Abstract
The production of J/$\psi$ and $\psi(2S)$ was measured with the ALICE detector in Pb-Pb collisions at the LHC. The measurement was performed at forward rapidity ($2.5 < y < 4 $) down to zero transverse momentum ($p_{\rm T}$) in the dimuon decay channel. Inclusive J/$\psi$ yields were extracted in different centrality classes and the centrality dependence of the average $p_{\rm T}$ is presented. The J/$\psi$ suppression, quantified with the nuclear modification factor ($R_{\rm AA}$), was studied as a function of centrality, transverse momentum and rapidity. Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/$\psi$ production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization. Results on the $\psi(2S)$ suppression are provided via the ratio of $\psi(2S)$ over J/$\psi$ measured in pp and Pb-Pb collisions.
Highlights
At high temperature, lattice quantum chromodynamics predicts the existence of a deconfined phase of quarks and gluons where chiral symmetry is restored [1]
Comparisons with similar measurements at lower collision energy and theoretical models indicate that the J/ψ production is the result of an interplay between color screening and recombination mechanisms in a deconfined partonic medium, or at its hadronization
After quarkonium suppression was suggested as a strong evidence of Quark Gluon Plasma (QGP) formation, the first ideas of charmonium enhancement via recombination of c andc appeared [8, 9]
Summary
Lattice quantum chromodynamics predicts the existence of a deconfined phase of quarks and gluons where chiral symmetry is restored [1]. Since the charm quark density produced in hadronic collisions increases with energy [15], recombination mechanisms are predicted to give rise to a sizable J/ψ production at LHC energies, which is likely to partially compensate or exceed the J/ψ suppression due to color-screening in the QGP. J/ψ suppression was observed experimentally in the most central heavy-nucleus collisions at the SPS [18, 19], RHIC [20,21,22,23] and LHC [24,25,26,27,28], ranging from a center-of-mass energy per nucleon pair (√sNN) of about 17 GeV to 2.76 TeV.
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