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Energy dependence of JΨ production in Au+Aucollisions at = 39 624 and 200 GeV from theSTAR experimentTo cite this article Wangmei Zha and the STAR collaboration 2013 J Phys Conf Ser 458 012009

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Energy dependence of J production in Au+Au collisions at sNN 39 624 and 200 GeV from the STAR experiment

Wangmei Zha (for the STAR collaboration)University of Science and Technology of China Heifei City Anhui Province ChinaBrookhaven National Laboratory Upton NY USA

E-mail wangmeircfrhicbnlgov

Abstract In this article we report on the measurements of J invariant yields as a function oftransverse momentum at midrapidity (|y|lt10) in Au+Au collisions at = 39 624 and 200GeV taken in 2010 by STAR with full Time-of-Flight detector and Barrel ElectromagneticCalorimeter detector in operation Centrality dependence of J production and nuclearmodification factors are presented Comparisons among different collision energies and modelcalculations are discussed

1 IntroductionThe Relativistic Heavy Ion Collider (RHIC) is built to search for the Quark-gluon Plasma (QGP) andto study its properties in laboratory through high energy heavy-ion collisions [1] J suppression inheavy-ion collisions due to color screening of quark and anti-quark has been proposed as a signatureof QGP formation [2] Various measurements of J have been performed in different collisionsystems and at different energies and indeed a suppression of J production has been observed [3 45 6] A similar pattern of suppression was found at SPS and RHIC even though the temperature andenergy density reached in these collisions are significantly different Furthermore a strongersuppression at forward rapidity compared to midrapidity was observed at RHIC [7] Theseobservations indicate that effects other than color screening contribute to J production Theregeneration of J from the statistical coalescence of charm quarks was suggested to explain thesimilar suppressions at SPS and RHIC [8] Despite the increase in collision energy the increasedregeneration contribution from the larger charm quark density could compensate for the additionalsuppression due to color-screening This also explains a stronger suppression at forward rapidity atRHIC where the charm quark density is lower compared to midrapidity In this paper we further studythe collision energy dependence of J production under these two competing mechanisms

We present the measurement of the J production at midrapidity with the STAR experiment inAu+Au collisions at = 39 624 and 200 GeV using data collected during RHIC year 2010 runand study the nuclear modification factors at these energy points

2 Experiment and AnalysisThe STAR experiment is a large-acceptance multi-purpose detector which covers full azimuth andpseudorapidity of ||lt1 [9] The Au+Au data were obtained using a minimum-bias trigger byselecting on coincidences in the Vertex Position Detector (VPD) and the Zero Degree Calorimeter(ZDC) The total number of minimum-bias events used in analysis is 182 million 94 million 304

NNs

NNs

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

Content from this work may be used under the terms of the Creative Commons Attribution 30 licence Any further distributionof this work must maintain attribution to the author(s) and the title of the work journal citation and DOI

Published under licence by IOP Publishing Ltd 1

Figure 1 Invariant mass distribution of e+e- pairs in 0 - 60central Au+Au collisions at 624 GeV

million for 39 624 and 200 GeV respectively In this analysis the Jis reconstructed through itsdecay into electron-positron pairs J rarr e+e- (branching ratio Be+e- = 59) The primary detectorsused in this analysis are the Time Projection Chamber (TPC) [10] the Time-of-Flight (TOF) [11] andthe Barrel Electromagnetic Calorimeter (BEMC) [12] The TPC provides tracking and particleidentification via the ionization energy loss (dEdx) of charge particles In year 2010 STAR hasinstalled 100 of TOF trays (which measure the time of flight and velocity of particles) at midrapidityThis detector combined with TPC can clearly identify electrons by rejecting hadrons in the low andintermediate pT range The BEMC is a lead-scintillator calorimeter and has been used to improve theelectron identification at high pT We use two methods to estimate the combinatorial background inthis analysis

a Mixed-Event Events are categorized according to the z-position of event vertex and thecentrality of event Electrons from one event are paired with positrons from other random events froman event pool with similar global features

b Like-Sign Electrons (or positrons) of the same charge sign are paired within same eventFigure 1 shows the invariant mass distribution of e+e- paris in 0 - 60 central Au+Au collisions at 624GeV For the results reported in this paper we use Mixed-Event method for the combinatorialbackground estimation and the Mixed-Event background is normalized to the Like-Sign in a massrange of 20 - 40 GeVc2 Good Signal-to-Background ratios (for 624 GeV SB = 039 for 39 GeVSB = 062) are observed

3 ResultsFigure 2 shows the Jinvariant yield as a function of pT for 0 - 60 central Au+Au collisions at 39624 and 200 GeV As expected the J invariant yields are larger in Au+Au collisions at largercenter-of-mass energy

There are several different ways to quantify the suppression of J production Since no p+preference baselines at = 39 or 624 GeV were measured at RHIC we first discuss the J RCPwhich defined as follows

(1)

where ltNcollgt is the average number of nucleon-nucleon collisions in relative centrality bins RCP is aratio of J production in central collisions (where QGP formation is expected) to peripheral collisions(which naively should be a superposition of p+p interactions)

NNs

l)(peripheraN

dNdy

(central)N

dNdy

R

coll

collCP

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

2

Figure 2 J invariant yields for Au+Aucollisions (centrality 0 - 60) at 39 624 and200 GeV as a function of pT The error barsdepict the statistical uncertainties The boxesrepresent the systematic uncertainties

Figure 3 J RCP results with respect to 40 -60 (peripheral) for Au+Au collisions at 39624 and 200 GeV as a function of the numberof participating nucleons The error barsrepresent the statistical uncertainties Theboxes represent the systematic uncertaintiesThe shaded bands around unity on the right-hand axis represent the normalizationuncertainty from the average number of binarynucleon-nucleon collisions (ltNcollgt) indifferent centrality bins

The RCP as a function of the average number of participants (ltNpartgt) for Au+Au collisions at39 624 and 200 GeV are shown in Fig 3 Note that the peripheral bin selection for Au+Aucollisions at these three energy points is 40 - 60 centrality Significant suppression is observed incentral Au+Au collisions at 624 GeV which is similar as at 200GeV

R is another way to quantify the suppression of J production It is defined as follows

(2)

where d2NABdpTdy is the invariant J yield in A+A collisions and d2 σ ppdpTdy is the J crosssection in p+p collisions The nuclear overlap function is defined as TAB = ltNcollgt and takes intoaccount the inelastic cross section in p+p collisions ( ) and the number of nucleon-nucleoncollisions in A+A collisions (ltNcollgt) The STAR experiment has no J cross section measurementfor p+p collisions at 39 and 624 GeV There are several p+p measurements from fixed target p+Aexperiment [13 14 15] and from Intersecting Storage Ring (ISR) collider experiments [16 17] nearthese two energy points However the pT shapes from ref [16] and ref [17] at 63 GeV are inconsistentwith each other and the cross section measurements at 39 GeV are comparable to (or even larger than)that at 63 GeV Therefore we use Color Evaporation Model (CEM) prediction as our p+p referencebaselines for = 39 and 624 GeV [18] because CEM calculation describes the pT and rapiditydistribution in p+p 200 GeV collisions [18] Figure 4 shows the RAA of J as a function of Npart forAu+Au collisions at 39 624 and 200 GeV The theoretical calculation curves which contain twomain components initial suppression and regeneration are from reference [7] As the collision energyincreases the QGP temperature increases thus the J color screening (initial suppression) becomesmore significant However in this theoretical calculation the regeneration contribution increases withcollision energy due to the increase in the charm pairs production and nearly compensates theadditional suppression arising from higher temperature Significant suppression of J production is

dydpσddydpNd

T1 R

Tpp2

TAA2

AAAA

ppinelσ

NNs

ppinelσ

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

3

observed in Au+Au collisions from 39 to 200 GeV with respect to Ncoll scaled p+p yields Nosignificant energy dependence is observed for RAA with uncertainties Theoretical calculationdescribes the data within error bars

Figure 4 J RAA results as a function of NpartAu+Au collisions at 39 624 and 200 GeV The theoretical curves are from reference[7]The error bars represent the statisticaluncertainties The boxes represent thesystematic uncertainties The shaded bandsindicates the uncertainties from ltNcollgt Theboxes on the vertical axis represent theuncertainties from CEM estimation for 39 and624 GeV and the statistical uncertainty for200 GeV p+p baseline

Figure 5 J RAA results for Au+Au collisions(centrality 0 - 60) at 39 624 and 200 GeVas a function fo pT The error bars represent thestatistical uncertainties The boxes representthe systematic uncertainties The boxes on thevertical axis represent the uncertainties fromCEM estimation for 39 and 624 GeV andltNcollgt uncertainties

Figure 5 shows the J RAA as a function of pT for Au+Au collisions at 39 624 and 200 GeV TheCEM estimation is used as reference baseline for 39 and 624 GeV Significant suppression isobserved from 39 to 200 GeV Similar suppression pattern within uncertainties is observed for theseenergies

4 summaryIn summary we report on recent STAR measurements of J production in Au+Au collisions at 39624 and 200 GeV at midrapidity Significant suppression of J production with respect to number ofbinary collisions scaled p+p yields is observed for these three energies No significant energydependence of nuclear modification factor (both for RAA and RCP) is found within uncertainties Modelcalculations which include direct suppression and regeneration describe the centrality dependence ofRAA within uncertainties Precise p+p reference measurements at 39 and 624 GeV are needed forfurther understanding of the J interactions with the nuclear matter at those energies

References[1] Harrison M Ludlam T and Ozaki S 2003 Nucl Instr Meth A 499 235[2] Matsui T and Satz H 1986 Phys Lett B 178 416[3] Lansberg J P 2006 Int J Mod Phys A 21 3857[4] Abreu M C et al 1999 Phys Lett B 449 128[5] Arnaldi R et al 2007 Phys Rev Lett 99 132302[6] Atomssa E T 2009 Eur Phys J C 61 683[7] Zhao X and Rapp R 2010 Phys Rev C 82 064905 ( private communication )

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

4

[8] Adare A et al 2007 Phys Rev Lett 98 232301[9] Ackermannn K H et al 2003 Nucl Instr Meth A 499 624[10] Anderson M et al 2003 Nucl Instr Meth A 499 659[11] Llope W J et al 2012 Nucl Instr Meth A 661 S110[12] Beddo M et al 2003 Nucl Instr Meth A 499 725[13] Alexopoulos T et al 1997 Phys Rev D 55 3927[14] Schub M H et al 1995 Phys Rev D 52 1307[15] Gribushin A et al 2000 Phys Rev D 62 012001[16] Clark A G et al 1978 Nucl Phys B 142 29[17] Kourkounelis C et al 1980 Phys Lett B 91 481[18] Nelson R and Vogt R et al 2012 arXiv 12104610v1 (private communication)

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

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Figure 1 Invariant mass distribution of e+e- pairs in 0 - 60central Au+Au collisions at 624 GeV

million for 39 624 and 200 GeV respectively In this analysis the Jis reconstructed through itsdecay into electron-positron pairs J rarr e+e- (branching ratio Be+e- = 59) The primary detectorsused in this analysis are the Time Projection Chamber (TPC) [10] the Time-of-Flight (TOF) [11] andthe Barrel Electromagnetic Calorimeter (BEMC) [12] The TPC provides tracking and particleidentification via the ionization energy loss (dEdx) of charge particles In year 2010 STAR hasinstalled 100 of TOF trays (which measure the time of flight and velocity of particles) at midrapidityThis detector combined with TPC can clearly identify electrons by rejecting hadrons in the low andintermediate pT range The BEMC is a lead-scintillator calorimeter and has been used to improve theelectron identification at high pT We use two methods to estimate the combinatorial background inthis analysis

a Mixed-Event Events are categorized according to the z-position of event vertex and thecentrality of event Electrons from one event are paired with positrons from other random events froman event pool with similar global features

b Like-Sign Electrons (or positrons) of the same charge sign are paired within same eventFigure 1 shows the invariant mass distribution of e+e- paris in 0 - 60 central Au+Au collisions at 624GeV For the results reported in this paper we use Mixed-Event method for the combinatorialbackground estimation and the Mixed-Event background is normalized to the Like-Sign in a massrange of 20 - 40 GeVc2 Good Signal-to-Background ratios (for 624 GeV SB = 039 for 39 GeVSB = 062) are observed

3 ResultsFigure 2 shows the Jinvariant yield as a function of pT for 0 - 60 central Au+Au collisions at 39624 and 200 GeV As expected the J invariant yields are larger in Au+Au collisions at largercenter-of-mass energy

There are several different ways to quantify the suppression of J production Since no p+preference baselines at = 39 or 624 GeV were measured at RHIC we first discuss the J RCPwhich defined as follows

(1)

where ltNcollgt is the average number of nucleon-nucleon collisions in relative centrality bins RCP is aratio of J production in central collisions (where QGP formation is expected) to peripheral collisions(which naively should be a superposition of p+p interactions)

NNs

l)(peripheraN

dNdy

(central)N

dNdy

R

coll

collCP

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

2

Figure 2 J invariant yields for Au+Aucollisions (centrality 0 - 60) at 39 624 and200 GeV as a function of pT The error barsdepict the statistical uncertainties The boxesrepresent the systematic uncertainties

Figure 3 J RCP results with respect to 40 -60 (peripheral) for Au+Au collisions at 39624 and 200 GeV as a function of the numberof participating nucleons The error barsrepresent the statistical uncertainties Theboxes represent the systematic uncertaintiesThe shaded bands around unity on the right-hand axis represent the normalizationuncertainty from the average number of binarynucleon-nucleon collisions (ltNcollgt) indifferent centrality bins

The RCP as a function of the average number of participants (ltNpartgt) for Au+Au collisions at39 624 and 200 GeV are shown in Fig 3 Note that the peripheral bin selection for Au+Aucollisions at these three energy points is 40 - 60 centrality Significant suppression is observed incentral Au+Au collisions at 624 GeV which is similar as at 200GeV

R is another way to quantify the suppression of J production It is defined as follows

(2)

where d2NABdpTdy is the invariant J yield in A+A collisions and d2 σ ppdpTdy is the J crosssection in p+p collisions The nuclear overlap function is defined as TAB = ltNcollgt and takes intoaccount the inelastic cross section in p+p collisions ( ) and the number of nucleon-nucleoncollisions in A+A collisions (ltNcollgt) The STAR experiment has no J cross section measurementfor p+p collisions at 39 and 624 GeV There are several p+p measurements from fixed target p+Aexperiment [13 14 15] and from Intersecting Storage Ring (ISR) collider experiments [16 17] nearthese two energy points However the pT shapes from ref [16] and ref [17] at 63 GeV are inconsistentwith each other and the cross section measurements at 39 GeV are comparable to (or even larger than)that at 63 GeV Therefore we use Color Evaporation Model (CEM) prediction as our p+p referencebaselines for = 39 and 624 GeV [18] because CEM calculation describes the pT and rapiditydistribution in p+p 200 GeV collisions [18] Figure 4 shows the RAA of J as a function of Npart forAu+Au collisions at 39 624 and 200 GeV The theoretical calculation curves which contain twomain components initial suppression and regeneration are from reference [7] As the collision energyincreases the QGP temperature increases thus the J color screening (initial suppression) becomesmore significant However in this theoretical calculation the regeneration contribution increases withcollision energy due to the increase in the charm pairs production and nearly compensates theadditional suppression arising from higher temperature Significant suppression of J production is

dydpσddydpNd

T1 R

Tpp2

TAA2

AAAA

ppinelσ

NNs

ppinelσ

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

3

observed in Au+Au collisions from 39 to 200 GeV with respect to Ncoll scaled p+p yields Nosignificant energy dependence is observed for RAA with uncertainties Theoretical calculationdescribes the data within error bars

Figure 4 J RAA results as a function of NpartAu+Au collisions at 39 624 and 200 GeV The theoretical curves are from reference[7]The error bars represent the statisticaluncertainties The boxes represent thesystematic uncertainties The shaded bandsindicates the uncertainties from ltNcollgt Theboxes on the vertical axis represent theuncertainties from CEM estimation for 39 and624 GeV and the statistical uncertainty for200 GeV p+p baseline

Figure 5 J RAA results for Au+Au collisions(centrality 0 - 60) at 39 624 and 200 GeVas a function fo pT The error bars represent thestatistical uncertainties The boxes representthe systematic uncertainties The boxes on thevertical axis represent the uncertainties fromCEM estimation for 39 and 624 GeV andltNcollgt uncertainties

Figure 5 shows the J RAA as a function of pT for Au+Au collisions at 39 624 and 200 GeV TheCEM estimation is used as reference baseline for 39 and 624 GeV Significant suppression isobserved from 39 to 200 GeV Similar suppression pattern within uncertainties is observed for theseenergies

4 summaryIn summary we report on recent STAR measurements of J production in Au+Au collisions at 39624 and 200 GeV at midrapidity Significant suppression of J production with respect to number ofbinary collisions scaled p+p yields is observed for these three energies No significant energydependence of nuclear modification factor (both for RAA and RCP) is found within uncertainties Modelcalculations which include direct suppression and regeneration describe the centrality dependence ofRAA within uncertainties Precise p+p reference measurements at 39 and 624 GeV are needed forfurther understanding of the J interactions with the nuclear matter at those energies

References[1] Harrison M Ludlam T and Ozaki S 2003 Nucl Instr Meth A 499 235[2] Matsui T and Satz H 1986 Phys Lett B 178 416[3] Lansberg J P 2006 Int J Mod Phys A 21 3857[4] Abreu M C et al 1999 Phys Lett B 449 128[5] Arnaldi R et al 2007 Phys Rev Lett 99 132302[6] Atomssa E T 2009 Eur Phys J C 61 683[7] Zhao X and Rapp R 2010 Phys Rev C 82 064905 ( private communication )

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

4

[8] Adare A et al 2007 Phys Rev Lett 98 232301[9] Ackermannn K H et al 2003 Nucl Instr Meth A 499 624[10] Anderson M et al 2003 Nucl Instr Meth A 499 659[11] Llope W J et al 2012 Nucl Instr Meth A 661 S110[12] Beddo M et al 2003 Nucl Instr Meth A 499 725[13] Alexopoulos T et al 1997 Phys Rev D 55 3927[14] Schub M H et al 1995 Phys Rev D 52 1307[15] Gribushin A et al 2000 Phys Rev D 62 012001[16] Clark A G et al 1978 Nucl Phys B 142 29[17] Kourkounelis C et al 1980 Phys Lett B 91 481[18] Nelson R and Vogt R et al 2012 arXiv 12104610v1 (private communication)

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

5

Figure 2 J invariant yields for Au+Aucollisions (centrality 0 - 60) at 39 624 and200 GeV as a function of pT The error barsdepict the statistical uncertainties The boxesrepresent the systematic uncertainties

Figure 3 J RCP results with respect to 40 -60 (peripheral) for Au+Au collisions at 39624 and 200 GeV as a function of the numberof participating nucleons The error barsrepresent the statistical uncertainties Theboxes represent the systematic uncertaintiesThe shaded bands around unity on the right-hand axis represent the normalizationuncertainty from the average number of binarynucleon-nucleon collisions (ltNcollgt) indifferent centrality bins

The RCP as a function of the average number of participants (ltNpartgt) for Au+Au collisions at39 624 and 200 GeV are shown in Fig 3 Note that the peripheral bin selection for Au+Aucollisions at these three energy points is 40 - 60 centrality Significant suppression is observed incentral Au+Au collisions at 624 GeV which is similar as at 200GeV

R is another way to quantify the suppression of J production It is defined as follows

(2)

where d2NABdpTdy is the invariant J yield in A+A collisions and d2 σ ppdpTdy is the J crosssection in p+p collisions The nuclear overlap function is defined as TAB = ltNcollgt and takes intoaccount the inelastic cross section in p+p collisions ( ) and the number of nucleon-nucleoncollisions in A+A collisions (ltNcollgt) The STAR experiment has no J cross section measurementfor p+p collisions at 39 and 624 GeV There are several p+p measurements from fixed target p+Aexperiment [13 14 15] and from Intersecting Storage Ring (ISR) collider experiments [16 17] nearthese two energy points However the pT shapes from ref [16] and ref [17] at 63 GeV are inconsistentwith each other and the cross section measurements at 39 GeV are comparable to (or even larger than)that at 63 GeV Therefore we use Color Evaporation Model (CEM) prediction as our p+p referencebaselines for = 39 and 624 GeV [18] because CEM calculation describes the pT and rapiditydistribution in p+p 200 GeV collisions [18] Figure 4 shows the RAA of J as a function of Npart forAu+Au collisions at 39 624 and 200 GeV The theoretical calculation curves which contain twomain components initial suppression and regeneration are from reference [7] As the collision energyincreases the QGP temperature increases thus the J color screening (initial suppression) becomesmore significant However in this theoretical calculation the regeneration contribution increases withcollision energy due to the increase in the charm pairs production and nearly compensates theadditional suppression arising from higher temperature Significant suppression of J production is

dydpσddydpNd

T1 R

Tpp2

TAA2

AAAA

ppinelσ

NNs

ppinelσ

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

3

observed in Au+Au collisions from 39 to 200 GeV with respect to Ncoll scaled p+p yields Nosignificant energy dependence is observed for RAA with uncertainties Theoretical calculationdescribes the data within error bars

Figure 4 J RAA results as a function of NpartAu+Au collisions at 39 624 and 200 GeV The theoretical curves are from reference[7]The error bars represent the statisticaluncertainties The boxes represent thesystematic uncertainties The shaded bandsindicates the uncertainties from ltNcollgt Theboxes on the vertical axis represent theuncertainties from CEM estimation for 39 and624 GeV and the statistical uncertainty for200 GeV p+p baseline

Figure 5 J RAA results for Au+Au collisions(centrality 0 - 60) at 39 624 and 200 GeVas a function fo pT The error bars represent thestatistical uncertainties The boxes representthe systematic uncertainties The boxes on thevertical axis represent the uncertainties fromCEM estimation for 39 and 624 GeV andltNcollgt uncertainties

Figure 5 shows the J RAA as a function of pT for Au+Au collisions at 39 624 and 200 GeV TheCEM estimation is used as reference baseline for 39 and 624 GeV Significant suppression isobserved from 39 to 200 GeV Similar suppression pattern within uncertainties is observed for theseenergies

4 summaryIn summary we report on recent STAR measurements of J production in Au+Au collisions at 39624 and 200 GeV at midrapidity Significant suppression of J production with respect to number ofbinary collisions scaled p+p yields is observed for these three energies No significant energydependence of nuclear modification factor (both for RAA and RCP) is found within uncertainties Modelcalculations which include direct suppression and regeneration describe the centrality dependence ofRAA within uncertainties Precise p+p reference measurements at 39 and 624 GeV are needed forfurther understanding of the J interactions with the nuclear matter at those energies

References[1] Harrison M Ludlam T and Ozaki S 2003 Nucl Instr Meth A 499 235[2] Matsui T and Satz H 1986 Phys Lett B 178 416[3] Lansberg J P 2006 Int J Mod Phys A 21 3857[4] Abreu M C et al 1999 Phys Lett B 449 128[5] Arnaldi R et al 2007 Phys Rev Lett 99 132302[6] Atomssa E T 2009 Eur Phys J C 61 683[7] Zhao X and Rapp R 2010 Phys Rev C 82 064905 ( private communication )

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

4

[8] Adare A et al 2007 Phys Rev Lett 98 232301[9] Ackermannn K H et al 2003 Nucl Instr Meth A 499 624[10] Anderson M et al 2003 Nucl Instr Meth A 499 659[11] Llope W J et al 2012 Nucl Instr Meth A 661 S110[12] Beddo M et al 2003 Nucl Instr Meth A 499 725[13] Alexopoulos T et al 1997 Phys Rev D 55 3927[14] Schub M H et al 1995 Phys Rev D 52 1307[15] Gribushin A et al 2000 Phys Rev D 62 012001[16] Clark A G et al 1978 Nucl Phys B 142 29[17] Kourkounelis C et al 1980 Phys Lett B 91 481[18] Nelson R and Vogt R et al 2012 arXiv 12104610v1 (private communication)

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

5

observed in Au+Au collisions from 39 to 200 GeV with respect to Ncoll scaled p+p yields Nosignificant energy dependence is observed for RAA with uncertainties Theoretical calculationdescribes the data within error bars

Figure 4 J RAA results as a function of NpartAu+Au collisions at 39 624 and 200 GeV The theoretical curves are from reference[7]The error bars represent the statisticaluncertainties The boxes represent thesystematic uncertainties The shaded bandsindicates the uncertainties from ltNcollgt Theboxes on the vertical axis represent theuncertainties from CEM estimation for 39 and624 GeV and the statistical uncertainty for200 GeV p+p baseline

Figure 5 J RAA results for Au+Au collisions(centrality 0 - 60) at 39 624 and 200 GeVas a function fo pT The error bars represent thestatistical uncertainties The boxes representthe systematic uncertainties The boxes on thevertical axis represent the uncertainties fromCEM estimation for 39 and 624 GeV andltNcollgt uncertainties

Figure 5 shows the J RAA as a function of pT for Au+Au collisions at 39 624 and 200 GeV TheCEM estimation is used as reference baseline for 39 and 624 GeV Significant suppression isobserved from 39 to 200 GeV Similar suppression pattern within uncertainties is observed for theseenergies

4 summaryIn summary we report on recent STAR measurements of J production in Au+Au collisions at 39624 and 200 GeV at midrapidity Significant suppression of J production with respect to number ofbinary collisions scaled p+p yields is observed for these three energies No significant energydependence of nuclear modification factor (both for RAA and RCP) is found within uncertainties Modelcalculations which include direct suppression and regeneration describe the centrality dependence ofRAA within uncertainties Precise p+p reference measurements at 39 and 624 GeV are needed forfurther understanding of the J interactions with the nuclear matter at those energies

References[1] Harrison M Ludlam T and Ozaki S 2003 Nucl Instr Meth A 499 235[2] Matsui T and Satz H 1986 Phys Lett B 178 416[3] Lansberg J P 2006 Int J Mod Phys A 21 3857[4] Abreu M C et al 1999 Phys Lett B 449 128[5] Arnaldi R et al 2007 Phys Rev Lett 99 132302[6] Atomssa E T 2009 Eur Phys J C 61 683[7] Zhao X and Rapp R 2010 Phys Rev C 82 064905 ( private communication )

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

4

[8] Adare A et al 2007 Phys Rev Lett 98 232301[9] Ackermannn K H et al 2003 Nucl Instr Meth A 499 624[10] Anderson M et al 2003 Nucl Instr Meth A 499 659[11] Llope W J et al 2012 Nucl Instr Meth A 661 S110[12] Beddo M et al 2003 Nucl Instr Meth A 499 725[13] Alexopoulos T et al 1997 Phys Rev D 55 3927[14] Schub M H et al 1995 Phys Rev D 52 1307[15] Gribushin A et al 2000 Phys Rev D 62 012001[16] Clark A G et al 1978 Nucl Phys B 142 29[17] Kourkounelis C et al 1980 Phys Lett B 91 481[18] Nelson R and Vogt R et al 2012 arXiv 12104610v1 (private communication)

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

5

[8] Adare A et al 2007 Phys Rev Lett 98 232301[9] Ackermannn K H et al 2003 Nucl Instr Meth A 499 624[10] Anderson M et al 2003 Nucl Instr Meth A 499 659[11] Llope W J et al 2012 Nucl Instr Meth A 661 S110[12] Beddo M et al 2003 Nucl Instr Meth A 499 725[13] Alexopoulos T et al 1997 Phys Rev D 55 3927[14] Schub M H et al 1995 Phys Rev D 52 1307[15] Gribushin A et al 2000 Phys Rev D 62 012001[16] Clark A G et al 1978 Nucl Phys B 142 29[17] Kourkounelis C et al 1980 Phys Lett B 91 481[18] Nelson R and Vogt R et al 2012 arXiv 12104610v1 (private communication)

29th Winter Workshop on Nuclear Dynamics (WWND2013) IOP PublishingJournal of Physics Conference Series 458 (2013) 012009 doi1010881742-65964581012009

5