An Introduction To Gauge Theories And The ’New Physics’

517 Pages·1982·27.6 MB·English

by  Elliot Leader, Enrico Predazzi

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Inthe last few years there has been a
veritable revolution in the field of
elementary particle physics.
On the one hand, the experimental
discovery of the remarkable J/\¥ particle in
1974heraldedatotallyunforeseen newstage
in the evolution of our ideas about the
fundamental particles. A succession of
extraordinary discoveries has followed,
culminating in the finding of an entirely
novel class of objects, the 'charmed'
particles, and a most unexpected massively
heavylepton, theT, andthere isgoodreason
to suppose that yet other families of
particles, endowed with the tantalizing
sounding qualities of 'truth' and 'beauty'
exist, and will be studied when the new
generation of colliding-beam accelerators
comesintooperation. Indeed, particleswith
beauty have recently been identified.
On theotherhand,andinparallelwith this
experimentaldevelopment, there has been a
deepchangeofemphasisandapproachinthe
theoretical picture, which is now framed in
the esoteric language of quarks,partons and
gauge theories. The weak and
electromagnetic interactions have been
unified into a single beautiful gauge field
theory, which has produced remarkable
agreement with a host of experimental data,
and which holds out the possibility of the
discovery of some truly massive new vector
mesons with masses close to 100 times the
proton mass! The strong interactions seem
also to be controlled byagaugefield theory,
quantum chromodynamics or QeD, which,
although still plagued by unanswered
questions, does appear to give a satisfactory
explanation for many recent experimental
discoveries, and for whose characteristic
continued on back flap
AN INTRODUCTION TO
GAUGE THEORIES AND THE 'NEW PHYSICS'
Textbook charm productionas AACHEN-BONN-CERN·MUNICH-OXFORD COLLABORATION
seeninneutrinointeractionsin WA 21
the BEBCbubblechamberby
EVENT 294/099~
theAachen-Bonn-CERN
Munich-Oxford collaboration. lIP-'O*Pp.-
Although their short lifetime
Lo°7r+
preventsthe twocharmed
L 7
mesonsfrombeingseendi
\...JL+II
rectly,allother particlesfrom P
le+Y 1.71
theproduction vertexand sub
K-Tr+
saenqduegnivtedoebcaseyrsvaarbelechtraarcgkesd. L+p....I7r+
Ln7r-
Thisgivesa veryreliablein
L+
dication ofthekinematics of p-.np
thedecaychain.(Photo
CERN.)
Explanationofthecharm pro
duction eventseenin BEBC.
Aswellasthe productionand
decayofcharmed mesons,the
...
photographshowsanegative
•
kaon stopping and interacting ••
•
witha proton,withinteresting
consequences.Theweakdecay
ofa positivepion can alsobe
followed,thedecaypoint and
emissionofaneutrinoshowing in
t
up asadefinitekink inthe
spiral. NEUTRINO
.BEAM
MOMENTUM IN GeVIc
AN INTRODUCTION TO
GI
GilliE TIIIIHIIIIIIII
AND THE
«mNIIII' ~~~~IIHIIII IIIII
SIIW
ELLIOT LEADER
Professor ofTheoretical Physics, Westfield College, UniversityofLondon
ENRICO PREDAZZI
Professor ofTheoretical Physics, University ofTorino
CAMBRIDGE UNIVERSITY PRESS
Cambridge
London New York New Rochelle
Melbourne Sydney
Published bythe Press Syndicateofthe University ofCambridge
The Pitt Building,TrumpingtonStreet,CambridgeCB21RP
32East 57th Street,NewYork,NY 10022,USA
296BeaconsfieldParade,Middle Park,Melbourne 3206,Australia.
!JCambridge University Press 1982
First published 1982
Printed inGreat Britain at the University Press,Cambridge
Library ofCongresscatalogue card number: 81-3860
British Librarycataloguing inpublicationdata
Leader, Elliot
An introductionto gaugetheories and the
'newphysics'.
1. Gauge fields(Physics)
I. Title II.Predazzi,Enrico
539.7'2 QC793.3.F3
ISBN 0521233755hard covers
ISBN 0521 299373paperback
To Christiana and Joan
CONTENTS
Frontispiece ii Foreword xi Notational conventions xiii
1 Field theory and pre-gauge theory weakinteractions 1
1.1 Abriefintroduction to fieldtheory 1
1.2 Pre-gauge theory weak interactions 4
1.3 Some usefultechnical results 14
1.3.1 The spin or helicitystructure 14
1.3.2 Relation between particle and anti-particle amplitudes 16
1.3.3 The isospin structure 16
2 Theneedfora gaugetheory 19
2.1 The intermediate vector boson 19
2.2 Towards a renormalizable theory 23
2.3 Gauge symmetry 25
2.3.1 Global gauge invariance- the Abelian case 26
2.3.2 Local gauge invariance- the Abelian case 27
2.3.3 Global gauge invariance- the non-Abelian case 29
2.3.4 Non-Abelian local gauge invariance-Yang-Mills theories 31
2.4 Freedom to choose the gauge 34
2.5 Summary 34
3 Spontaneoussymmetry breaking:theGoldstone theorem and the
Higgsphenomenon 36
3.1 Spontaneously broken symmetriesin fieldtheory 37
3.1.1 Spontaneously broken global symmetry 37
3.2 The Higgs mechanism 40
3.3 Unitarity and renormalizability 43
3.4 Summary 44
4 Unificationofthe weakandelectromagneticinteractions 45
4.1 The Weinberg-Salam model 46
4.2 Phenomenology ofpurely leptonic reactions 56
v
Contents
VI
5 Extensionto thehadrons 66
5.1 Charm 66
5.2 Colour 72
5.2.1 The quark statistics 72
5.2.2 nO-.2y 74
5.2.3 Triangle anomalies 76
5.2.4 The cross-sectionfor e+e- --+hadrons 80
5.3 Summary ofthe WS model 82
6 Phenomenologyofsemi-leptonicreactions 84
6.1 Modelindependent tests 85
6.2 Parity violation in electron-nucleus scattering 92
6.3 Optical rotation 97
6.4 Summary 103
7 Experimentalidentificationofthe gaugebosons 104
7.1 W production 104
7.2 The Higgs boson 109
8 Experimentaland theoreticalintroductionto thenewparticles 112
8.1 Introduction 112
8.2 The 'new' particles 114
8.3 Rudiments ofquantum chromodynamics 116
8.4 Quark-lepton parallelism 119
8.5 Flavour-changingreactions 121
8.6 8U(4)classification ofmesons and baryons 122
8.7 CP violation 127
8.8 Electron-positron storage rings 128
8.9 Physics with e+e- machines 137
8.10 Angular distribution of hadrons produced in e+e- collisions 146
9 The narrowvector resonances 151
9.1 The OZI rule and theIIt/!(3097) 152
9.2 Experimentalstatus ofthe lit/! spectroscopy 158
9.3 Properties ofthe lit/! (3097) and tjI'(3684) 163
9.3.1 1It/!and t/!' widths 164
9.3.2 JPC assignments 165
9.3.3 IG assignments 170
9.3.4 8U(3)assignments 172
9.3.5 Miscellaneous properties 172
9.3.6 Radiative decay ofthe IItj1family and new states 173
9.4 Charmonium 174
9.5 Charmonium decay rates 181
9.6 bb bound states 188
10 Charm-and beauty 194
10.1 Discovery ofcharmed particles 194
Contents Vll
10.1.1 Charge of the charmed quark 200
10.1.2 Charmed particle masses 200
10.2 Charm decay 201
10.2.1 Purely leptonic decay of charmed mesons 202
10.2.2 Semi-leptonic and hadronic decay ofcharmed mesons 203
10.2.3 Production ofcharmed mesons 206
10.2.4 Charmed baryon decay 206
10.3 Properties ofD and F mesons 207
10.3.1 Production of the D 207
10.3.2 Decay of the D 211
10.3.3 D mesons above 4 GeV 213
10.3.4 The F mesons 215
10.4 'Naked beauty' 216
11 Theheavyleptonr 217
11.1 Discovery ofthe r lepton 218
11.2 Properties ofthe r lepton 222
11.2.1 The r mass 222
11.2.2 The r lifetime 224
11.2.3 The spin of the r 224
11.2.4 Point-like structure 225
11.3 r decay 225
11.3.1 Semi-leptonic r decays 226
11.4 The r neutrino 227
11.5 Status ofthe quark-lepton spectroscopy 228
12 Towardsthepartonmodel-deepinelasticscattering 230
12.1 Electron-muon scattering 231
12.2 Elastic electron-proton scattering 235
12.3 Inelastic electron-nucleon scattering 238
12.4 Inelastic neutrino-nucleon scattering 245
12.5 Deep inelastic scattering and scaling behaviour 250
12.6 Polarization effectsin deep inelastic scattering 254
13 Thesimplepartonmodel 260
13.1 The introduction ofpartons 260
13.2 Anti-partons 268
13.3 Partons as quarks 270
13.4 The detailed quark-parton model 273
13.4.1. The electromagnetic scalingfunctions 274
13.4.2 Neutrino charged current scalingfunctions 275
13.4.3 Neutrino neutral current scalingfunctions 278
13.4.4 Experimental tests of scaling functions in quark-parton model 278
13.5 Behaviour ofscalingfunctions as x--+'O 291
13.6 The missingconstituents- gluons 292
13.7 The parton model in polarized deep inelastic scattering 294
Contents viii
14 Thekinematicalbasisofthe partonmodel 298
14.1 The parton model as an impulse approximation 298
14.2 The parton model with Fermi motion 302
14.3 Applications ofthe parton model to related processes 309
14.3.1 e+e- annihilation into hadrons 310
14.3.2 The Drell-Yan process 311
14.3.3 Production of heavy mesons by Drell-Yan mechanism 323
14.4 'Wee' and 'hard' partons 325
15 The renormalizationgroup, gauge theories and
quantum chromodynamics 327
15.1 Introduction 327
15.2 Parameters and physical observables in a field theory 328
15.3 Theidea ofrenormalization 331
15.4 Introduction to the renormalization group 336
15.5 Scaling and asymptoticfreedom 342
15.6 Gauge theories:QED and QCD 346
15.6.1 QED 346
15.6.2 QeD 351
15.7 The renormalization groupfor QCD 354
15.8 Applications 358
15.8.1 e+e- -+hadrons 358
15.8.2 Deep inelastic lepton scattering 362
15.8.3 The Drell-Yan process 380
15.8.4 Inclusive hadronicreactions 382
15.8.5 Summary 383
16 LargeP hadronic phenomena 385
T
16.1 Introduction 385
16.2 Hard scattering ofquarks 387
16.3 From quark to hadron cross-sections 393
16.4 Prompt photons 395
16.5 Elastic data 396
16.6 Conclusions 398
17 Jetsinhadronic physics 399
17.1 Generalities on hadronicjets 399
17.2 Experimental evidencefor towardsjets 402
17.3 Experimentalevidencefor awayjets 404
17.4 Trigger bias (experimental) 406
17.5 Relation betweenjet and particle distributions 410
17.6 Transverse momentum distribution of hadrons with respect to
the jet axis 412
17.7 Scalingin x, and longitudinalfragmentation 413
17.8 More on trigger bias (theoretical) and on jetcross-sections 415