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Cambridge University Press 0521835097 - High PT Physics at Hadron Colliders Dan Green Frontmatter More information

HIGH PT PHYSICS AT HADR ON COLLIDERS
This book provides a comprehensive introduction to high transverse momentum reactions at hadron (proton­proton or proton­antiproton) colliders. It begins by introducing the Standard Model of high energy physics and describes the specialized detectors used. It then gives a general treatment of the reactions to be studied and summarizes the state of the art in hadron collider physics, defined by Tevatron results. The experimental program at the detectors being built for the Large Hadron Collider at CERN is described, with details of the search program and the general strategy to find the postulated Higgs particle. Speculations of physics beyond the Standard Model are also discussed. The book includes links to online freeware programs, freeware utilities, and high energy physics library resources. This book is suitable for graduate students and researchers in high energy physics. dan green received his Ph.D. from the University of Rochester in 1969. He held a post-doctoral position at Stony Brook from 1969 to 1972 and worked for a time at the Intersecting Storage Rings (ISR) at CERN. His next appointment was as an Assistant Professor at Carnegie Mellon University from 1972 to 1978 during which time he was also Spokesperson of a BNL Baryonium Experiment. He has been a Staff Scientist at Fermilab from 1979 to the present, and has worked in a wide variety of roles on experiments both at Fermilab and elsewhere. He participated in the D0 Experiment as Muon Group Leader from 1982 to 1990 and as B Physics Group Co-Convener from 1990 to 1994. He led the US Compact Muon Solenoid (CMS) Collaboration as Spokesperson and then was Project Manager for the US groups working at the Large Hadron Collider (LHC) at CERN. At Fermilab, he was Physics Department Deputy Head from 1984 to 1986 and Head from 1986 to 1990. From 1993 to the present he has served as the CMS Department Head in the Particle Physics Division.

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CAMBRIDGE MONOGRAPHS ON P AR TICLE PHYSICS NUCLEAR PHYSICS AND COSMOLOGY 22
General Editors: T. Ericson, P. V. Landshoff

1. K. Winter (ed.): Neutrino Physics 2. J. F. Donoghue, E. Golowich and B. R. Holstein: Dynamics of the Standard Model 3. E. Leader and E. Predazzi: An Introduction to Gauge Theories and Modern Particle Physics, Volume 1: Electroweak Interactions, the `New Particles' and the Parton Model 4. E. Leader and E. Predazzi: An Introduction to Gauge Theories and Modern Particle Physics, Volume 2: CP-Violation, QCD and Hard Processes 5. C. Grupen: Particle Detectors ¨ 6. H. Grosse and A. Martin: Particle Physics and the Schrodinger Equation 7. B. Anderson: The Lund Model 8. R. K. Ellis, W. J. Stirling and B. R. Webber: QCD and Collider Physics 9. I. I. Bigi and A. I. Sanda: CP Violation 10. A. V. Manohar and M. B. Wise: Heavy Quark Physics 11. R. K. Bock, H. Grote, R. Fruhwirth and M. Regler: Data Analysis Techniques for High-Energy Physics. ¨ Second edition 12. D. Green: The Physics of Particle Detectors 13. V. N. Gribov and J. Nyiri: Quantum Electrodynamics 14. K. Winter (ed.): Neutrino Physics, Second edition 15. E. Leader: Spin in Particle Physics 16. J. D. Walecka: Electron Scattering for Nuclear and Nucleon Structure 17. S. Narison: QCD as a Theory of Hadrons 18. J. F. Letessier and J. Rafelski: Hadrons and Quark­Gluon Plasma 19. A. Donnachie, H. G. Dosch, P. V. landshoff and O. Nachtmann: Pomeron Physics and QCD 20. A. Hofmann: The Physics of Synchrotron Radiation 21. J. B. Kogut and M. A. Stephanov: The Phases of Quantum Chromodynamics 22. D. Green: High PT Physics at Hadron Colliders

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Cambridge University Press 0521835097 - High PT Physics at Hadron Colliders Dan Green Frontmatter More information

HIGH PT PHYSICS AT HADR ON COLLIDERS
D AN GREEN
Fermi National Accelerator Laboratory Batavia, Illinois

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published by the press syndica te of the university of cambridge The Pitt Building, Trumpington Street, Cambridge, United Kingdom cambridge university press The Edinburgh Building, Cambridge, CB2 2RU, UK 40 West 20th Street, New York, NY 10011­4211, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcon 13, 28014 Madrid, Spain ´ Dock House, The Waterfront, Cape Town 8001, South Africa http://www.cambridge.org
C

D. Green 2005

This book is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2005 Printed in the United Kingdom at the University Press, Cambridge Typeface Times 10/13 pt.
A System L TEX2 [tb]

A catalog record for this book is available from the British Library Library of Congress Cataloging in Publication data Green, Dan. High PT physics at hadron colliders / Dan Green. p. cm. ­ (Cambridge monographs on particle physics, nuclear physics, and cosmology; 22) Includes bibliographical references and index. ISBN 0 521 83509 7 1. Hadron colliders. 2. Proton­proton interactions. 3. Proton­antiproton interactions. I. Title. II. Series. QC787.C59G74 2004 539.7 3723 ­ dc22 2004045198 ISBN 0 521 83509 7 hardback

The publisher has used its best endeavors to ensure that the URLs for external websites referred to in this book are correct and active at the time of going to press. However, the publisher has no responsibility for the websites and can make no guarantee that a site will remain live or that the content is or will remain appropriate.

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Science is an integral part of culture. It's not this foreign thing, done by an arcane priesthood. It's one of the glories of the human intellectual tradition. Stephen Jay Gould (1990) . . . some of our thinking should reveal the true structure of atoms and the true movements of the stars. Nature, in the form of Man, begins to recognize itself. Victor Weisskopf (1962)

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Cambridge University Press 0521835097 - High PT Physics at Hadron Colliders Dan Green Frontmatter More information

Contents

1

2

Acknowledgments Acronyms Introduction Overview Scope Units Tools The Standard Model and electroweak symmetry breaking 1.1 The energy frontier 1.2 The particles of the Standard Model 1.3 Gauge boson coupling to fermions 1.4 Gauge boson self-couplings 1.5 COMPHEP evaluation of boson self-couplings 1.6 The Higgs mechanism for bosons and fermions 1.7 Higgs interactions and decays 1.8 Questions unanswered by the SM Questions Exercises References Further reading Detector basics 2.1 SM particles ­ mapping into detector subsystems 2.2 Tracking and "b tags" 2.3 EM calorimetry ­ e and 2.4 Hadron calorimetry ­ jets of q and g and neutrino (missing ET ) 2.5 Muon systems 2.6 Typical inelastic events 2.7 Complex event topologies in D0 and CDF Exercises References Further reading

page x xi 1 1 2 2 3 5 5 6 9 11 12 16 20 23 24 24 25 26 27 27 32 36 40 55 60 63 65 66 67

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viii 3

Contents Collider physics 3.1 Phase space and rapidity ­ the "plateau" 3.2 Source functions ­ protons to partons 3.3 Two body formation kinematics 3.4 Point like scattering of partons 3.5 Two-to-one Drell­Yan processes 3.6 Two-to-two decay kinematics ­ "back to back" 3.7 Jet fragmentation Exercises References Further reading Tevatron physics 4.1 QCD ­ jets and dijets 4.2 s determination 4.3 Prompt photons 4.4 b production at FNAL 4.5 t production at Fermilab 4.6 DY and lepton composites 4.7 EW production 4.8 Higgs mass from precision EW measurements Exercises References Further reading Higgs search strategy 5.1 Cross sections at the LHC 5.2 Higgs direct and "loop" couplings 5.3 Higgs production rates 5.4 Higgs branching ratios and search strategy 5.5 Luminosity and discovery limits 5.6 Lower limit on Higgs mass Exercises References Further reading SUSY and open questions in HEP 6.1 Generations 6.2 Parameters for mixing 6.3 Mass scales 6.4 Grand unification 6.5 SUSY ­ p stability and coupling constants 6.6 SUSY ­ cross sections at the LHC 6.7 SUSY signatures and spectroscopy 6.8 Cosmological constants (and SUSY?) 68 69 72 79 81 83 91 100 105 106 107 108 108 112 116 118 122 126 129 140 145 146 146 147 147 149 151 163 183 185 187 188 188 189 190 192 194 195 203 206 208 215

4

5

6

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Contents 6.9 SUSY and gravity Summary for hadron collider physics Exercises References Further reading Appendix A The Standard Model Appendix B A worked example in COMPHEP Appendix C Kinematics Appendix D Running couplings Index

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Acknowledgments

This text began as a series of lectures given to graduate students in Brazil and then later in expanded form to students at Fermilab. The comments and questions of the students have proved to be invaluable in improving this book. The secretarial work of Ms T. Grozis has made it possible to go smoothly from chaotic lecture notes to a complete and polished text. Finally, the many high energy physicists working on D0 and CMS as collaborators have shared their knowledge and insights countless times.

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Acronyms

ALEPH ATLAS BaBar Belle Bose­Einstein Breit­Wigner CDF CERN CKM

CM CMS COMPHEP CP CTEQ D(z)

DELPHI

One of the four experiments at the electron­positron collider (LEP) at CERN. One of the two general purpose experiments at the Large Hadron Collider (LHC) at CERN. The experiment running at the electron­positron collider (PEP-II) at SLAC. The experiment running at the electron­positron collider at KEK, Japan. The statistics obeyed by integral spin particles. The mass distribution for resonant (unstable) particles, characterized by a central mass, Mo , and a decay width, . One of the two general purpose experiments at the Tevatron proton­antiproton collider at Fermilab (FNAL). The European Centre for Nuclear Research located in Geneva, Switzerland. The unitary 3 â 3 matrix which describes the mixing of the strong interaction eigenstates (quarks) appropriate to the weak eigenstates active in decays. The center of momentum frame, where the total momentum of the system is zero. One of the two general purpose experiments at the LHC at CERN. A program to do calculations in high energy physics. The combined operation of charge conjugation (C) and parity inversion (P). One of the sets of distribution functions of quarks and gluons available in COMPHEP. The fragmentation function describing how a jet fragments into a collection of particles which carry a fraction z of the jet momentum. One of the four experiments at the electron­positron collider (LEP) at CERN. xi

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xii Dirac Equation D0 Drell­Yan EM EW Fermi­Dirac

Acronyms The equation which describes the motion of spin 1/2 particles. One of the two general purpose experiments at the Tevatron proton­antiproton collider at Fermilab (FNAL). A process in which a quark from one hadron annihilates with an antiquark from another hadron to create a boson. The electromagnetic compartment of a calorimeter. The electroweak theory which unifies electromagnetic and weak interactions. The statistics obeyed by half integral spin particles. Such particles obey the Fermi Exclusion principle where two fermions cannot be in the same quantum state. A national laboratory in the USA with a proton accelerator, located in Illinois. A diagrammatic representation of a fundamental interaction as it occurs in space and time. The decay width for a specific process. The inverse of the decay width is the lifetime for that process. The effective coupling constant for a four fermion weak interaction. A Grand Unified Theory, which proposes to unify the electroweak and strong interaction theories at a high mass scale. The hadronic compartment of a calorimeter. The proposed particle in the Standard Model which has spin zero and whose field takes on a non-zero expectation value in the vacuum. A collection of "stable" particles which is the result of the fragmentation of a quark or gluon. The jet has a parent quark or gluon. The Japanese center for high energy physics located in Tskuba, Japan. The equation which describes a relativistic particle that has no intrinsic spin. A parameter that is defined to "cutoff " the mass scale for a theory, which is badly behaved outside that mass range. One of the four experiments at the electron­positron collider (LEP) at CERN. Linear Collider. This is a proposed electron­positron collider which will have sufficient energy to directly form the Higgs boson. The Large Electron Positron collider which operated at CERN prior to the LHC construction.

Fermilab (FNAL) Feynman diagram G GUT

HAD Higgs

Jet

KEK Klein­Gordon L3 LC

LEP

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Acronyms LHC

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QCD

LSP

Luminosity Monte Carlo MMSM

MRS OPAL Pseudorapidity

PT

PYTHIA

QED QCD

R, G, B

Rapidity

The Large Hadron Collider is a proton­proton collider with a total CM energy of 14 TeV, which will begin operations at CERN in 2007. The cutoff energy in QCD below which the strong interactions become very strong. The strong interactions approach zero strength at very high energy scales. Lightest supersymmetric particle. In SUSY models the LSP is usually assumed to be absolutely stable. Therefore, the LSP is a candidate for the dark matter. The quantity which when multiplied by the cross section gives the reaction rate for a particular process. A numerical technique to simulate processes by choosing various quantities from specified distribution functions. Minimal SUSY model. The SUSY hypothesis has many possible realizations. The minimal model allows for specific predictions by making assumptions having minimal extensions to the SM. One of the sets of distribution functions of quarks and gluons available in COMPHEP. One of the four experiments at the electron­positron collider (LEP) at CERN. A variable which approaches rapidity for particles with mass less than transverse momentum and which is a function only of polar angle. Transverse momentum. The transverse direction is perpendicular to the incident hadrons in a p­p collision. Therefore, a large value of this parameter indicates a violent collision probing small distance scales. A Monte Carlo program which has a model for the fragmentation of quarks and gluons and also models the "underlying event" caused by the fragments of the fractured hadrons. Quantum electrodynamics. The relativistic theory of the interaction of photons with fundamental, point like fermions. Quantum chromodynamics. The relativistic theory of the interaction of colored gluons with fundamental point like colored quarks. The color labels, red, green, and blue. The assignments are arbitrary and simply label the three distinct color charges contained in SU(3). A variable used in high energy physics because it is additive under "boost" or Lorentz transformation. It is the relativistic

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xiv

Acronyms analog of velocity. One particle phase space implies a uniform rapidity distribution. The Stanford Linear Accelerator Center located in California and operating an electron­positron collider. The detector operating at the SLAC Linear Collider (SLC) which studied the properties of the Z by resonant formation. Standard Model. The model of high energy physics which describes fermions, quarks and leptons, interacting by electroweak interactions and strong interactions. Gravity is not included in the SM. A simplified SUSY model which has only five free parameters, thus giving predictive power. Supersymmetry. The postulated symmetry relates fermions to bosons. Therefore, each particle in the SM has a partner, all as yet undiscovered. The proton­antiproton collider operated at Fermilab at a CM energy of 2 TeV. The underground area experiments using the proton­antiproton collider operated at CERN at 0.27 TeV. The coupling of weak currents to fermions is by way of vector and axial vector interactions. Parity and charge conjugation violation are an immediate consequence of the V-A form. The angle that specifies the unitary rotation of the basic neutral gauge bosons into the physically realized Z and photon. The process whereby a quark emits a W from both initial state hadrons, thereby initiating W­W scattering or fusion into a variety of final states. A linear interaction between two fermions and a boson. If the boson has a mass, the range of the interaction is limited in space. "Off shell" gauge bosons which are out on the allowed, but improbable, "tail" of the Breit­Wigner mass distribution.

SLAC SLD SM

SUGRA SUSY

Tevatron UA1, UA2 V-A

Weinberg angle WW fusion

Yukawa interaction

Z* (W*)

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