Measurements of Non-photonic Electron Production and Azimuthal Anisotropy in $\sqrt {s_{NN}} = 39$, 62.4 and 200 GeV \auau\ Collisions from STAR at RHIC

0.17 MB·English

by  Mustafa Mustafa

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]
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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
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