发表机构
Joint Institute for Nuclear Research; Weizmann Institute of Science; Shandong University; National Research Nuclear University MEPhI (Moscow Engineering Physics Institute)（俄罗斯联合核研究所; 魏茨曼科学研究所; 山东大学; 莫斯科工程物理国立研究大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过模拟Bi+Bi碰撞，评估了MPD实验在NICA能区双电子测量的性能，采用多层感知机优化电子鉴别并开发配对分析策略，将信号本底比提升约3.5倍，展示了其强大潜力。
AI 中文摘要
NICA的多用途探测器（MPD）实验旨在通过重离子测量的广泛项目，研究高净重子密度下强相互作用物质的性质。双电子是该计划中的关键探针之一，其贡献贯穿碰撞的整个时空演化过程。然而，其实验测量面临大量组合本底的挑战，这些本底主要来自不完全重建的光子转换和轻中性介子的Dalitz衰变。在本工作中，我们利用模拟的质心能量为$\sqrt{s_{NN}}$ = 9.2 GeV的最小偏置$^{209}$Bi+$^{209}$Bi碰撞，研究了MPD实验在双电子测量中的性能和能力。电子鉴别利用TPC、TOF探测器和ECal的联合信息进行。采用多层感知机分类器优化电子鉴别，相比顺序的一维选择，显著提高了电子探测效率，同时在大动量范围内保持了接近1的电子样本纯度。为应对主要的组合本底来源，开发了一种利用部分重建电子径迹的配对分析策略。该方法结合配对开角、TPC的dE/dx信号和配对不变质量的近似重建，在配对层面标记来自光子转换和$\pi^0$ Dalitz衰变的径迹。在质量区间0.2 < $m_{ee}$ < 0.7 GeV/$c^2$内，该方法在当前径迹重建算法下将信号本底比提高了约3.5倍。该研究展示了MPD实验在NICA能量下进行双电子测量的强大潜力，并强调了进一步改进低$p_{\rm T}$径迹重建的重要性。
英文摘要
The Multi-Purpose Detector (MPD) experiment at NICA is designed to investigate strongly interacting matter at high net-baryon density through a broad program of heavy-ion measurements. Dielectrons constitute one of the key probes in this program, with contributions emitted throughout the entire space-time evolution of the collision. Their experimental measurement is, however, challenged by a large combinatorial background arising primarily from incompletely reconstructed photon conversions and Dalitz decays of light neutral mesons. In this work, we study the performance and capabilities of the MPD experiment for dielectron measurements using simulated minimum-bias $^{209}$Bi+$^{209}$Bi collisions at $\sqrt{s_{NN}}$ = 9.2 GeV. Electron identification is performed using the combined information from the TPC, the TOF detector and the ECal. A multilayer-perceptron classifier is used to optimize electron identification, leading to a substantial increase in electron detection efficiency relative to sequential one-dimensional selections while preserving an electron-sample purity close to unity over a broad momentum range. To address the dominant sources of combinatorial background, a pair-analysis strategy is developed that exploits partially reconstructed electron tracks. The method combines the pair opening angle, the TPC dE/dx signal, and an approximate reconstruction of the pair invariant mass to tag tracks from photon conversions and $π^0$ Dalitz decays at the pair level. In the mass interval 0.2 $< m_{ee}<0.7 $ GeV/$c^2$, the method improves the signal-to-background ratio by a factor of about 3.5 with the current track reconstruction algorithm. The study demonstrates the strong potential of the MPD experiment for dielectron measurements at NICA energies and highlights the importance of further improvements in low-$p_{\rm T}$ track reconstruction.
Comments23 pages, 13 figures
