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AGH University of Science and Technology, FPACS, Cracow 30-059, Poland.
University of Kentucky, Lexington, Kentucky 40506-0055.
Phys Rev Lett. 2017 May 26;118(21):212301. doi: 10.1103/PhysRevLett.118.212301.
We report the first measurement of the elliptic anisotropy (v_{2}) of the charm meson D^{0} at midrapidity (|y|<1) in Au+Au collisions at sqrt[s_{NN}]=200 GeV. The measurement was conducted by the STAR experiment at RHIC utilizing a new high-resolution silicon tracker. The measured D^{0} v_{2} in 0%-80% centrality Au+Au collisions can be described by a viscous hydrodynamic calculation for a transverse momentum (p_{T}) of less than 4 GeV/c. The D^{0} v_{2} as a function of transverse kinetic energy (m_{T}-m_{0}, where m_{T}=sqrt[p_{T}^{2}+m_{0}^{2}]) is consistent with that of light mesons in 10%-40% centrality Au+Au collisions. These results suggest that charm quarks have achieved local thermal equilibrium with the medium created in such collisions. Several theoretical models, with the temperature-dependent, dimensionless charm spatial diffusion coefficient (2πTD_{s}) in the range of ∼2-12, are able to simultaneously reproduce our D^{0} v_{2} result and our previously published results for the D^{0} nuclear modification factor.
我们报告了在√[sNN]=200 GeV的金金碰撞中，对中心快度（|y|<1）处粲介子D⁰的椭圆各向异性（v₂）的首次测量。该测量由相对论重离子对撞机（RHIC）上的STAR实验利用新型高分辨率硅追踪器进行。在0%-80%中心度的金金碰撞中测量得到的D⁰ v₂，对于横动量（pT）小于4 GeV/c的情况，可以用粘性流体动力学计算来描述。在10%-40%中心度的金金碰撞中，作为横向动能（mT - m₀，其中mT = √[pT² + m₀²]）函数的D⁰ v₂与轻介子的情况一致。这些结果表明，粲夸克已与此类碰撞中产生的介质达到局部热平衡。几个理论模型，其温度依赖的无量纲粲空间扩散系数（2πTDs）在~2 - 12范围内，能够同时重现我们的D⁰ v₂结果以及我们之前发表的D⁰核修正因子的结果。
