Direct Photons in Hydrodynamic Modeling of Relativistic Nuclear Collisions

TL;DR

This paper reviews the role of direct photons in understanding the space-time evolution of relativistic nuclear collisions, emphasizing the importance of pre-equilibrium photons alongside thermal and prompt photons.

Contribution

It provides a comprehensive overview of direct photon phenomenology and highlights the significance of pre-equilibrium photons in hydrodynamic models.

Findings

Pre-equilibrium photons are as important as thermal and prompt photons.

Transverse momentum spectra and azimuthal anisotropies are analyzed within hydrodynamic models.

The study underscores the need to consider pre-equilibrium photons for accurate interpretation.

Abstract

We review direct photons in the phenomenology of nuclear collisions at relativistic energies. Direct photons carry information about the space-time evolution of nuclear collisions because the QCD medium is transparent against colorless particles. After a status summary of theoretical and experimental studies, transverse momentum spectra and azimuthal momentum anisotropies of direct photons are studied in the context of the hydrodynamic modeling of relativistic nuclear collisions with emphasis on pre-equilibrium photons. It is implied that pre-equilibrium photons can be as important as thermal and prompt photons for comprehensive understanding of direct photon production.