arXiv 1503.017902015-03-05nucl-ex

在RHIC的PHENIX实验中探索具有重味的热且稠密的QCD物质的性质

Probing Properties of Hot and Dense QCD Matter with Heavy Flavor in the PHENIX Experiment at RHIC

Rachid Nouicer

备注：: 7 pages, 4 figures, Invited talk at the 3rd International Conference on New Frontiers in Physics (ICNFP2014),31 July to 6 August 2014, Greece. To be published in the European Physical Journal (EPJ)

摘要：

携带重夸克（粲夸克或底夸克）的强子是相对论性重离子碰撞中产生的热密介质的重要探针。重夸克-反夸克对主要产生于部分子的初始硬散射过程。虽然一些产生的对形成束缚夸克偶，但绝大多数强子化为带有开放重味的粒子。在RHIC的PHENIX实验中，通过测量半轻子衰变产生的单轻子，在中快度电子通道和前快度μ子通道中研究了重夸克的产生。在200 GeV的Au+Au碰撞中观察到了单电子的大的抑制和方位各向异性。这些结果表明，在热的、致密的物质中有大量的能量损失和重夸克的流动。PHENIX实验还测量了在$\sqrt{s_{nn}}$ = 200 GeV的p+p、d+Au、Cu+Cu和Au+Au碰撞中的${J/ψ}$产生，包括中快度和前快度，以及前快度下的Cu+Au和U+U。在能量最大的碰撞中，前向快度比中心快度有更多的抑制。这既可以解释为夸克复合的迹象，也可以解释为额外的冷核物质效应的暗示。在$\sqrt{s_{nn}}$ = 193 GeV的U+U碰撞中，${J/ψ}$的核修饰因子RAA的中心度依赖性与较轻的系统Au+Au和Cu+Cu在类似的能量200 GeV下表现出类似的趋势。

英文摘要：

Hadrons carrying heavy quarks, i.e. charm or bottom, are important probes of the hot and dense medium created in relativistic heavy ion collisions. Heavy quark-antiquark pairs are mainly produced in initial hard scattering processes of partons. While some of the produced pairs form bound quarkonia, the vast majority hadronize into particles carrying open heavy flavor. Heavy quark production has been studied by the PHENIX experiment at RHIC via measurements of single leptons from semi-leptonic decays in both the electron channel at mid-rapidity and in the muon channel at forward rapidity. A large suppression and azimuthal anisotropy of single electrons have been observed in Au+Au collisions at 200 GeV. These results suggest a large energy loss and flow of heavy quarks in the hot, dense matter. The PHENIX experiment has also measured ${J/ψ}$ production at $\sqrt{s_{nn}}$ = 200 GeV in p+p, d+Au, Cu+Cu and Au+Au collisions, both at mid- and forward-rapidities, and additionally Cu+Au and U+U at forward-rapidities. In the most energetic collisions, more suppression is observed at forward rapidity than at central rapidity. This can be interpreted either as a sign of quark recombination, or as a hint of additional cold nuclear matter effects. The centrality dependence of nuclear modification factor, RAA, for ${J/ψ}$ in U+U collisions at $\sqrt{s_{nn}}$ = 193 GeV shows a similar trend to the lighter systems, Au+Au and Cu+Cu, at similar energy 200 GeV.

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