The polarized and unpolarized photon content of the nucleon [Elektronische Ressource] / vorgelegt von Cristian Pisano

Description

The Polarized and UnpolarizedPhoton Content of theNucleonDissertationzur Erlangung des Grades einesDoktors der Naturwissenschaftender Abteilung Physikder Universit at Dortmundvorgelegt vonCristian PisanoMai 2005Contents1 Introduction 12 The Structure of the Nucleon 92.1 Elastic Form Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.2 Unpolarized Structure Functions . . . . . . . . . . . . . . . . . . . . . . . . 152.3 Polarized Structure Functions . . . . . . . . . . . . . . . . . . . . . . . . . 192.4 Parton Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222.5 Structure Functions in QCD . . . . . . . . . . . . . . . . . . . . . . . . . . 243 The Equivalent Photon Distributions of the Nucleon 313.1 Unpolarized Photon . . . . . . . . . . . . . . . . . . . . . . . 313.1.1 Elastic Component . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.1.2 Inelastic Component . . . . . . . . . . . . . . . . . . . . . . . . . . 363.2 Polarized Photon Distributions . . . . . . . . . . . . . . . . . . . . . . . . 373.2.1 Elastic Component . . . . . . . . . . . . . . . . . . . . . . . . . . . 373.2.2 Inelastic Component . . . . . . . . . . . . . . . . . . . . . . . . . . 403.3 Numerical Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414 Measurement of the Equivalent Photon Distributions 474.1 Theoretical Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484.1.

Sujets

• Physik

Informations

• Publié par: technischen_universitat_dortmund
• Publié le: 01 janvier 2005
• Nombre de lectures: 17
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

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1

2TheStructureoftheNucleon9
2.1ElasticFormFactors..............................9
2.2UnpolarizedStructureFunctions........................15
2.3PolarizedStructureFunctions.........................19
2.4PartonModel..................................22
2.5StructureFunctionsinQCD..........................24

3TheEquivalentPhotonDistributionsoftheNucleon31
3.1UnpolarizedPhotonDistributions.......................31
3.1.1ElasticComponent...........................32
3.1.2InelasticComponent..........................36
3.2PolarizedPhotonDistributions........................37
3.2.1ElasticComponent...........................37
3.2.2InelasticComponent..........................40
3.3NumericalResults................................41

4MeasurementoftheEquivalentPhotonDistributions47
4.1TheoreticalFramework.............................48
4.1.1DimuonProduction...........................48

ii

CONTENTS

4.1.2Electron-PhotonProduction......................53
4.2NumericalResults................................55
4.3Summary....................................61

5TheUnpolarizedQEDComptonScatteringProcess63
5.1RadiativeCorrectionstoElectron-ProtonCollisions.............64
5.2ElasticQEDComptonScattering.......................66
5.3InelasticQEDComptonScattering......................70
5.4NumericalResults................................73
5.5Summary....................................80

6SuppressionoftheBackgroundtoQEDComptonscattering81
6.1ElasticChannel.................................82
6.2InelasticChannel................................84
6.3NumericalResults................................85
6.4Summary....................................94

7ThePolarizedQEDComptonScatteringProcess95
7.1ElasticQEDComptonScattering.......................96
7.2InelasticQEDComptonScattering......................98
7.3BackgroundfromVirtualComptonScattering................100
7.4NumericalResults................................101
7.4.1HERMES................................102
7.4.2COMPASS...............................107
7.4.3eRHIC..................................109
7.5Summary....................................113

8WProductioninep→WX

115

CONTENTS

8.1TheoreticalFramework.............................116
8.2NumericalResults................................120
8.3Summary....................................124

9ConclusionsandSummary

ANotationsandConventions

127

131

135SectionsCrossPhoton-inducedBB.1DimuonProduction...............................135
B.2ComptonScattering..............................139

CKinematicsoftheQEDComptonScatteringProcess143
C.1ElasticChannel.................................143
C.2InelasticChannel................................146

DMatrixElementsfortheUnpolarizedQEDCSandVCSProcesses149
D.1ElasticChannel.................................149
D.2InelasticChannel................................151

EMatrixElementsforthePolarizedQEDCSandVCSProcesses155
E.1ElasticChannel.................................155
E.2InelasticChannel................................157

iii

1Chapter

Inductiontro

Inthisthesisthepolarizedandunpolarizedphotondistributionsofthenucleon(proton,
neutron),evaluatedintheequivalentphotonapproximation,arecomputedtheoretically
andthepossibilityoftheirexperimentaldeterminationisdemonstrated.Thethesisis
basedonthefollowingpublications[1–6]:

M.Gluck,C.Pisano,E.Reya,Thepolarizedandunpolarizedphotoncontentofthe
nucleon,Phys.Lett.B540,75(2002)[Chapter3].

M.Gluck,C.Pisano,E.Reya,I.Schienbein,Delineatingthepolarizedandunpola-
rizedphotondistributionsofthenucleonineNcollisions,Eur.Phys.J.C27,427
4].[Chapter(2003)

A.Mukherjee,C.Pisano,ManifestlycovariantanalysisoftheQEDComptonprocess
inep→epandep→eX,Eur.Phys.J.C30,477(2003)[Chapter5].
A.Mukherjee,C.Pisano,SuppressingthebackgroundprocesstoQEDCompton
scatteringfordelineatingthephotoncontentoftheproton,Eur.Phys.J.C35,509
6].[Chapter(2004)

A.Mukherjee,C.Pisano,Accessingthelongitudinallypolarizedphotoncontentof
theproton,Phys.Rev.D70,034029(2004)[Chapter7].

C.Pisano,Testingtheequivalentphotonapproximationoftheprotonintheprocess
ep→WX,Eur.Phys.J.C38,79(2004)[Chapter8].

2

ductiontroIn

Theresultsof[5]havebeensummarizedin[7]aswell.FurthermoreinSection2.5we
shortlyrecallthemainndingsoftherecentpaper[8],alsoconcerningthestructureof
ucleon:nthe

M.Gluck,C.Pisano,E.Reya,ProbingtheperturbativeNLOpartonevolutionin
thesmall-xregion,Eur.Phys.J.C40,515(2005).

Theequivalentphotonapproximation(EPA)ofachargedfermionisatechnicaldevice
whichallowsforarathersimpleandecientcalculationofanyphoton-inducedsubpro-
cess.TherstexplicitformulationandquantitativeapplicationoftheEPAweregivenin
1924byFermi[9],whoutilizedittoestimatetheelectro-excitationandelectro-ionization
ofatoms,andalsotheenergyloss,duetoionization,of-particlestravellingthroughmat-
ter.Inseveralcases,heobtainedasatisfactorynumericalagreementwithexperimental
data.Tenyearslater,inordertosimplifycalculationsofprocessesinvolvingrelativistic
collisionsofchargedparticles,Williams[10]andWeizsacker[11]furtherdevelopedFermi’s
semi-classicaltreatmentandextendedittohigh-energyelectrodynamics.Theyobserved
thattheelectromagneticeldgeneratedatagivenpointbyafastchargedparticlepassing
closetoitcontainspredominantlytransversecomponents.BymakingaFourieranalysis
oftheeld,theyconcludedthattheincidentparticlewouldproducethesameeectsas
abeamofphotonsandcomputedtheirdistributioninenergy.Thismodelassumesthat
theparticlemotionisnotappreciablyaectedduringtheinteraction,inparticularthat
small.isanglescatteringitsThersteld-theoreticalderivationsweregivenintheftiesbyDalitzandYennie[12],
Curtis[13],KesslerandKessler[14],andlaterbyChenandZerwas[15].Theequivalent
photonmethodforpointlikefermions,liketheelectron,hasbeeninvestigatedandutilized
widely,forexampleithasbeenappliedtopionproductioninelectro-nucleoncollisions
[12,13]andtotwo-photonprocessesforparticleproductionathighenergies[16–18].A
detailedhistoryofthemethod,itsvariousformulationsanditsrstapplicationsare
containedinKessler’sreviewarticle[19].Inmorerecenttimes,thevalidityofthisap-
proximationhasbeenexaminedbyBawaandStirling[20]inthecontextoftheproduction
oflargetransversemomentumphotonsattheHERAcollider,bycomparingtheexactand
approximatecrosssections.Frixione,Mangano,NasonandRidolinawell-knownpaper
[21]furthermodi