Different space-time freeze-out picture -- an explanation of different $\Lambda$ and $\bar{\Lambda}$ polarization?

Abstract

Thermal vorticity in non-central Au+Au collisions at energies $7.7 \leq \sqrt{s} \leq 62.4$ GeV is calculated within the UrQMD transport model. Tracing the $\Lambda$ and $\bar{\Lambda}$ hyperons back to their last interaction point we were able to obtain the temperature and the chemical potentials at the time of emission by fitting the extracted bulk characteristics of hot and dense medium to statistical model of ideal hadron gas. Then the polarization of both hyperons was calculated. The polarization of $\Lambda$ and $\bar{\Lambda}$ increases with decreasing energy of nuclear collisions. The stronger polarization of $\bar{\Lambda}$ is explained by the different space-time distributions of $\Lambda$ and $\bar{\Lambda}$ and by different freeze-out conditions of both hyperons.