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在sqrt（s_NN）=200 GeV的Au+Au碰撞中直接光子的增强产生及其对初始温度的影响

Enhanced production of direct photons in Au+Au collisions at sqrt(s_NN)=200 GeV and implications for the initial temperature

The PHENIX Collaboration, A. Adare

备注：
421 authors from 58 inst., 6 p., 4 figs. Sub. to PRL. v2 has minor changes to title, astract, and text. Data points for mass spectra are moved insignificantly. Expanded version submitted to PRC and arXiv:0912.0244. Plain text data tables are at http://www.phenix.bnl.gov/papers.html
发表信息：
Phys.Rev.Lett.104:132301,2010
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摘要：

在sqrt（s_NN）=200 GeV的p+p和Au+Au碰撞中，测量到了m_{e+e-} < 300 MeV/c^2和1 < p_T <5 GeV/c的低质量e+e对的产生。强子源以上的增强产额观察。把多余的光子视为内转换，导出了直接光子的不变产额。在中心Au+Au碰撞中，直接光子产额超过p+p在横向动量上是指数的，具有反斜率T = 221 +/- 19（stat）+/- 19（syst）MeV。初始温度范围为300- 600 MeV，碰撞后时间为~ 0.6 - 0.15 fm/c的流体动力学模型与数据定性一致。格点量子色动力学预言了在~ 170 MeV处的一个向夸克-胶子等离子体的相变。

英文摘要：

The production of low mass e+e- pairs for m_{e+e-} < 300 MeV/c^2 and 1 < p_T <5 GeV/c is measured in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. Enhanced yield above hadronic sources is observed. Treating the excess as internal conversions, the invariant yield of direct photons is deduced. In central Au+Au collisions, the excess of direct photon yield over p+p is exponential in transverse momentum, with inverse slope T = 221 +/- 19 (stat) +/- 19 (syst) MeV. Hydrodynamical models with initial temperatures ranging from 300--600 MeV at times of ~ 0.6 - 0.15 fm/c after the collision are in qualitative agreement with the data. Lattice QCD predicts a phase transition to quark gluon plasma at ~ 170 MeV.

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