Detailed measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mi>e</mml:mi><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>pair continuum in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>p</mml:mi><mml:mo>+</mml:mo><mml:mi>p</mml:mi></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Au</mml:mi><mml:mo>+</mml:mo><mml:mi mathvariant="normal">Au</mml:mi></mml:mrow></mml:math>collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msqrt><mml:mrow><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi mathvariant="italic">NN</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:msqrt><mml:mo>=</mml:mo><mml:mn>200</mml:mn></mml:mrow></mml:math>GeV and implications for direct photon production

PHENIX has measured the ${e}^{+}{e}^{\ensuremath{-}}$ pair continuum in $\sqrt{{s}_{\mathit{NN}}}=200$ GeV $\mathrm{Au}+\mathrm{Au}$ and $p+p$ collisions over a wide range of mass and transverse momenta. The ${e}^{+}{e}^{\ensuremath{-}}$ yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the $\ensuremath{\phi}$ and the $J/\ensuremath{\psi}$ meson, the yield is consistent with expectations from correlated $c\mathrm{c\ifmmode \bar{}\else \={}\fi{}}$ production, although other mechanisms are not ruled out. In the low-mass region, below the $\ensuremath{\phi}$, the $p+p$ inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the $\mathrm{Au}+\mathrm{Au}$ minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of $4.7\ifmmode\pm\else\textpm\fi{}{0.4}^{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{1.5}^{\mathrm{syst}}\ifmmode\pm\else\textpm\fi{}{0.9}^{\mathrm{model}}$. At low mass (${m}_{\mathit{ee}}&lt;0.3$ GeV/${c}^{2}$) and high ${p}_{T}$ ($1&lt;{p}_{T}&lt;5$ GeV/$c$) an enhanced ${e}^{+}{e}^{\ensuremath{-}}$ 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 $\mathrm{Au}+\mathrm{Au}$ collisions, the excess of the direct photon yield over the $p+p$ is exponential in ${p}_{T}$, with inverse slope $T=221\ifmmode\pm\else\textpm\fi{}{19}^{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{19}^{\mathrm{syst}}$ MeV. Hydrodynamical models with initial temperatures ranging from ${T}_{\mathrm{init}}\ensuremath{\simeq}300--600$ MeV at times of $0.6--0.15$ fm/$c$ after the collision are in qualitative agreement with the direct photon data in $\mathrm{Au}+\mathrm{Au}$. For low ${p}_{T}&lt;1$ GeV/$c$ the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of $T\ensuremath{\simeq}100$ MeV. Theoretical models underpredict the low-mass, low-${p}_{T}$ enhancement.