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arXiv · 2603.09732

Event-by-Event Multiplicity Cumulants as Probes of Partonic Energy Loss and Phase Structure in Au+Au Collisions within a Modified HIJING Model

Y. A. Rusak·L. F. Babichev
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Abstract

Event-by-event fluctuations of charged hadron multiplicity, net-baryon, 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 QCD-based partonic energy loss formalisms in both hot (quark-gluon plasma) and cold media, eliminating free tuning parameters. At energies above 100 GeV/nucleon, multiplicity and net-charge fluctuations serve as sensitive probes for medium properties, showing strong agreement with STAR data when hot-medium finite-size effects are included. By introducing a probabilistic distribution for a first-order phase transition, we demonstrate that multiplicity cumulant ratios ($\sigma^2/M$ and $S\sigma$) provide distinctive signatures of a binodal transition, whereas net-charge and net-baryon fluctuations remain relatively insensitive. Furthermore, expanding the kinematic acceptance significantly enhances the sensitivity of these multiplicity fluctuations to the phase transition boundary.

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Y. A. Rusak, L. F. Babichev. 2026-03-10. Event-by-Event Multiplicity Cumulants as Probes of Partonic Energy Loss and Phase Structure in Au+Au Collisions within a Modified HIJING Model. https://arxiv.org/abs/2603.09732

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