Net-Proton Fluctuations at FAIR Energies Using PHQMD Model

One of the main goals of the Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) is to investigate the properties of strongly interacting matter under high baryon densities and explore the QCD phase diagram. Fluctuations of conserved quantities like baryon number (B), electric charge (Q), and strangeness (S) are key probes for phase transitions and critical behavior, as they are theoretically connected to thermodynamic susceptibilities predicted by lattice QCD calculations. In this work, we report the measurements on cumulants of (net-)proton number distributions up to fourth-order in Au+Au collisions at sNN = 3.5-19.6 GeV using Parton-Hadron-Quantum-Molecular-Dynamics (PHQMD) model generated data. Protons and anti-protons are selected at midrapidity (|y|<0.5) within a transverse momentum range of 0.4<pT<2.0 GeV/c and also at 1.08<y<2.08, 0.4<pT<2.0 for CBM acceptance. The results obtained from the PHQMD model are compared with existing experimental data to investigate potential signatures of critical behavior and to probe the vicinity of the critical end point within the CBM energy range. Our results with the PHQMD calculations for κσ2 are consistent with the overall trend of the previously published results for the most central (0–5%) Au+Au collisions, although they slightly overestimate the experimental values.