Hydrodynamic helicity polarization in relativistic heavy ion collisions

TL;DR

This study investigates helicity polarization in relativistic heavy ion collisions using viscous hydrodynamic models, highlighting the dominance of thermal vorticity and its potential to probe vorticity in quark-gluon plasma.

Contribution

It introduces a detailed analysis of helicity polarization contributions beyond global equilibrium, emphasizing the role of thermal vorticity in low-energy collisions.

Findings

Thermal vorticity dominates helicity polarization.

Fluid vorticity is crucial in low-energy collisions.

Simulation confirms space reversal symmetry.

Abstract

We study helicity polarization through the (3+1) dimensional relativistic viscous hydrodynamic models at $\sqrt{s_{NN}}=200$GeV Au+Au collisions. Similar to the local spin polarization, we consider the helicity polarization beyond global equilibrium and investigate the contributions induced by thermal vorticity, shear viscous tensor, and the fluid acceleration. We find that the local helicity polarization induced by thermal vorticity dominates over other contributions. It also implies that in the low-energy collisions, the the fluid vorticity as part of thermal vorticity may play the crucial role to the total helicity polarization. Such a finding could be useful for probing the local strength of vorticity in rotational quark gluon plasmas by measuring helicity polarization. Our simulation confirms the strict space reversal symmetry, whereas we also compare our numerical results with approximated relations derived from ideal Bjorken flow. Our studies also provide a baseline for the future investigation on local parity violation through the correlations of helicity polarization.