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arXiv 1801.00271nucl-thhep-phnucl-ex
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13 TeV质子-质子碰撞的流体力学集体性

Hydrodynamic Collectivity in Proton--Proton Collisions at 13 TeV

Wenbin Zhao, You Zhou, Hao-jie Xu, Weitian Deng, Huichao Song

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7 pages, 6 figures, published version
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摘要：

本文采用iEBE-VISHNU混合模型，在HIJING初始条件下，研究了13 TeV质子-质子（pp）碰撞中的流体动力学集体性.通过适当的参数调整，我们的模型模拟可以很好地描述所有测量到的2粒子关联，包括所有带电和已识别强子的积分和微分椭圆流系数（$K_S^0$，$Λ$）。然而，我们的模型计算在高多重数pp碰撞中显示了正的4粒子累积量$c_{2}\{4\}$，而不能再现实验测量的负的$c_{2}\{4\}$.对HIJING初始条件的进一步研究表明，二阶各向异性系数$\varepsilon_{2}$的波动随其平均值的增大而增大，从而导致了流动波动的相似趋势。为了在流体力学框架内同时描述2粒子和4粒子的累积量，需要对pp碰撞的初始条件进行重大改进，目前还缺乏知识。

英文摘要：

In this paper, we investigate the hydrodynamic collectivity in proton--proton (pp) collisions at 13 TeV, using iEBE-VISHNU hybrid model with HIJING initial conditions. With properly tuned parameters, our model simulations can remarkably describe all the measured 2-particle correlations, including integrated and differential elliptic flow coefficients for all charged and identified hadrons ($K_S^0$, $Λ$). However, our model calculations show positive 4-particle cumulant $c_{2}\{4\}$ in high multiplicity pp collisions, and can not reproduce the negative $c_{2}\{4\}$ measured in experiment. Further investigations on the HIJING initial conditions show that the fluctuations of the second order anisotropy coefficient $\varepsilon_{2}$ increases with the increase of its mean value, which leads to a similar trend of the flow fluctuations. For a simultaneous description of the 2- and 4- particle cumulants within the hydrodynamic framework, it is required to have significant improvements on initial condition for pp collisions, which is still lacking of knowledge at the moment.

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