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 $d_{\min }$ between two nucleons in the initialization. It was found that the initial density fluctuations increased with the decrease of $d_{\min }$ from 1.6 fm to 1.0 fm, and the influence of $d_{\min }$ on the magnitude of the net-proton number fluctuation in a narrow pseudorapidity window ($\mathsf{\Delta }\eta \le$ 4) was negligible even if it indeed affected the density evolution during the collision. At a broad pseudorapidity window ($\mathsf{\Delta }\eta \ge$ 4), the cumulant ratios were enlarged when the initial density fluctuations were increased with the smaller value of $d_{\min }$, 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.

中文翻译：

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初始密度波动对 sNN = 7.7 GeV 时 Au + Au 碰撞中累积量的影响

在超相对论量子分子动力学 (UrQMD) 模型中，初始密度波动对 Au + Au 碰撞中净质子多重性分布累积量的影响$\sqrt{s_{ññ}}$= 7.7 GeV 通过改变最小距离进行了研究$d_{\mathrm{分钟}}$初始化中的两个核子之间。发现初始密度波动随着密度的减小而增大$d_{\mathrm{分钟}}$从 1.6 fm 到 1.0 fm，以及影响$d_{\mathrm{分钟}}$关于窄伪快速窗口中净质子数波动的幅度（$\mathsf{\Delta }\eta \le$4）即使它确实影响了碰撞过程中的密度演化，也可以忽略不计。在一个宽泛的伪快速窗口（$\mathsf{\Delta }\eta \ge$4），当初始密度波动随着较小的值而增加时，累积量比增大$d_{\mathrm{分钟}}$，并且这种增强与在存在核平均场电位的情况下观察到的增强相当。此外，增强的累积量在具有较大影响参数的碰撞中更为明显。目前的工作表明，在较宽的伪快速窗口中，累积量的初始密度波动指纹清晰可见，而随着伪快速窗口变窄，则不明显。