Precision Measurements of Kinematic Scan for Fluctuations of (Net-)proton Multiplicity Distributions in Au+Au Collisions from RHIC-STAR

TL;DR

This study measures net-proton fluctuations in Au+Au collisions across various energies to search for signs of the QCD critical point, revealing power-law scaling with deviations and indicating a possible critical region at higher baryon densities.

Contribution

It provides high-precision measurements of net-proton cumulants over a wide rapidity range, offering new insights into the QCD phase diagram near the critical point.

Findings

Power-law scaling of cumulants with rapidity window with sub-expected exponents

Indication of critical baryon chemical potential region at 550-650 MeV

Deviation from theoretical expectations suggests the critical point may be at higher densities

Abstract

This work presents measurements of the rapidity-window dependence of event-by-event net-proton cumulants and proton factorial cumulants in Au+Au collisions at $\sqrt{s_\mathrm{NN}}=$7.7 -- 27 GeV, using high-statistics data from RHIC BES-II. Protons and antiprotons are identified with improved detector performance within $0.4<p_\mathrm{T}<2.0$ GeV/$c$ and $|y|<0.6$, enabling a wide coverage in momentum space to probe long-range correlations near the QCD critical point. In the most central collisions, the proton number $\kappa_2/\kappa_1$ and $\kappa_3/\kappa_1$ exhibit power-law scaling with the rapidity window, but with exponents below the theoretical expectation, suggesting that the critical point, if it exists, may lie at higher baryon densities. A finite-size scaling analysis of the susceptibility and Binder cumulant study points out a critical baryon chemical potential region in 550 -- 650 MeV.