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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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