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PHYSICS THROUGH THE 1990s Elementary-Particle Physics Elementary-Particle Physics Pane} Physics Survey Committee Board on Physics and Astronomy Commission on Physical Sciences, Mathematics, and Resources National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1986
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NATIONAL ACADEMY PRESS 2101 Constitution Avenue, NW Washington, DC 20418 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineermg, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the institute of Medicine. The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863, which establishes the Academy as a private, nonprofit, self- governing membership corporation. The Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the government, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the institute of Medicine were established in 1964 and 1970, respectively, under the charter of the National Academy of Sciences. The Board on Physics and Astronomy is pleased to acknowledge generous support for the Physics Survey from the Department of Energy, the National Science Foundation, the Department of Defense, the National Aeronautics and Space Administration, the Department of Commerce, the American Physical Society, Coherent (Laser Products Division), General Electric Company, General Motors Foundation, and international Business Machines Corporation. Library of Congress Cataloging In Publication Data National Research Council (U.S.). Elementary- Particle Physics Panel. Elementary-particle physics. (Physics through the 1990s) Bibliography: p. includes index. 1. Particles (Nuclear physics) Congresses. 2. National Research Council (U.S.). Elementary- Particle Physics Panel~ongresses. I. Title. II. Series. QC793.N36 1985 ISBN 0-309-0357~7 539.7'2 85-15210 Printed in the United States of America First Printing, April 1986 Second Pnnnng, October 1986 Bird Pnnung, Mat 1987 Fourth Punting, Novanber 1990
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PANEL ON ELEMENTARY-PARTICLE PHYSICS MARTIN L. PERL, Stanford Linear Accelerator Center, Chairman CHARLES BALTAY, Columbia University MARTIN BRE~DENsAcH, Stanford Linear Accelerator Center GERALD FEINBERG, Columbia University HOWARD A. GORDON, Brookhaven National Laboratory LAWRENCE W. JONES, University of Michigan BOYCE D. McDAN~E~, Cornell University FRANK S. MERRITT, The University of Chicago ROBERT B. PALMER, Brookhaven National Laboratory JAMES M. PATERSON, Stanford Linear Accelerator Center John PEoP~Es, JR., Fermi National Accelerator Laboratory CHRIS QUIGG, Fermi National Accelerator Laboratory DAVID M. RITSON, Stanford University DAVID N. SCHRAMM, The University of Chicago A. J. STEWART SMITH, Princeton University MARK W. STROVINK, University of California, Berkeley DONALD C. SHAPERo, National Research Council, Executive Secretary Liaison Members D. BERLEY, National Science Foundation, Liaison for National Science Foundation L. S. BROWN, University of Washington, Liaison for Division of Particles and Fields, American Physical Society W. A. WALLENMEYER, Department of Energy, Liaison for Department of Energy Panel Editor W. T. KIRK, Stanford Linear Accelerator Center . . .
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PHYSICS SURVEY COMMITTEE WILLIAM F. BRINKMAN, Sandia National Laboratories, Chairman JOSEPH CERNY, University of California, Berkeley, and Lawrence Berkeley Laboratory RONALD c. DAVIDSON, Massachusetts Institute of Technology JOHN M. DAWSON, University Of California, Los Angeles MILDRED s. DRESSELHAUS, Massachusetts Institute Of Technology VAL L. FITCH, Princeton University PAUL A. FLEURY, AT&T Bell Laboratories WILLIAM A. FOWLER, w. K. Kellogg Radiation Laboratory THEODOR w. HANSCH, Stanford University VINCENT JACCARINO, University of California, Santa Barbara DANIEL KLEPPNER, Massachusetts Institute of Technology AEEXE! A. MARADUDIN, University of California, Irvine PETER D. MACD. PARKER, Yale University MARTIN L. PERK, Stanford University WATT w. WEBB, Cornell University DAVID T. WILKINSON, Princeton University DONALD c. SHAPERO, Stay Director ROBERT L. RIEMER, Staff Officer CHARLES K. REED, Consultant lV
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BOARD ON PHYSICS AND ASTRONOMY HANS ~RAUENFELDER, University of Illinois, Chairman FELIX H. BOEHM, California institute of Technology RICHARD G. BREWER, IBM San Jose Research Laboratory DEAN E. EASTMAN, IBM T.J. Watson Research Center JAMES E. GUNN, Princeton University LEO p. KADANOFF, The University of Chicago w. CARL LINEBERGER, University of Colorado NORMAN F. RAMSEY, Harvard U Diversity MORTON s. ROBERTS, National Radio Astronomy Observatory MARSHALL N. ROSENBEUTH, University Of Texas at Austin WILLIAM p. SEICHTER, AT&T Bell Laboratories SAM B . TRE] MAN, Princeton U Diversity DON A ED C . S. HAPERO, Staff Direc tor ROBERT L. R'EMER, Staff Optic er HELENE PATTERSON, Sta~Assistant S USAN WYATT, Stc`.ff Assistant v
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COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND RESOURCES HERBERT FRIEDMAN, National Research Council, Chairman THOMAS D. BARROW, Standard Oil Company (Retired) ELKAN R. BLOUT, Harvard Medical School WILLIAM BROWDER, Princeton University BERNARD F. BURKE, Massachusetts Institute Of Technology GEORGE F. CARRIER, Harvard University CHARLES L. DRAKE, Dartmouth College MILDRED s. DRESSEEHAUS, Massachusetts Institute Of Technology JOSEPH L. FISHER, Office Of the Governor, Commonwealth of Virginia JAMES c. FLETCHER, University Of Pittsburgh WILLIAM A. FOWLER, California Institute of Technology GERHART FRIEDLANDER, Brookhaven National Laboratory EDWARD D. GOLDBERG, Scripps Institution Of Oceanography MARY L. GOOD, Signal Research Center J. ROSS MACDONALD, University Of North Carolina THOMAS F. MALONE, Saint Joseph College CHARLES J. MANKIN, Oklahoma Geological Survey PERRY L. MCCARTY, Stanford University WILLIAM D. PHILLIPS, Mallinckrodt, Inc. ROBERT E. SIEVERS, University of Colorado JOHN D. SPENGEER, Harvard School of Public Health GEORGE W. WETHERIEE, Carnegie Institution of Washington RAPHAEL G. KASPER, Executive Director LAWRENCE E. MCCRAY, Associate Executive Director Vl
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Preface This report on elementary-particle physics is part of an overall survey of physics carried out for the National Academy of Sciences by the National Research Council. The panel that wrote this report had three goals. The first goal was to explain the nature of elementary- particle physics and to describe how research is carried out in this field. The second goal was to summarize our present knowledge of the elementary particles and the fundamental forces. The third goal was to consider the future course of elementary-particle physics research and to propose a program for this research in the United States. It is the hope and intention of the panel that this volume will be read and found useful outside the physics community. Therefore the text does not assume that the reader has any special knowledge of mathe- matics or of physics beyond an acquaintance with general notions such as mass and energy. Nor do we assume that the reader has any previous knowledge of the techniques of elementary-particle physics research, namely, accelerators and particle detectors. indeed we have presented basic introductions to these techniques. In the last two decades there has been a revolution in our knowledge of elementary-particle physics. We have identified three types of elementary particles the quarks, the leptons, and the force-carrying particles; we have learned a great deal more about three of the fundamental forces; and the weak force and electromagnetic force have been unified in a beautiful and powerful theory. Major innovations have been made in the technologies of accelerators and of particle . . V11
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~ . ~ Vlll PREFACE detectors. In order to present all of this in a few chapters, we have had to limit ourselves to describing the main ideas and the major experi- mental and theoretical accomplishments. We apologize to our col- leagues for leaving out descriptions or even mention of so much other important and beautiful work in elementary-particle physics. Elementary-particle physics is an international science, and in describing its content and its methods we have used the work of all the world's elementary-particle physicists. In looking to the future needs and future opportunities of elementary-particle physics we have mostly limited our work and our presentation to the United States. We have done so because this was the charge to the Physics Survey Committee from the National Academy of Sciences of the United States and because we are constituted primarily as a panel of physicists from the United States who are not qualified to speak for physics abroad. Since one of the audiences for this report consists of members of the federal government of the United States who are concerned with science policy, in describing needs and opportunities we have naturally tended to use examples from the elementary-particle physics community in the United States. We hope that our colleagues abroad will understand that this was one of the purposes of the report and will not feel slighted by our inability in this limited space to present more examples from work of the elementary-particle physics community abroad. The Elementary-Particle Physics Panel acknowledges the help it has had from many physicists who have graciously given their time for discussions on the contents of this volume, who have read and reviewed individual sections, and who have been kind enough to review and make suggestions for the entire volume. We are very grateful to John Ellis of CERN, who attended the early meetings of the Panel and wrote some of the first drafts of this report. We have tried to represent the views of the elementary-particle physics community as a whole, but of course it is only panel members who bear the responsi- bility for the material in this volume. We thank the Chairman of the Physics Survey Committee, William F. Brinkman, for his guidance, leadership, and wisdom. We express our gratitude to the Staff Director of the Board on Physics and Astronomy, Donald C. Shapero, who was so patient and generous in passing on to us his knowledge and experience of how to represent the views of a scientific community and of how to prepare a report of this nature. Finally, we thank the technical typists and illustrators who so patiently worked and re- worked the many drafts of this report: Lydia Beers, Edythe Christianson, and the members of the Publications Office of the Stanford Linear Accelerator Center.
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Contents EXECUTIVE SUMMARY 1 INTRODUCTION ...... Elementary-Particle Physics, 12 What We Know, 12 What We Want to Know, 15 The Tools of Elementary-Particle Physics, 15 The Future Tools of Elementary-Particle Physics, 16 2 WHAT IS ELEMENTARY-PARTICLE PHYSICS? What Is an Elementary Particle? 19 How Many Kinds of Elementary Particles Are There? 19 The Size of Elementary Particles, 23 Elementary Particles and High Energy, 23 The Known Basic Forces and Fundamental Particles, 25 · — The Four Basic Forces9 25 The Known Families of Elementary Particles9 26 The Force-Carrying Particles, 27; The Leptons, 27; The Quarks, 28; The Hadrons, 29; Particles and Antiparticles, 30 1X . 18
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X CONTENTS Collisions and Decays, 3 Collisions of Particles, 3 Collision Diagrams, 3 ~ Collisions and Interactions, 33 Spontaneous Disintegration of Particles, 35 Conservation Laws and Symmetry Ideas, 35 What Are Conservation Laws? 35 Symmetry and Invariance, 36 Symmetry Breaking, 39 Experiments, Accelerators, and Particle Detectors, 40 Experimental Methods in Elementary-Particle Physics, 40 Experiments at Fixed-Target Accelerators, 40 Fixed-Target Accelerators, 41 Targets, 42 Particle Detectors for Charged Particles, 42 Secondary Particle Beams, 43 Particle Colliders, 43 Experiments at Particle Colliders, 46 The Decays of Particles, 47 Experiments in Elementary-Particle Physics Without Accelerators, 47 3 WHAT WE HAVE LEARNED IN THE PAST TWO DECADES . . . . . . . . . . Development of the Quark Mode] of Hadrons, 48 The Beginnings of the Quark Model, 48 The Discovery of the Charmed Quark, 50 Charmonium States, 51 Discovery of the Third Generation of Leptons and Quarks, 53 The Discovery of the Tau Lepton, 53 The Discovery of the Bottom Quark, 55 The Third Generation, 56 How Quarks Interact, 59 Hadron Interactions, 59 Lepton-Proton Scattering Experiments, 59 Hadron Jets, 62 . 48
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CONTENTS Xl Unification of the Weak and Electromagnetic Interactions, 65 Strong Interaction Among Quarks, 70 Unified Theories, 76 4 ELEMENTARY-PARTICLE PHYSICS: WHAT WE WANT TO KNOW Introduction, 81 The Problem of Mass, 83 Where Do Al] These Mass Scales Originate? 85 Composite Quarks and Leptons? 86 Unification of the Fundamental Forces? 86 Interaction of Hadrons, 87 Using Existing Accelerators and Accelerators Under Construction, 87 The Need for Higher-Energy Accelerators, 91 Some Fundamental Issues, 96 · e 81 5 ACCELERATORS FOR ELEMENTARY-PARTICLE PHYSICS 98 Introduction to Accelerators, 98 The Why and How of Accelerators, 98 Particle Colliders, 101 Superconducting Magnets in Accelerators, 103 Progress in Accelerators and the Energy Frontier, 104 Elementary-Particle Physics and the Variety of Accelerators, 104 Study of the Properties of Known Particles, 104 Study of the Known Forces, 106 Tests of New Ideas and Theories, 107 The Search for New Particles and the Mass Scale, 108 Searches for Clues to Puzzles and Exploration of the Unknown, 109 Accelerators We Are Using and Building, ~10 Proton Accelerators: Fixed Target, ~ ~ ~ Proton-Proton and Proton-Antiproton Colliders at CERN, ~ 13 .
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· ~ Xll CONTENTS The 2-TeV Proton-Antiproton Collider at Fermilab, ~ 15 Electron Accelerators: Fixed Target, Il5 Circular Electron-Positron Colliders, Il5 The TRISTAN and LEP Electron-Positron Circular Colliders, ~ 16 Linear Electron-Positron Colliders, ~ IS Electron-Proton Colliders, 120 The Superconducting Super Collider, a Very-High-Energy Proton-Proton Collider, 120 Physics Goals, 120 Collider Goals, 121 Design Studies, 122 Superconducting Magnets, 123 Preliminary Collider Designs and Considerations, 124 Schedule and Cost, 127 Research and Development for Very-High-Energy Linear Colliders, 128 Physics Motivation, 128 Present Technology and Concepts, 128 Research on Advanced Concepts for Accelerators and Colliders, 129 Linear Accelerators and Colliders, 129 Ultrahigh-Energy Circular Colliders, 131 The Need for Advanced Research on Accelerators and Colliders, 131 6 INSTRUMENTS AND DETECTORS FOR ELEMENTARY-PARTICLE PHYSICS. . Introduction, 132 Detector Requirements and Physical Principles of Detection, 135 Detectors for Collider Experiments, 139 Close-in Detection: Vertex Detectors, 140 Charged-Particle Tracking Chambers, 141 Identification of Particle Types, 143 · — 132
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CONTENTS Xiii Calorimetric Detection and Energy Measurement, 143 Detectors in Fixed-Target Experiments, 144 Small or Simple Fixed-Target Experiments, 144 Large or Complex Fixed-Target Experiments, 147 Bubble Chamber, 147 Data Reduction and Computers, 149 Facilities and Detectors for Experiments Not Using Accelerators, 152 Atomic, Optical, Electronic, and Cryogenic Experiments, 152 Experiments Using Radioactive Material or Reactors, 152 Experiments Using Cosmic Rays, 153 The Solar Neutrino Experiment, 155 Searches for the Decay of the Proton, 155 Summary and Future Prospects, 156 7 INTERACTIONS WITH OTHER AREAS OF PHYSICS AND TECHNOLOGY.. . . . . · ~ Cosmology and Astrophysics, 158 Cosmic-Ray Physics, 160 Nuclear Physics, 161 Atomic Physics, 164 Condensed-Matter Theoretical Physics, 165 Other Applications of Accelerators, 166 Synchrotron Radiation, 166 Accelerators in Medicine, 169 High-lntensity Neutron Sources, 169 Accelerators and Plasma Physics, 170 Large-Scale Uses of Superconductivity, 170 Support and Stimulation of New Technology, 171 8 EDUCATION, ORGANIZATION, AND DECISION MAKING IN ELEMENTARY- PARTICLE PHYSICS............ Historical Background, 172 Before 1960, 172 157 172
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XiV CONTENTS After 1960 in the United States, 173 After 1950 Abroad, 175 Pace and Planning in Accelerator Construction and Use, 176 Conception, ~ 76 Proposal, 177 Decision, 177 Construction, 177 U se of Accelerators for Physics, ~ 78 The Death of an Accelerator, 178 Summary, 179 The Nature of Elementary-Particle Physics Experimentation, 179 Graduate Education, I81 Interaction Between the Particle-Physics Community and the Federal Government, I82 Universities, ~ 82 Accelerator Laboratories, I83 Decision Making and Advice, I83 International Cooperation and Competition, IS5 Future Trends and Issues, I89 Graduate Students' Role, I89 Scientific Manpower in Particle Physics, 189 Advanced Accelerator and Detector Research. 190 Laboratory Management, 192 Advisory Structure, 193 9 CONCLUSIONS AND RECOMMENDATIONS The Revolution of the Past Two Decades, 194 How the Revolution Was Made, 195 What We Want to Know, 195 Recommendations for University-Based Research Groups and Use of Existing Facilities in the United States, 196 Recommendations for New Accelerator Facilities in the United States, 197 Recommendations for Accelerator Research and Development, 198 194
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CONTENTS XV Recommendations for Theoretical Research in Particle Physics, 198 Recommendations for Nonaccelerator Physics Experiments, 199 Recommendations for International Cooperation in Elementary-Particle Physics, 199 Conclusion, 200 APPENDIXES A The Worid's High-Energy Accelerators B Particle Colliders Under Construction · ~ 203 e 207 C Statistical Information on Elementary-Particle Physics Research in the United States . . . . . . . . . . 209 GLOSSARY INDEX 213 223
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