Global polarization of QGP in non-central heavy ion collisions at high energies

TL;DR

This paper investigates how large orbital angular momentum in non-central heavy-ion collisions causes quark polarization, leading to observable effects like hyperon polarization and vector meson spin alignment, with predictions and ongoing measurements at RHIC.

Contribution

It introduces a comprehensive calculation of global quark polarization in high-energy collisions using effective models and QCD, predicting measurable polarization effects.

Findings

Quarks and anti-quarks are polarized opposite to the reaction plane.

Global hyperon polarization is predicted to be independent of hadronization scenarios.

Spin alignment of vector mesons results from quark polarization.

Abstract

Due to the presence of a large orbital angular momentum of the parton system produced at the early stage of non-central heavy-ion collisions, quarks and anti-quarks are shown to be polarized in the direction opposite to the reaction plane which is determined by the impact-parameter and the beam momentum. The global quark polarization via elastic scattering was first calculated in an effective static potential model, then using QCD at finite temperature with the hard-thermal-loop re-summed gluon propagator. The measurable consequences are discussed. Global hyperon polarization from the hadronization of polarized quarks are predicted independent of the hadronization scenarios. It has also been shown that the global polarization of quarks and anti-quarks leads also to spin alignment of vector mesons. Dedicated measurements at RHIC are underway and some of the preliminary results are obtained. In this presentation, the basic idea and main results of global quark polarization are presented. The direct consequences such as global hyperon polarization and spin alignment are summarized.