2025/07/31 by Sung, Haesom, Ko, Che Ming, Lee, Su Houng
#FOS: Physical sciences #Nuclear Theory (nucl-th)
paper · doi:10.48550/arxiv.2507.23238
The effect of Σ^*(1385) baryon resonance on the time evolution of the Λ hyperon polarization in hadronic matter is studied using a kinetic approach. This approach explicitly includes the production of the Σ^* resonance from the Λ-π and Σ(1192)-π scatterings as well as its decay into Λ+π or Σ+π. The resulting coupled kinetic equations governing the time evolution of Λ, Σ and Σ^* numbers and polarizations are solved for Au-Au collisions at √sNN=7.7 GeV and 20-50% centrality, using initial values determined by thermal yields and the thermal vorticity at chemical freeze-out temperature. As the hadronic matter expands and cools, the Λ polarization is found to increase slightly during early times and then decreases very slowly afterwards, while the Σ polarization remains nearly constant and the Σ^* polarization continuously decreases. Including feed-down contributions to the Λ polarization from the decays of partially polarized Σ0, Σ^*, and Ξ(1322) hyperons, where the Ξ polarization is obtained by solving coupled kinetic equations for the Ξ and Ξ^*(1532) system, the resulting Λ polarization becomes smaller and decreases over time. In both cases, however, the time variation of the Λ polarization is sufficiently small to support the assumption of an early freeze-out of Λ spin degree of freedom in relativistic heavy ion collisions.