Spin Effects In Heavy Ion Collisions at High Energies

TL;DR

This paper reviews the phenomenon of global polarization in heavy ion collisions, where large orbital angular momentum induces spin polarization of quarks, providing insights into quark-gluon plasma properties.

Contribution

It summarizes the theoretical predictions, experimental confirmation, and ongoing challenges related to spin polarization effects in high-energy heavy ion collisions.

Findings

Global polarization confirmed by STAR at RHIC

Orbital angular momentum induces quark spin polarization

Advances in understanding quark-gluon plasma properties

Abstract

In non-central high energy heavy ion collisions, the colliding system possesses a huge orbital angular momentum along the normal direction of the reaction plane. Due to the spin orbit interaction in the system, such a huge orbital angular momentum leads to the spin polarization of quarks and anti-quarks in the quark matter system produced in the collision. Such an effect, known as the global polarization effect, was predicted many years ago and has been confirmed by the STAR collaboration at RHIC. The discovery of the global polarization effect opens a new avenue in heavy ion physics in general and in studying the properties of quark-gluon plasma in particular. This talk will briefly review the original ideas and calculations that lead to the prediction and summarize progresses and problems in related aspects.