Core-corona approach to describe hyperon global polarization in semi-central relativistic heavy-ion collisions

TL;DR

This paper develops a core-corona model to explain hyperon global polarization in semi-central relativistic heavy-ion collisions, emphasizing the roles of vorticity transfer and corona contributions across different energies.

Contribution

It introduces a refined core-corona model that accounts for hyperon polarization from both core and corona, improving the understanding of polarization excitation functions.

Findings

The model describes the polarization balance between core and corona contributions.

Including corona polarization improves the fit to experimental data.

Results suggest a small positive polarization contribution from corona hyperons.

Abstract

We report on the core-corona model developed to describe the main features of hyperon global polarization in semicentral relativistic heavy-ion collisions as a function of the collision energy. We first neglect the contribution to polarization from hyperons produced in the corona. In this scenario, the global polarization turns out to be described by a delicate balance between the vorticity-to-spin transferring reactions in the core and the predominance of corona over core matter at low energies. We show how this last feature provides a key ingredient missing in our original model that helps to better describe the excitation function for $\Lambda$ and $\overline{\Lambda}$ global polarization. To improve the description, we then introduce the contribution to the global polarization coming from the transverse polarization of $\Lambda$s produced in the corona, which is hereby assumed to be similar to the well-known polarization produced in p + p reactions. The results show a small positive contribution to the global polarization, however they are not yet conclusive due to the small size of the MC sample used in the analysis.