Global Polarization Theory Overview

Jian-Hua Gao,G David,A Kalweit,S Mukherjee,Z Xu,P Garg,T Ullrich,I.-K Yoo

doi:10.1051/epjconf/202225902003

Abstract

We give a brief overview about theory development of spin polarization in relativistic heavy ion collisions, which includes how the polarization could be generated by single scattering, what the polarization could be in equilibrium, how to address some recent puzzles in spin polarization in heavy ion collisions and how much progress we have made in spin hydrodynamics and spin kinetic theory. We will also discuss the possible helicity polarization in relativistic heavy ion collisions.

Highlights

Spin freedom plays an important role to understand the nuclei’s structure in low energy nuclear physics
When two nuclei collide at low energy, they can combine together, exhibit a collective rotation and becomes a high spin state
A natural question is: could this local orbital angular momentum be transformed into the spin angular momentum — spin polarization? As such polarization is always along the initial global orbital angular momentum, it has been given a specific name as global polarization

Summary

Introduction

Spin freedom plays an important role to understand the nuclei’s structure in low energy nuclear physics. The magic numbers can only be explained by adding a spin-orbital coupling term in nuclear shell model Another example is high spin states in heavy ion fusion evaporation reaction. When two nuclei collide at low energy, they can combine together, exhibit a collective rotation and becomes a high spin state. Such high spin state can be regarded as a rigid rotating body and collective rotation can align the nucleon’s angular momentum along the direction of the angular velocity due to Coriolis force, termed as angular momentum alignment. At high-energy heavy ion collisions, the colliding nuclei can not fusion into high spin states like a rigid rotating body any more. A natural question is: could this local orbital angular momentum be transformed into the spin angular momentum — spin polarization? As such polarization is always along the initial global orbital angular momentum, it has been given a specific name as global polarization

Global spin polarization

Local spin polarization

Spin hydrodynamics and spin kinetic theory

Helicity polarization in relativistic heavy ion collisions

Summary and outlook