Evolution of global polarization in relativistic heavy-ion collisions within a perturbative approach

TL;DR

This paper develops a perturbative approach to model quark polarization evolution in the quark-gluon plasma of heavy-ion collisions, linking initial conditions, hydrodynamics, and polarization outcomes, and suggests hyperon polarization as a new diagnostic tool.

Contribution

It introduces a coupled perturbative and hydrodynamic framework to describe quark polarization evolution, incorporating realistic initial conditions and QGP dynamics for the first time.

Findings

Different initial energy density profiles lead to ~15% variation in quark polarization.

Hyperon polarization can help constrain initial conditions of the QGP.

The approach unifies initial scatterings, QGP interactions, and hydrodynamics in polarization modeling.

Abstract

Extremely large angular orbital momentum can be produced in non-central heavy-ion collisions, leading to a strong transverse polarization of partons that scatter through the quark-gluon plasma (QGP) due to spin-orbital coupling. We develop a perturbative approach to describe the formation and spacetime evolution of quark polarization inside the QGP. Polarization from both the initial hard scatterings and interactions with the QGP have been consistently described using the quark-potential scattering approach, which has been coupled to realistic initial condition calculation and the subsequent (3+1)-dimensional viscous hydrodynamic simulation of the QGP for the first time. Within this improved approach, we have found that different spacetime-rapidity-dependent initial energy density distributions generate different time evolution profiles of the longitudinal flow velocity gradient of the QGP, which further lead to an approximately 15% difference in the final polarization of quarks collected on the hadronization hypersurface of the QGP. Therefore, in addition to the collective flow coefficients, the hyperon polarization may serve as a novel tool to help constrain the initial condition of the hot nuclear matter created in high-energy nuclear collisions.