Spin polarization of heavy quarks in matter: predictions from effective field theories

TL;DR

This paper predicts heavy quark spin polarization in heavy-ion collisions at the LHC using effective field theories, linking polarization to vorticity and providing testable predictions for experiments.

Contribution

It introduces a novel EFT-based framework to connect heavy quark spin polarization with local vorticity in the quark-gluon plasma.

Findings

Polarization depends on a single free parameter proportional to vorticity.

Polarization predictions are consistent across different heavy hadrons.

Charm and bottom quarks show similar polarization behavior.

Abstract

The spin polarization of heavy quarks in heavy-ion collisions at the LHC is estimated from effective field theories (EFTs). One EFT is similar to the HQET used at zero temperature. This gives a coupling of the heavy quark spin to colour and electromagnetic fields in heavy-ion collisions. The second EFT describes the interaction of heavy quarks and hydrodynamic modes, and gives the coupling between the heavy quark spin and the local vorticity of the fireball. Using these, we find that the measurement of polarization of the heavy quark from small to moderate p_T at the LHC is predicted with a single free parameter proportional to the vorticity. As a result, the heavy quark polarization is the same whether it is derived from the spin alignment of heavy vector mesons or the polarization of heavy baryons. We also predict that the parameter does not differ much between charm and bottom quarks.