Vorticity and Spin Polarization in Heavy Ion Collisions: Transport Models

TL;DR

This paper reviews how strong fluid vorticity in heavy ion collisions can induce measurable spin polarization of hadrons, discussing theoretical models and recent experimental findings.

Contribution

It provides a comprehensive review of vorticity formation and spin polarization mechanisms using transport models and the Wigner function formalism.

Findings

Vorticity in heavy ion collisions can lead to observable hyperon polarization.

Theoretical models predict both global and local spin polarization effects.

Recent experimental data support the presence of spin polarization induced by vorticity.

Abstract

Heavy ion collisions generate strong fluid vorticty in the produced hot quark-gluon matter which could in turn induce measurable spin polarization of hadrons. We review recent progress on the vorticity formation and spin polarization in heavy ion collisions with transport models. We present an introduction to the fluid vorticity in non-relativistic and relativistic hydrodynamics and address various properties of the vorticity formed in heavy ion collisions. We discuss the spin polarization in a vortical fluid using the Wigner function formalism in which we derive the freeze-out formula for the spin polarization. Finally we give a brief overview of recent theoretical results for both the global and local spin polarization of $\Lambda$ and $\bar\Lambda$ hyperons.