# Thermal photon $v_2$ with slow quark chemical equilibration

## TL;DR

This paper investigates how slow quark chemical equilibration in the quark-gluon plasma affects the elliptic flow of thermal photons, potentially explaining the unexpectedly large photon $v_2$ observed experimentally.

## Contribution

It introduces a hydrodynamic model incorporating slow quark chemical equilibration to explain the enhanced thermal photon elliptic flow.

## Key findings

- Thermal photon $v_2$ is increased with slow quark chemical equilibration.
- The model reduces the discrepancy between observed and expected photon $v_2$.
- Hydrodynamic simulations support the impact of chemical non-equilibrium on photon flow.

## Abstract

Elliptic flow of direct photons in high-energy heavy ion collisions has been a topic of great interest as it is experimentally found larger than most hydrodynamic expectations. I discuss the implication of possible late formation of quark component in the hot QCD medium on the photon elliptic flow as quarks are the source of thermal photons in the deconfined phase. Hydrodynamic equations are numerically solved with the evolution equations for quark and gluon number densities. The numerical results suggest that thermal photon $v_2$ is visibly enhanced by the slow chemical equilibration of quarks and gluons, reducing the aforementioned problem.