Andronic, Anton

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Perspectives for charmonium measurements at the LHC with the ALICEupgrade program∗A. Andronic1 and the ALICE Collaboration1EMMI & GSI DarmstadtAmong the various suggested probes of deconfinement,charmonium plays a distinctive role. It is the first hadronfor which a clear mechanism of suppression in deconfinedmatter (QGP) was proposed early on, based on the coloranalogue of Debye screening [1]. The idea of statisticalhadronization of charm quarks in nucleus-nucleus colli-sions [2] has gained support from data, in particular thatrecently measured at the LHC [4]. An alternative mecha-nism of quarkonium production (and destruction), that dur-ing the entire lifetime of the QGP (realized in a transportapproach, see [3] and refs. therein) is also able to reproducethe RHIC and LHC data. Based on these observations, theJ/ψ production can be considered a probe of QGP as ini-tially proposed [1], but may not be a “thermometer” of themedium. Discriminating the two pictures implies provid-ing an answer to fundamental questions related to the fateof hadrons in a hot medium.High-quality J/ψ data over broad ranges in pT and yand a precision measurement of ψ(2S) and χc charmo-nium states could allow this and is a major component ofphysics envisaged with the ALICE Upgrade Project [5].The unique capability of the ALICE detector is to measurecharmonium production down to pT =0. This will be com-plemented by a challenging data taking at very high rate. Inthe following we present estimates of the performance ofthe ALICE measurement of J/ψ and ψ(2S) in the CentralBarrel (|y| <0.9, measurement done in the e+e− channel).The measurement performance has been estimated for inte-grated luminosities of 1 nb−1 and 10 nb−1, correspondingto the data sample expected for the baseline ALICE datataking and after the upgrade, respectively.The expected absolute statistical error of the elliptic flow(v2) measurement is shown in Figure 1 (a vJ/ψ2 magnitudein the range 0.06-0.1 is expected around pT =3 GeV/c [6]).The measurement of elliptic flow of J/ψ is only possiblewith the 10 nb−1 Pb-Pb data (1010 collisions) expectedwith the upgrade. A measurement with a good significanceover a broad range in pT (up to 5-6 GeV/c) can be achievedwith the usage of the TRD electron identification. In thiscase, a direct measurement of elliptic flow of J/ψ from Bhadrons could become also feasible.In the dielectron channel the measurement of ψ(2S) pro-duction is challenging and can be achieved with good sig-nificance only with the 10 nb−1 Pb-Pb data expected withthe full upgrade, see Figure 2. Such a measurement will al-low, together with the measurement in the dimuon channel,to disentangle between a statistical production at the phaseboundary [2] and production during the QGP lifetime [3].∗Work supported by GSI, BMBF, Helmholtz Alliance HA216/EMMI (GeV/c)Tp0 1 2 3 4 5 6 7ψJ/ 2Absolute error on v00.010.020.030.040.050.060.070.08, current readout-1=1 nbintL-1=10 nbintLcentrality: 10-40%full: TPC PID, open: TPC+TRD PID (|y|<0.9)Figure 1: The absolute statistical error of the elliptic flowof J/ψ vJ/ψ2 as a function of transverse momentum for thecentrality range 10-40%.partN0 50 100 150 200 250 300 350 400ψJ/ AA/R(2S)ψ AAR00.20.40.60.811.2symbols: expected ALICE data (|y|<0.9)) scalingcollpp (N=2.76 TeV)NNstransport model ((dashed: w. shadowing)statistical modelFigure 2: Centrality dependence of the expected statisticalerror of the ψ(2S) measurement in the Central Barrel with10 nb−1 Pb-Pb data in the hypothesis of pp scaling andof the statistical model production for the ratio of nuclearmodification factors of ψ(2S) and J/ψ.References[1] T. Matsui, H. Satz, Phys. Lett. B 178 (1986) 416.[2] P. Braun-Munzinger, J. Stachel, Phys. Lett. B 490 (2000)196; A. Andronic et al., this Report[3] X. Zhao, R. Rapp, Nucl. Phys. A 859 (2011) 114,[4] J. Wiechula et al., this Report.[5] ALICE Collaboration, CERN-LHCC-2012-012.[6] H. Yang [ALICE Collab.], arXiv:1211.0799.PHN-NQM-EXP-58 GSI SCIENTIFIC REPORT 201288

Perspectives for charmonium measurements at the LHC with the ALICE upgrade  program

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Perspectives for charmonium measurements at the LHC with the ALICE upgrade program

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