arXiv 0810.08722008-10-21nucl-ex

RHIC的直接光子

Direct Photons at RHIC

G. David

备注：: 4 pages, 2 figures, parallel talk at ICHEP08; fixed Fig. 2 problem

摘要：

直接光子是研究重离子碰撞的运动学和动力学条件的理想工具，因为它们从碰撞的所有阶段发射，并且一旦产生，它们就离开相互作用区域而不被介质进一步修改。RHIC的PHENIX实验测量了200 GeV的p+p和Au+Au碰撞在宽横向动量（$p_T$）范围内的直接光子产生。$p$ + $p$测量允许QCD的基本测试，并且当我们试图解开在Au+Au中产生高$p_T$直接光子的更复杂机制时，可以作为基线。对于Au+Au中的热光子，我们通过测量“几乎真实”的虚光子克服了强子衰变的大背景所带来的困难，虚光子表现为低不变质量的$e^+e^-$对：在上述次领先阶微扰量子色动力学计算之上测量到了显著过量的直接光子。通过研究方位各向异性，可以获得关于直接光子起源的更多见解，方位各向异性的研究受益于RHIC 7年数据中增加的统计数据和反应平面分辨率。

英文摘要：

Direct photons are ideal tools to investigate kinematical and thermodynamical conditions of heavy ion collisions since they are emitted from all stages of the collision and once produced they leave the interaction region without further modification by the medium. The PHENIX experiment at RHIC has measured direct photon production in p+p and Au+Au collisions at 200 GeV over a wide transverse momentum ($p_T$) range. The $p$ + $p$ measurements allow a fundamental test of QCD, and serve as a baseline when we try to disentangle more complex mechanisms producing high $p_T$ direct photons in Au+Au. As for thermal photons in Au+Au we overcome the difficulties due to the large background from hadronic decays by measuring "almost real" virtual photons which appear as low invariant mass $e^+e^-$ pairs: a significant excess of direct photons is measured above the above next-to-leading order perturbative quantum chromodynamics calculations. Additional insights on the origin of direct photons can be gained with the study of the azimuthal anisotropy which benefits from the increased statistics and reaction plane resolution achieved in RHIC Year-7 data.

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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