Search for the QCD Critical Point in High Energy Nuclear Collisions: A Status Report

TL;DR

This paper reviews recent experimental results on net-proton fluctuations from RHIC to locate the QCD critical point, comparing data with theoretical models and discussing fluctuation effects and future research directions.

Contribution

It provides the first comprehensive comparison of net-proton fluctuation data with multiple theoretical models across different collision modes.

Findings

Net-proton cumulant ratios up to fourth order are analyzed.

Comparison shows consistency and discrepancies with theoretical models.

Initial volume fluctuations significantly affect fixed-target energy results.

Abstract

We review recent results of net-proton multiplicity fluctuations from STAR experiment, aiming to locate the QCD critical point in high-energy nuclear collisions at RHIC. We show net-proton number cumulant and proton number factorial cumulant ratios up to fourth order using experimental data from RHIC BES-II Au+Au collisions in collider mode and fixed-target mode. The comparison is made between experimental data and non-critical model calculations from Lattice QCD, HRG, hydrodynamic simulations and transport model UrQMD. In addition, we discuss initial volume fluctuation effect, which plays significant role in fixed-target energies. Finally, an outlook on experimental research on the QCD critical point in future experiments will be presented.