Speaker
Description
Charmonium production is a direct probe of deconfinement in heavy-ion collisions. For J/$\psi$, a bound state of ${c}\bar{c}$ quarks, its (re-)generation within the QGP or at the phase boundary, is found to be the dominant production mechanism at low transverse momentum ($p_{\rm T}$) and in central Pb–Pb collisions at the LHC energies. The relative production of the $\psi$(2S) excited state with respect to the J/$\psi$ is one possible discriminator between the two different regeneration scenarios. In addition, the non-prompt component of J/$\psi$ production from b-hadron decays allows one to access the interaction of b-hadrons with the QGP down to low transverse momentum. In this talk, we present for the first time new results on the $\psi$(2S)-to-J/$\psi$ double ratio in Pb–Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV with respect to a new pp reference with improved precision, thanks to a new Run 2 data sample with an increase of the statistics collected by a factor 10. The combined Run 2 data set of ALICE allows the extraction of a significant $\psi$(2S) signal in central Pb–Pb collisions at forward rapidity down to 0 transverse momentum. The $\psi$(2S) nuclear modification factor $R_{AA}$ as a function of $p_{\rm T}$ and centrality will also be shown, as well as the inclusive J/$\psi$ $R_{AA}$ at forward rapidity. At midrapidity, the inclusive, prompt and non-prompt J/$\psi$ $R_{AA}$ as a function of centrality and $p_{\rm T}$ will be presented, based on the full Run 2 statistics. The extraction of the non-prompt J/$\psi$ fraction extends down to very low $p_{\rm T}$ and its precision is improved significantly compared to the previous publications. Additionally, the measurements of inclusive, prompt and non-prompt J/$\psi$ in p–Pb collisions will be discussed in view of the interpretation of the Pb–Pb data. All the results will be compared with model calculations.
