Shear-induced spin polarization and “strange memory” in heavy-ion collisions

Shuai Y F Liu,Baochi Fu,Longgang Pang,G David,I.-K Yoo,S Mukherjee,Z Xu,A Kalweit,P Garg,T Ullrich

doi:10.1051/epjconf/202225913004

Abstract

We discuss the theory of the spin polarizations induced by hydrodynamic gradients, which includes a newly discovered shear-induced polarization (SIP) term. In the phenomenological study using a hydrodynamic model, we discover that the local polarization contributed by SIP is substantial and has the “same sign” as the experimental measurements. Also, we find that the “sign” property of the local polarization observed in experiments seems to be related to “memory” effects on the polarizations of strange quarks in quark-gluon plasma.

Highlights

In the non-central ultra-relativistic heavy-ion collisions, a significant amount of orbital angular momentum is deposited into the quark-gluon plasma (QGP) created in these high-energy collisions
We will study the phenomenology of shear-induced polarization (SIP), especially on local polarizations, and discuss the insights related to the "memory" effects on the strange quark polarizations in QGP phase
We discover a new mechanism–shear-induced polarization (SIP) to generate spin polarization in a fluid

Summary

Introduction

In the non-central ultra-relativistic heavy-ion collisions, a significant amount of orbital angular momentum is deposited into the quark-gluon plasma (QGP) created in these high-energy collisions. Considering the spin-orbit coupling, it has be proposed [1] that the orbital angular momentum of the rotating QGP could induce a global (spin) polarization of the hyperons. This global polarization has been observed later in the ground-breaking experiment [2] and the predictions using the thermal-vorticity formula [3,4,5] agree well with experimental measurements [6]. The pattern of the local polarizations predicted [8] using thermal-vorticity formula demonstrate the "opposite sign" compared to experimental results [10, 11] This discrepancy is sometimes called the "spin sign puzzle". We will study the phenomenology of SIP, especially on local polarizations, and discuss the insights related to the "memory" effects on the strange quark polarizations in QGP phase

Theoretical formalism

Phenomenological study

Summary and perspective