Dissociation-driven quarkonium spin alignment in Pb�Pb collisions at pffiffiffiffiffiffiffi sNN = 5.02 TeV

Abstract

The observation of spin alignment of quarkonia in ultrarelativistic 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=?, ?(2S)] and bottomonium [?(1S), ?(2S)] in a rotating thermal medium, including collisional damping and gluonic dissociation effects. We evaluate the observable ?00 for Pb�Pb collisions at pffiffiffiffiffiffiffi sNN � 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. � 2026 American Physical Society