Relaxation time for the alignment between the spin of a finite-mass quark or antiquark and the thermal vorticity in relativistic heavy-ion collisions

Alejandro Ayala,David De La Cruz,L A Hernández,Jordi Salinas

doi:10.1103/physrevd.102.056019

Abstract

We study the relaxation time required for the alignment between the spin of a finite-mass quark/antiquark and the thermal vorticity, at finite temperature and baryon chemical potential, in the context of relativistic heavy-ion collisions. The relaxation time is computed as the inverse of the total reaction rate that in turn is obtained from the imaginary part of the quark/antiquark self-energy. We model the interaction between spin and thermal vorticity within the medium by means of a vertex coupling quarks and thermal gluons that, for a uniform temperature, is proportional to the global angular velocity and inversely proportional to the temperature. We use realistic estimates for the angular velocities for different collision energies and show that the effect of the quark mass is to reduce the relaxation times as compared to the massless quark case. Using these relaxation times we estimate the intrinsic quark and antiquark polarizations produced by the thermal vorticity. We conclude by pointing out that, in spite of the former being larger than the latter, it is still possible to understand recent results from the STAR Beam Energy Scan when accounting for the fact that only a portion of quarks/antiquarks come from the denser and thus thermalized region in the collision.

Highlights

Results from heavy-ion collisions experiments have contributed significantly to our understanding of the properties of strongly interacting matter at high temperature and density
We model the interaction between spin and thermal vorticity within the medium by means of a vertex coupling quarks and thermal gluons that, for a uniform temperature, is proportional to the global angular velocity and inversely proportional to the temperature
We have used a thermal field theoretical framework to compute the relaxation times for massive quarks and antiquarks whose spin interacts with the thermal vorticity produced in peripheral heavy-ion collisions

Summary

INTRODUCTION

Results from heavy-ion collisions experiments have contributed significantly to our understanding of the properties of strongly interacting matter at high temperature and density In these reactions, two atomic nuclei collide at relativistic energies producing a deconfined state of hadronic matter, the so-called quark-gluon plasma (QGP). The STAR Beam Energy Scan (BES) program has measured the Λ and Λglobal polarizations as functions of the collision energy [17,18,19] showing that as the latter decreases, the Λpolarization rises more steeply than the Λ polarization This intriguing result motivates the search for a deeper understanding of the conditions for the relaxation between angular momentum and spin degrees of freedom and of its dependence on the collision parameters such as energy, impact parameter, temperature, and baryon chemical potential. IV provides a summary along with a discussion on the consequences of this calculation for hyperon polarization

QUARK INTERACTION RATE AT FINITE DENSITY AND TEMPERATURE

RESULTS AND DISCUSSION

SUMMARY AND CONCLUSIONS