标题： 相对论核碰撞中集体流涨落的系统大小和形状依赖性 显示英文标题

标题： System size and shape dependences of collective flow fluctuations in relativistic nuclear collisions

摘要： 量子涨落在这类相对论重离子碰撞中形成的强子集体流的形成过程中起着至关重要的作用。集体流事件之间的涨落可能来源于初始几何形状、流体力学膨胀、强子化以及核物质的强子演化等多个方面，但每个来源的具体贡献仍是一个开放性问题。通过使用一个耦合到 Monte Carlo Glauber 初始条件的 (3+1) 维相对论流体动力学模型、Cooper-Frye 强子化方法和强子输运模型，我们研究了 Au+Au、Cu+Au 和 O+O 在$\sqrt{s_\mathrm{NN}}=200$GeV 能量下集体流涨落的系统大小和形状依赖性。我们的计算结果（粒子产额、平均横动量、2-粒子和4-粒子累积量椭圆流$v_2\{2\}$和$v_2\{4\}$）与 RHIC 当前的实验数据一致。由于不同碰撞系统的大小和形状差异，我们发现由$v_2\{4\}/v_2\{2\}$比率量化出的流涨落呈现出不同的中心依赖性。 通过比较不同强子种类之间的$v_2\{4\}/v_2\{2\}$，以及将$v_2\{4\}/v_2\{2\}$与用累积量椭圆度比值表征的初始状态几何涨落$\varepsilon_2\{4\}/\varepsilon_2\{2\}$进行对比，我们发现虽然初始状态涨落在大碰撞系统中是$v_2$涨落的主要来源，但在小系统中，非线性流体动力学响应、强子化及强子后置燃烧等其他来源也可以显著影响$v_2$的涨落。 显示英文摘要

摘要： Quantum fluctuations plays an essential role in forming the collective flow of hadrons observed in relativistic heavy-ion collisions. Event-by-event fluctuations of the collective flow can arise from various sources, such as the fluctuations in the initial geometry, hydrodynamic expansion, hadronization, and hadronic evolution of the nuclear matter, while the exact contribution from each source is still an open question. Using a (3+1)-dimensional relativistic hydrodynamic model coupled to a Monte-Carlo Glauber initial condition, Cooper-Frye particlization and a hadronic transport model, we explore the system size and shape dependences of the collective flow fluctuations in Au+Au, Cu+Au, and O+O collisions at $\sqrt{s_\mathrm{NN}}=200$~GeV. The particle yields, mean transverse momenta, 2-particle and 4-particle cumulant elliptic flows ($v_2\{2\}$ and $v_2\{4\}$) from our calculation agree with the currently existing data from RHIC. Different centrality dependences of the flow fluctuations, quantified by the $v_2\{4\}/v_2\{2\}$ ratio, are found for different collision systems due to their different sizes and shapes. By comparing $v_2\{4\}/v_2\{2\}$ between different hadron species, and comparing $v_2\{4\}/v_2\{2\}$ to the initial state geometric fluctuations quantified by the cumulant eccentricity ratio $\varepsilon_2\{4\}/\varepsilon_2\{2\}$, we find that while the initial state fluctuations are the main source of the $v_2$ fluctuations in large collision systems, other sources like nonlinear hydrodynamic response, hadronization, and hadronic afterburner can significantly affect the $v_2$ fluctuations in small systems.