Collectivity of $J/\psi$ Mesons in Heavy-Ion Collisions

TL;DR

This paper improves theoretical models of $J/$ meson production in heavy-ion collisions by incorporating advanced charm quark transport and correlations, successfully explaining experimental elliptic flow data up to high transverse momenta.

Contribution

It introduces enhanced recombination and suppression models for $J/$ mesons, extending their applicability to higher momenta and resolving previous discrepancies with experimental data.

Findings

Good agreement with ALICE data on $v_2$ and nuclear modification factor

Recombination processes are relevant up to $$8 GeV in $p_T$

Resolves the $v_2$ puzzle for $J/$ mesons in heavy-ion collisions.

Abstract

The production of $J/\psi$ mesons in heavy-ion collisions at the Large Hadron Collider is believed to be dominated by the recombination of charm and anti-charm quarks in a hot QCD medium. However, measurements of the elliptic flow ($v_2$) of $J/\psi$ mesons in these reactions are not well described by existing calculations of $J/\psi$ recombination for transverse momenta $p_T\geq$4 GeV. Here, we revisit these calculations in two main aspects. By employing the resonance recombination model, we implement distribution functions of charm quarks transported through the quark-gluon plasma using state-of-the-art Langevin simulations, and we account for the space-momentum correlations of the diffusing charm and anti-charm quarks in the hydrodynamically expanding fireball. These improvements extend the relevance of the recombination processes to substantially larger momenta than before. In addition, we revisit the suppression of the primordially produced $J/\psi$ mesons by propagating them through the same hydrodynamic medium, leading to a marked increase of the $v_2$ of this component over previous estimates. Combining these developments into a calculation of the $p_T$-dependent nuclear modification factor and $v_2$ of inclusive $J/\psi$ production in semi-central Pb-Pb collisions at the LHC, we find a good description of the experimental results by the ALICE collaboration. Our results thus resolve the above-mentioned $v_2$ puzzle and imply the relevance of recombination processes for $p_T$'s of up to $\sim$8 GeV.