Dissociation-driven quarkonium spin alignment in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

TL;DR

This paper investigates how medium vorticity in heavy-ion collisions influences quarkonium spin alignment through dissociation mechanisms, using a relativistic hydrodynamics framework to compute observable effects in Pb--Pb collisions at 5.02 TeV.

Contribution

It introduces a medium-modified potential and spin-dependent dissociation mechanism to explain quarkonium spin alignment in a rotating QGP, advancing understanding of spin transport in vortical media.

Findings

Medium vorticity affects quarkonium decay widths and spin alignment.

Spin-dependent dissociation contributes to observed spin alignment.

Results align with experimental measurements of $ ho_{00}$ in Pb--Pb collisions.

Abstract

The observation of spin alignment of quarkonia in ultra-relativistic heavy-ion collisions provides deep insight into the possible formation of the quark-gluon plasma (QGP). The present study investigates the spin alignment of quarkonia induced by dissociation mechanisms arising from medium effects imposed on quarkonia. We implement an effective Hamiltonian with a medium-modified color-singlet potential to incorporate the coupling of quarkonium spin with medium vorticity. This coupling gives rise to spin-dependent dissociation, which we identify as a plausible mechanism contributing to quarkonium spin alignment. Within the ambit of second-order relativistic viscous hydrodynamics, we calculate the spin-dependent decay widths of charmonium ($J/\psi$, $\psi$(2S)) and bottomonium ($\Upsilon$(1S), $\Upsilon$(2S)) in a rotating thermal medium, including collisional damping and gluonic dissociation effects. We evaluate the observable $\rho_{00}$ for Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV as a function of transverse momentum of the quarkonia, charged particle multiplicity, and medium rotation. The results demonstrate that medium vorticity modifies the quarkonia net decay width and, as a consequence, quarkonia spin alignment gets modified. These findings suggest new directions for understanding spin transport and the microscopic dynamics of vortical QGP.