Spin alignment of quarkonia: a possible probe of deconfined QCD matter in Pb+Pb collisions at sNN=5.02 TeV

Abstract

In this study, we investigate the influence of deconfined QCD matter on quarkonium spin alignment in ultra-relativistic heavy-ion collisions. We estimate the spin alignment of charmonium (J/ψ, and ψ(2 S)) and bottomonium (Υ(1 S), and Υ(2 S)) states for Pb+Pb collisions at sNN=5.02 TeV as a function of transverse momentum by calculating the energy eigenvalues in a thermal rotating medium. We solve the Schrödinger equation with a medium-modified color-singlet potential, considering the coupling of spin with vorticity and magnetic field. Furthermore, we evaluate the effect of medium temperature, vorticity, magnetic field, and momentum-space anisotropy on the elements of the spin density matrix. Our findings reveal that vorticity increases the spin alignment, while the magnetic fields and anisotropy modify the observables in a state-dependent manner. These findings deepen our understanding of quarkonium spin alignment in an anisotropic magneto-vortical thermal medium, shedding light on spin transport phenomena in heavy-ion collisions. © The Author(s) 2026.