Cumulants of the multiplicity distributions of identified particles measured in heavy-ion collisions by HADES

Institut für Kernphysik, Frankfurt, Germany

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Published online: 17 April 2026

Abstract

The HADES experiment investigates the reaction products of heavy-ion collisions at a few GeV, providing access to QCD matter at high net-baryon densities. A particular focus is the reconstruction of higher-order cumulant ratios of proton and light nuclei multiplicity distributions, which are considered sensitive probes of criticality through their connection to event-by-event (E-by-E) net-baryon number fluctuations. In this contribution, we summarize the experimental setup and outline the analysis strategy. The fluctuations are reconstructed using a novel approach that circumvents E-by-E particle identification by treating it probabilistically. We present several approaches for efficiency correction and apply a data-driven event-mixing procedure to correct for centrality fluctuations. The fully corrected normalized factorial cumulants of proton and deuteron multiplicity distributions are then presented and compared to corresponding STAR data. Our measurements extend the trends observed by STAR toward lower energies for the ratios C₂/C₁ and C₃/C₁. Finally, we show the rapidity dependence of factorial cumulant ratios and confront the results with canonical ensemble baselines that incorporate correlated particle production via local attractive interactions.