Spin polarization measurements in relativistic heavy-ion collisions

TL;DR

This paper discusses how measurements of particle spin polarization in relativistic heavy-ion collisions can reveal detailed properties of the quark-gluon plasma, offering insights into its velocity, vorticity, and internal structure.

Contribution

It highlights the significance of spin polarization measurements as a novel probe for understanding the substructure and dynamics of the quark-gluon plasma.

Findings

Global and local hyperon spin polarization observed at LHC and STAR.

Spin alignment measurements provide insights into QGP vorticity and flow.

Spin polarization is sensitive to medium gradients, offering a new diagnostic tool.

Abstract

The hot and dense matter formed in relativistic heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) is termed quark-gluon plasma (QGP). The evolution of the medium is characterized by non-trivial velocity and vorticity fields, resulting in the polarization of the produced particles. The spin polarization, being sensitive to the hydrothermal (flow velocity and temperature) gradients, is unique compared to conventional observables that are sensitive to the hydrothermal fields only. Hence, the recent measurements of global and local hyperon spin polarization and vector meson spin alignment by the LHC and STAR collaborations provide a unique opportunity to probe the QGP substructure with finer details.