Elementary-Particle Physics

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Elementary-Particle Physics Revealing the Secrets of Energy and Matter Committee on Elementary-Particle Physics Board on Physics and Astronomy Commission on Physical Sciences, Mathematics, and Applications National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1998

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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 Engineering, 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 project was supported by the Department of Energy under Grant No. DE-FG0296ER40974, the National Science Foundation under Grant No. PHY-9600688, and a grant from the National Research Council's Basic Science Fund. International Standard Book No 0-309-06037-0 Library of Congress Catalog Card No. 97-81203 Additional copies are available from: National Academy Press 2404 Constitution Ave., NW Box 285 Washington, DC 20055 800-624-6242 202-334-3313 (in the Washington metropolitan area) http://www.nap.edu Copyright 1998 by the National Academy of Sciences. All rights reserved. Front cover: The power of micro-vertex detectors, a new technology, is used to depict an interesting high-energy event. The detectors (shown in grey) are made of silicon and surrounded the collision point where high-energy interactions took place at 300,000 per second. The inner detector was located 3 cm from the collision point, and all detectors had spatial resolutions of about a thousandth of a centimeter. This fine resolution, needed to resolve the high density of tracks (some of which are shown in green and red), allows accurate extrapolation into the interaction region, inside the beam pipe—shown by the inner circle. The green tracks come from the original interaction, whereas the red ones come from two disconnected points. The latter are actually from B mesons that were created at the collision point but traveled several millimeters before decaying. The detector technology clearly reveals such decays even though the mean life is only a billionth of a second. From other information collected, one knows that this event is an example of the production of a pair of the very heavy top quarks, recently discovered by the CDF and DO collaborations at Fermilab. (Courtesy of Joseph Incandela, CDF and Fermilab.) Printed in the United States of America

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COMMITTEE ON ELEMENTARY-PARTICLE PHYSICS BRUCE WINSTEIN, Enrico Fermi Institute, University of Chicago, Chair EUGENE BEIER, University of Pennsylvania JAMES BRAU, University of Oregon PERSIS DRELL, Cornell University GARY FELDMAN, Harvard University JEROME FRIEDMAN, Massachusetts Institute of Technology HOWARD GEORGI, Harvard University DAVID J. GROSS, Institute for Theoretical Physics, University of California at Santa Barbara LAWRENCE J. HALL, Lawrence Berkeley National Laboratory STEPHEN HOLMES, Fermi National Accelerator Laboratory EUGENE LOH, University of Utah HUGH E. MONTGOMERY, Fermi National Accelerator Laboratory NAN PHINNEY, Stanford Linear Accelerator Laboratory THOMAS ROSER, Brookhaven National Laboratory MARJORIE SHAPIRO, Lawrence Berkeley National Laboratory MELVYN SHOCHET, Enrico Fermi Institute, University of Chicago FRANK WILCZEK, Institute for Advanced Study MICHAEL WITHERELL, University of California at Santa Barbara MICHAEL E. ZELLER, Yale University DONALD C. SHAPERO, Director ROBERT L. RIEMER, Senior Program Officer

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BOARD ON PHYSICS AND ASTRONOMY ROBERT C. DYNES, University of California at San Diego, Chair ROBERT C. RICHARDSON, Cornell University, Vice Chair IRA BERNSTEIN, Yale University STEVEN CHU, Stanford University VAL FITCH, Princeton University IVAR GIAEVER, Rensselaer Polytechnic Institute JOHN P. HUCHRA, Harvard-Smithsonian Center for Astrophysics ANTHONY C.S. READHEAD, California Institute of Technology R.G. HAMISH ROBERTSON, University of Washington KATHLEEN C. TAYLOR, General Motors Corporation J. ANTHONY TYSON, Lucent Technologies GEORGE WHITESIDES, Harvard University DAVID WILKINSON, Princeton University DONALD C. SHAPERO, Director ROBERT L. RIEMER, Associate Director DANIEL F. MORGAN, Program Officer NATASHA CASEY, Senior Administrative Associate GRACE WANG, Project Assistant

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COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND APPLICATIONS ROBERT J. HERMANN, United Technologies Corporation, Cochair CARL LINEBERGER, University of Colorado, Cochair PETER M. BANKS, Environmental Research Institute of Michigan WILLIAM BROWDER, Princeton University LAWRENCE D. BROWN, University of Pennsylvania RONALD G. DOUGLAS, Texas A&M University JOHN E. ESTES, University of California, Santa Barbara MARTHA P. HAYNES, Cornell University L. LOUIS HEGEDUS, Elf Atochem North America, Inc. JOHN E. HOPCROFT, Cornell University CAROL M. JANTZEN, Westinghouse Savannah River Company PAUL G. KAMINSKI, Technovation, Inc. KENNETH H. KELLER, University of Minnesota KENNETH I. KELLERMANN, National Radio Astronomy Observatory MARGARET G. KIVELSON, University of California, Los Angeles DANIEL KLEPPNER, Massachusetts Institute of Technology JOHN KREICK, Sanders, a Lockheed Martin Company MARSHA I. LESTER, University of Pennsylvania NICHOLAS P. SAMIOS, Brookhaven National Laboratory CHANG-LIN TIEN, University of California, Berkeley NORMAN METZGER, Executive Director

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of 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. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council.

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Preface The Committee on Elementary-Particle Physics (CEPP) was established by the Board on Physics and Astronomy as part of its decadal survey series Physics in a New Era. CEPP met six times over the course of 18 months, and it heard from program managers at the Department of Energy and the National Science Foundation and from congressional staff. The committee solicited input from the elementary-particle physics community through an email address, an Internet Web page, and a meeting after the 1996 Snowmass meeting of the American Physical Society's Divisions of Particles and Fields and Physics of Beams. At the seminar run by the International Committee for Future Accelerators at its October 1996 meeting in Japan, members of the committee initiated and participated in discussions on international collaboration. CEPP was charged to describe what has been learned over the last two decades and to identify key physics objectives for the coming decades. The committee considered the facilities, instruments, and detectors that are required to carry out research in this field and outlined future options under realistic scenarios. The committee also outlined the field's relationships with other areas of physics and technology, and considered the general issues of education, manpower, and international cooperation; elementary-particle physic's relevance to society; its contributions to the welfare of the country; and the practical benefits of accelerator science and technology. The committee would like to thank Donald C. Shapero and Robert L. Riemer from the Board on Physics and Astronomy for their efforts throughout the course of this study, attempting to steer its work toward a completed manuscript with the proper message, properly written. Katharine Metropolis edited parts of the report, and it is much to the better due to her efforts. The committee grate

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fully acknowledges the contributions of the following individuals who provided either material or particular advice that influenced its study: Jonathan A. Bagger, R. Michael Barnett, David G. Cassel, Gordon Cates, Ernie Fontes, Gerald Gabrielse, Christopher T. Hill, Joseph Robert Incandela, Judy Jackson, Andreas S. Kronfeld, Paul Langacker, Peter J. Limon, Yorikiyo Nagashima, Rene A. Ong, Michael Peskin, Nir Polonsky, Chris Quigg, Frank Sciulli, Stephen H. Shenker, Michael S. Turner, and Bill Willis. The committee also thanks Stephanie Selice, who edited the final production draft of the report. The committee's work was supported by grants from the National Research Council's Basic Science Fund, the U.S. Department of Energy's Office of Energy Research, and the National Science Foundation's Physics Division. The committee thanks them for their support. Finally, the committee would like to acknowledge David N. Schramm, who inspired this new survey of all fields of physics and was chair of the Board on Physics and Astronomy for most of the period of this study. We share with the physics and astronomy communities a deep regret for his untimely passing (shortly before this report was completed) and for the loss of his leadership. BRUCE WINSTEIN CHAIR COMMITTEE ON ELEMENTARY-PARTICLE PHYSICS

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Acknowledgments This report has been reviewed by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council's (NRC's) Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the authors and the NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The content of the review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their participation in the review of this report: Robert K. Adair, Yale University Lawrence M. Krauss, Case Western Reserve University Leon Lederman, Fermilab Francis Low, Massachusetts Institute of Technology Michael Riordan, Stanford Linear Accelerator Center John Schwarz, California Institute of Technology Sam B. Treiman, Princeton University Edward Witten, Institute for Advanced Study, Princeton University Although the individuals listed above have provided many constructive comments and suggestions, responsibility for the final content of this report rests solely with the authoring committee and the NRC.

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Contents     Executive Summary   1 1   Introduction   16 2   What Is Elementary-Particle Physics?   21     Introduction   21     Fundamental Constituents of Matter   22     Earth, Air, Fire, and Water   22     Chemical Elements, the Periodic Table, and Atoms   22     Protons, Neutrons, and the Electron   23     Today's Fundamental Constituents   23     The Neutrino and Leptons   23     Particle "Generations   24     Relativity, Quantum Mechanics, and Particle Accelerators   25     Forces   26     Gravity   27     Electric and Magnetic Forces; Electromagnetism   27     Weak and Strong Forces   28     What "Transmits" Forces?   29     Unification of Forces   30     Laws of Nature   30     Particle Collisions   31     Scattering Experiments   31     Colliders   31     Summary   32

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3   Symmetries, Forces, and Particle   33     Introduction   33     Symmetries   34     Symmetries and Particle Physics   35     Local or Gauge Symmetries   37     The Standard Model   39     Spontaneous Symmetry Breaking   42     Higgs Boson   43     Generation-Changing Interactions   43     Beyond the Standard Model   45     Symmetry Breaking and Supersymmetry   45     Grand Unification   47     Why Are There Three Generations?   48     Physics of the Planck Scale   49     String Theory   50 4   The Past 25 Years: Establishing the Standard Model   52     Introduction   52     The World of Elementary-Particle Physics Circa 1972   52     The Forces   53     The Electroweak Force   53     The Strong Force   56     Constituent Particles   59     Discovery of the Charm Quark   59     Discovery of the Tau Lepton   59     Discovery of the Bottom Quark   61     Discovery of the Top Quark   62     Counting the Number of Generations   63     Particle-Antiparticle Asymmetry   63     Other Studies   65     Measuring the Mass of Neutrinos   65     Searching for Proton Decay   66     Other Physics Beyond the Standard Model   66     Summary   66 5   The Physics of the Next Decade   68     Overview   68     What Is the Origin of Mass?   70     Why Are There Energy Scales that Are So Vastly Different?   71     What Is the Origin of Matter-Antimatter Asymmetry?   72     Patterns of Quark and Lepton Masses and Transitions   73     Understanding the Strong Force   75     Are There Unexpected Phenomena?   76     Summary   77

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6   Accelerators and Detectors: The Tools of Elementary-Particle Physics   78     Introduction   78     Particle Accelerators   84     Performance of Existing Accelerators   84     Accelerator Facilities Under Construction   86     Options for Future Facilities   88     Detectors in Elementary-Particle Physics   91     Particle Detection   92     Particle Detector Topologies   93     Challenges for the Next 10 to 20 Years   98 7   The Role of New Facilities   101     Overview   101     The Landscape in 2010   102     Future Colliders   104     The Physics Need   105     Colliders to Address the Physics Need   105     The Next Steps   108 8   Accelerator-Detector Technology and Benefits to Society   110     Introduction   110     The Machine Frontier   111     Synchrotron Radiation: Using X-Ray Light to See the World in Atomic Detail   111     Science and Industry in a Partnership Down to the Wire   114     The Detector Frontier   115     The Computing Frontier and Elementary-Particle Physics   116     Technologies for the Next 20 Years   119 9   Interactions with and Connections to Other Branches of Physics and Technology   121     Introduction   121     Cosmology   121     Dark Matter   122     Structure Formation   125     Baryogenesis and Nucleosynthesis   126     Astrophysics   127     Physics of the Sun   127     Supernovas   127     Cosmic Rays   127     Nuclear Physics   129     Atomic Physics   130     Condensed-Matter Physics   131

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    Fluid Dynamics,   133     Mathematical and Computational Physics,   133 10   Elementary-Particle Physics in Today's Society   135     Introduction,   135     Historical Background,   135     Particle Physics Until World War II (the First 50 Years),   135     Particle Physics After World War II (the Second 50 Years),   136     Impact of the Termination of the Superconducting Super Collider,   137     Organizational Structures,   139     Universities,   140     Laboratories,   140     Experimental Collaborations,   141     The Advisory System,   142     International Cooperation,   143     Future Challenges,   144     Education in Elementary-Particle Physics,   148     Particle Physics Graduate Education,   148     Outreach to the Public,   149 11   Conclusions and Recommendations   151     Introduction,   151     Recommendations for U.S. Elementary-Particle Physics,   153     1. Recommendations Concerning the High-Energy Frontier,   154     2. Recommendation for Addressing Important Fundamental Physics Problems Below the TeV Mass Scale,   158     Conclusion   159     Appendix Glossary, Abbreviation, and Acronyms   161

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Plates 1 Fig. 4.6   CDF Experiment   174 2 Fig 6.2   SLAC   175 3 Fig. 6.3   Reconstructed B-Decay   176 4 Fig 8.2   (Top) Macro Molecular Crystalography (Bottom) Structural Elements of AIDS Virus   177

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Elementary Particle Physics