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

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.