Effects of quark chemical equilibration on thermal photon elliptic flow

TL;DR

This paper explores how late-stage quark chemical equilibration in a gluon-rich medium can significantly enhance thermal photon elliptic flow, potentially addressing the photon v2 puzzle in heavy-ion collisions.

Contribution

It introduces a numerical analysis showing that quark chemical equilibration impacts thermal photon v2, highlighting the importance of equilibration and expansion dynamics.

Findings

Thermal photon v2 can be visibly enhanced by late quark production.

Interplay of equilibration processes and collective expansion is crucial.

Results suggest a potential solution to the photon v2 puzzle.

Abstract

Large hadronic elliptic flow $v_2$ is considered as an evidence for the existence of a strongly-coupled QGP fluid in high-energy heavy-ion collisions. On the other hand, direct photon $v_2$ has recently been found to be much larger than hydrodynamic estimations, which is recognized as "photon $v_2$ puzzle". In this study, I discuss the implication of late production of quarks in an initially gluon-rich medium because photons are coupled to quarks. Numerical analyses imply that thermal photon $v_2$ can be visibly enhanced. This indicates that interplay of equilibration processes and collective expansion would be important.