qgp and high‐pt physicsreygers/...jets as auto‐generated probes of the qgp • thermalizaon of...

Obergurgl 2010 - QGP and High-pT Physics Klaus Reygers

PDDr.KlausReygersPhysikalischesIns5tutUniversitätHeidelberg

1

QGPandHigh‐pTPhysicsLecture2:JetsandJetQuenching

HelmholtzGraduateSchoolofFundamentalPhysicsWinterSchoolObergurgl2010January29‐February2,2010


Outline

• Introduc*on:HardSca0eringandJetQuenching

• TheDiscoveryPhase(ca.2000‐2003)

• FurtherExperimentalResultsRelatedtoJetQuenching

• FutureJetQuenchingMeasurements

2

Obergurgl 2010 - QGP and High-pT Physics Klaus Reygers3

Introduc*on:HardSca0eringandJetQuenching


Theore5calDescrip5onofHigh‐pTPar5cleProduc5on:

Perturba5veQCD

• Sca0eringofpointlikepartonsdescribedbyQCDperturba*ontheory(pQCD)

• SoPprocessesdescribedbyuniversal,phenomenologicalfunc*ons‣ Partondistribu*onfunc*onfromdeepinelas*csca0ering‣ Fragmenta*onfunc*onsfrome+e‐collisions

Leading hadron:

z = phadron / pparton

≈ 0.25

factoriza5on:

4


HadronProduc5oninLeadingOrderQCD

Fragmenta5onfunc5onInv.Crosssec5on

Phenomenologicalfactorwhichtakeshigherordercontribu5onsintoaccount

Partondistribu5ons(func5onsofxBjorkenandmomentumtransferQ2)

ElementaryQCDparton‐partoncrosssec5on

E d3σ

dp3= K dxa

xa ,min

1

∫ dxbxb ,min

1

∫ fa A xa ,Q2( ) fb B xb ,Q2( )dσab→cd

dt̂1πzc

Dh c zc ,Q2( )a,b,c ,d =q,q , g∑

zc = pT,Hadron / pT,c

5


PartonDistribu5ons:HighPrecisionDatafromHERA

Fitting procedure

proton pdf

Bjorken-x6


Example:Gluonandu‐QuarkFragmenta5onFunc5ons

Albino,Kniehl,Kramer,Nucl.Phys.B725(2005),181

Fragmenta*onfunc*ons:Numberdensityfortheproduc*onofahadronhwithfrac*onalenergyzinthefragmenta*onofaparton(e.g.determinedfrom) e

+e− → Z 0 → qq

7


NLOpQCDWorksatRHIC

p + p→ π0 + X

sNN = 200GeV

AgreementwithpQCDinp+pshowsthathigh‐pTpionsareacalibratedprobeofthemediumcreatedinA+Acollisions

8


Modifica5onoftheStructureFunc5onsinNuclei

x<0.1:“shadowingregion”

0.1<x<0.3:“an5‐shadowing”

0.3<x<0.7:“EMCeffect”

0.7<x<1.0:Fermi‐mo5onofnucleonsinnuclei

9


AnExample:NuclearPDF‘sinPb(EPS09NLO)

Valencequarks Seaquarks gluons

Largeuncertain5esforgluonPDF’satsmallx Eskola et al., arXiv:0902.4154v2 [hep-ph]

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http://arxiv.org/abs/0902.4154v2

http://arxiv.org/abs/0902.4154v2


JetQuenching:BasicIdea

Expecta*on:Simplescalingfromp+ptod+Au

Expecta*on:PionsuppressioninA+A

Expecta*on:Simplescalingfromp+ptoA+Afordirectphotons

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JetsasAuto‐GeneratedProbesoftheQGP

• Thermaliza*onofthedeconfinedquark‐gluonma0erexpectedatτ0<∼1fm/c

• Hardprobes(jets,high‐pTdirectphotons,c‐andb‐quarks)producedinearlyhardpartonsca0eringspriortoQGP⇒idealQGPprobes

Earlyhardparton‐partonscalerings(Q2>> Λ2

QCD)

Thermalizedmedium(QGP!?)(T0>Tc,Tc≈150–200MeV)

Transi5onQGP → hadrongas

Freeze‐out

%me

12


WhatCanWeHopetoLearnfromJetQuenching?

• Objec*vesofheavy‐ionphysics:‣ LearnsomethingaboutQCDintheregimeofhightemperaturesand

densi*es(QCDthermodynamics)‣ Studythedeconfinementtransi*onatTc=150‐200MeVpredictedby

lacceQCDcalcula*ons

• ObservablesrelatedtoJetQuenchingmayhelpto‣ characterizethenewstateofma0eraboveTc‣ understandthemechanismofpartonenergyloss

• Basiclogic

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QGP SuppressionofhadronsathighpT⇒⇐


HowCanWeStudyJetQuenching?

• Measurementofpar*clemul*plici*esathighpT

• Measurementoftwo‐par*cleangularcorrela*ons

• Jetreconstruc*ononanevent‐by‐eventbasis‣ Challengingincentralnucleus‐nucleuscollisionsatRHICduetolarge

par*clemul*plicityfromtheunderlyingevent‣ Situa*onimprovessignificantlyforPb+PbattheLHCduetothe

increasedcrosssec*onforjetproduc*on

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JetQuenchingHistory

15

• Energylossviaelas*csca0eringwaslaterbelievedtohaveonlyaminoreffectonjets

• Radia*veenergylosswasdiscussedintheliteraturefrom1992onbyGyulassy,Pluemer,Wang,Baier,Dokshitzer,Mueller,Pegne,Schiff,Levai,Vitev,Zhakarov,Wang,Salgado,Wiedemann,…


Analogy:EnergylossofChargedPar5clesinNormalMaler

• μ+onCu:Radia*onalenergyloss(„bremsstrahlung“)startstodominateovercollisionalenergyloss(„Bethe‐Blochformula“)forp>>100GeV/c

• Forenerge*cquarksandgluonsinQCDma0er,radia*veenergylossviainducedgluonemissionis/wasexpectedtobethedominantprocess

μ CuE E´

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PartonEnergyLoss–ExpectedProper5es

ΔE∝αsCFq̂L2 EnergylossΔEinasta5cmediumoflengthLforE→∞(BDMPSresults)

Radia5veenergylossdominant(?): µ

2 : Typicalmomentumtransferfromthemediumtotheparton

λ : Meanfreepath

q̂ =

µ2

λMediumparameter

Energylossforgluonjetslargerthanforquarkjets

CF =

34 / 3

for gluon jets for quark jets

⎧⎨⎪⎪⎩⎪⎪

L2dependence:Non‐abeliannatureofQCD+quantenm.interference

Nucl.Phys.B483:291‐320,1997

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PartonEnergyLoss:WhyΔE∝L2?

Probabilityforradia*ngagluon:

Coherentgluonwavefunc*onaccumulatestransversemomentumkT.Numberofsca0eringswithmomentumtransferkTun*litdecoheres:

Totalenergyloss:

∝ L

ΔE∝ L2

∝ L

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Rela5onbetweenTransportCoefficientandEnergyDensityoftheMedium

• increasessmoothlywithenergydensity

• Nuclearma0er

ideal qgphot, massless pion gas

cold pion gas• QGP(andhothadrongas):

Mediumcharacterizedby(Momentumtransferpermeanfreepath)

q̂nuclear matter < 0.5−1 GeV2 / fm

q̂qgp q̂nuclear matter

q̂ = µ 2 / λ

energydensity(GeV/fm3)

q̂ (G

eV2/fm

)

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Medium‐ModifiedFragmenta5onFunc5ons

energylossparton

hadron h, energy

Prob.Distr.forpartonenergylossε(“Quenchingweight”)

Considerfixedpartonenergylossε:

Averageoverenergylossprobability:Hadronsresul5ngfromgluonbremsstrahlungneglected

z =Eh

(1−ε)Eq

, x =Eh

Eq

=x

(1−ε)

dndx

=dndz⋅

dzdx

= Dh / q (z,Q2 ) ⋅ 11−ε

(1−ε)Eq Eq

P(ε) Dh / q (z,Q2 )

Dh / q

med(x,Q2 ) = dεP(ε) Dh / q ( x1−ε

,Q2 ) 11−ε

0

1

∫

PartonenergylosscanbeconvenientlyincludedinapQCDcalcula5onviamodifiedfragmenta5onfunc5ons

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EnergylossintheGLVFormalismforPb+PbattheLHC

energy loss # radiated gluons

CentralPb+Pbat√sNN=5500GeV: L≈6fm,dNg/dy=2000,3000,4000

I. Vitev, Phys.Lett.B639:38-45,2006

∆Egluon/∆Equark=9/4onlyinthelimitE→∞

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Radia5vevs.Collisional(i.e.,Elas5c)EnergyLoss

• ∆Eradia*ve>∆Ecollisonalforu,daswellascquarkswithE>10GeV

• ∆Eradia*ve≈∆Ecollisonalforbquarks

Wicks,Horowitz,DjordjevicGyulassy,Nucl.Phys.A784,426‐442

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High‐EnergyCollisionswithAlice:JetsinNucleus‐NucleusCollisionsKlausReygers

TheNuclearModifica5onFactor(I):Digression:LuminosityofaCollider

Rateofeventsforagivenphysicsprocess:

Luminosity [(s⋅cm2)-1]

Cross section [cm2]

Event rate [s-1]

Iftwobunchesofpar5clescollidewithfrequencyfthen:

Transverse area of the beam

ni: number of particles in bunch i

Example:Au+Au at RHIC: L = 2 x 1026 cm-2 s-1

N = L ⋅σ

L = f

n1n2

Abeam

= fn1n2

4πσxσ y

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• Calculateincreaseoftheeffec*veluminosityofnucleons(orpartons,respec*vely)basedonknownnucleargeometry

• Result:Par*cleyieldsscalewiththeaveragenumber〈Ncoll〉ofinelas*cnucleon‐nucleoncollisionsintheabsenceofnucleareffects

Only changecompared to p+p

TheNuclearModifica5onFactor(II):Par5cleYieldsfromHardScaleringinA+A

dNhartA+B

dpT

= TAB ⋅dσhart

p+ p

dpT

TAB = Ncoll / σNNunel.

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• TABistheeffec*venucleonorpartonluminosityperA+Acollision

• Inprac*ce:〈Ncoll〉fromGlauberMonteCarlocalcula*on

• Intheabsenceofnucleareffects:RAB=1athighpT(pT>2GeV/c)

• Thisfollowsimplicitlyfromthefactoriza*ontheorem

“no medium effects”RAB = 1

RAB

RAB < 1

pT (GeV)

TheNuclearModifica5onFactor(III):RAA(pT)

RAB ( pT ) =d2 N / dpTdy

A+B

Ncoll ×d2 N / dpTdyp+ p

=d2 N / dpTdy

A+B

TAB ×d2σ / dpTdyp+ p

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TAB = Ncoll / σinelNN


Thediscoveryphase(ca.2000‐2003)


• Hadronsaresuppressed,directphotonsarenot

• Nosuppressionind+Au(notshownhere)

• Evidenceforpartonenergyloss

DiscoveryofJetQuenchingatRHIC(ca.2000‐2003)(I)

27

energy lossfor q and g

No energyloss for γ‘s

RAB =dN / dpT A+B

TAB ×dσinv / dpT p+p

,

where TAB = Ncoll / σinelNN

PHENIX: Phys.Rev.Lett.88:022301, 2002PHENIX: Phys.Rev.Lett.91:072301, 2003PHENIX: Phys.Rev.Lett.94:232301, 2005

STAR: Phys.Rev.Lett.89:202301,2002STAR: Phys.Rev.Lett.90:082302,2003STAR: Phys.Rev.Lett.91:172302,2003


DiscoveryofJetQuenchingatRHIC(ca.2000‐2003)(II)

28

DirectphotonsfollowTABscalingasexpectedforahardprobenotaffectedbythemedium

CentralityDependenceoftheπ0anddirectγRAA:


DiscoveryofJetQuenchingatRHIC(ca.2000‐2003)(III)

29

• Nojetcorrela*onaround180°incentralAu+Au• Consistentwithjetquenchingpicture

Au+Au peripheral Au+Au central

background and ellip. flow subtracted

Trigger particle: pT > 4 GeV/cAssociated particle: pT > 2 GeV/c trigger particle


FurtherExperimentalResultsRelatedtoJetQuenching


RAAwithHigherSta5s5cs(2004Run)

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RAA approximately constant up pT = 20 GeV/c

PHENIX: Phys.Rev.Lett.101:232301, 2008


SimpleInterpreta5onoftheConstantRAA

Inthissimplis*cviewtheconstantRAA≈0.25impliesaconstantfrac*onalenergylossofabout20%incentralAu+Auat200GeV

π0spectraatRHICenergy(√sNN=200GeV)describedwithn≈8

π0spectrumwithoutenergyloss:

Constantfrac*onalenergyloss:

Thisleadsto:

32

RAA = (1− Sloss )n−2 ⇒ Sloss = 1− RAA

1/(n−2) ≈ 0.2 for RAA ≈ 0.25

withoutenergyloss

withenergyloss(Sloss=0.2)


PathLengthDependence:π0RAAasaFunc5onoftheAnglew.r.t.theReac5onPlane

NPart

R AA

• Longerpathlengthforout‐of‐planejets• Hence,strongersuppressionforout‐of‐

planejetsinqualita*veagreementwithpartonenergyloss

33

in-plane

out-of-plane


DependenceontheSizeoftheNucleus:√sNNDependenceoftheπ0RAAforCu+Cu(A=63)

34

Phenix, Physical Review Letters 101,162301 (2008)

62.4and200GeVπ0produc*onlesssuppressedthaninAu+Au

22.4GeV• Nosuppression• Enhancementconsistentwithacalcula*onthatdescribesCronineffectinp+A

Sameconclusionasforheaviernuclei:PartonenergylossstartstoprevailoverCroninenhancementbetween√sNN=22.4GeVand62.4GeV


HierarchyExpectedforDifferentTypesofPartons

35

ΔEGluon >ΔEQuark ,m=0 >ΔEQuark ,m≠0

largercolorfactorforgluons:

CF =

34 / 3

for gluon jets for quark jets

⎧⎨⎪⎪⎩⎪⎪

Deadconeeffect:Heavyquarks(c,b)areslowerandradiatefewergluons

Dokshitzer&Kharzeev,PLB519(2001)199


PionRAAvs.ProtonRAA

36

RA

A A

u+

Au

ce

ntr

al

STAR QM08 JPG35(2008)104006

pRAA> π RAA eventhoughprotonsresultmostlyfromgluonfragmenta*on:

→ Differencebetweenquarkandgluonenergylossnotobserved


RAAforElectronsfromc‐andb‐QuarkDecays

37

e± from heavy flavor

e+ande‐fromcandbdecaysasstronglysuppressedaspions:

ΔEGluon >ΔEQuark ,m=0 >ΔEQuark ,m≠0 notobserved!

Phys.Rev.Lel.98,172301(2007)


RAAforElectronsfromHeavyQuarks:NotUnderstoodwithCurrentEnergyLossModels

PHENIX

GLV Parton energy loss calculation

• Radia*veenergylossnotsufficienttodescribeexcesselectronRAA• Includingelas*csca0eringimprovesthesitua*ononlyslightly

Radiative energy loss

Radiative energy loss +elastic scattering

38

Au+Auat√sNN=200GeV


FurtherResultsfromTwo‐Par5cleCorrela5ons(I):Away‐SideJetsVisibleAgainForHigherJetpT

• Chargedhadroncorrela*on

• Triggerpar*cle:pT>8GeV/c

• Associatedpar*cle:pT>6GeV/c

triggerpar5cle

Forhigherjetenergiesthecorrela*onatΔφ=180°incentralAu+Auisnotfullysuppressedanymore

39


FurtherResultsfromTwo‐Par5cleCorrela5ons(IIa):StrikingModifica5onoftheAway‐SideatLowpT

Trigger > 2.5 GeVpartner > 1 GeV

40



FurtherResultsfromTwo‐Par5cleCorrela5ons(IIb):Away‐SideCorrela5onatLow‐pTNotFullyUnderstood

D D

PHENIX preliminary

Possibleexplana*onsofthesplicngoftheaway‐sidepeakinclude

•Machcones

•flowinducedjetdeflec*on•andmanymore….

Mach cone?

41


CurrentStatusofJetQuenchingModels(I)

• Currentlyfourmajortheore*calpartonenergylossschemes:(HT,BDMPS‐Z‐ASW,AMY,GLV)

• Schemesmakedifferentapproxima*onsandmodelthemediumdifferently

• AllschemesbasedonpQCDfactoriza*onapproach

• Thefinalhadroniza*onisalwaysassumedtooccurinthevacuum(aPersomeenergyloss)

42

Dh / q

med(x,Q2 ) = dεP(ε) Dh / q ( x1−ε

,Q2 ) 11−ε

0

1

∫Forexample:

energylossprobability

vacuumfragmenta5onfunc5onmediummodifiedfragmenta5onfunc5on


CurrentStatusofJetQuenchingModels

• Allschemescanessen*allybereducedto1‐parametermodels(parametere.g.fixedbyficngthepionRAA(pT))

• Noschemedescribesalloftheobservedhigh‐pTobservables(RAAforlightandheavyquarks,RAAvs.reac*onplane,RAAfordifferentpar*clespecies,two‐par*clecorrela*ons)

• Largedifferences(uptoafactor4)betweenextractedmediumparameterslike

• Sofar:„AdvantageData“

43

q̂


JetAlgorithms


JetEventinap+pCollisionat√s =63GeV

Legoplotshowsenergyvs.pseudorapidityηandazimuthalangleφ

CERN ISR, ca. 1982

45


JetEventattheTevatron

46


Evolu5onofaJetEvent

HardProcess→PartonCascade→Hadroniza5on

describablewithpQCD

notdescribablewithpQCD(onlyphenomenologicalmodels)

47


Jet‐FindingAlgorithms

• Objec*ve:reconstructenergyanddirec*onofini*alparton

• Mustbeunambiguouslyapplicableatthelevelofexperimentaldata(tracks/towers)andinperturba*veQCDcalcula*on(partonlevel)

• Star*ngpoint:listofcalorimetertowersand/orchargedhadrontracks

• Twoclassesofalgorithms:‣ Conealgorithm:tradi*onalchoiceinhadron‐hadroncollisions

‣ kTalgorithm:tradi*onalchoiceine+e‐collisions

Cone algorithm:

Sumcontentinconewithradius

kT algorithm:

Successivelymerge“par5cles”inorderofrela5vetransversemomentum.

Termina5onofmergingcontrolledbyaparameterD

Typicalchoice:R=0.7

48


ConeAlgorithm

• (Normally)startwithseed(e.g.calorimetermodulewithhighenergy)• Considerallpar*clesinconearoundseedandcalculate

• Repeatthisprocedurewithnewconecenter(ηC,φC)• Terminatewhen“flow”ofconecenterstops• Calculatejetenergyas

• Apar*clemaybelongtotwocones:splitenergyamongjets

• Subtractbackgroundenergyfromunderlyingevent

Fermilab Run II jet physics:hep-ex/0005012

49


kTAlgorithm(I)

• Alorithmsstartswithalistofpreclusters(calorimetercells,par*cles,orpartons)

• CalculatepTandrapidityyforeachprecluster

• Foreachpreclusterdefine

• Foreachpair(i,j)ofpreclustersdefine

• ForD=1and∆Rij2<<1,dijistheminimaltransversemomentumkT(squared)ofonevectorwithrespecttotheother

• Findminimumdminofalldianddij

• Mergepreclustersiandjifdminisadij

• Else:Removepreclusteriwithdmin=difromlistofpreclustersandaddittothelistofjets

• Repeatun*llistofpreclustersisempty50


kTAlgorithm(II):ASimpleExample

openarrows:preclusters closedarrows:

jets

51


WhythekTAlgorithmisTypicallyOnly

usedine+e‐Collisions?

kTjethasnofixedshape/area→Difficulttosubtractbackgroundfromunderlyingevent

52


JetFindingAlgorithms:TypicalRequirements(I)

Thereconstructedjetsshouldnotchangeincaseof

• collinearspli|ng,i.e.,ifonepartonisreplacedbytwopartonsatthesameplace

• so}emission,i.e.,ifalowenergypartonisadded

Twotypesofdivergences:

collinear infrared

53


JetFindingAlgorithms:TypicalRequirements(II)

• Infraredsafety

Exampleofinfraredsensi5vity:So}radia5on(rightplot)causesmergingofjetswhichwouldhavebeenseparatedotherwise

• Collinearsafety

Exampleofcollinearsensi5vity:Seedandthereforejetnotfoundinle}picture

Exampleofcollinearsensi5vity:Reconstructedjetdependsonseed

FermilabRunIIjetphysics:hep‐ex/0005012

54


JetCrossSec5onsattheTevatron

Pre0ygoodagreementbetweendataandNLOpQCDpredic*ons

hlp://www‐d0.fnal.gov/Run2Physics/displays/presenta5ons/klima_lecture_jan2003/Lecture_1.pdf

ET = E sinϑ

55


FutureJetQuenchingMeasurements


ProblemswithRelyingonHadronSpectra

• Energylossbias‣ Hadrons biased to jets that lose

the least energy‣ Geometry („surface bias“)‣ Radiation fluctuations

• Averaging‣ Hadron measurements average

over jet energies‣ Indirect measurement of jet

quenching

• Solu*ons‣ Direct γ - hadron correlation‣ Full jet reconstruction

57

Surfacebias:Survivingjetsbiasedtowardsthesurfaceoftheoverlapregion:DifficulttoprobethehotcoreoftheQGP

Wicks,Horowitz,DjordjevicGyulassy,Nucl.Phys.A784,426‐442


WhyisJetReconstruc5onDifficultinCentralAu+AuCollisionsatRHIC?


CentralAu+Aucollisionat√sNN=130GeV:

ConsiderjetconewithradiusR:

Totaltransverseenergyinthiscone:

• BackgroundenergylargecomparedtojetenergyinA+AatRHIC.

• Increasedjetcrosssec*onhelpsatLHCenergies

ETcone =

d 2 ET

dηdϕ⋅πR2

=1

2πdET

dη⋅πR2 ≈ 40 GeV

R = Δη( )2

+ Δϕ( )2= 0.4

dET

dηη=0

≈ 500 GeV

ET = Ei sinϑ i

i∑ , dET / dη ≈ mT ⋅ dNch / dη

58


SinglePar5cleCrossSec5onattheLHC

p+p

Hardsca0eringcrosssec*onsincreasesignificantlyattheLHC

59


ChoiceoftheOp5malConeRadius

Smallconeradius:Smallbackgroundfromtheunderlyingeventattheexpenseofsomelossofjetpar*cles

Largeconeradius:Largebackgroundfromtheunderlyingeventbutnearlyalljetpar*clesincluded

Duetohigherbackgroundstheconeradiusinheavy‐ioncollisionstypicallysmallerthaninp+p(R~0.3‐0.4isagoodcompromiseinA+A)

60


HowCanOneStudyPartonEnergyLosswithReconstructedJetsattheLHC?

• MeasureJetRAAfordifferentconeradiiR

• Studymediuminducedmodifica*onoflateraljetprofile

• Studymodifica*onofthefragmenta*onfunc*on

61


JetRAAforDifferentConeRadiiR

• LargeconeradiusR:Allenergylostwillberecovered:RAAjet=1

• Outofconeradia*onwillreduceRAA

• Studyenergylossbyreconstruc*ngjetswithdifferentR

62

Calcula5onbyVitev,Wicks,andZhang(JHEP11,(2008),093):


LateralJetProfile

Broadeningoftheenergydistribu*onexpectedinPb+Pb

63


Medium‐ModifiedFragmenta5onFunc5ons

• Reconstruc*onofthefulljetenergyallowstomeasurefragmenta*onfunc*on

• PartonenergylosswillshiPpar*clestolowz(andthushigherξ)

• Moreover,themediumisexpectedtochangethepar*clecomposi*onofthejet,e.g.,theK/πra*o

• PromisingmeasurementforAliceduetoitsexcellentlowpTpar*cleID

Sapeta, Wiedemann, Eur.Phys.J.C55:293-302,2008.

64

http://www-library.desy.de/spires/find/wwwhepau/wwwscan?rawcmd=fin+%22Sapeta%2C%20Sebastian%22

http://www-library.desy.de/spires/find/wwwhepau/wwwscan?rawcmd=fin+%22Sapeta%2C%20Sebastian%22

http://www-library.desy.de/spires/find/wwwhepau/wwwscan?rawcmd=fin+%22Wiedemann%2C%20Urs%20Achim%22

http://www-library.desy.de/spires/find/wwwhepau/wwwscan?rawcmd=fin+%22Wiedemann%2C%20Urs%20Achim%22


PointstoTakeHome

• RHICresultshaveestablishedjetquenchingasanexperimentalfact

• Heavyquarksareasstronglysuppressedaslightquarkswhichisnotfullyunderstoodincurrentjetquenchingmodels

• Theul*mategoal,theconsistentcharacteriza*onofthemedium,isnotyetpossiblesincedifferentmodelsyielddifferentresults

• PHENIXandSTARareworkingonfulljetreconstruc*oninA+Acollisions

• Increasedjetcrosssec*onmakesfulljetreconstruc*oneaseratLHCenergies

65


ExtraSlides


SearchforJetQuenchinginthe1990‘s:S+SandPb+Pbat√sNN≈20GeVattheCERNSPS

67

X.N. Wang, PRL 98, 2655, 1998

• pQCD+Croninenhancementdescribesdata:apparentlynopartonenergyloss

• Conclusions‣ NoQGPatCERNSPS

(orveryshort‐lived)

‣ Nopar*clesuppressionathighpTduetointerac*onsinthehadronicphase(advantageousforRHIC!)


√sNNDependence:π0RAAforHeavyNucleiat√sNN=17.3,62.4,and200GeV

68

Onsetofsuppressionbetween√sNN=~20GeVund62.4GeV

central collisions

CERNSPSdata:WA98experiment,Phys.Rev.Lel.100:242301,2008


Direct‐γ‐TriggeredAway‐sideCorrela5ons:JetFragmenta5onFunc5oninp+pandAu+Au

• Nosurfacebiasforγastriggerpar*cle

• Jetenergyknown:Ejet≈Eγ

• Effec*vefragmenta*onfunc*onD(zT)canbemeasured:

69

zT =

pTh

pTγ

D(zT ) = 1

N trig

dN (zT )dzT

• DifferentslopeofD(zT)inp+pandAu+Aureflectsinfluenceofthemedium

• Datawithhigherprecisionneededtodrawquan*ta*veconclusions


JetsinPb+PbattheLHC

JetswithET>~50GeVinPb+Pbat√s=5500GeVattheLHCcanbeiden*fiedabovethebackgroundonanevent‐by‐eventbasis

ALICEsimula5on

Conesizeforjetreconstruc5on

background

InfluenceofbackgroundfromtheunderlyingeventminimizedwithconesizeR~0.3–0.4

70


FirstResultsfromFullJetReconstruc5onatRHIC:JetRAAinAu+Auat200GeVfromSTAR

• EvidenceforjetbroadeninginAu+AuatRHIC

• Situa*onmuchmorefavorableattheLHC(increasedjetcrosssec*on)71

STAR, arXiv0908.1799v3


FirstResultsfromFullJetReconstruc5onatRHIC:JetRAAinCu+Cuat200GeVfromPHENIX

• PHENIXhasdevelopedacone‐likealgorithm(Gaussianfilter)wheretheconeradiusisreplacedbyaGaussianwidthσ

• JetsuppressionobservedincentralCu+Cuat200GeVforσ=0.3

72

Y.-s. Lai (PHENIX collaboration), arXiv:0911.3399

qgp and high‐pt physicsreygers/...jets as auto‐generated probes of the qgp • thermalizaon of...

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