Charmonium production in Pb-Pb collisions with ALICE at the LHC

TL;DR

This paper reports on charmonium production measurements in Pb-Pb collisions at the LHC, analyzing suppression and regeneration mechanisms of J/ψ and ψ' mesons across rapidities and transverse momenta, and comparing results to theoretical models.

Contribution

It provides new experimental data on charmonium suppression and regeneration in heavy-ion collisions, including separation of prompt and non-prompt J/ψ production at low transverse momentum.

Findings

J/ψ nuclear modification factor varies with centrality and p_T

Evidence of J/ψ regeneration at low p_T

Measurement of ψ' production and comparison to models

Abstract

We report on published charmonium measurements performed by ALICE, at the LHC, in Pb-Pb collisions at a center of mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}} = 2.76$ TeV, at both mid ($|y|<0.8$) and forward ($2.5<y<4$) rapidities. The nuclear modification factor of inclusive ${\rm J}/\psi$ is presented as a function of the collision centrality and the ${\rm J}/\psi$ transverse momentum, $p_{\rm T}$. The variation of the ${\rm J}/\psi$ mean transverse momentum square as a function of the collision centrality is also discussed. These measurements are compared to state of the art models that include one or several of the following mechanisms: color screening of the charm quarks, statistical hadronization at the QGP phase boundary, balance between ${\rm J}/\psi$ dissociation and regeneration in the QGP, ${\rm J}/\psi$ interaction with a dense comoving medium. Results on the production of the heavier and less bound $\psi'$ meson in Pb-Pb collisions at forward-rapidity are also presented and compared to both models and measurements performed by other experiments. At mid-rapidity we also report on ALICE unique capability to separate prompt and non-prompt ${\rm J}/\psi$ production down to low $p_{\rm T}$ ($\geq 1.5$ GeV/$c$) and thus disentangle between effects on prompt ${\rm J}/\psi$ mesons and energy loss of $b$ quarks in the QGP.