发表机构
Joint Institute for Nuclear Research（俄罗斯联邦核研究中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用UrQMD模型微观分析低能重离子碰撞中的重子阻止，发现中间快度输运质子多源于初始中子（同位旋转换），并揭示其与核透明度及化学平衡偏离的关联。
AI 中文摘要
在低能重离子碰撞中，重子阻止是一个重要过程，其中来自初始碰撞核的质子在中间快度区域被阻止。量化这种阻止可以揭示核介质性质的信息，如净重子密度。尽管净质子快度谱的实验测量提供了约束，但这些质子的微观起源并未完全可知。因此，输运模型研究可以提供对从初始核输运来的质子微观起源更深入的理解，补充实验测量。本文介绍了在最小偏置Au+Au碰撞中，在广泛的束流能量范围$\sqrt{s_{NN}} = 2.4-17.3$ GeV（$E_{\rm lab} = 1.23A-158A$ GeV）内对重子阻止的研究。通过分析UrQMD模型中的相互作用历史，根据最终态质子的来源对其进行分类。在中间快度处，相当大比例的输运质子来源于初始中子而非初始质子，称为同位旋转换质子，并量化了它们作为碰撞能量和中心度函数的贡献。估算了不同质子类别的各向异性流系数，并与实验测量结果进行了比较。此外，对$\pi^{-}/\pi^{+}$比率和同位旋转换率进行了比较。后者进一步与Kitazawa-Asakawa形式主义的$\alpha$参数进行了比较，揭示了在$\sqrt{s_{NN}} \lesssim$ 10~GeV以下，与化学平衡假设$\alpha_N = \alpha_\pi$存在显著偏差。最后，发现同位旋转换率的饱和与核透明度的出现相吻合，表明在NICA/FAIR能量范围内的强子输运中，同位旋随机化和重子阻止是耦合现象。
英文摘要
In low-energy heavy-ion collisions, baryon stopping is an important process, in which protons from the initial colliding nuclei are stopped at mid-rapidity region. Quantifying such stopping can reveal information on the properties of the nuclear medium, such as net-baryon density. Though experimental measurement of net-proton rapidity spectra provides constraints, microscopic origin of such protons is not fully accessible. Transport model studies can therefore provide deeper insight into the microscopic origin of protons transported from initial nuclei, complementing experimental measurements. This article presents an investigation of baryon stopping in minimum-bias Au+Au collisions over a wide range of beam energies, $\sqrt{s_{NN}} = 2.4-17.3$ GeV ($E_{\rm lab} = 1.23A-158A$ GeV). Final-state protons are classified based on their origin by analyzing their interaction history in the UrQMD model. A significant fraction of transported protons at mid-rapidity originates from initial neutrons rather than initial protons, referred to as \textit{isospin-converted} protons, and their contribution as a function of collision energy and centrality is quantified. Anisotropic flow coefficients of different proton categories are estimated and compared with experimental measurements. Furthermore, a comparison between the $π^{-}/π^{+}$ ratio and \textit{isospin conversion} rate is performed. The latter is further compared with the $α$ parameters of the Kitazawa-Asakawa formalism, revealing a significant deviation from the chemical equilibrium assumption $α_N = α_π$ below $\sqrt{s_{NN}} \lesssim$ 10~GeV. Finally, the saturation of the isospin conversion rate is found to coincide with the onset of nuclear transparency, demonstrating that isospin randomization and baryon stopping are coupled phenomena in hadronic transport across the NICA/FAIR energy range.
Comments16 pages, 13 figures
Journal refPhys. Rev. C 114, 034908 (2026)
