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

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.