Event-by-Event Multiplicity Cumulants as Probes of Partonic Energy Loss and Phase Structure in Au+Au Collisions within a Modified HIJING Model
Rusak Y.A., Babichev L.F.

Received: August 13, 2026

DOI: 10.31857/S0044451026120066

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Event-by-event fluctuations of charged hadron multiplicity, net-proton number, and net electric charge are investigated in central Au+Au collisions at \sqrt s_NN=20-200 GeV using a modified HIJING Monte Carlo generator. The model incorporates partonic energy-loss formalisms inspired by quantum chromodynamics in hot (quark-gluon plasma) and cold media, reducing reliance on the default HIJING energy-loss parameter. At energies above 100 GeV/nucleon, multiplicity and net-charge fluctuations show sensitivity to the assumed medium properties, while net-proton results provide an additional comparison with available STAR measurements. By introducing a probabilistic distribution for a first-order phase transition, we find within the present modified-HIJING framework that multiplicity cumulant ratios (σ ²/M and Sσ ) show a pronounced nonlinear response to the adopted phase-allocation ansatz near the selected binodal energy, whereas net-charge and net-proton fluctuations remain relatively insensitive. Furthermore, expanding the kinematic acceptance enhances the sensitivity of multiplicity fluctuations to the selected transition region in the present phenomenological ansatz. Keywords: heavy-ion collisions, event-by-event fluctuations, multiplicity cumulants, partonic energy loss, first-order phase transition, HIJING