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 [$J/\psi$, $\psi$(2S)] and bottomonium [$\mathrm{\Upsilon }$(1S), $\mathrm{\Upsilon }$(2S)] in a rotating thermal medium, including collisional damping and gluonic dissociation effects. We evaluate the observable ${\rho }_{00}$ for Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ 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.

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• QCD phase transitions
• Quantum chromodynamics
• Quark-gluon plasma
• Relativistic heavy-ion collisions
• Strong interaction