标题： LHC能区重离子碰撞中鉴别粒子谱的非平衡现象学 显示英文标题

标题： Nonequilibrium Phenomenology of Identified Particle Spectra in Heavy-Ion Collisions at LHC Energies

摘要： 我们采用 Zubarev 的非平衡统计算符方法来研究 pion 谱低-$p_T$区域的增强，并引入一个有效的 pion 化学势以描述低能 pion 态的过度占据。 通过分析 ALICE 合作组最近利用 CERN LHC 中 Pb+Pb 碰撞精确测量的鉴别粒子的横向动量谱，我们检验了相应的冻结出方法。 使用了一个爆轰波模型和一个基于爆轰波的粒子生成器，该生成器耦合到一个强子输运模型。 应用贝叶斯推断方法提取化学冻结面最可能的一组热力学参数。 对于过度占据 pion 态的这两种模型——强子输运模型和具有非零 pion 化学势的热模型——均能很好地描述观测到的 pion 谱。 然而，两种方法都包含可以在此系统非平衡方法下改进的近似。 我们证明，引入非平衡 pion 化学势提供了一种有效的替代传统解释低-$p_T$增强的方法，通常归因于共振衰变后的热化。 类似讨论也适用于 kaon 谱。 显示英文摘要

摘要： We employ the Zubarev approach of the non-equilibrium statistical operator to investigate the enhancement of the low-$p_T$ region of pion spectra, introducing an effective pion chemical potential to describe the overpopulation of low-energy pion states. We test a corresponding freeze-out approach by analyzing the transverse-momentum spectra of identified particles measured recently with high precision by the ALICE Collaboration in Pb+Pb collisions at CERN LHC. A blast-wave model and a blast-wave-based particle generator, coupled to a hadronic transport model, are utilized. Bayesian inference methods are applied to extract the most probable sets of thermodynamic parameters at the chemical freeze-out hypersurface. Both models for the overpopulated pion states, the hadronic transport model and the thermal model with a nonzero pion chemical potential, provide a satisfactory description of the observed pion spectra. However, both approaches contain approximations which can be improved within a systematic nonequilibrium approach. We demonstrate that the introduction of a nonequilibrium pion chemical potential offers an efficient alternative to the conventional explanation of the low-$p_T$ enhancement, typically attributed to resonance decays with subsequent thermalization. A similar discussion holds also for the kaon spectra.