Event-by-event direct photon anisotropic flow in relativistic heavy-ion collisions

TL;DR

This paper investigates direct photon anisotropic flow in heavy-ion collisions using event-by-event hydrodynamics, emphasizing the importance of photon multiplicity weighting and exploring uncertainties in emission rates and pre-equilibrium effects.

Contribution

It introduces a refined method for calculating photon flow coefficients by including multiplicity weighting and analyzes the impact of emission rate uncertainties and pre-equilibrium dynamics.

Findings

Photon multiplicity weighting significantly affects flow coefficient calculations.

Uncertainties in emission rates influence the predicted photon spectra and flow.

Pre-equilibrium dynamics impact the direct photon anisotropic flow results.

Abstract

We consider directly emitted and hadronic decay photons from event-by-event hydrodynamic simulations. We compute the direct photon anisotropic flow coefficients and compare with recent experimental measurements. We find that it is crucial to include the photon multiplicity as a weighting factor in the definition of $v^\gamma_n$. We also investigate the sensitivity of the direct photon spectrum and elliptic flow to the theoretical uncertainty of the photon emission rate in the quark-hadron transition region and to the pre-equilibrium dynamics of relativistic heavy-ion collisions.