN budget 213, 222, 225-226, 228, 234-235, 239, 259 competing project at Fermilab 209-210, 213-214, 216-218, 221, 225, 228, 230-231, 239-242 and the Council 226, 228, 236 (different) designs for 214-218, 221, 222, 233-234, 504-508 and disruption of SPS fixed target programme 227-230, 237, 252, 259 electron cooling and 215, 499-502

646

Thematic subject index

feasibility of (ICE experiment) 220, 222-223, 230-232, 255, 259, 502-504 and the SPC 220, 223, 225-226, 228 staff for 220-221, 233 stochastic cooling and 215, 447, 499-504, 510-512 SC: design and construction 329, 332, 370-371, 480 finances 393 machine time for physics 22 management attitudes to 22-23 operating status 22, 401-402 research at 306, 329-330, 336-338, 341, 343-344, 350-354 and SCIP 22-23, 370-374, 377-379, 381, 496 see also SIN SCISR 223, 227-228, 484 SISR 484 SPS approval of 32-33, 68, 482 beam extraction 539-541 and competition with US 481 and computers 493, 542-547 conversion to ppbar 28, 446-447, 489, 502, 504-508 design and construction of 74-76, 83-84, 88-89, 91, 481-482 and detectors 561, 587, 600 finances of 78, 85, 88-89, 481 magnets 482, 526, 552 neutrino beam improved 433 and other CERN machines 15, 22, 150, 152-155, 482-484, 490, 497, 504 research at 6, 15, 418, 427, 429, 435, 463 and site debate 32-33, 68-69, 71-73, 79, 82, 85-91 vacuum system, 536 Particular machines elsewhere: 10 TeV world machine 210 ADA 499 ADONE 98, 181 AGS see BNL Bevalac 399 CESR 144 DORIS 531 EPIC 181 GANIL 380, 399 Heidelberg cyclotron 366 Isabelle 228, 242 LAMPF 351, 373, 542 NIMROD 181, 228, 453, 528 NINA 181, 228, 486 PEP 144, 590, 599 PETRA 144, 181, 197, 210, 424, 430, 490, 532, 537, 590, 595 see also DESY SIN 22-23, 373, 351, 375-378, 393-400

Thematic subject index SPEAR 140 SSC 604 Tevatron 98, 125, 242, 526, 542 see also Fermilab TRIUMPF 351, 373 VEPP - 4 144 analyticity, and strong interactions 287, 301-303 anomalies, theory of 299-300 antiscience moyement 183-184 Austria 75, 79, 86, 259, 526 Axial Field Spectrometer 136-137, 150, 590, 596, 598 Belgium 75, 86-87, 90, 180-181 Big European Bubble Chamber (BEBC) design and construction 27-28, 30, 56, 58-59, 92, 605 finances 27-28, 55-59, 92 first tests 59-60 and industry 57-9, 82 management of facility 57, 61 and research at 431-2, 441-5 see also Detector types: Bubble chambers bubble chambers see Detector types Cabibbo theory 291-292, 296-297, 416-417, 443-445, 456-^58, 460-469 calorimeters 98-99, 136-137, 150-151, 580 CERN: Committees, Groups and Divisions Accelerator Research Division 112, 116 Accelerator Schools (CAS) 494 ACCU 196 Beam Equipment Interaction Committee 117 Council and bubble chambers 50, 57-58 changing role of 12-13, 32-35, 70, 80-82, 92 pioneers in (CERN lobby) 10, 30, 69, 80-82, 92 and ppbar project 226, 228, 236 and SPS machine 67-68, 74, 79-82, 89 and support for SC 375-376 and Theory Division 280, 294-295 and voting procedures 32, 67-68, 74, 79-82, 108-111 EEC Committee 581 Experimental committees system 10, 129, 185-190, 198, 333-334 Finance Committee 50, 57-58, 108-112, 376 ISOLDE Committee 356-357 ISR Committee 8-10

647

648

Thematic subject index

NPR Committee 333, 340, 354, 378 Nuclear Chemistry Group 332, 334^336, 354, 359-363 Nuclear Structure Committee 333, 354-356 Orbit Dynamics Group 372 Physics III Committee 333, 342, 350, 357, 375, 377-379 see also PSC Committee PSC Committee 334, 342 see also Physics III Committee RF Group 379 SC Committee 334, 379 Scientific Policy Committee 44, 46-47, 50, 52, 55-56, 79, 82, 90,125, 220, 223, 225-226, 228, 237-239, 256, 375, 377-378, 488 SPSC 10 SPS Site Evaluation Panel 72-74, 79-80 Track Chamber Committee 8, 44, 46-47, 60-61 Theory Division administration of 293-294 budgets 280, 282 character of 294-296, 304, 312 contribution to Standard Model 307-312 at Copenhagen 279-289 expansion of 292-294 moves to Geneva 282, 288-289, 292 origins 279-283 recruitment policy 295-296, 323-324 salaries in 279-280, 296 and SC experimental programme 351 search for director 294 staff 107, 281, 292-293, 310 success evaluated 289 and visitor programme 15, 280, 295-297, 323 see also chapter 8 CERN: administration of 9, 45-46, 48^9, 67-68, 77, 80-81, 333-334, 354-357, 362, 394 see also CERN: Committees and BEBC collaboration 27, 45-46, 48^9, 60-61 and border arrangements 90-91, 107 as concentrating all European effort at one site 6, 13, 15, 71, 173-175, 199 convention of 70-71, 84-85, 87, 98-99, 108 decision-making at 67-68, 73-74, 76-77, 79-80, 84-85, 401 Director-General 7-9, 289 engineers and technicians at 6, 379 and European integration 6-7, 29-30, 34, 75, 78 finances of 10-12, 50, 76, 81, 84, 86, 88-89, 92, 107-109, 400 see also under individual CERN machines, finances of; CERN: Committees, Finance Committee history of, ways of writing 4-5, 66-67, 208-209, 248 internal organization of 9

Thematic subject index interaction between theorists and experimentalists 279, 306, 351 and medium/low energy physics 375-376 member state pressure on 7, 29-30, 33-34, 213 ongoing member state support for 12-13 and multinational collaboration 29, 14, 421-422 staff employment policy 182-5, 198, 295-296, 323-324 staff numbers 12, 14-15 staff salaries 193-196, 198, and universities 176-177, 183-184 see also industry, users community collaborations: Aachen-Padova 418, 429 Aarhus-Copenhagen 366, 381 ALEPH 590 British 130-131 CDHS 433^35 CERN-Aachen-Torino 455 CERN-Aarhus-Gothenburg 364 CERN-Columbia-Rockefeller (CCR) 145-146, 150-152, 596 CERN-Heidelberg 366-367, 455^56, 461, 467, 577, 580-584, 592-593, 595 CERN-Imperial College-EPF-Milan 580 CERN-Orsay 454 CERN-Orsay-Rutherford 455 CERN-Orsay-Vienna 465^66 CERN-Saclay-Stony Brook 604 CERN-Saclay-Zurich 453 Columbia-Stony Brook 453 DELPHI 590, 598, 604 FNAL-Caltech 440 FNAL-Harvard-Penn-Wiscosin 439 Geneva-Saclay 466 Gothenburg 364, 366 Gothenburg-Oxford 349 MSS 347 Oxford 467 Rutherford-Westfield-Sussex 453 "Scandinavian" 130-131, 135 UAl 35, 420, 508, 561, 574, 590, 596 detector 28, 208, 224, 229, 237, 239, 242-243, 447, 580 and internal organization of 260-263, 268-269 and SPC 237-239, 256 see also ppbar collider at SPS UA2 238-239, 420, 447, 508, 574 UA4 238-239 UA5 238-239

649

650

Thematic subject index

computing 124, 336, 492-494, 521, 541-545, 547, 549, 562-563, 566-569, 579-580 conferences: HEP and Nuclear Structure 332 on Instrumentation 592 Intermediate Energy Physics 374-375, 399 LEP Summer Study, Les Houches 489 Nuclei Far From Stability (Lysekil and subsequent) 331-332, 353, 380-381 Shelter Island 283 Symposium on Accelerators and Pion Physics 481 on technological spin-offs 34, 548 on wire chamber 596-597 control systems see computing cosmic ray physics 283, 565 CP violation 283, 285, 288, 297-298, 416-^17, 450-454 current algebra 299-300, 307, 310 decision making see CERN: decision making at Denmark 70, 91-92, 362 detectors: {see also calorimeters; collaborations; experiments; Axial Field Spectrometer; European Hybrid Spectrometer; Omega Spectrometer; Mark I) Detector design 341-342, 346, 418^20, 426, 429-435, 446, 451-452, 455^56, 460-462 at e^e" facilities 144 parallel plate counter 564 and Standard Model 141-144 Detector types Bubble Chambers: 80 cm Saclay 17, 19, 460 CERN 2 m 17-18 compared to other detectors 13, 43, 61, 151, 453, 562, 565-566, 569, 605 costs of 27-28, 4 1 ^ 2 and decision-making at CERN 54 debates on design and construction 40-42, 48, 534 early development of 40, 561-562, 565, 569, 605 Ecole Polytechnique heavy liquid 19, 465 experimental use of 26-27, 174^175, 199, 418, 433, 459-461, 465 hydrogen 27, 4 3 ^ 4 , 46-^7, 53, 55 and the ISR 128 Mirabelle 33, 179 as a mixed detector 47, 53-55, 61, 605 number of pictures taken at CERN 18 in U.S. 40-43 see also BEBC, Gargamelle

Thematic subject index Drift chambers: compared to other chambers 590, 594 construction of 591-594, 597-598 development of 560, 562, 589-592, 595 at different experiments 136, 589-590 electronics 594 gas choice 595 problems with 590-591 Electronic detectors in general: compared to other detectors 13, 61, 461^62, 560-562, 564^566 development of 561, 563-569, 604^06 experimental practice with 13, 26-27, 174^175, 178-179, 199, 605 and neutrino physics 418 and weak current 429-430 and W search 433^35 MSC detectors: compared to other detectors 600 development of 560, 562, 600-604 MWPC detectors: compared to other detectors 569-571, 598 costs 575, 577, 586, 589 design and construction 572-575, 580-583, 585-589, 597-598 development 560, 562, 569-589 electronics of 575-580, 583, 586 in experiments 580 gas choice 574-575 and physics results 455, 587-589, 598 properties 570-572 TPC detectors 560, 562, 598-600 ECFA 13-14, 69, 75-79, 90, 173, 176-178, 194, 227, 488-490 ELDO 71, 81 electronics, miniaturization of 577-578 electroweak theory 99, 420, 424^26, 428^30, 445^46, 487 E S 0 34 ESRO 71, 81 European Hybrid Spectrometer 605 experimental practice changing role of physicists in 252, 266, 268-272 creativity in 267-272 credit in 265-267 bubble chamber and electronic experiments 13, 17-18, 26-27, 46, 60-61, 174-175, 199, 604-606

651

652

Thematic subject index

industrialisation of 253-254, 260-261, 263-264, 267-268 at ISOLDE 363 at the ISR 25, 98, 105-107, 129-132 experiments lA (FNAL) 433 CDHS 426, 439-440, 443 CHARM II 430 E605 (FNAL) 604 EAl (FNAL) 421 EMC 561, 598 HPWF (FNAL) 443 Jade 590, 595, 596 NA2 598 Ting's proposal at SPS ppbar collider 238 WAl 418, 426, 561, 589, 598, 604 WA18, 420, 426, 428-430, 435 WA79 420 see also collaborations Federal Republic of Germany and Atomic Energy Advisory Committee 32, 75-78, 81-82, 92 and BEBC 27, 33, 44^5, 48, 56-57 role of Council delegates 32-33, 81-82, 93, 236 and industry 32, 45 and ISR 109, 111-112, 127 national policy 13, 16, 33, 92-93, 180-181 and ppbar collider project 236 and SPS 32-33, 68-70, 73, 75-78, 81-82, 86, 92-93, 482 Ford Foundation 280 France and bubble chambers 27, 33, 42, 44-45, 48, 50-51, 56-57, 82 role of Council delegates 81 and ISR 111-112, 127 national policy 13, 16, 33-34, 41, 44^5, 48, 86, 180-181 and PS 69 and Serpukhov 33 and SPS 73, 75, 78-79, 86-87, 90, 93 and Theory Division 282 Gargamelle as a CERN facility 10, 61 design and construction 27-29 finances of 50 and industry 51-52

Thematic subject index physics research at 20, 35, 52, 139, 418-422, 426, 44(M41 support for 47, 418, 433 see also bubble chambers gauge theories (in general) 278, 283-284, 286, 308, 312-313, 315-316 see also renormalization theory: quantum electrodynamics and quantum chromodynamics geometry and theoretical physics see topology Germany See Federal Republic of Germany grand unification theory (GUT) 313-315, 317, 323-324 see also supersymmetry, string theory, supergravity Greece 73, 91, 112 hadron physics theory 152, 296, 298, 301, 304 industry AEG 371, 378 and CERN projects 34, 45, 57-59, 68, 82, 118, 120, 371, 375, 526-528, 535, 537, 547 fair return policy 45, 57-59, 82, 92 IBM 545 Motorola 578 Norsk Data 547 relations with 34, 271, 371-2, 378, 547-550, 577 in U.S. 535 ISOLDE faciUty administration of 354^357, 360, 362-363, 367, 370, 394^398, 401 construction of 329, 354-356, 375 design of 354^358, 366-367, 383-386, 400 design of experiments 363-364, 367 finances of 354, 383-384 and other CERN machines/facilities 375, 393^00 and radiation levels 356, 363 research and results 336, 360-361, 365-377, 379-383, 390-393, 401 and users 22-23, 351, 356, 396-399 why at CERN 369-370 Italy and bubble chambers 41-42 role of Council delegates 81 industry in 537 a n d I S R 1 0 8 , 111-112, 127 national policy 13, 16 and SPS machine 78, 83, 87, 90, 93

653

654

Thematic subject index

Japan 565 Keyhole physics 35, 100, 134-137 Laboratories and Institutions see also collaborations, experiments, CERN Laboratories: Annecy (LAPP) 151, 238, 256-257, 261-262 Bohr Institute, Copenhagen 279, 352-353 see also CERN: Theory Division Brookhaven (BNL) 40, 55, 68, 139-141, 145, 197, 209-210, 279, 297, 450-^51, 454, 463 Culham 79 Daresbury 24, 486 DESY 8, 13, 24, 58, 128, 141, 531, 544 see also Accelerators: PETRA ELETTRA 544 Fermi National Accelerator Laboratory (FNAL) 14, 75-76, 83-85, 92, 144, 150, 152, 316, 418, 465, 501-502, 552 see also Particular machines at CERN: ppbar collider at SPS, competing project at Fermilab Frascati 76, 180-181 GSI 338, 380 Gustaf Werner Institute 335 Harwell National Physics Lab 492 IHEP 538 KEK 488, 544 KfK, Karlsruhe 151, 531, 535 JET 544 Lawrence Berkeley Laboratories 40, 141, 241 MPI, Munich 188 National Physics Lab, Teddington (UK) 119 Novosibirsk 144, 215 Oak Ridge 398 Orsay 76, 238, 256, 386, 388 Paul Scherrer Institute see SIN Rutherford HEL 180-181, 188, 238, 256-257, 259, 261-262, 526, 544 Saclay 33, 42-43, 49, 51, 53, 58, 150, 152, 179, 238, 256-257, 261-262, 380, 591, 592 Serpukhov 13, 33-34, 43, 179, 534 SLAC 138, 140, 141, 144, 197, 209, 211, 218, 298, 311, 426, 437, 440, 488, 604 Stony Brook 131-132, 380, 453 Vienna HEP Institute 256, 258-259, 261-262 Universities: Aachen 131, 238, 256-257, 261-262 Aarhus 357 Bergen 130 Bern 256 Birmingham 238, 256-257, 262 Bologna 131, 151, 152 Cagliari 380 College de France 151, 238, 256-257, 261-262 Columbia 139, 577 Copenhagen 130, 256, 380

Thematic subject index Cornell 144 Darmstadt 380 Ecole Normale Superieure 320 Ecole Polytechnique 289 Frankfurt 380 Geneva 131, 151 Glasgow 280 Harvard 151, 257, 592 Heidelberg 151, 380, 591, 592 Lancaster 130-131 Liverpool 280 Lund 130, 380 Manchester 130-131 MIT 140-141, 151 Michigan 131 Munich 151 Novosibirsk 144 Oxford 150 Pavia 256 Pisa 131, 132, 151 Queen Mary College, London 238, 256-257, 262 Riverside (University of California) 151, 238, 256-257, 261-262 Rome 256-258, 261-262 Rome (Institute Superiore di Sanita) 131, 132 Stanford 141 Strasbourg 380 Stockholm 130 Turin 131, 380 Uppsala 130, 280 Warsaw 151 Westfield College, London 180 Wisconsin 257 MAD 493 see also LEP, and computers Mark 1 141, 598 mathematical physics 305, 312 meson factories 373 see also LAMPF, SIN, TRIUMPF muon physics 131, 133, 135, 340-342, 344-347, 349-350 national interests, at CERN 29, 32-34, 49, 60-61, 69, 74, 80-81 national science bureaucracies 6-7, 29-30, 93

655

656

Thematic subject index

Netherlands 87, 91, 109, 127, 130-131 neutrino physics 42, 297, 417^21, 425^26, 435^W1, 566 Nobel prize 35, 208, 218, 243, 266, 449, 560, 605 Norway 60, 91-92, 127, 130-131, 362 nuclear physics: experimental investigations at CERN 334^341, 369-370, 379-390 influence on other fields 352 isotope separation techniques 352-353 theory 283, 305-307, 336-340 Omega Spectrometer 28, 31, 89, 134, 180, 188-189, 577 parity violation see CP violation patents 547 phenomenology 302-303, 317 physics, decline in prestige of 7, 30, 81, 92 pion physics 343-349 quantum chromodynamics see renormalization theory quantum electromodynamics see renormalization theory quantum field theory 283 CPT theorem 285 origins 283-284 see also CP violation quantum mechanics theory 307 quark mixing see Cabbibo theory radiation hazards see safety issues at CERN, renormalization theories: quantum electrodynamics 284-286, 344-347 quantum chromodynamics 99, 300, 311, 316 see safety systems at CERN 104, 118, 357-358, 393-394 Spain 70 Split Field Magnet see ISR: and Split Field Magnet Standard Model 137-145, 151-152, 432, 443, 456, 461 and CERN Theory Division 307-312, 315-316, 323-324 and W and Z search 208-209, 420, 433-^35, 445^50 see also chapters 6 & 7

Thematic subject index Standard Model, beyond the see supersymmetry, GUT, supergravity string theory, strange particle theory 287-291 string theory 314-315, 320-324 strong interaction theory 135, 285, 287, 289-290, 301, 309-311 superconducting magnets 75, 84, 91, 114, 126, 484, 525-526, 548 see also Particular machines at CERN: ISR, low P insertion supergravity 319-320, 324 supersymmetry 314^315, 317-319, 324 Sweden 70, 85, 87, 91-92, 127, 362 Switzerland, 86-87 see also Accelerators: SIN symmetry 283, 286-287 breaking 309-310 chiral 298-299, 309 strong interactions and 298 weak interactions and 290-291, 293, 296-297 see also supersymmetry technology lag 7, 30, 525 see also industry, computing topology and geometry, in theoretical physics 278, 284, 300, 312 United Kingdom and bubble chambers 41, 44 role of Council delegates 82 and ISR 108-112, 127, 130-131 national policy 13, 16, 78 and SCIP 376 and SPS machine 69, 72, 75, 77-79, 81, 85, 91-93 and Theory Division 282 United States of America comparisons with CERN 14, 80, 297, 350, 398 industry in 535 national science poUcy 398 research connections to CERN 7, 16, 332, 341

657

658

Thematic subject index

user community and access to CERN facilities 190-193, 198, 200, 400 and bubble chamber practice 13, 17-18, 26-27, 46, 60-61, 174^175, 199 CERN staff attitudes to 370, 376-379 and electronics experiments practice 13, 15, 174-175, 199 general discussion of 13-18 global numbers 18, 174 by nationality 16-17, 255-256 as keeping SC/ISOLDE alive 23, 370, 374, 376-379, 396-399 US users at CERN 16-17 see also chapter 5 U.S.S.R. 511,538 weak interaction symmetry, and weak interactions 99, 285-289, 296-297, 308-310 see also chapter 10