J/ψ polarization in relativistic heavy ion collisions

Understanding the polarization property of J/psi is critical to constrain its production mechanism. In addition, the polarization of J/psi can reveal the impact of strong electromagnetic and vorticity fields in relativistic heavy ion collisions. In this study, we analyzed the yield and polarization of J/psi in relativistic heavy ion collisions at different centrality and transverse momentum regions, using three different reference frames: the Collins-Soper frame, the helicity frame, and the event plane frame. The polarization of initially produced J/psi is determined by the NRQCD calculation and is similar to that of pp collisions. However, both unpolarization and transverse polarization are considered for the regenerated J/psi. Our results indicate that the polarization at high pT is similar to that observed in pp collisions. However, at low pT, where regenerated J/psi dominates, it is likely that the polarized charm quarks in the rotational QGP medium are responsible for this phenomenon. Our study supplies a baseline for future research on the effects of strong electromagnetic and vorticity fields on J/psi polarization.