Anisotropic chromo-field fluctuations and spin alignment of quarkonia

Abstract

Spin correlations are believed to contribute significantly to vector-meson spin alignment. In this work, we study the generation of spin correlations through fluctuations of the chromomagnetic field in the quark-gluon plasma. We show that anisotropic fluctuations generically lead to finite vector-meson spin alignment. We study two sources of anisotropic chromomagnetic-field fluctuations: one arises from the motion of a vector meson relative to the medium, which makes isotropic fluctuations in the medium anisotropic in the meson rest frame; the other arises from QGP shear flow through viscous corrections to the chromomagnetic field fluctuations. We find both corrections to be sensitive to magnetic scale. We apply the mechanism to study spin alignment of J/ψ in heavy ion collisions. With QGP evolution modeled by Bjorken flow, we obtain negative spin alignment from both sources, with the shear induced contribution numerically suppressed compared to the motion induced contribution.