arXiv 0904.47642009-04nucl-ex

光子在PHENIX

Photons at PHENIX

Baldo Sahlmueller

备注：: 8 pages, 7 figures, submitted to the proceedings of the 4th international workshop High-pT physics at LHC, Prague 2009 v2 (referee comments): relatively minor changes
发表信息：: PoS High-pTphysics09:035,2009

摘要：

直接光子是研究超相对论性重离子碰撞中产生的独特物质性质的有力探针。它们携带着重离子碰撞各个阶段的信息。在不同的横动量下，不同的产生过程决定了重离子碰撞中的直接光子产额。高pT的光子可用于研究初始硬散射过程，而低和中等pT的光子提供了关于在这种碰撞中产生的热而致密的介质的直接信息，因为它们主要来自射流-介质相互作用和介质本身的热辐射。PHENIX测量了Au+Au和Cu+Cu等不同碰撞体系中宽pT和能量范围内的直接光子产额，从而可以系统地研究重离子碰撞中直接光子的行为。两种不同的方法已被用于测量直接光子。通过内转换首次测量到Au+Au碰撞中在低pT下的直接光子超出了p+p碰撞的预期。此外，方位各向异性参数v2已被测量。直接光子v2揭示了产生直接光子的不同过程。相同能量下的p+p数据为理解重离子数据提供了一个基线，但它们本身也很有趣，例如用于测试pQCD计算，或者-当RHIC碰撞极化质子时-用于约束胶子对质子自旋的贡献模型。

英文摘要：

Direct photons are a powerful probe to study the properties of the unique matter created in ultrarelativistic heavy-ion collisions. They carry information on the various stages of a heavy-ion collision. At different transverse momenta (pT), different production processes dominate the direct photon yield in heavy-ion collisions. Photons at high pT can be used to study initial hard scattering processes while photons at low and intermediate pT provide direct information on the hot and dense medium created in such collisions since they origin predominantly from jet-medium interactions and from thermal radiation from the medium itself. PHENIX has measured direct-photon yields over a broad pT and energy range in different collision systems such as Au+Au and Cu+Cu, allowing systematic studies of the behavior of direct photons in heavy-ion collisions. Two different methods have been used to measure the direct photons. An excess of direct photons in Au+Au collisions at low pT beyond the expectation from p+p collisions was measured for the first time via internal conversion. Furthermore, the azimuthal anisotropy parameter v2 has been measured. The direct photon v2 sheds light on the different processes contributing to the production of direct photons. The p+p data at the same energy provide a baseline for understanding the heavy-ion data, but are also interesting in their own right, e.g. for testing pQCD calculations or - as RHIC collides polarized protons - for constraining models on the gluon contribution to the proton spin.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

摘要：

英文摘要：

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