Influence of initial state fluctuations on the production of thermal photons

TL;DR

Initial state fluctuations in QCD matter significantly enhance thermal photon production and elliptic flow in hydrodynamic models, especially in peripheral collisions, smaller systems, and lower energies, providing a new probe for density inhomogeneities.

Contribution

This study demonstrates how initial density fluctuations affect thermal photon yields and flow, offering a novel method to probe initial state inhomogeneities in heavy-ion collisions.

Findings

Enhanced thermal photon production due to fluctuations, especially at high transverse momentum.

Normalized central-to-peripheral yield ratio reduces initial condition uncertainties.

Increased elliptic flow of thermal photons from fluctuating initial conditions.

Abstract

Inhomogeneities in the initial QCD matter density distribution increase the production of thermal photons significantly compared to a smooth initial-state-averaged profile in the region $p_T > 1$ GeV/$c$ in an ideal hydrodynamic calculation. This relative enhancement is more pronounced for peripheral collisions, for smaller size systems as well as for lower beam energies. A suitably normalized ratio of central-to-peripheral yield of thermal photons reduce the uncertainties in the hydrodynamical initial conditions and can be a useful parameter to study the density fluctuations and their size. The fluctuations in the initial density distribution also lead to a larger elliptic flow of thermal photons for $p_T >$ 2.0 GeV/$c$ compared to the flow from a smooth profile.