AI 中文总结
ALICE合作组在5.36 TeV超中心Pb-Pb碰撞中测量v₃{2}/v₂{2}比值，将结果与流体动力学模型对比，以解决超中心碰撞中各向异性流建模偏差的难题。
AI 中文摘要
重离子碰撞中的各向异性流测量对初始态的空间分布以及夸克胶子等离子体的输运性质（如剪切粘度与熵密度之比η/s）敏感。最先进的相对论流体动力学模型可成功描述较宽中心度范围内的此类流测量结果，但超中心碰撞（UCC）中各向异性流的流体动力学描述与实验数据存在偏差——此时系统的平均几何各向异性很小，初始态几何由涨落主导。这种差异构成了“超中心碰撞难题”，因为当前建模方法无法完全重现预期的流谐层级。向超中心碰撞区域探测时，初始空间各向异性对流涨落的影响被抑制，测量到的流可由²⁰⁸Pb核能量分布的量子涨落解释；已有研究提出²⁰⁸Pb核的八极形变可作为修正项，以改进对测量到的v₃{2}/v₂{2}比值的建模。本研究中，我们利用ALICE合作组的第3代探测器，测量了质心系核子-核子对撞能量√s_NN=5.36 TeV下超中心Pb-Pb碰撞中的v₃{2}/v₂{2}比值，并将其与近期流体动力学模型计算结果进行了对比。
英文摘要
Anisotropic flow measurements in heavy-ion collisions are sensitive to the spatial distribution of the initial state, and quark-gluon plasma transport properties such as the shear viscosity to entropy density ratio $(η/s)$. State-of-the-art relativistic hydrodynamic models successfully describe such flow measurements over a wide centrality range. However, the hydrodynamic description of anisotropic flow deviates from the experimental data in ultra-central collisions (UCC), where the average geometric anisotropy of the system becomes small and fluctuations dominate the initial-state geometry. This discrepancy constitutes the UCC puzzle, as the expected hierarchy of flow harmonics is not fully reproduced by current modeling approaches. Probing towards ultra-central collisions, effects on flow fluctuations due to the initial spatial anisotropies are suppressed. The measured flow can be explained by quantum fluctuations on the energy distribution of $^{208}$Pb nuclei. An octupole deformation of the $^{208}$Pb nuclei has been proposed as a remedy to improve the modeling of the measured $v_{3} \{2\} / v_{2} \{2\}$ ratio. In this contribution, we present measurements of $v_{3}\{2\}/v_{2}\{2\}$ ratio in ultra-central Pb\textendash Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.36$ TeV with ALICE Run 3 detector and compare them with recent hydrodynamic model calculations.
