Hyperon polarization and its relation with directed flow in high-energy nuclear collisions

TL;DR

This paper models hyperon polarization and directed flow in high-energy nuclear collisions, revealing their interrelation and sensitivity to initial QGP conditions, with predictions testable by future experiments.

Contribution

It introduces a modified 3D Glauber model coupled with viscous hydrodynamics to simultaneously describe hyperon polarization and directed flow, highlighting their dependence on initial QGP geometry and flow.

Findings

Successful simultaneous description of directed flow and hyperon polarization

Identification of non-monotonic transverse momentum dependence of Λ polarization

Potential for combined observables to constrain initial QGP conditions

Abstract

We investigate the hyperon polarization and its relation with the directed flow of the quark-gluon plasma (QGP) in non-central Au+Au collisions at $\sqrt{s_{\textrm{NN}}} = 27$ GeV. A modified 3-dimensional (3D) Glauber model is developed and coupled to a (3+1)-D viscous hydrodynamic evolution of the QGP. Within this framework, we obtain a satisfactory simultaneous description of the directed flow of identified particles and $\Lambda$ polarization, and show sensitivity of polarization to both the tilted geometry and the longitudinal flow profile of the QGP. A non-monotonic transverse momentum dependence of the $\Lambda$ polarization is found in our calculation, which is absent from hydrodynamic simulation using other initialization methods and can be tested by future experimental data with higher precision. The relation between the global polarization and directed flow of $\Lambda$ is explored as the longitudinal flow field or the medium deformation varies. Due to the common origin of these two observables, their combination may provide a more stringent constraint on the initial condition of the QGP.