Measurements of Non-photonic Electron Production and √ Azimuthal Anisotropy in s = 39, 62.4 and 200 GeV Au+Au NN Collisions from STAR at RHIC MustafaMustafa(fortheSTARCollaboration)1 Dept.OfPhysics,PurdueUniversity,WestLafayette,[email protected] 2 1 0 Abstract 2 t DuringRHIC2010run,STARhascol√lectedalargeamountofminimum-bias,centralandhigh c p triggerdatainAu+Aucollisionsat s =39,62.4and200GeVwithdetectorconfiguration O T NN forminimumphotonicconversionbackground. Inthisarticlewereportonanewhighprecision 8 measurementofnon-photonicelectronmid-rapidityinvariantyield,improvednuclearmodifica- √ 1 tionfactorandv inAu+Aucollisionsat s = 200GeV.Wealsopresentmeasurementsof 2 √ NN √ mid-rapidityinvariantyieldat sNN =62.4andv2at sNN =39and62.4GeV. ] x e - l c 1. Introduction u n [ Exploiting the merits of heavy quarks is one of the most important and promising tools to probethestronglyinteractingpartonicmediumcreatedinheavy-ioncollisions.Heavyquarksare 1 mostlycreatedthroughgluonfusion[1],almostexclusively[2]earlyintheheavy-ioncollision, v therefore, they experience the different stages of the medium evolution. Also, their masses are 9 9 external to QCD [3] and thus are not modified by the presence of the medium. Hence, the 1 kinematics of emerging heavy quarks carry a memory of their interactions with the medium. 5 Bycomparingtheheavyquarkproductioninheavy-ioncollisionstothebaselineproductionin 0. p+pandd+Aucollisions,weseektofurtherunderstandflavordependenceofenergylossinthe 1 medium. Azimuthal anistropy of heavy quarks provides further information on the strength of 2 their interaction with the medium, and more experimental discrimination power for theoretical 1 models. : v Inthisarticlewereportonthepreliminaryresultsofmeasuringtheproductionofelectrons i X from heavy flavor semi-leptonic decays, so-called non-photonic electrons (NPE). We show a new high precision measurement of NPE production at mid-rapidity in Au+Au collisions at r √ a s = 200GeV,thenusingourpreviouslypublished p+ pmeasurement[4]weshowanim- NN proved nuclear modification factor R and compare it to theoretical models. Then we show AA measurementsofNPEazimuthalanistropy,v {2},v {4}andv {EP}. Finally,weshowmeasure- 2 √2 2 mentsofNPEproductioninAu+Aucollisionsat s =62.4GeV,andv {2}measurementsat √ NN 2 s =39and62.4GeV. NN 1AlistofmembersoftheSTARCollaborationandacknowledgementscanbefoundattheendofthisissue. PreprintsubmittedtoNuclearPhysicsA October19,2012 2. DatasetsandAnalyses In RHIC run 2010, STAR has sampled nearly 2.6 nb−1 luminosity of Au+Au collisions at √ s = 200 GeV. Minimum Bias (MB) trigger data is used for low p electrons. High p NN T T trigger (HT) data is used for higher statistical precision at high p . We have also utilized data T √ fromanindependent0−5%centralitytrigger. Weuseabout1nb−1 forthe s = 200GeV NN results we show here. During the same RHIC run STAR has also collected Au+Au collisions √ dataat s =39and62.4GeV,whichisusedforthemeasurementsweshowhere. NN For analyses in all collision energies, the most important detector is the STAR Time Pro- jectionChamber(TPC)withlargeacceptance,whichprovidestrackinganddE/dxforelectrons identification. HadronrejectionisdoneutilizingTimeofFlight(TOF)[6]informationatlow p T andtheBarrelElectromagneticCalorimeter(BEMC)[7]athigh p . TheBEMCisalsousedfor T triggeringonhigh p electrons. T ToextractNPE,westatisticallysubtractthecontributionofphotonicelectrons(PE)fromthe identifiedinclusiveelectrons. Byreconstructingtheinvariantmassofelectronpairsweestimate thePEcontributionfromgammaconversion, andπ0, ηDalitzdecays. ExtractedyieldofPEis thencorrectedbya p dependentreconstructionefficiencydeterminedfromsimulationtobeat T thelevelof30-60%. 3. Results Figure 1 left shows the new measurement of NPE mid-rapidity differential invariant yield for p = 1.5 - 10 GeV/c. The novelty of this measurement lies in the achieved high statistical T precision.Thelargeamountofstatisticsallowsdifferentiatingthemeasurementsinfivecentrality bins,inadditiontoa0−5%centralitybinfromacentraltrigger.Withsuchaprecisionandguided bythescaledFONLLupperbound, onecanqualitativelynoticethesuppressionoftheyieldin Au+Aucollisionscomparedto p+pcollisionsdespitethelargelog-scalespannedinthefigure. J/ψcontributionhasbeensubtractedfromthisresult. Figure1upper-rightpanelshowsNPER using0−10%centralityspectraandSTARpub- AA lished p+p[4]resultscomparedtoacollectionofmodelsofdifferentenergylossmechanisms. AsweseeintheFigure, despitethesuccessofdescribingthesuppressionoflighthadrons[9], gluonradiationalonefailstoexplaintheobservedlargeNPEsuppressionathigh p . Thelarge T uncertaintyfromourbaselinep+pmeasurementdominatesthecurrentoveralluncertainty.Anal- ysisofthelargeamountofcollectedhighqualitydatafromRHICruns2009and2012areneeded toimprovethebaselineprecision.Withthecurrentprecisionthepredictionsfromallotherenergy energylossmodelsdescribethedata. Figure 1 lower-right shows NPE v measurements from 2- and 4- particle correlations and 2 √ eventplanemethod,representedasv {2},v {4}andv {EP}inAu+Aucollisionsat s =200 2 2 2 NN GeV.MinimumBiasdataisusedforlow p v {2}andv {4}measurements. HTdataisusedfor T 2 2 high p v {2} and v {EP} measurements. The v {2} and v {EP} are consistent with each other T 2 2 2 2 for p > 3 GeV/c. While both show a pronounced systematic increase in v towards high p , T 2 T at this point we cannot distinguish whether this rise is due to jet-like correlations unrelated to the reaction plane or due to the path length dependence of partonic energy loss. For p < 3 T GeV/c we show both v {2} and v {4}. In v {4} the non-flow contribution is negligible and the 2 2 2 flowfluctuationscontributionisnegative,henceprovidingalowerboundonthev ofNPE.Both 2 √ v measurementsarefinite,whichindicatesastrongcharm-mediuminteractionat s = 200 2 NN GeV. 2 2 STAR Preliminary 0-10%(Ncoll:941) 102 DDGGLLVVRRaadd.+dENLg/dy=1000 MMiinnbbiiaassXX11ee++0044 1100--2200%%XX11ee++0000 1.5 CUJET 10 TMatrix 00--55%%XX22ee++0022 2200--4400%%XX11ee--0011 Collisonaldissociation. 1 00--1100%%XX11ee++0011 4400--6600%%XX11ee--0022 AA 1 Ads/CFTD=3 10-1 pp++pp//4422mmbbXX22ee--0022 R 10-2 STAR Preliminary 0.5 -2]c) 10-3 V/ 10-4 0 e 2 4 6 8 10 G 10-5 p (GeV/c) [( T y 10-6 Nd 2d1πdppTT1100--87 00.02..253 NNNPPPEEE vvv222{{{224}}} 222000000 GGGeeeVVV 000---666000%%% MHMTBB STAR Preliminary 2 10-9 NPE v2{EP} 200 GeV 0-60% 0.15 10-10 v20.1 10-11 0.05 10-12 FFOONNLLLL((uuppppeerrlliimmiittxxNN )) 0 ccoollll 10-13 FFOONNLLLL -0.05 FFOONNLLLL((lloowweerrlliimmiitt)) 10-14 -0.1 2 4 6 8 10 0 1 2 3 4 5 6 7 8 p (GeV/c) p (GeV/c) T T √ Figure1:(Coloronline)(Left)Invariantyieldsvs. pT ofnon-photonicelectronat sNN =200GeV,andscaledSTAR publishedp+p[4].Errorbarsandboxesarestatisticalandsystematicerrors,respectively.FONLLpredictionsarescaled √ byNcollshownascurves. (Upper-right)Non-photonicelectronsnuclearmodificationfactor,RAA,at sNN =200GeV comparedtomodels[9]-[13]. GreybandisthelighthadronsRAA. ErrorbarsandbracketsareAu+Austatisticaland systematicerrors,respectively. Errorboxesaretheuncertaintiesfromourbaseline p+pmeasurement. (Lower-right) √ Non-photonicelectronsazimuthalanistropyv2{2},v2{4}andv{EP}at sNN = 200GeV.Errorbarsandbracketsare statisticalandsystematicerrors,respectively. ToprovidemoreexperimentaldiscriminationpowerfortheoreticalmodelsSTARisextend- ing its NPE program to lower energies. The quest is to see if the energy loss of heavy quarks islessenedorturnedoffatlowerenergies. Figure2showsNPEinvariantyieldinAu+Aucol- √ lisionsat s = 62.4GeVtogetherwithascaledFONLLprediction. Whileaprevious p+p NN measurementbyISR[8]seemstoagreewithFONLLupper-band,ourmeasurementissystem- aticallyhigherthanboth. Measurementofv {2}atlowerenergiesshowninFigure3seemtobe √ 2 consistentwithinerrorswiththatat s = 200GeVfor p > 1.0GeV/c. Theresultsfordata NN T pointsatp <1.0GeV/cseemtoindicateamildercharm-mediuminteractioncomparedtothose √ T at s =200GeV. NN 4. Summary InthisarticlewereportedonSTARnewpreliminaryresultsofnon-photonicelectronmea- √ surements. ThenewNPEmeasurementsin s = 200GeVcollisionsarepreciseinabroad NN p region. NPEnuclearmodificationfactormeasurementshowalargesupressionofNPEpro- T ductionincentralAu+Aucollisions. WeobservelargeNPEv atlow p whichindicateastrong 2 T charm-mediuminteraction. Thev increasestowardshigher p (> 3GeV/c)ispossiblydueto 2 T jet-correlations unrelated to the reaction plane and/or due to path-length dependence of heavy quarkenergyloss. 3 2Nd1-2 (GeV/c) h pdpdTT111100001234 STFFIFFISSAOOOORRRNNNN ·· LLLLP LLLLNNr ecc((((ooucuclllieellppm//nn33pptt66eeirrnrrmmaa lla·· bb··r NNy NNccooccllooll//llll33//336666mmmmbbbb))))Au+Au @M210 00i--n-1s42-00NB0%N%%i a = s ··· · 6 111 20100.20-0424GeV 0.3 1 p2Nevt1100--21 40-60% · 10-3 0.25 NNPPEE vv22{{22}} 220000 GGeeVV 00--6600%% MHTB STAR Preliminary NPE v{2} 39 GeV 0-60% MB 10-3 0.2 NPE v2{2} 62 GeV 0-60% MB 2 10-4 0.15 10-5 v2 0.1 10-6 0.05 10-7 0 10-8 -0.05 10-9 -0.1 10-10 0 0.5 1 1.5 2 2.5 3 3.5 4 10-11 p (GeV/c) 10-12 T 10-13 2 2.5 3 3.5 4 4.5 5 5.5 6 Figure 3: (Color online) Non-photonic electrons at p(GeV/c) √ T sNN =39,62.4GeVazimuthalanistropyv2{2}. Er- rorbarsandboxesarestatisticalandsystematicerrors, Figure 2: (Color online) Invariant yields vs. pT respectively. of non-photonic electrons in Au+Au collisions at √ sNN = 62.4 GeV. Error bars and brackets are sta- tisticalandsystematicerrors,respectively. ISRp+p √ collisionsat sNN=62.2GeVscaledbyNcollisalso plotted [8]. FONLL predictions are scaled by Ncoll shownascurves. AtlowerenergieswereportedonmeasurementofNPEinvariantyieldinAu+Aucollisions √ at s = 62.4 GeV which is systematically higher than a FONLL prediction. We have also NN √ presented our results of azimuthal anistropy at s = 39 and 62.4 GeV by measuring v {2} NN √ 2 whichfor p <1.0GeV/cseemtoindicateamildercharm-mediuminteractionthanat s = T NN 200GeV. References References [1] Cacciari,et.al.Phys.Rev.Lett.95122001(2005). [2] Le´vaiet.al.Phys.Rev.C56,2707(1997). [3] Mu¨ller,Nucl.Phys.A,750,84?97(2005). [4] Agakishievetal.,(STARCollaboration)Phys.Rev.D83,052006(2011). 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