Effects of Initial Density Fluctuations on Cumulants in Au + Au Collisions at sNN = 7.7 GeV

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 sNN = 7.7 GeV was investigated by varying the minimum distance dmin between two nucleons in the initialization. It was found that the initial density fluctuations increased with the decrease of dmin from 1.6 fm to 1.0 fm, and the influence of dmin on the magnitude of the net-proton number fluctuation in a narrow pseudorapidity window (Δη≤ 4) was negligible even if it indeed affected the density evolution during the collision. At a broad pseudorapidity window (Δη≥ 4), the cumulant ratios were enlarged when the initial density fluctuations were increased with the smaller value of dmin, 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.