摘要:
利用UrQMD-3.3p1 模型模拟了在质心能量√sNN = 7.7, 11.5, 19.6, 27, 39 和62.4 GeV 的Au+Au 碰撞，在中心快度区域分析了质子，π+，K+ 以及它们相应的反粒子的椭圆流。分析了粒子与相应的反粒子的v2 差值随横动量pT 的变化。分析结果表明，在UrQMD 模型中在整个BES 能区K- 的v2 值大于K+ 的。在能区7.7 ~ 62.4GeV π+ 和π-的v2(pT) 值几乎相同。然而实验上在低能区7.7, 11.5 和19.6 GeV, 在所考察的pT 值范围内v2(π-)大于v2(π+)。能清楚看到在UrQMD模型中在整个BES 能区反质子的v2 大于质子的，这与实验结果相反。理论结果与实验数据相反，表明我们还需要不断深化对重离子碰撞的强耦合性和输运过程的非平衡性的理解。
Abstract:
The elliptic flow for proton, π+, K+ and their corresponding antiparticles are investigated at mid-rapidity for Au+Au collisions at √sNN =7.7, 11.5, 19.6, 27, 39, 62.4 GeV, utilizing ultrarelativistic quantum molecular dynamics (UrQMD-3.3p1). We analyze the difference in v2(pT) between the particles and the corresponding antiparticles as a function of the transverse momentum pT. We find that in UrQMD the v2 for K is larger than that for K+ at all BES energies. The v2(pT) values are almost identical for π+ and π-􀀀at 7.7s62.4 GeV. While in experiments, at lower energies, 7.7, 11.5 and 19.6 GeV,v2(π-) is larger than v2(π+) for all pT values. We can clearly see that in UrQMD the v2 for antiproton is larger than that for proton at all BES energies, which is in contradiction to the experimental result.The opposite trend observed in experiment is therefore an indication that the strong coupling in heavy ion collision and the non equilibrium in transport process may need further understanding.
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