Rise and fall of $\Lambda$ and $\bar{\Lambda }$ global polarization in semi-central heavy-ion collisions at HADES, NICA and RHIC energies from the core-corona model

Abstract

We compute the $\Lambda$ and $\overline{\Lambda }$ global polarizations in semi-central heavy-ion collisions using the core-corona model where the source of $\Lambda$'s and $\overline{\Lambda }$'s is taken as consisting of a high-density core and a less dense corona. We show that the overall properties of the polarization excitation functions can be linked to the relative abundance of $\Lambda$s coming from the core versus those coming from the corona. For low collision energies, the former are more abundant whereas for higher energies the latter become more abundant. The main consequence of this reversing of the relative abundance is that both polarizations peak at collision energies $\sqrt{s_{NN}}\lesssim 10$ GeV. The exact positions and heights of these peaks depend not only on this reversal of relative abundances, but also on the centrality class, which is directly related to the QGP volume and lifetime, as well as on the relative abundances of $\Lambda$s and $\overline{\Lambda }$s in the core and corona regions.The intrinsic polarizations are computed from a field theoretical approach that links the alignment of the strange quark spin with the thermal vorticity and modeling the QGP volume and lifetime using a Bjorken expansion scenario. We predict that the $\Lambda$ and $\overline{\Lambda }$ global polarizations should peak at the energy range accessible to NICA and HADES.

Comments: 11 pages, 13 figures. Updated to published version with added comments and two new figures, conclusions unchanged