Locating the critical point for the hadron to quark-gluon plasma phase transition from finite-size scaling of proton cumulants in heavy-ion collisions

TL;DR

This study uses finite-size scaling of proton cumulants in heavy-ion collisions to identify the QCD critical point, providing experimental evidence consistent with theoretical predictions at specific baryon chemical potential and temperature.

Contribution

First experimental finite-size scaling analysis of proton cumulants to locate the QCD critical point in heavy-ion collisions.

Findings

Evidence for a critical point near μ_B ≈ 625 MeV and T ≈ 140 MeV.

Binder cumulants support the critical point location.

Analysis covers a range consistent with theoretical models.

Abstract

We perform a finite-size scaling analysis of net-proton number cumulants in Au+Au collisions at center-of-mass energies between $\sqrt{s_{\rm{NN}}} = 2.4$ GeV and 54.4 GeV to search for evidence of a critical point in the QCD phase diagram. In our analysis, we use both susceptibility and Binder cumulants which we extract from the second and fourth moments of the net-proton number distributions. We take measurements in different rapidity bin widths, corresponding to different subvolumes of the system, as probes of different length scales. We use model simulations to verify the applicability of this approach, then apply it to data and find evidence for a critical point near the baryon chemical potential of $\mu_{B} \approx 625$ MeV and temperature of $T \approx 140$ MeV. The Binder cumulants, also analyzed in varying rapidity bin widths, provide complementary evidence for a critical point in a similar region. This is the first analysis of experimental data to locate the critical point in a range consistent with theoretical predictions.