Axial anomaly and energy dependence of hyperon polarization in heavy-ion collisions

Abstract

We address the issue of energy and charge dependence of global polarization of $\Lambda$ hyperons in peripheral $Au-Au$ collisions recently observed by the STAR collaboration at RHIC. We compare different contributions to the anomalous mechanism relating polarization to vorticity and hydrodynamic helicity in QCD matter. We stress that the suppression of the gravitational anomaly contribution in strongly correlated matter observed in lattice simulations confirms our earlier prediction of rapid decrease of polarization with increasing collision energy. Our mechanism leads to polarization of $\bar \Lambda$ of the same sign and larger magnitude than the polarization of $\Lambda$. The energy and charge dependence of polarization is suggested as a sensitive probe of fine details of QCD matter structure.