初始状态对$\u221a s_{NN}=5.36$ TeV Pb--Pb碰撞中纵向$\Lambda$极化的涡度--剪切竞争的调控

中文摘要 AI 辅助

我们研究了横向初始能量密度分布如何控制$\u221a s_{NN}=5.36$ TeV Pb--Pb碰撞中纵向$\Lambda$极化的第二正弦谐波。我们使用(3+1)维粒子网格相对论理想流体动力学和Becattini--Buzzegoli--Palermo等温局域平衡方案。在选定的十二个初始状态中，运动学涡度贡献$P_{z,s2}^{\omega}$为负，而运动学剪切贡献$P_{z,s2}^{\Xi}$为正。改变初始能量密度归一化$e_{\mathrm{peak}}$、横向平滑宽度$\sigma_\perp$或约化碰撞参数$b_0$会改变两个贡献的相对大小，而不仅仅是重新缩放它们的总和。减小横向平滑宽度$\sigma_\perp$通常会增强两个贡献，而增加初始能量密度归一化$e_{\mathrm{peak}}$可以优先削弱$P_{z,s2}^{\Xi}$并反转总谐波。在固定的$e_{\mathrm{peak}}$下，碰撞参数依赖性在较窄的横向平滑下主要由剪切驱动，在较宽的横向平滑下主要由涡度驱动。将Liu--Yin方案应用于两个测试的流体动力学背景会反转总符号，表明符号取决于极化公式以及流体场。我们使用理想流体动力学和ILE方案获得的结果与ALICE在$50$--$70\\%$中心度区间外围Pb--Pb碰撞的测量结果具有相同的符号和数量级，表明这种正谐波可以源于初始状态控制的、在解耦时剪切主导的平衡。

英文摘要

We investigate how the transverse initial energy-density distribution controls the second sine harmonic of longitudinal $Λ$ polarization in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.36\,\mathrm{TeV}$. We use (3+1)-dimensional Particle-In-Cell Relativistic ideal hydrodynamics and the Becattini--Buzzegoli--Palermo isothermal local-equilibrium prescription. Across the twelve selected initial states, the kinematic-vorticity contribution $P_{z,s2}^ω$ is negative, whereas the kinematic-shear contribution $P_{z,s2}^Ξ$ is positive. Changing the initial energy-density normalization $e_{\mathrm{peak}}$, transverse smoothing width $σ_\perp$, or reduced impact parameter $b_0$ modifies the relative magnitudes of the two contributions rather than merely rescaling their sum. Reducing the transverse smoothing width $σ_\perp$ generally strengthens both contributions, whereas increasing the initial energy-density normalization $e_{\mathrm{peak}}$ can preferentially weaken $P_{z,s2}^Ξ$ and reverse the total harmonic. At fixed $e_{\mathrm{peak}}$, the impact-parameter dependence is mainly shear driven for narrower transverse smoothing and mainly vorticity driven for broader transverse smoothing. Applying the Liu--Yin prescription to the two tested hydrodynamic backgrounds reverses the total sign, showing that the sign depends on the polarization formula as well as on the fluid fields. Our results obtained with ideal hydrodynamics and the ILE prescription have the same sign and order of magnitude as the ALICE measurements for peripheral Pb--Pb collisions in the $50$--$70\%$ centrality interval, showing that such a positive harmonic can arise from an initial-state-controlled, shear-dominated balance at decoupling.

发表机构

• School of Mathematics and Physics, China University of Geosciences (Wuhan)（中国地质大学（武汉）数学与物理学院）

机构由 AI 辅助整理，请以论文原文为准。