Medium-induced optical effects for prompt photons

TL;DR

This paper investigates how refraction effects in hot QCD matter can influence the anisotropic flow of prompt photons, potentially explaining observed phenomena in heavy-ion collision experiments.

Contribution

It introduces the concept of medium-induced optical effects as a mechanism affecting photon flow harmonics in heavy-ion collisions.

Findings

Refraction can act as a lens, converting geometrical anisotropy into momentum anisotropy.

Numerical estimates suggest small but phenomenologically significant flow effects.

Potential explanation for the mismatch in direct photon flow measurements.

Abstract

Electromagnetic aspects of a QCD matter have been a hot topic in recent years. High-energy heavy-ion experiments revealed that flow harmonics of direct photons are not explained by most hydrodynamic models. In this work I discuss possible effects of refraction by the hot medium since it can work as a lens which converts its geometrical anisotropy into momentum anisotropy of photons. Then elliptic flow and higher-order harmonics of prompt photons are estimated numerically. The results indicate that they could be small but have phenomenologically non-trivial consequences.