约束相对论重离子碰撞中的轻味与奇异味化学平衡
Constraining Light and Strange Flavor Equilibration in Relativistic Heavy-Ion Collisions
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中文总结 AI 辅助
本研究开发轻与奇异夸克化学平衡的动力学框架，结合贝叶斯分析与多阶段模型，从RHIC的Au+Au碰撞数据推断相关参数，发现奇异夸克平衡更缓慢，表明夸克胶子等离子体味组分在流体动力学阶段仍未平衡。
中文摘要 AI 辅助
相对论重离子碰撞是已知唯一能产生夸克胶子等离子体（夸克胶子退禁闭的量子色动力学物质态）的手段。流体动力学建模已证实该介质表现为强耦合、低粘滞流体，但通常假设其夸克与胶子组分在流体动力学阶段开始时已达到化学平衡，这一假设仍存不确定性：胶子主导的初态表明，夸克产生过程会持续到流体动力学阶段，且轻夸克与奇异夸克的产生速率可能存在差异。本论文开发了轻夸克与奇异夸克化学平衡的动力学框架，通过随时间变化的夸克逸度描述每种味的不完全平衡，该逸度会同时改变介质的状态方程与粒子化过程。该模型被整合至包含涨落初态、粘滞流体动力学、粒子化及强子输运的多阶段框架中，用于研究平衡过程对流体动力学演化及强子、电磁可观测量的影响。该框架嵌入贝叶斯分析，其中基于模型计算训练的高斯过程模拟器，可从相对论重离子对撞机（RHIC）的金-金（Au+Au）碰撞数据中推断初始轻夸克与奇异夸克逸度、它们的平衡时标及选定的输运系数。研究发现奇异夸克 sector 初始时显著欠饱和，其抑制程度高于轻夸克 sector；数据进一步支持奇异夸克的平衡过程更缓慢，尽管时标本身仍受弱约束。这些结果表明，夸克胶子等离子体的味组分在流体动力学阶段仍在趋近化学平衡，而非在初始时就已固定，这为扩展到不同大小与能量的碰撞系统提供了动机。
英文摘要
Relativistic heavy-ion collisions are the only known means of creating the quark-gluon plasma, a deconfined state of QCD matter. Hydrodynamic modeling has established that this medium behaves as a strongly coupled, low-viscosity fluid, but typically assumes that its quark and gluon composition reaches chemical equilibrium by the onset of the hydrodynamic phase. This assumption remains uncertain: gluon-dominated initial states suggest that quark production continues well into the hydrodynamic stage, with potentially different rates for light and strange quarks. This dissertation develops a dynamical framework for light and strange quark chemical equilibration. Incomplete equilibration of each flavor is described through time-dependent quark fugacities that modify both the equation of state and the particlization of the medium. Implemented within a multistage framework of fluctuating initial conditions, viscous hydrodynamics, particlization, and hadronic transport, the model is used to study the effects of equilibration on the hydrodynamic evolution and on hadronic and electromagnetic observables. The framework is embedded within a Bayesian analysis in which Gaussian process emulators trained on the model calculations infer the initial light and strange quark fugacities, their equilibration timescales, and selected transport coefficients from Au+Au collision data at RHIC. The strange sector is found to begin substantially undersaturated, more suppressed than the light sector; the data further favor a slower approach to equilibrium for strangeness, though the timescales themselves remain weakly constrained. These results favor a quark-gluon plasma whose flavor composition is still approaching chemical equilibrium during the hydrodynamic phase rather than fixed at its outset, and motivate extensions to collision systems of differing size and energy.
