从重离子碰撞中提取有限密度下的重子数 susceptibility
Extraction of baryon number susceptibilities at finite density from heavy-ion collisions
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中文总结 AI 辅助
本研究首次通过贝叶斯方法结合重离子碰撞数据，提取有限密度下QCD物质的重子数 susceptibility，获得χ₂ᴮ等参数的约束，并解释了质子阶乘累积量比值的非单调能量依赖性。
中文摘要 AI 辅助
据我们所知，我们首次利用贝叶斯方法从重离子碰撞的质子数累积量数据中提取有限重子密度下QCD物质的重子数 susceptibility。该框架通过最大熵冻结将任意物态 susceptibility χₙᴮ嵌入到真实的流体动力学粒子化超曲面中，将产生的（反）重子涨落映射到质子上，应用实验运动学接受度，并考虑精确的重子数守恒。将该框架应用于RHIC对撞机模式下束能量扫描中0-5%中心度Au-Au碰撞的（净）质子数涨落测量，我们在每个碰撞能量下提取了强子共振气体值归一化的二阶 susceptibility χ₂ᴮ/χ̄₂ᴮ，以及高阶 susceptibility 比值χ₃ᴮ/χ₁ᴮ和χ₄ᴮ/χ₂ᴮ。我们获得了χ₂ᴮ的严格约束，在化学冻结线处，当μ_B≲300 MeV时，提取值与格点QCD估计定量一致；在较大的μ_B时，提取值表明，相对于此处考虑的非临界格点外推和HRG基线，重子数涨落有所增强。三阶和四阶 susceptibility 的约束较弱。特别地，我们发现观测到的质子阶乘累积量比值 Ĉ₃/Ĉ₁的非单调碰撞能量依赖性可在无不可约的三或四重子关联的情况下描述，该行为源于χ₂ᴮ的能量依赖性与精确重子数守恒之间的相互作用。
英文摘要
We present, to our knowledge, the first Bayesian extraction of baryon number susceptibilities of QCD matter at finite baryon density from heavy-ion collision data on proton number cumulants. The framework embeds arbitrary equation-of-state susceptibilities $χ_n^B$ into realistic hydrodynamic particlization hypersurfaces through maximum-entropy freeze-out, maps the resulting (anti)baryon fluctuations onto protons, applies the experimental kinematic acceptance, and accounts for exact baryon number conservation. Applying the framework to measurements of (net-)proton number fluctuations in 0--5\% central Au-Au collisions from the RHIC Beam Energy Scan in the collider mode, we extract, at each collision energy, the second-order susceptibility normalized by the hadron resonance gas value, $χ_{2}^B/\barχ_{2}^B$, and the higher-order susceptibility ratios $χ_{3}^B/χ_{1}^B$ and $χ_{4}^B/χ_{2}^B$. We obtain tight constraints on $χ_{2}^B$, with extracted values in quantitative agreement with lattice QCD based estimates along the chemical freeze-out line for $μ_B \lesssim 300$~MeV. At larger $μ_B$, the extracted values indicate an enhancement of baryon number fluctuations relative to the noncritical lattice-based extrapolation and HRG baseline considered here. The third- and fourth-order susceptibilities are only weakly constrained. In particular, we find that the observed nonmonotonic collision-energy dependence of the proton factorial cumulant ratio $\hat{C}_{3}/\hat{C}_{1}$ can be described without irreducible three- or four-baryon correlations. This behavior emerges from the interplay between the energy dependence of $χ_{2}^B$ and exact baryon number conservation.
