# Geometrical scaling of prompt photons in heavy ion collisions

## TL;DR

This paper investigates geometrical scaling in prompt photon production during heavy ion collisions, analyzing data from RHIC and LHC to support the hypothesis of scaling related to participant number across different energies and collision systems.

## Contribution

It introduces the concept of geometrical scaling for prompt photons and demonstrates its applicability to heavy ion collision data from RHIC and LHC.

## Key findings

- Data support geometrical scaling in terms of participant number.
- Scaling observed across different centrality classes.
- Further data needed for comprehensive energy dependence analysis.

## Abstract

We discuss geometrical scaling (GS) for the prompt (direct) photons produced in heavy ion collisions. To this end we first introduce the concept of GS and illustrate its emergence on the example of charged particles. Next, we analyse direct photon data from RHIC and from the LHC. We show that the data support the hypothesis of GS in terms of participant number related to different centrality classes. We also study GS at different energies, however a more detailed study will be possible only when data for at least three different energies from one experiment will be available and also when we use the data obtained from the collisions of large systems (Cu+Cu, Au+Au, Pb+Pb) and small systems (p+p, d+Au, p+Au).