J/\(psi\) elliptic flow in Pb-Pb collisions at \(\sqrt{s_{\rm NN}}\) = 5.02 TeV

Abstract

We report a precise measurement of the J/\).psi\) elliptic flow in Pb-Pb collisions at \(\sqrt{s_{\rm NN}} = 5.02\) TeV with the ALICE detector at the LHC. The J/\).psi\) mesons are reconstructed at mid-rapidity \(|y| < 0.9\) 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/\).psi\) is studied as a function of transverse momentum and centrality. A positive \(v_2\) is observed in the transverse momentum range \(2 < p_{\rm T} < 8\) GeV/\).\) in the three centrality classes studied and confirms with higher statistics our earlier results at \(\sqrt{s_{\rm NN}} = 2.76\) TeV in semi-central collisions. At mid-rapidity, the J/\).psi\) \(v_2\) is investigated as a function of transverse momentum in semi-central 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 \(p_{\rm T}\) the elliptic flow of the J/\).psi\) originates from the thermalization of charm quarks in the deconfined medium, but suggests that additional mechanisms might be missing in the models.