Collisional energy loss and the suppression of high $p_T$ hadrons
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arXiv:nucl-th/0608058v1 25 Aug 2006CollisionalenergylossandthesuppressionofhighpThadrons
Jan-eAlama,AbheeK.Dutt-MazumderbandPradipRoyb
aVariableEnergyCyclotronCentre,1/AFBidhanNagar,Kolkata700064,India
bSahaInstituteofNuclearPhysics,1/AFBidhanNagar,Kolkata700064,India
Wecalculatenuclearsuppressionfactor(RAA)forlighthadronsbytakingonlythe
elasticprocessesandarguethatinthemeasuredpTdomainofRHIC,collisionalrather
thantheradiativeprocessesisthedominantmechanismforpartonicenergyloss.
1.Introduction
Jetquenchingisoneofthemostpromisingtoolstoextracttheinitialpartondensity
producedinhighenergyheavyioncollisions[1].Thisisrelatedtothefinalstateenergy
lossoftheleadingpartonscausingdepopulationofhadrons[2]athightransversemomen-
tum(pT).ThesuppressionsofhighpThadronsandunbalancedback-to-backazimuthal
correlationsofthedijeteventsinAu+AucollisionsmeasuredatRelativisticHeavyIon
Collider(RHIC)provideexperimentalevidenceinsupportofthequenching.Theob-
servednuclearsuppressionoflighthadrons(π,η)inAu+Aucollisionsat√2Alametal.
2.Formalism
WeuseFokkerPlanck(FP)equationtodynamicallyevolvepartonspectra.FPequation
canbederivedfromBoltzmannequationifoneofthepartnerofthebinarycollisionsis
inthermalequilibriumandthecollisionsaredominatedbythesmallanglescattering
involvingsoftmomentumexchange[7,9,10,11].Foralongitudinallyexpandingplasma,
FPequationreads:
∂
t∂
∂pi[piηf(p,t)]+1
∂p2[B(p)f(p,t)]+1
∂p2⊥[B⊥f(p,t)](1)
wherethesecondtermonthelefthandsidearisesduetoexpansion[12].Bjorken
hydrodynamicalmodel[13]hasbeenusedhereforspacetimeevolution.InEq.(1),f(p,t)
representsthenon-equilibriumdistributionofthepartonsunderstudy,η=(1/E)dE/dx,
denotesdragcoefficient,B=d(∆p)2/dt,B⊥=d(∆p⊥)2/dt,representdiffusion
constantsalongparallelandperpendiculardirectionsofthepropagatingpartons.
Inourcalculationsweincludesomeoftheimportantfeatureswhichwereignoredin
previouswork[14]inthecontextofjetquenching.Theseare:(i)thetermcorrespond-
ingtothelongitudinalexpansionisincluded,(ii)themomentumevolutionofparton
distributionsbothalonglongitudinalandtransversedirectionisconsideredand(iii)the
mechanismofhadronizationisintroduced.
Thetransportcoefficients,η,BandB⊥appearedineq.(1)havebeencalculatedin
Ref.[7].TheFPequationhasbeensolvedfortheinitialpartondistributionsparametrized
as[15]:
f(pT,pz,t=ti)≡dN
(1+pT
afa(p′,τi)|p′T=pT/z,Da/π0(z,Q2)dz(3)
wheref(p′,τi)andf(p′,τc)denotethepartondistributionsatpropertimeτiandτcrespectively.Hereτiistheinitialtimeandτcisthetimewhenthesystemcoolsdown
tothetransitiontemperatureTc(=190MeV).Wehavetakenαs=0.3andtheinitial
temperatureTi=450MeV.
3.Results
TheresultofourcalculationsforneutralpionisshowninFig.1whichdescribesthe
PHENIXdata[17]forAu+Auat√collisionalenergyloss..3
1611pT (GeV)0.00.20.40.60.81.0
RAA
π0 PHENIX dataη0 PHENIX data
Figure1.Nuclearsuppressionfactorfor
pion.Experimentaldataaretakenfrom
PHENIXcollaboration[17]forAu+Aucol-lisionsat√s=200
GeV/A.
Asatlower√
1NotethatEcisdefinedtobetheenergybelowwhichelasticlossdominates[6].4Alametal.
4.Summary
Inconclusion,ourinvestigationsclearlysuggestthatinthemeasuredpTrangeoflight
hadronsatRHICcollisional,ratherthantheradiative,isthedominantmechanismofjet
quenching.InclusionofthreebodyelasticchannelsmightevenincreaseEcmakingour
pointstronger.
REFERENCES
1.J.D.Bjorken,Fermilab-Pub-82/59-THY(1982)andErratum(Unpublished);M.Gyu-
lassy,I.Vitev,X.N.WangandB.W.Zhang,nucl-th/0302077;R.Baier,Y.L.Dok-
shitzer,S.PeigneandD.Schiff,Ann.Rev.Nucl.Part.Sci.50(2000)37.
2.FirstThreeYearsofOperationofRHIC,Nucl.Phys.A757(2005)1-283.
3.S.S.Adleretal.,PHENIXCollaboration,Phys.Rev.Lett.96(2006)032301.
4.S.Wicks,W.Horowitz,M.DjordjevicandM.Gyulassy,nucl-th/0512076.
5.N.Armesto,A.Dainese,C.A.SalgadoandU.A.Wiedemann,Phys.Rev.D71(2005)
064027.
6.A.K.Dutt-Mazumder,J.Alam,P.RoyandB.Sinha,Phys.Rev.D71(2005)094016.
7.P.Roy,A.K.Dutt-MazumderandJ.Alam,Phys.Rev.C73,044911(2006).
8.M.Djordjevic,nucl-th/0603066;S.Peigne,P.B.GossiauxandT.Gousset,J.High
EnergyPhys.04,(2006)011;I.P.LokhtinandA.M.Snigirev,Eur.Phys.C45(2006)
211;M.G.Mustafa,Phys.Rev.C72(2005)014905.
9.J.Alam,S.RahaandB.Sinha,Phys.Rev.Lett73(1994)1895.
10.B.Svetitsky,Phys.Rev.D37(1988)2484.
11.G.D.MooreandD.Teaney,Phys.Rev.C71064904(2005)064904;M.B.G.Ducati,
V.P.GoncalvesandL.F.Mackedanz,hep-ph/0506241;J.BjorakerandR.Venu-
gopalan,Phys.Rev.C63(2001)024609;H.v.HeesandR.Rapp,Phys.Rev.C71
(2005)034907.
12.G.Baym,Phys.Lett.B138(1984)18.
13.J.D.Bjorken,Phys.Rev.D27(1983)140.
14.M.G.MustafaandM.Thoma,ActaPhys.HungA22(2005)93.
15.B.Muller,Phys.Rev.C67(2003)061901R.
16.R.K.Ellis,W.J.StirlingandB.R.Webber,QCDandColliderPhysics,Cambridge
UniversityPress,1996.
17.S.S.Adleretal.,PHENIXcollaboration,Phys.Rev.Lett.96(2006)202301.
18.D.d’Enterria,Eur.Phys.JC43(2005)295.
