Vorticity in the QGP liquid and hyperon polarization at the RHIC BES energies

TL;DR

This paper investigates how the polarization of Lambda hyperons in heavy-ion collisions varies with collision energy, using advanced hydrodynamic models to connect polarization signals with thermal vorticity and hadronic effects.

Contribution

It provides a detailed analysis of Lambda hyperon polarization across a range of energies using a state-of-the-art 3+1D cascade and viscous hydrodynamics model, highlighting the energy dependence and underlying mechanisms.

Findings

Lambda polarization decreases with increasing collision energy.

Thermal vorticity is closely related to hyperon polarization.

Hadronic rescattering influences the observed polarization.

Abstract

We calculate the polarization of $\Lambda$ hyperons in Au-Au collisions at RHIC Beam Energy Scan range $\sqrt{s_{\rm NN}}=7.7, \dots, 200$ GeV in a state-of-the-art 3+1 dimensional cascade + viscous hydro model vHLLE+UrQMD. We find that the polarization of $\Lambda$ in the out-of-plane direction decreases substantially with collision energy. We explore the connection between the polarization signal and thermal vorticity and discuss the feed-down and hadronic rescattering effects on the mean polarization of all produced $\Lambda$ hyperons.