Yiwen Huang* (UCLA) for the STAR collaboration · background contributions have not been evaluated. In this poster, we present the correlation results with identified particles (protons,

Correlation signal is contaminated with the background contributions due to collective motion of the collision system (flow) • decay of the clusters will contribute to the charge separation

signal • elliptic flow coupled with transverse momentum conservation

(TMC) and local charge conservation (LCC)H: background-subtracted correlator, CME contributions

Chiralityimbalancecouldoccurinlocaldomainsinsidethehotnuclearmatterformedinhigh-energyheavy-ioncollisions.Inthepresenceofastrongmagneticfield,thischiralityimbalancewillinduceanelectricchargeseparationalongthemagneticfielddirectionduetothechiralmagneticeffect(CME)[1].Previousazimuthal-anglecorrelationmeasurements[2]withunidentifiedchargedparticleshavemanifestedchargeseparationsignalsconsistentwiththepredictionsoftheCME.Butthemagnitudesofthebackgroundcontributionshavenotbeenevaluated.Inthisposter,wepresentthecorrelationresultswithidentifiedparticles(protons,pionsandkaons)usingSTARdataof39GeVAu+Aucollisions.TheresultswillbecomparedwiththosefromAu+Auat√sNN=200GeV,aswellasthepublishedresultsofunidentifiedparticlesat√sNN=39GeV.

: baseline unrelated to the magnetic fieldBIN - BOUT: background contribution, suppressed to a level close to the magnitude of v2P-even quantity: still sensitive to separation effect, i.e., different for “same sign” and “oppo sign”

Identifiedparticleresultsforp-πandK-πbehaveasexpected:Oppositesignsignalisabovethesamesignsignal,andthethesignalissmallerformorecentralcollisions.Cannotclaimacharge-separationsignalinp-πorK-πbecausethenormalizedsignal+backgroundvalueiscompatiblewithbackgroundatthislevelofprecision.Studyofphysicsbackground,e.g.flow,areunderwayforthechargedpairs.

*e-mail: evahuang@ucla.edu Knudsen 5-137, 475 Portola Plaza, Los Angeles, CA 90095-1547

Yiwen Huang* (UCLA) for the STAR collaboration

Search for Chiral Magnetic Effect with Identified Particles in Au+Au Collisions

at √sNN = 39 GeV from RHIC/STAR

Chiral Magnetic Effect (CME)

Localchirallyimbalanceddomainsmaybecreatedinheavy-ioncollisionsonanevent-by-eventbasis.Achiralsystembearsanon-zeroaxialchemicalpotential,μ5.Innon-centralcollisions,astrongmagneticfield(B~1017-1018Gauss)willbeproduced.AnelectriccurrentwillbeinducedinchirallyimbalanceddomainsalongtheBfield:ChiralMagneticEffect(CME).Chargeseparationfluctuationsforallchargedparticleshavebeenexperimentallyobserved.Foridentifiedparticles:IsthereanindicationofCME?

dN±d�

/ 1 + 2a±sin(�± � RP )

� = hcos(�↵

+ �

�

� 2 RP

)i= [hv1,↵v1,�i+B

in

]� [ha↵

a

�

i+B

out

]

Motivation

Background Contribution: suppressed to a level close to the magnitude of v2

Directed flow: baseline unrelated to the magnetic field

P-even quantity: still sensitive to separation effect, i.e., different for “same sign” and “oppo sign”

Identified Particle Analysis

References

AcknowledgementsThankstotheSTARCollaborationfortheopportunityofthisproject.ThankstoProfessorHuanZhongHuangandDr.GangWangformentorship,supportandguidance.ThankstoLiwenWenforhelponcodeanddata.

Flow BackgroundExperimental Approach

“Three-point-correlation” observable “γ” to avoid zero value yield by direct measurement of “a”.

Observable: γ correlator

Summary

Event Plane Reconstruction

Solenoidal Tracker At RHIC (STAR)

DataofAu+Auat39GeV200GeVwerecollectedbySTARdetectorinRHICrun2010.ParticleIdentification:TimeProjectionChamber(TPC)dE/dxisusedforproton/pion/kaonidentification;TimeofFlight(TOF)detectorprovidesmassinformationusedforparticleidentification.

Shiftingmethodisusedtomakecorrectionstotheeventplane.

Baseline:κestimatedtobe1.2-1.4[3]forthreemethods[4][5][6].Indicationofsignalifhigherthanbaseline:κthatforcesΔH=0κmightbedifferentfordifferentparticlepairs:differentpossibleimplications

Correlationsignaliscontaminatedwiththebackgroundcontributionsduetocollectivemotionofthecollisionsystem(ilow)• ellipticilowcoupledwithtransversemomentumconservation(TMC),localchargeconservation(LCC)andalsodecayoftheclusters.

H:background-subtractedcorrelator,CMEcontributions

Inconclusivetoclaimacharge-separationsignalinproton-pionorinkaon-pionbecausesignal+backgroundisconsistentwithbackgroundatthislevelofprecision.

[1]D.Kharzeev,Phys.Lett.B633(2006)260.[2]L.Adamczyketal.,Phys.Rev.Lett.113(2014)052302.[3]F.Wen,L.WenandG.Wang.arXiv:1608.03205[nucl-th].[4]B.Zhang,C.M.Ko,B.-A.LiandZ.-W.Lin,Phys.Rev.C61,067901(2000).[5]B.alveretal.[PHOBOSCollaboration],Phys.Rev.C83,024913(2011);[6]B.BBacketal.[PHOBOSCollaboration],Phys.Rev.C72,051901(R)(2005).

CutsVertexZ(cm) (-40,40)

Eta (-1,1)

Dca(cm)Kaon <1Pion <2

Proton <1

Tofβ >0

Ylocal* (-1.8,1.8)

Mass2(GeV2/c4)

Proton (0.8,1)

Pion (0.01,0.1)

Kaon (0.2,0.35)

pT(GeV/c)

Proton >0.4

Pion >0.15

Kaon >0.2

P(GeV/c)

Proton <2

Pion <1.6

Kaon <1.6

nSigmaofProton (-2,2)

nSigmaofKaon (-2,2)

nSigmaofPion (-2,2)

IdentiiiedParticles

Event

Particles

Oppositesignsignalisabovethesamesignsignal,andthethesignalissmallerformorecentralcollisions.

Proton-Pion

*YlocalisthedistancebetweenaTOFhitandtheTPCtrackprojection.

Kaon-Pion