Measurement of $D^0$ Meson Production and Azimuthal Anisotropy in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV

0.51 MB·

by  Guannan Xie

Nuclearand
ParticlePhysics
Proceedings
NuclearandParticlePhysicsProceedings00(2017)1–4
Measurement of D0 Meson Production and Azimuthal Anisotropy in Au+Au
√
Collisions at s = 200 GeV
NN
GuannanXie(fortheSTARCollaboration)1
UniversityofScienceandTechnologyofChina,Hefei,230026,China
LawrenceBerkeleyNationalLaboratory,Berkeley,CA94720,USA
7
1
0
2

n
a Abstract
J

7 Due to the large masses, heavy-flavor quarks are dominantly produced in initial hard scattering processes and
experiencethewholeevolutionofthemediumproducedinheavy-ioncollisionsatRHICenergies. Theyarealsoex-

] pectedtothermalizeslowerthanlight-flavorquarks. Thusthemeasurementofheavyquarkproductionandazimuthal
x
e anisotropycanprovideimportantinsightsintothemediumpropertiesthroughtheirinteractionswiththemedium.
- Intheseproceedings,wereportmeasurementsofD0productionandellipticflow(v )viatopologicalreconstruction
l 2
c using STAR’s recently installed Heavy Flavor Tracker (HFT). The new measurement of the nuclear modification
√
u factor(R )of D0 mesonsincentralAu+Aucollisionsat s =200GeVconfirmsthestrongsuppressionathigh
n AA NN
transverse momenta (p ) reported in the previous publication with much improved precision. We also report the
[ T
measurementofellipticflowfor D0 mesonsinawidetransversemomentumrangein0-80%minimum-biasAu+Au

1 collisions. TheD0ellipticflowisfinitefor p >2GeV/candissystematicallybelowthatoflighthadronsinthesame
T
v
centralityinterval. Furthermore,severaltheoreticalcalculationsarecomparedtobothR andv measurements,and
8 AA 2
thecharmquarkdiffusioncoefficientisinferredtobebetween2and∼12.
7
8
Keywords: Quark-gluonplasma,Nuclearmodificationfactor,Ellipticflow,HeavyFlavorTracker
1
0
.
1 1. Introduction cross-sectionversustransversemomentum(p )inp+p
0 √ T
collisions at s = 200 GeV-7 TeV [1, 2, 3, 4]. Ex-
7
The mass of the charm quark is significantly larger
1 perimental data are compared with Fixed-Order Next-
thanthoseoflightquarks,theQCDscale,andthetem-
: to-Leading-Log(FONLL)pQCDcalculationsshownas
v perature of the quark-gluon plasma (QGP) created at
grey bands [5]. Within uncertainties, FONLL calcula-
i
X RHIC energies. The charm quark mass is mostly un-
tions describe the data over a broad range of collision
affectedbytheQCDmedium,andthecharmquarksare
r energies.AtRHICenergies,charmquarksareproduced
a dominantlyproducedattheearlystageofheavy-ioncol-
mostlyviainitialhardscatterings. Thisisconfirmedin
lisionsthroughhardscatteringprocessesatRHIC.They
Figure 2 where the total charm quark cross sections in
experience the whole evolution of the system. There-
p+p, d+Au and Au+Au collisions are shown to scale
fore, charm quarks provide unique information on the
with the number of binary nucleon-nucleon collisions
propertiesofhotanddensestrongly-coupledQGP.
(N )[1,5,6,7,8].
The charm quark production has been systemati- coll
cally studied in p+p (p) collisions at various experi- Recent measurements at both the RHIC and the
ments. Figure 1 shows the charm quark differential LHC show that high pT charmed meson production is
considerably suppressed in the central heavy-ion col-
1AlistofmembersoftheSTARCollaborationandacknowledg- lisions, which indicates strong interactions between
mentscanbefoundattheendofthisissue. charmquarksandthemedium. Itisalsofoundthatthe
/NuclearandParticlePhysicsProceedings00(2017)1–4 2
D-meson elliptic flow measured at the LHC is compa- decay channel, with a branching ratio of ∼ 3.9% and
rablewiththatoflighthadrons[9]. a lifetime of cτ ∼ 123 µm. The kaons and pions are
identifiedusingtheenergyloss(dE/dx)measuredbythe
Time Projection Chamber (TPC) and the time of flight
measured by the Time-Of-Flight (TOF) detector [10].
Thesecondaryverticesarereconstructedasthemiddle
points at the Distance of the Closest Approach (DCA)
betweenthetwodaughterparticles. WiththeHFT,the
followingtopologicalcutsareappliedtogreatlyreduce
the combinational background: decay length (distance
between primary and decay vertices), DCA between
daughter tracks, DCA between reconstructed D0 and
the primary vertex, DCA between daughter tracks and
STARPreliminary
the primary vertex. Topological cuts are optimized in
eachD0 p binsusingtheToolkitforMultivariateData
T
Analysis(TMVA)packagetoachievethebestD0signal
significance.
Figure1: Charmquarkpairproductioncrosssectionvs. pT atmid-
rapidityinp+p(p)collisions[1,2,3,4].
850 Au+Au 200GeV, 0-80%
3 < p < 4 GeV/c
T
800 vo2bs = 0.080 ± 0.023
345000 (dD+0A+eu) SSNyNs =. e2r0ro0r GeV ed yield770500
ht
300 NLO err. eig650
W
p+p
NNdb) (/dy|σµccy=0122505000 (D0+Dr*u)n12 Au+Au (D0) 5650000 0.S2TA0R.4Pre0l.6imin0.a8ry 1 1.2 1.4 1.6
(cid:113)-(cid:94)
100run9
FONLL in p+p
50 STARPreliminary FONLL err. Figure3: D0 yieldasafunctionoftheanglerelativetotheevent
0 plane(φ−Ψ)for3<pT <4GeV/c,in0-80%Au+Aucollisions.
1 10 102 103
number of binary collisions N
bin
Theeventplanemethodisusedtoextractthesecond-
Figure2: Charmquarkcrosssectionsatmid-rapidityinp+p,d+Au
order azimuthal anisotropy (v ) for D0. The second-
andAu+AucollisionsmeasuredbytheSTARexperiment. 2
ordereventplane(Ψ)isreconstructedusingTPCtracks
excluding decay products of D0 mesons and corrected
for non-uniform detector efficiency. In order to reduce
2. ExperimentandAnalysis the non-flow contribution, a η-gap of |∆η| > 0.15 be-
tween D0 mesons and charged tracks used for event
TheSTARexperimentisalarge-acceptancedetector plane reconstruction is required. The azimuthal distri-
covering full azimuth and pseudorapidity of |η| < 1 at bution of D0 mesons with respect to the event plane
the RHIC. Data were taken by the STAR experiment (φ−Ψ) is then obtained and weighted by 1/((cid:15)*R) for
using the newly installed Heavy Flavor Tracker (HFT) each centrality, where (cid:15) is the D0 reconstruction ef-
in the year 2014. The HFT is a high resolution silicon ficiency and R the event plane resolution. The ob-
detector which provides a track pointing resolution of served v (vobs) is obtained by fitting the distribution
lessthan50µmforkaonswith pT =750MeV/c. of D0 yi2eld2versus (φ − Ψ) with a functional form of
About 780M minimum bias Au+Au events are used A(1 + 2vobscos(2(φ − Ψ))) taking into account the fi-
2
inthisanalysis.Theseeventsareselectedtocontainpri- nitebinwidtheffect. Finally,thetruev isobtainedby
2
maryverticeswithin6cmtothecenteroftheSTARde- scalingvobswith1/Rtocorrectfortheeventplanereso-
2
tectoralongthebeamdirectionforuniformHFTaccep- lution. Figure3showstheweightedyieldasafunction
tance. D0andD0arereconstructedthroughthehadronic of(φ−Ψ)forD0candidateswith3<p <4GeV/c.The
T
/NuclearandParticlePhysicsProceedings00(2017)1–4 3
remaining contribution of non-flow effects to the mea- D v isstillbelowthatoflighthadrons,thedifference
0 2
sured v is estimated by scaling the non-flow effect in isreduced.Asthecomparisonisdoneinawidecentral-
2
p+pcollisionstoAu+Aucollisions[11]. ity range (0-80%) in which the D0 production is more
biased towards central collisions than light hadrons, a
fair comparison in finer centrality ranges is needed to
1.8 Au+Au 200GeV, 0-10% drawfirmconclusions[16,17,18,19].
1.6 D0 2014
D0 2010/11
1.4
1.2 STAR Preliminary
RAA1.0
0.8
p+p uncert.
0.6 pp norm. uncert.
AuAu Ncoll uncert.
0.4
0.2
0.0
0 1 2 3 4 5 6 7 8
Transverse Momentum p (GeV/c)
T
STSATRA PRrePlirmeilnimariyn ary
Figure4: D0RAAin0-10%centralAu+Aucollisions.
3. PhysicsResultsandDiscussion Figure6: D0v2/nqasafunctionof(mT−m0)/nqcomparedwiththat
oflighthadrons.
Figure4showstheR forthemostcentral(0-10%)
AA
Au+Au collisions. The new results from the HFT are
consistentwiththepublishedonesabove2GeV/cwith 1.8 Au+Au 200GeV, 0-10%
D0 2014
significantly improved precision for Au+Au measure- 1.6 D02010/11
TAMU
ments. Thegreybandsshowuncertaintiesfromthep+p 1.4 SUBATECH
Duke
baselinemeasuredbeforetheHFTinstallation[1]. The 1.2
RAA shows a strong suppression at high pT indicating RAA 1
0.8
strongcharm-mediuminteractionsatthiskinematicre-
0.6
gion.
0.4
0.2 STARPreliminary
0.3 00 1 2 3 4 5 6 7 8
Au+Au 200GeV, 0-80% Non-flow est. Transverse Momentum p (GeV/c)
0.25 D0 EP T
Ks
0.2
Figure7: D0RAAcomparedtovariousmodels.
0.15
v2
0.1 Figures7and8showthemeasuredD0RAAfor0-10%
centralAu+Aucollisionsandv for0-80%Au+Aucol-
0.05 2
lisionscomparedwithvariousmodelcalculations. The
0
STASRT PAreRlimPirnealriym inary Duke model uses a Langevin simulation with an input
(cid:60)0.050 1 2 3 4 5 6 7 charm quark diffusion coefficient parameter- (2πTD )
S
Transverse Momentum pT (GeV/c) fixedto7,whereDS isthecharmquarkspacialdiffusion
coefficientandT ismediumtemperature. Theparame-
Figure5: D0v2asafunctionofpT,comparedwiththatofKs. ter in the DUKE model is tuned to the LHC D-meson
R data [15, 20]. The TAMU calculation uses a non-
Figure5showsthev ofD0mesonscomparedtothat AA
2 perturbative approach and the full T-matrix calculation
of K . The measured D0 v is non-zero and systemati-
s 2 withtheinternalenergyasthepotential,whichpredicts
cally below that of K in the range 1 < p < 6 GeV/c.
s T 2πTD tobe∼3-11[15]. TheSUBATECHgroupuses
To account for the different particle masses and num- S
theMC@sHQcalculationwiththelatestEPOS3initial
ber of constituent quarks (n ), another comparison is
q conditions and the resulting 2πTD ∼2-4 [15]. These
shown in Fig. 6, i.e. v /n vs. (m − m )/n where S
(cid:113) 2 q T 0 q threemodelscandescribethemeasuredD0RAAreason-
mT = p2T +m20. Afterthenq scaling,eventhoughthe ablywell.Meanwhile,theTAMUandSUBATECHcal-
/NuclearandParticlePhysicsProceedings00(2017)1–4 4
0.3 ouslythemeasuredD0 RAA andv2 inAu+Aucollisions
Au+Au 200GeV, 0-80% Non-flow est. atRHIC.
0.25 D0
TAMU Afactorof2-4improvementintheD0 signalsignifi-
0.2 SUBATECH
Duke canceisexpectedfromthereprocessedRun2014data.
0.15 With additional 2 billion minimum-bias events taken
v2
0.1 in Run 2016 with full Al-cables, another factor of 2-3
furtherimprovementisexpected. Theseimprovements
0.05
willallowprecisemeasurementsofthecentralitydepen-
0
STARPreliminary denceoftheD R andv inthenearfuture.
0 AA 2
−0.05
0 1 2 3 4 5 6 7
Transverse Momentum p (GeV/c)
T
Acknowledgement
Figure8: D0v2comparedtovariousmodels.
We express great gratitude to RNC group at LBNL
andHEPgroupatUSTCfortheirsupport.FromUSTC,
culationscandescribethemeasuredD0v2aswell,while theauthorissupportedinpartbytheNSFCunderGrant
theDUKEcalculationwith2πTDS = 7underestimates No.s11375172,11375184and11675168,andMoSTof
theD0v2.Tofurtherconstrainthemediumdiffusionco- ChinaunderNo. 2014CB845400.
efficient,itwillbebeneficialtosystematicallystudythe
effectofeachingredientindifferentmodelcalculations.
References
T2×π40 LLaattttiiccee QQCCDD:: BDainnge erjet ea l.et al. pQCD LO STAR 40 [1] L07.2A0d1a3m(2c0z1y2k).et al. (STAR Collaboration), Phys. Rev. D 86,
D 30 In 30 [2] Z.Ye,QM14(STARCollaboration), Nucl.Rhys.A931, 520
STARPreliminary fe (2014).
T-Matrix F-pot. rre [3] D.Acostaetal.(CDFCollaboration),Phys.Rev.L91,241804
d
20 20 (2003).
[4] B.Abelevetal.(ALICECollaboration),Jour.ofHighEnergy
10 HRG T-Matrix U-pot. 10 [5] PMh.yCs.a0c1c,ia1r2i8et(2a0l.1,2P)h.ys.Rev.L95,122001(2005).
MC@sHQ [6] L. Adamczyk et al. (STAR Collaboration), Phys. Rev. L 94,
62301(2005).
0 0
0.5 1 1.5 [7] L.Adamczyketal.(STARCollaboration), Phys.Rev.L113,
T/T 142301(2014).
c
[8] R.Vogt,Eur.Phys.J.ST155,213(2008).
Figure 9: Charm quark diffusion coefficient from models and the [9] B. Abelev et al. (ALICE Collaboration), Phys. Rev. L 111,
102301(2013)
inferredrangefromSTARmeasurements.
[10] Ackermannetal.Nucl.Instrum.Meth.A499624-632(2003).
[11] A.M. Poskanzer and S. A.Voloshin. , Phys. Rev C 58, 1671
Figure 9 shows the extracted diffusion coefficient (1998)
fromdifferentmodelcalculationscomparedtotheyel- [12] L.Adamczyketal.(STARCollaboration),Phys.Lett.B655,
low band indicating the inferred values from current 104-113(2007)
[13] B. Abelev et al. (ALICE Collaboration), arXiv:1509.06888
measurements.
[nucl-ex]
[14] G.Xie,QM15(STARCollaboration),Nucl.Rhys.A956,473-
476(2016).
4. SummaryandOutlook [15] A.Andronicetal.,arXiv:1506.03981[nucl-ex]
[16] L. Adamczyk et al. (STAR Collaboration), Phys. Rev. L 93,
WereportthefirstmeasurementoftheD0 R inthe 252301(2004)
AA
[17] L. Adamczyk et al. (STAR Collaboration), Phys. Rev. C 77,
most central 0-10% centrality bin and v in the 0-80%
√2 54901(2008).
centralitybininAu+Aucollisionsat sNN =200GeV [18] L.Adamczyketal.(STARCollaboration), Phys.Rev.L116,
using the recently installed HFT at the STAR experi- 62301(2016).
ment. ThenewR resultsconfirmthestrongsuppres- [19] M.Lomnitz,QM15(STARCollaboration),Nucl.Rhys.A956,
AA 256-259(2016).
sion of the D0 yield at high p with much improved
T [20] S.Caoetal.,Phys.Rev.C92,024907(2015)
precision. ThemeasuredD0 v isnon-zeroandsystem-
2
aticallybelowthev oflighthadronsin0-80%Au+Au
2
collisions. Theoreticalmodelswithcharmquarkdiffu-
sioncoefficient2πTD ∼2-12canreproducesimultane-
S