Effects of Initial Density Fluctuations on Cumulants in Au + Au Collisions at $\sqrt{s_{NN}}$ = 7.7 GeV

TL;DR

This study uses the UrQMD model to examine how initial density fluctuations influence net-proton cumulants in Au+Au collisions at 7.7 GeV, revealing their impact is more prominent in broad pseudorapidity windows and larger impact parameters.

Contribution

It demonstrates the effect of initial density fluctuations on cumulants in heavy-ion collisions, highlighting their visibility in broad pseudorapidity windows and under specific initial conditions.

Findings

Initial density fluctuations increase as the minimum nucleon distance decreases.

Cumulant ratios are significantly affected in broad pseudorapidity windows.

Impact parameter influences the prominence of fluctuation effects.

Abstract

Within the ultrarelativistic quantum molecular dynamics (UrQMD) model, the effect of initial density fluctuations on cumulants of the net-proton multiplicity distribution in Au + Au Collisions at $\sqrt{s_{NN}}$ = 7.7 GeV was investigated by varying the minimum distance $d_{\rm min}$ between two nucleons in the initialization. It was found that the initial density fluctuations increased with the decrease of $d_{\rm min}$ from 1.6 fm to 1.0 fm, and the influence of $d_{\rm min}$ on the magnitude of the net-proton number fluctuation in a narrow pseudorapidity window ($\Delta \eta \leq$ 4) was negligible even if it indeed affected the density evolution during the collision. At a broad pseudorapidity window ($\Delta \eta \geq$ 4), the cumulant ratios were enlarged when the initial density fluctuations were increased with the smaller value of $d_{\rm min}$, and this enhancement was comparable to that observed in the presence of the nuclear mean-field potential. Moreover, the enhanced cumulants were more evident in collisions with a larger impact parameter. The present work demonstrates that the fingerprint of the initial density fluctuations on the cumulants in a broad pseudorapidity window is clearly visible, while it is not obvious as the pseudorapidity window becomes narrow.