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

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PHENIX has measured the e+e- pair continuum in sqrt(sₙN)=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 cᵇar-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 (mₑe<0.3 GeV/c²) and high pₜ (1<pₜ<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 pₜ, with inverse slope T=221+/-19(stat)+/-19(syst) MeV. Hydrodynamical models with initial temperatures ranging from Tᵢnit =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 pₜ<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 pₜ enhancement.