Abstract
We report a precise measurement of the J/ψ elliptic flow in Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV with the ALICE detector at the LHC. The J/ψ mesons are reconstructed at midrapidity (|y|<0.9) in the dielectron decay channel and at forward rapidity (2.5<y<4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v_{2} of the J/ψ is studied as a function of the transverse momentum and centrality. A positive v_{2} is observed in the transverse momentum range 2<p_{T}<8 GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at sqrt[s_{NN}]=2.76 TeV in semicentral collisions. At midrapidity, the J/ψ v_{2} is investigated as a function of the transverse momentum in semicentral collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low p_{T} the elliptic flow of the J/ψ originates from the thermalization of charm quarks in the deconfined medium but suggests that additional mechanisms might be missing in the models.
Highlights
TeV with the ALICE detector at the LHC
At forward rapidity, the elliptic flow v2 of the J=ψ is studied as a function of the transverse momentum and centrality
Extreme conditions of temperature and pressure created in ultrarelativistic heavy-ion collisions enable the exploration of the phase diagram region where quantum chromodynamics (QCD) predicts the existence of a deconfined state, the quark-gluon plasma (QGP) [1,2]
Summary
TeV with the ALICE detector at the LHC. The J=ψ mesons are reconstructed at midrapidity (jyj < 0.9) in the dielectron decay channel and at forward rapidity (2.5 < y < 4.0) in the dimuon channel, both down to zero transverse momentum. The angle of the reaction plane of the collision is estimated, event by event, by the secondharmonic EP angle Ψ [38], which is obtained from the azimuthal distribution of reconstructed tracks in the TPC or track segments in the SPD for the mid- and forward rapidity analyses, respectively. A similar method was used to extract the uncorrected (for detector acceptance and efficiency) average transverse momentum of the reconstructed J=ψ in each centrality and pT class, which is used to locate the data points when plotted as a function of pT. Nonflow effects (J=ψ-EP correlations not related to the initial geometry symmetry plane, such as higher-mass particle decays or jets) were estimated to be small with respect to the other uncertainties by repeating the analysis at forward rapidity using the EP determined in either the V0-A (Δη 1⁄4 5.3) or the V0-C (no η gap) detector. A systematic uncertainty of 1% on the EP determination was estimated exploiting the availability of different subevents, built from the multiplicity measurement in the
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