Is nucleon spin thermalized in intermediate-energy heavy-ion collisions?

TL;DR

This paper investigates whether nucleon spin polarization in intermediate-energy heavy-ion collisions can be considered thermalized, finding that spin-thermalized models overestimate polarization compared to transport simulations.

Contribution

It compares spin-thermalized approaches with spin-dependent transport models, revealing limitations of thermalization assumptions at lower energies.

Findings

Spin-thermalized models overestimate nucleon polarization.

Transport simulations show lower polarization levels.

Relativistic effects and temperature gradients are negligible in this context.

Abstract

Despite the success of the spin-thermalized assumption in explaining hyperon spin polarizations in relativistic heavy-ion collisions, challenges begin to arise especially at lower collision energies. The present study compares the nucleon spin polarization during the collision process and at the freeze-out stage from a non-relativistic spin-dependent transport model with spin-thermalized approaches in intermediate-energy heavy-ion collisions, where the relativistic effect and the temperature gradient have shown to be unimportant. It is found that both the global and local spin polarizations are largely overestimated from spin-thermalized approaches, compared to those generated by the spin-orbit mean-field potential in transport simulations.