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arXiv 0912.0244nucl-ex
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在sqrt（s_NN）=200 GeV的p+p和Au+Au碰撞中e+e对连续谱的详细测量和直接光子产生的意义

Detailed measurement of the e+e- pair continuum in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV and implications for direct photon production

PHENIX Collaboration, A. Adare

备注：
422 authors from 59 institutions, 56 pages, 50 figures, and 13 tables. Submitted to Physical Review C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html
发表信息：
Phys.Rev.C81:034911,2010
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摘要：

PHENIX在sqrt（s_NN）=200 GeV的Au+Au和p+p碰撞中测量了e^+e^-对连续谱，其质量和横动量范围很广。e^+e^-产额与基于PHENIX测量的强子源的预期值进行了比较。在质量介于φ和J/psi介子之间的中间质量区域，产额与相关c^bar-c产生的预期一致，尽管不排除其他机制。在低质量区（低于φ），包含p+p的质谱可以很好地用轻介子衰变的贡献来描述。相比之下，Au+Au最小偏压质谱在这个区域显示出4.7+/-0.4（stat）+/-1.5（syst）+/-0.9（model）的增强因子。在低质量（m_ee<0.3 GeV/c^2）和高p_T（1<p_T<5 GeV/c）下，观察到e^+e^-对产额的增强，这与虚直接光子的产生一致。这个过量被用来推断实际直接光子的产额。在Au+Au中心碰撞中，直接光子产额超过p+p的部分与pT成指数关系，其斜率T=221+/-19（stat）+/-19（syst）MeV。初始温度T_init ~=300- 600 MeV，碰撞后时间为0.6- 0.15 fm/c的流体动力学模型与Au+Au中的直接光子数据定性一致。在低p_T<1GeV/c时，低质量区表现出进一步显著的增强，增强随中心度的增加而增加，并具有T ~=100 MeV的反斜率。理论模型预测低质量，低p_T增强。

英文摘要：

PHENIX has measured the e^+e^- pair continuum in sqrt(s_NN)=200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e^+e^- yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated c^bar-c production, though other mechanisms are not ruled out. In the low mass region (below the phi) the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7+/-0.4(stat)+/-1.5(syst)+/-0.9(model) At low mass (m_ee<0.3 GeV/c^2) and high p_T (1<p_T<5 GeV/c) an enhanced e^+e^- pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in p_T, with inverse slope T=221+/-19(stat)+/-19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T_init ~=300--600 MeV at times of 0.6--0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low p_T<1 GeV/c the low mass region shows a further significant enhancement that increases with centrality and has an inverse slope of T ~=100 MeV. Theoretical models under predict the low mass, low p_T enhancement.

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