Spin alignment of vector mesons in heavy-ion collision

TL;DR

This paper reviews how strong fields and shear stress in heavy-ion collisions influence the spin alignment of vector mesons, highlighting experimental observations and theoretical explanations for these phenomena.

Contribution

It provides a concise overview of the mechanisms behind spin alignment in heavy-ion collisions, connecting experimental data with theoretical models.

Findings

Positive deviation of $\, ext{phi}$ meson spin alignment from 1/3 explained by strong field anisotropy.

Shear-induced spin alignment is estimated at 10^{-4} to 10^{-5} for typical shear tensor magnitudes.

Abstract

We give a brief review on the spin alignment induced by the strong field and the shear-stress tensor. In experiments, a significant positive deviation from 1/3 is observed for the $\phi$ meson, which can be explained by the anisotropy of the strong field fluctuation in the meson's rest frame, while the anisotropy is mainly a consequence of the motion of meson relative to the quark-gluon plasma. On the other hand, the shear-induced spin alignment is of the order $10^{-4}\sim10^{-5}$ if the magnitude of thermal shear tensor is $10^{-2}$.