利用UrQMD在SPS能量下Pb-Pb碰撞中强密集型可观测量$\Sigma$探究前后多重数关联与涨落

中文摘要 AI 辅助

强密集型可观测量$\Sigma$，由分离的前向（F）和后向（B）赝快度区间$\Delta\eta$内的带电π介子多重数构建，在UrQMD输运模型中对SPS能量下的Pb-Pb碰撞进行了研究。$\Sigma$对$\Delta\eta$的依赖性作为碰撞能量、中心度和接收度的函数被探究，以探测多重数涨落与关联的纵向结构。对于$\sqrt{s_{NN}}>6$ GeV，$\Sigma$表现出对$\Delta\eta$的非单调依赖，从小间隔时接近1的值增加，在中等$\Delta\eta$处达到最大值，并在更大间隔处向1减小。分解为标度方差和协方差项表明，这种行为源于它们对$\Delta\eta$的不同依赖。关闭共振衰变的计算表明，共振主导短程关联，而$\Sigma>1$在较大$\Delta\eta$处表明涨落和关联延伸至更宽的赝快度区间。$\Sigma$的幅度及其涨落和协方差分量从中心碰撞到周边碰撞增加，在较大$\Delta\eta$处涨落主导协方差。随着碰撞能量增加，$\Sigma>1$持续的赝快度区间显著增大，而在较低能量下，共振动力学主导粒子产生，$\Sigma$几乎不依赖于$\Delta\eta$。接收度标度研究揭示了在强关联区域偏离简单二项式标度。这些结果展示了$\Sigma$对重离子碰撞中多重数涨落与前后关联之间相互作用的敏感性。

英文摘要

The strongly intensive observable $Σ$, constructed from charged-pion multiplicities in separated forward (F) and backward (B) pseudorapidity intervals $Δη$, is studied within the UrQMD transport model for Pb--Pb collisions at SPS energies. The dependence of $Σ$ on $Δη$ is investigated as a function of collision energy, centrality, and acceptance to probe the longitudinal structure of multiplicity fluctuations and correlations. For $\sqrt{s_{NN}}>6$ GeV, $Σ$ exhibits a non-monotonic dependence on $Δη$, increasing from values near unity at small separation, reaching a maximum at intermediate $Δη$, and decreasing towards unity at larger separation. Decomposition into scaled variance and covariance terms shows that this behavior arises from their different $Δη$ dependences. Calculations with resonance decays switched off show that resonances dominate short-range correlations, while $Σ>1$ at larger $Δη$ indicates fluctuations and correlations extending over broader pseudorapidity intervals. The magnitude of $Σ$, together with its fluctuation and covariance components, increases from central to peripheral collisions, with fluctuations dominating over covariance at large $Δη$. As the collision energy increases, the pseudorapidity interval over which $Σ>1$ persists becomes significantly larger, whereas at lower energies, where resonance dynamics dominate particle production, $Σ$ is nearly independent of $Δη$. An acceptance-scaling study reveals deviations from simple binomial scaling in regions of strong correlations. These results demonstrate the sensitivity of $Σ$ to the interplay between multiplicity fluctuations and forward--backward correlations in heavy-ion collisions.

发表机构

• Variable Energy Cyclotron Centre（可变能量回旋加速器中心）
• GSI Helmholtzzentrum für Schwerionenforschung GmbH (GSI)（GSI亥姆霍兹重离子研究中心有限公司）

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