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arXiv 1607.02572hep-phhep-ex
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Au+Au碰撞中$\sqrt{s_{NN}}=200$ ~ GeV与EPOS3的直接光子和热双轻子的各向异性发射

Anisotropic emission of direct photons and thermal dileptons from Au+Au collisions at $\sqrt{s_{NN}}=200$~GeV with EPOS3

Sheng-Xu Liu, Fu-Ming Liu, Klaus Werner, Meng Yue

备注：
14 pages, 20 figures. arXiv admin note: text overlap with arXiv:1508.05160
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摘要：

直接光子和双轻子等电磁探针是研究重离子碰撞中产生的夸克-胶子等离子体（QGP）性质的关键。基于（3+1）维逐事件粘性流体动力学模型EPOS 3.102，计算了相对论重离子对撞机（RHIC）能量为$\sqrt{s_{NN}}=200$ ~GeV的Au+Au碰撞中热光子和双轻子的各向异性发射.考虑了QGP相和强子气相的热辐射，其中光子的AMY率和QGP相中双轻子的基于格点量子色动力学的速率。对于强子气相辐射，光子和双轻子都采用基于速率的矢量介子主导模型。用次首阶QCD计算了非热效应对直接光子的贡献。STAR鸡尾酒数据直接用于双轻子的非热贡献。在碰撞系统的时空演化相同的情况下，光子和双轻子这两种穿透探针表现出一定的一致性，即与PHENIX合作组测量的直接光子的横动量谱和STAR合作组测量的双轻子不变质量谱相比，对于所有的中心性类，热光子和双轻子的发射都被低估了.通过带电强子的椭圆流和三角流对等离子体的各向异性进行了很好的约束，得到的直接光子的椭圆流和三角流与PHENIX测量结果相当吻合。从而对热双轻子流作了预言。热双轻子的椭圆流的预测大于其他模型的可用结果，并与STAR测量指的是所有双轻子（热+鸡尾酒）的最小偏置碰撞。

英文摘要：

Electromagnetic probes such as direct photons and dileptons are crucial to study the properties of a Quark-Gluon Plasma (QGP) created in heavy ion collisions. Based on the (3+1)-dimensional event-by-event viscous hydrodynamic model EPOS 3.102, we calculated the anisotropic emission of thermal photons and dileptons in Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) energy $\sqrt{s_{NN}}=200$~GeV. Thermal emissions from both QGP phase and hadronic gas phase are considered, with AMY rate for photons and Lattice QCD based rates for dileptons in QGP phase. For emission from hadron gas phase, rates based vector meson dominant model are used for both photons and dileptons. Non-thermal contribution to direct photons is calculated with next to leading order QCD. STAR cocktail data are directly used for non-thermal contribution to dileptons. With the same space-time evolution of the collision systems, the two penetrating probes, photons and dileptonsshow some consistency, ie, the emission of both thermal photons and dileptons are underestimated, compared with the transverse momentum spectra of direct photons measured by PHENIX collaboration and the invariant mass spectra of dileptons measured by STAR collaboration, for all centrality classes. With a good constraint of anisotropy of the plasma via the elliptic flow and triangular flow of charged hadrons, the resulted elliptic flow and triangular flow of direct photons agree with PHENIX measurements reasonably well. Thus we made predictions to the flows of thermal dileptons. The elliptic flow of thermal dileptons is predicted larger than the available results from other models, and comparable to the STAR measurement referring to all dileptons (thermal + cocktail) for minimal bias collisions.

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