# Searching for the QCD critical point with net-proton number fluctuations

## TL;DR

This paper investigates net-proton number fluctuations in heavy ion collisions to identify signs of the QCD critical point, using a phenomenological model that reproduces experimental trends in cumulant ratios.

## Contribution

It introduces a model coupling critical mode fluctuations to protons and anti-protons, capturing both monotonic and non-monotonic behaviors observed experimentally.

## Key findings

- The model reproduces the monotonic behavior of the first cumulant ratio.
- The model captures the non-monotonic behavior of higher-order cumulant ratios.
- Results depend on the coupling strength and the critical point location.

## Abstract

Net-proton number fluctuations can be measured experimentally and hence provide a source of important information about the matter created during relativistic heavy ion collisions. Particularly, they may give us clues about the conjectured QCD critical point. In this work the beam-energy dependence of ratios of the first four cumulants of the net-proton number is discussed. These quantities are calculated using a phenomenologically motivated model in which critical mode fluctuations couple to protons and anti-protons. Our model qualitatively captures both the monotonic behavior of the lowest-order ratio as well as the non-monotonic behavior of higher-order ratios, as seen in the experimental data from the STAR Collaboration. We also discuss the dependence of our results on the coupling strength and the location of the critical point.