Precision measurements of kinematic scan for fluctuations of (net-)proton multiplicity distributions in Au+Au collisions from RHIC-STAR

¹ Key Laboratory of Quark and Lepton Physics (MOE) & Institute of Particle Physics, Central China Normal University, 430079, Wuhan, China
² GSI Helmholtzzentrum für Schwerionenforschung, 64291, Darmstadt, Germany

^* e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 17 April 2026

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 √s_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_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 κ₂/κ₁ and κ₃/κ₁ 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.