Hyperon--anti-hyperon polarization asymmetry in relativistic heavy-ion collisions as an interplay between chiral and helical vortical effects

TL;DR

This paper explains the observed difference in hyperon and anti-hyperon polarization in heavy-ion collisions through the interplay of chiral and helical vortical effects, providing a parameter-free description consistent with STAR data.

Contribution

It introduces a novel explanation involving helical vortical effects for hyperon polarization asymmetry, extending the understanding of vortical phenomena in quark-gluon plasma.

Findings

The helical vortical effect dominates over other vortical effects in generating electric current.

The model reproduces STAR hyperon polarization ratios without fitting parameters.

Helical charge relates to particle-antiparticle axial charge differences.

Abstract

We argue that the enhancement in the spin polarization of anti-hyperons compared to the polarization of the hyperons in noncentral relativistic heavy-ion collisions arises as a result of an interplay between the chiral and helical vortical effects. The chiral vortical effect generates the axial current of quarks along the vorticity axis while the recently found helical vortical effect generates the helicity flow -- the projection of the quark's polarization vector onto its momentum -- along the same axis. For massless fermions, the helical charge corresponds to a difference in the contributions of particles and anti-particles to the axial charge. Assuming that the spin of light quarks transfers to the strange quarks via the vector kaon states ("the spin-vector dominance"), we are able to describe the ratio of the (anti)hyperon spin polarizations, obtained by the STAR group, without fitting parameters. We also argue that the helical vortical effect dominates over the chiral vortical effect and the chiral magnetic effect in the generation of the electric current.