The large values and constituent-quark-number scaling of the elliptic flow of low- D mesons imply that charm quarks, initially produced through hard processes, might be partially thermalized through strong interactions with quark-gluon plasma (QGP) in high-energy heavy-ion collisions. To quantify the degree of thermalization of low- charm quarks, we compare the meson spectra and elliptic flow from a hydrodynamic model to experimental data as well as transport model simulations. We use an effective charm chemical potential at the freeze-out temperature to account for the initial charm quark production from hard processes and assume that they are thermalized in the local comoving frame of the medium before freeze-out. mesons are sampled statistically from the freeze-out hyper-surface of the expanding QGP as described by the event-by-event (3+1)D viscous hydrodynamic model CLVisc. Both the hydrodynamic and transport models can describe the elliptic flow of mesons at GeV/c as measured in Au+Au collisions at GeV. Though the experimental data on spectra are consistent with the hydrodynamic result at small GeV/c, they deviate from the hydrodynamic model at high transverse momentum, GeV/c. The diffusion and parton energy loss mechanisms in the transport model can describe the measured spectra reasonably well within the theoretical uncertainty. Our comparative study indicates that charm quarks only approach local thermal equilibrium at small , even though they acquire sizable elliptic flow comparable to light-quark hadrons at both small and intermediate .

低 D介子椭圆流的大值和成分夸克数标度意味着最初通过硬过程产生的粲夸克可能通过与高能重质中的夸克胶子等离子体 (QGP) 的强相互作用而部分热化。 -离子碰撞。为了量化低粲夸克的热化程度，我们将流体动力学模型的介子谱和椭圆流与实验数据以及输运模型模拟进行了比较。我们使用冻结温度下的有效粲化学势来解释硬过程产生的初始粲夸克，并假设它们在冻结前在介质的局部共同移动框架中被热化。如逐事件 (3+1)D 粘性流体动力学模型 CLVisc 所述，介子从膨胀 QGP 的冻结超表面进行统计采样。流体动力学模型和输运模型都可以描述GeV/ c下介子的椭圆流动，如在GeV 的Au+Au 碰撞中测量的。尽管光谱实验数据与小GeV/ c时的流体力学结果一致，但与高横向动量GeV/ c 时的流体力学模型有偏差. 传输模型中的扩散和部分能量损失机制可以在理论不确定性范围内合理地描述测量的光谱。我们的比较研究表明，粲夸克只在小的时候接近局部热平衡，即使它们在小和中等时都获得了与轻夸克强子相当的相当大的椭圆流。