# Possible non-prompt photons in $pp$ collisions and their effects in $AA$ analyses

## TL;DR

This paper investigates the potential impact of non-prompt photon sources, like pre-equilibrium photons, on direct photon spectra in proton-proton and heavy-ion collisions at LHC energies, challenging conventional assumptions.

## Contribution

It introduces the consideration of pre-equilibrium photons as a significant source affecting direct photon measurements in high-energy collisions.

## Key findings

- Pre-equilibrium photons can significantly alter the direct photon $p_T$ spectra.
- Traditional prompt and thermal photon estimates may be incomplete without considering pre-equilibrium contributions.
- Implications for interpreting QCD matter properties in heavy-ion collisions.

## Abstract

Direct photons are a powerful tool for elucidating the properties of the hot QCD matter in heavy-ion collisions. They are conventionally estimated by assuming prompt photon contributions in proton-proton collisions and thermal and prompt photon contributions in heavy-ion collisions. On the other hand, there could also be other sources of photons such as pre-equilibrium photons. I investigate prompt, pre-equilibrium and thermal photons and their effects on the direct photon $p_T$ spectra at CERN Large Hadron Collider energies.