J/psi production and correlation in p+p and Au+Au collisions at STAR
aa r X i v : . [ h e p - e x ] J u l J/ψ production and correlation in p + p and Au+Aucollisions at STAR Zebo Tang (for the STAR collaboration)
Department of Modern Physics, University of Science and Technology of China,Hefei, Anhui, China, 230026E-mail: [email protected]
Abstract.
The results on
J/ψ p T spectra in 200 GeV p + p and Au+Au collisions atSTAR with p T in the range of 3-10 GeV/ c are presented. Nuclear modification factorof high- p T J/ψ is found to be consistent with no suppression in peripheral Au+Aucollisions and significantly smaller than unity in central Au+Au collisions. The
J/ψ elliptic flow is measured to be consistent with no flow at p T <
10 GeV/ c in 20-60%Au+Au collisions.
1. Introduction
J/ψ suppression in heavy-ion collisions due to color-screening of its constituent quarkswas proposed as the signature for the formation of quark-gluon plasma by T. Masuiand H. Satz 25 years ago [1]. But results from SPS and RHIC showed some othereffects such as cold nuclear matter (CNM) effect and recombination of charm quarksmay play an important role in the observed
J/ψ suppression in relativistic heavy-ioncollisions [2, 3]. It is believed that high- p T J/ψ is less affected by CNM effect andcharm quark recombination effect, thus providing a cleaner probe to search for evidenceof color-screening effect in relativistic heavy-ion collisions [4, 5, 6]. STAR’s previousmeasurements showed no suppression for high- p T J/ψ in Cu+Cu collisions at 200 GeV,but with limited statistics [7]. And system size for Cu+Cu collisions may be too small.The same measurement in Au+Au collisions with higher statistics is needed for betterunderstanding. On the other hand, the
J/ψ collective flow measurement is crucial forthe test of charm quark recombination effect. It is also a clean probe to the charm quarkflow in case of coalescence hadronization.The interpretation of
J/ψ modification by the medium created in heavy-ioncollisions also requires understanding of the quarkonium production mechanism inhadronic collisions, but no model at present fully explains the
J/ψ systematic observedin elementary collisions. The
J/ψ spectrum measurement at intermediate and high- p T range and high- p T J/ψ -hadron correlation measurement may provide additional insightsinto the basic processes underlying quarkonium production. /ψ production and correlation in p + p and Au+Au collisions at STAR J/ψ p T spectra at mid-rapidity withthe STAR experiment in p + p and Au+Au collisions at √ s NN = 200 GeV in RHIC year2009 and 2010 high luminosity runs. We also present the measurement of J/ψ ellipticflow v from low to high- p T range in 20-60% Au+Au collisions at √ s NN = 200 GeV.The high- p T J/ψ -hadron correlation in p + p collisions has been discussed in Ref. [8].
2. Results and Discussions
The
J/ψ reconstruction method is similar to what we used in year 2005 and year 2006data [7, 9]. The integrated luminosity used for this analysis is 1.8 pb − (1.4 nb − )with transverse energy threshold E T > p + p (Au+Au ) collisions.Since year 2009, STAR installed a large area Time-Of-Flight (TOF), consist of 72%and 100% full barrel system at mid-rapidity ( | η | < .
9) in year 2009 and 2010 runrespectively. Including TOF in the analysis increases the signal-to-background ratio of
J/ψ and reduces the statistical uncertainties. (GeV/c) T p ] d y ) [ nb / ( G e V / c ) T dp T p p / ( s B d -5 -4 -3 -2 -1 STAR Run9STAR Run5 & Run6PHENIX Run6Tsallis fitCEMdirect LO CS+COdirect NNLO* CS = 200 GeVs+X, y J/ fi p+p STAR Preliminary (GeV/c) T p ] - d y ) [( G e V / c ) T dp T p p N / ( B d -11 -10 -9 -8 -7 -6 -5 -4
10 STAR · PHENIX · NN s+X, y J/ fi Au+Au
STAR Preliminary =0) b TBW (fix TBW prediction=0) b TBW (fix TBW prediction
Figure 1.
J/ψ p T spectra in p + p (left) and Au+Au (right) collisions. The left panel of Fig. 1 shows the fully corrected
J/ψ p T spectra in p + p collisionsat √ s = 200 GeV. STAR new measurements are consistent with previous STAR andPHENIX measurements in the overlapping p T region. The solid line represents a Tsallisstatistics based Blast-Wave (TBW) model [10, 11] fit to all of the data points. Thedashed line and gray band depict theoretical calculations of NRQCD from color-coctet(CO) and color-singlet (CS) transitions [12] and NNLO ⋆ CS result [13] for direct
J/ψ in p + p collisions respectively. The CS+CO calculation leaves no room for feeddownfrom ψ ′ , χ c and B , estimated to be a factor of ∼ J/ψ . NNLO ⋆ CSpredicts a steeper p T dependence. The dot-dashed line shows the calculation fromcolor evaporation model (CEM) for inclusive J/ψ , which can reasonably well explainthe p T spectra at p T > J/ψ p T spectra in Au+Aucollisions with different centralities. STAR and PHENIX measurements are consistentwith each other at the overlapped p T range. The solid lines present TBW fits to STARand PHENIX data points simultaneously with radial flow velocity β fixed to 0, whichcan describe the data points very well. The dashed lines show the TBW predictions /ψ production and correlation in p + p and Au+Au collisions at STAR J/ψ has the same radial flow and freeze-out condition as light hadrons, andthey are much harder than the measurements [10, 11]. These indicate 1)
J/ψ has verysmall (or 0) radial flow; and/or 2) there are significant contribution from charm quarkrecombination at low p T . (GeV/c) T p AA R STAR Preliminary solid lines: Tsinghua U.dashed lines: Zhao+RappPHENIX0-20%40-60% part N AA R >5 GeV/c T STAR Au+Au, |y|<1, p >5 GeV/c T STAR Cu+Cu, |y|<1, pPHENIX Au+Au, |y|<0.35>5 GeV/c T , p – p STAR >5 GeV/c T Tsinghua U., Au+Au, p>4.5 GeV/c T Zhao+Rapp, Au+Au, p=200GeV NN s STAR Preliminary
Nbin err.p+p stat. err.
Figure 2. Left:
J/ψ R AA vs. p T in 0-20% and 40-60% Au+Au collisions. Right: R AA vs. N part for low- p T , high- p T J/ψ s and high- p T charged pion in Au+Au collisions. The
J/ψ nuclear modification factor R AA as a function of p T in Au+Au collisions atdifferent centralities measured by STAR at high p T are shown in the left panel of Fig. 2and compared to PHENIX measurements at low p T [3]. There is a increasing trend fromlow to high p T , maybe due to CNM or J/ψ formation time effect. The high- p T J/ψ R AA is consistent with no suppression in 40-60% centrality, but systematically smaller thanunity in 0-20% centrality. The solid and dashed lines show two theoretical calculationsincluding both primordial J/ψ and statistical charm quark regeneration
J/ψ [4, 5].The high- p T ( p T > c ) J/ψ R AA as a function of number of participants( N part ) in Au+Au collisions at √ s NN = 200 GeV are shown in the right panel of Fig. 2.In peripheral collisions (20-60%), high- p T J/ψ has no suppression, consistent with STARprevious measurements in Cu+Cu collisions at 200 GeV. In central collisions (0-20%),high- p T J/ψ is significantly suppressed, which may be due to color-screening effect. The R AA of low- p T (0 < p T < c ) J/ψ measured by PHENIX and high- p T ( p T > c ) charged pion measured by STAR are also shown for comparison. The high- p T J/ψ R AA is systematic higher than that for low- p T J/ψ , and has different trend fromhigh- p T charged pion.For J/ψ elliptic flow v analysis [15], we use all of the available data because thisanalysis does not need to correct for absolute normalization and efficiency. The eventplanes are reconstructed by using charged particles at mid-rapidity measured by TPC.The v results of inclusive charged hadrons using these event planes are consistent withprevious STAR measurement. J/ψ v as a function of p T in 20-60% Au+Au collisionsat √ s NN = 200 GeV are shown in the left panel of Fig. 3, with the vertical lines (caps)representing statistical (systematic) uncertainties, and the boxes depict uncertaintiesfrom non-flow effect. J/ψ v is consistent with zero in all of the measured p T range withinuncertainties, and significantly lower than φ and inclusive charged hadron v . Severalmodel calculations [16, 17, 18, 19, 20, 21] with slightly different centralities are shown in /ψ production and correlation in p + p and Au+Au collisions at STAR (GeV/c) T p0 2 4 6 8 10 v -0.1-0.0500.050.10.150.20.250.30.35 non-flow estimation Au+Au 200 GeVSTAR Preliminary 20-60% y J/ 0-80% f charged hadrons 20-60% (GeV/c) T p0 2 4 6 8 10 v -0.1-0.0500.050.10.150.2 at freeze-out, MB [1]in transport model, MB [2]in fireball, 7.8fm [3]+ initial mix, 20-40% [4]+ initial mix, 7.8fm [5] initially produced, 7.8fm [3]T=120 with viscosityT=165 with viscosityT=120 without viscosityT=165 without viscosity coalescence: hydro (20-60%): [6] Figure 3. Left: v vs. p T for J/ψ , φ and charge hadrons in Au+Au collisions. Right:
J/ψ v vs. p T from model calculations, see text for detail. the right panel of Fig. 3. The picture that J/ψ production is dominated by charm quarkrecombination with significant charm quark flow is disfavored by STAR measurements,but models can describe STAR measurements assuming that charm quark recombinationis dominant at low p T and primordial production is dominant at high p T . Acknowledgments
The author is supported in part by the National Natural Science Foundation of Chinaunder Grant No. 11005103 and the China Fundamental Research Funds for the CentralUniversities.
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