$\sqrt{s_{NN}}$ = 7.7 - 39 GeV Au + Au碰撞中的包含荷电强子椭圆流
Inclusive charged hadron elliptic flow in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 39 GeV
摘要：
本文系统地研究了$\sqrt{s_{NN}}$ = 7.7、11.5、19.6、27和39 GeV的Au+Au碰撞中包含的中快度带电强子椭圆流（$v_2$）对中心度、横动量（$p_T$）和赝快度（$η$）的依赖性.为了研究非流动关联和$v_2$涨落，给出了用不同方法得到的结果，包括与在由大赝快度间隙和4粒子累积量（$v_2{4}$）分隔的区域中重建的事件平面的关联。我们观察到，在较低的碰撞能量下，$v_2{2}$和$v_2{4}$之间的差异较小。由初始坐标空间偏心率，$v_{2}/\varepsilon$，作为$p_T$的函数缩放的$v_2$的值在更中心的碰撞中更大，这表明更强的集体流在更中心的碰撞中发展，类似于在更高的碰撞能量下的结果。这些结果进行了比较，在较高的能量在相对论重离子对撞机（$\sqrt{s_{NN}}$ = 62.4和200 GeV）和大型强子对撞机（铅+铅碰撞$\sqrt{s_{NN}}$ = 2.76 TeV）的测量。固定$p_T$的$v_2(p_T)$值在研究的$p_T$范围内（$< 2 {\rm GeV}/c$）随着碰撞能量的增加而升高。与粘性流体动力学模拟进行比较，可能有助于理解$v_{2}(p_{T})$的能量依赖性。我们还比较了$v_2$结果UrQMD和AMPT输运模型计算，并讨论了在束能量扫描（BES）能量下创建的系统中部分子与强子相的主导地位的物理意义。
英文摘要：
A systematic study is presented for centrality, transverse momentum ($p_T$) and pseudorapidity ($η$) dependence of the inclusive charged hadron elliptic flow ($v_2$) at midrapidity($|η| < 1.0$) in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27 and 39 GeV. The results obtained with different methods, including correlations with the event plane reconstructed in a region separated by a large pseudorapidity gap and 4-particle cumulants ($v_2{4}$), are presented in order to investigate non-flow correlations and $v_2$ fluctuations. We observe that the difference between $v_2{2}$ and $v_2{4}$ is smaller at the lower collision energies. Values of $v_2$, scaled by the initial coordinate space eccentricity, $v_{2}/\varepsilon$, as a function of $p_T$ are larger in more central collisions, suggesting stronger collective flow develops in more central collisions, similar to the results at higher collision energies. These results are compared to measurements at higher energies at the Relativistic Heavy Ion Collider ($\sqrt{s_{NN}}$ = 62.4 and 200 GeV) and at the Large Hadron Collider (Pb + Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV). The $v_2(p_T)$ values for fixed $p_T$ rise with increasing collision energy within the $p_T$ range studied ($< 2 {\rm GeV}/c$). A comparison to viscous hydrodynamic simulations is made to potentially help understand the energy dependence of $v_{2}(p_{T})$. We also compare the $v_2$ results to UrQMD and AMPT transport model calculations, and physics implications on the dominance of partonic versus hadronic phases in the system created at Beam Energy Scan (BES) energies are discussed.
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