# Vorticity in the QGP liquid and $\Lambda$ polarization at the RHIC Beam Energy Scan

## TL;DR

This paper models the polarization of Lambda hyperons in heavy-ion collisions using viscous hydrodynamics, revealing a decrease in polarization with increasing collision energy and analyzing underlying effects.

## Contribution

It introduces a 3+1D viscous hydrodynamic model with UrQMD initial conditions to study Lambda polarization across collision energies, highlighting energy dependence and correction effects.

## Key findings

- Polarization decreases from 1.5% at 7.7 GeV to 0.2% at 200 GeV.
- The model reproduces recent STAR results.
- Differences between Lambda and anti-Lambda polarization are analyzed.

## Abstract

Polarization of $\Lambda$ hyperons and their antiparticles is calculated in a 3+1 dimensional viscous hydrodynamic model with initial state from UrQMD hadron/string cascade. We find that, along with recent results from STAR, the mean polarization at fixed centrality decreases as a function of collision energy from 1.5% at $\sqrt{s_{\rm NN}}=7.7$ GeV to 0.2% at $\sqrt{s_{\rm NN}}=200$ GeV. We explore the effects which lead to such collision energy dependence, feed-down corrections and a difference between $\Lambda$ and $\bar\Lambda$.