The cumulants of the baryon number from central Au+Au collision at $E_{lab}$= 1.23 GeV$/$nucleon reveal the nuclear mean-field potentials

TL;DR

This study investigates how mean field potentials and clustering influence baryon number fluctuations in Au+Au collisions at 1.23 GeV/nucleon, revealing their significant impact on cumulant ratios relevant for understanding the QCD phase diagram.

Contribution

It provides the first detailed analysis of cumulant ratios at intermediate energies, highlighting the roles of mean fields and clustering effects using UrQMD and JAM models.

Findings

Cumulant ratios are highly time-dependent during collisions.

Mean fields enhance fluctuations during the expansion stage.

Clustering and mean fields significantly affect measured cumulant ratios.

Abstract

Fluctuations of the baryon number in relativistic heavy-ion collisions are a promising observable to explore the structure of the QCD phase diagram. The cumulant ratios in heavy ion collisions at intermediate energies ($\sqrt{s_{\textrm{NN}}} < 7$ GeV) have not been studied to date. We investigate the effects of mean field potential and clustering on the cumulant ratios of baryon and proton number distributions in Au+Au collisions at beam energy of 1.23 GeV$/$nucleon as measured by the HADES Collaboration at GSI. Ultrarelativistic Quantum Molecular Dynamics (UrQMD) and the JAM model are used to calculate the cumulants with different mean field potentials. It is found that the cumulant ratios are strongly time dependent. At the early stage, the effects of the potentials on the fluctuations of the particle multiplicity in momentum space are relatively weak. The mean fields enhance the fluctuations during the expansion stage, especially for small rapidity acceptance windows. The enhancement of cumulant ratios for free protons is strongly suppressed as compared to that for all baryons. The mean field potentials and the clustering play an important role for the measured cumulant ratios at intermediate energy.