Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main, Germany.
Department of Physics, Tsinghua University, Beijing 100084, China.
Phys Rev Lett. 2015 Mar 20;114(11):112301. doi: 10.1103/PhysRevLett.114.112301. Epub 2015 Mar 17.
The quark gluon plasma produced in ultrarelativistic heavy-ion collisions exhibits remarkable features. It behaves like a nearly perfect liquid with a small shear viscosity to entropy density ratio and leads to the quenching of highly energetic particles. We show that both effects can be understood for the first time within one common framework. Employing the parton cascade Boltzmann approach to multiparton scatterings, the microscopic interactions and the space-time evolution of the quark gluon plasma are calculated by solving the relativistic Boltzmann equation. Based on cross sections obtained from perturbative QCD with explicitly taking the running coupling into account, we calculate the nuclear modification factor and elliptic flow in ultrarelativistic heavy-ion collisions. With only one single parameter associated with coherence effects of medium-induced gluon radiation, the experimental data of both observables can be understood on a microscopic level. Furthermore, we show that perturbative QCD interactions with a running coupling lead to a sufficiently small shear viscosity to entropy density ratio of the quark gluon plasma, which provides a microscopic explanation for the observations stated by hydrodynamic calculations.
在相对论重离子碰撞中产生的夸克胶子等离子体表现出显著的特征。它的行为类似于一种近乎完美的液体，具有较小的剪切粘性与熵密度比，导致高能粒子的猝灭。我们首次在一个共同的框架内理解了这两种效应。采用多重散射的部分子级联玻尔兹曼方法，通过求解相对论玻尔兹曼方程，计算夸克胶子等离子体的微观相互作用和时空演化。基于考虑了跑动耦合的微扰 QCD 截面，我们计算了相对论重离子碰撞中的核修正因子和椭圆流。仅用一个与介质诱导的胶子辐射相干效应相关的单一参数，我们就可以从微观层面理解这两个可观测量的实验数据。此外，我们表明，具有跑动耦合的微扰 QCD 相互作用导致夸克胶子等离子体的剪切粘性与熵密度比足够小，这为流体力学计算所观察到的现象提供了微观解释。
