Quarkonium polarization in Pb+Pb collisions in the improved color evaporation model

TL;DR

This paper investigates the polarization of quarkonium in lead-lead collisions using an improved color evaporation model, finding polarization unaffected by cold nuclear matter effects and comparing results with experimental data.

Contribution

It introduces a calculation of $J/\psi$ polarization in Pb+Pb collisions within the improved color evaporation model at next-to-leading order, including cold nuclear matter effects.

Findings

Polarization is independent of cold nuclear matter effects.

Model predictions agree with ALICE experimental data.

Provides insights into quarkonium production mechanisms in heavy-ion collisions.

Abstract

We apply our calculation of direct $J/\psi$ production in the improved color evaporation mode at ${\mathcal O}(\alpha_s^3)$ in collinear factorization to Pb+Pb collisions. The cold nuclear matter effects of nuclear modifications of the parton densities and intrinsic transverse momentum broadening are included. We find that the polarization is independent of these effects. Our calculations are compared to the Pb+Pb polarization parameters extracted by the ALICE Collaboration at $\sqrt{s_{NN}} = 5.02$ TeV.