On the study of new proxies for second order cumulants of conserved charges in heavy-ion collisions with EPOS4

Proxies for cumulants of baryon number $B$, electric charge $Q$ and strangeness $S$ are usually measured in heavy-ion collisions via moments of net-number distribution of given hadronic species. Since these cumulants of conserved charges are expected to be sensitive to the existence of a critical point in the phase diagram of nuclear matter, it is crucial to ensure that the proxies used as substitutes are as close to them as possible. Hence, we use the EPOS4 framework to generate Au+Au collisions at several collision energies of the RHIC Beam Energy Scan. We compute $2^\text{nd}$ order net-cumulants of $\pi$, $K$ and $p$, for which experimental data has been published, as well as the corresponding conserved charge cumulants. We then compare them with proxies, defined in previous lattice QCD and Hadron Resonance Gas model studies, which are shown to reproduce more accurately their associated conserved charge cumulants. We investigate the impact of hadronic re-scatterings occurring in the late evolution of the system on these quantities, as well as the amount of signal actually originating from the bulk medium which endures a phase transition.
Comment: 14 pages, 11 figures