AI 中文总结
该研究旨在通过主成分分析寻找 FAIR 能量下重离子碰撞初始状态涨落。先利用 UrQMD 引入初始构型局部涨落，再用 PCA 技术分析产生π介子末态分布，研究主成分特征值对初始构型等的敏感性，探索初始热点构型的影响。
AI 中文摘要
在高能重离子碰撞中，碰撞核的初始构型对确定反应类型和产物起重要作用。碰撞核重叠区域内核子的初始排列通常不对称，这种不对称反映在末态动量各向异性测量中。核子的初始分布还受到大的量子涨落影响，导致在小区域内有大的能量沉积。末态可观测量虽对这种局部涨落敏感，但因是对一组事件平均计算而使真实效应被稀释，且初始态涨落随机不可控，难以从事件平均的末态可观测量中识别其效应。本文首先通过在 UrQMD 事件发生器中对 E$_{lab}$ = 20 AGeV（$\sqrt{s}$ = 6.27 GeV）的中心 Pb + Pb 碰撞中碰撞核内的核子位置进行空间重排来引入初始构型中的局部涨落（热点）。然后使用主成分分析（PCA）技术分析产生的π介子的一维或二维变量（如（$\eta$，$\phi$，$p_T$）和（$\eta - p_T$，$\phi - p_T$，$\eta - \phi$））的末态分布。研究了主成分的特征值对各种初始构型、初始条件下含热点的事件分数以及事件中心度的敏感性，以探寻其对初始热点构型的敏感性。
英文摘要
In high energy heavy ion collisions, the initial configurations of the colliding nuclei play an important role in determining the reaction type and the products of the reaction. The initial arrangement of nucleons within the overlap region of two colliding nuclei is generally asymmetric and such asymmetries reflect themselves in the measurement final state momentum anisotropy. Also initial distribution of the nucleons are subjected to large quantum fluctuation causing large energy deposition in a small region. The final state observables related momentum anisotropies although sensitive to such localized fluctuations but their true effect gets diluted because these observables are calculated by averaging over a set of events. Also, such fluctuations in the initial states are random and uncontrolled. Thus, identifying their effect from event-averaged final state observable is difficult. However, it would be interesting to know the origin of such fluctuations and how these fluctuation are eventually translated to the final state. In this work, we at first introduce such localized fluctuations in the initial configurations, also called hot spots, by implementing spatial rearrangements of nucleon position in the colliding nuclei in the central Pb+Pb collisions at E$_{lab}$=20 AGeV ($\sqrt{s}$=6.27 GeV) using the UrQMD event generator. Then the final state distributions of one or two dimensional variables e.g., ($η$, $ϕ$, $p_T$) and ($η-p_T$, $ϕ-p_T$, $η-ϕ$) of the produced pions are analysed using the principal component analysis (PCA) technique. The eigenvalues of the principal components have been studied for various initial configurations, event fractions containing hot spots in the initial condition and for event centralities with an aim to find it's sensitivity to the initial hot spot configurations.
Journal refEur.Phys.J.A 61 (2025) 2, 39
DOI：10.1140/epja/s10050-025-01504-w
