Abstract
PHENIX has measured the pair continuum in GeV and collisions over a wide range of mass and transverse momenta. The yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the and the meson, the yield is consistent with expectations from correlated production, although other mechanisms are not ruled out. In the low-mass region, below the , the inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of . At low mass ( GeV/) and high ( GeV/) an enhanced 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 collisions, the excess of the direct photon yield over the is exponential in , with inverse slope MeV. Hydrodynamical models with initial temperatures ranging from MeV at times of fm/ after the collision are in qualitative agreement with the direct photon data in . For low GeV/ the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of MeV. Theoretical models underpredict the low-mass, low- enhancement.
43 More- Received 1 December 2009
DOI:https://doi.org/10.1103/PhysRevC.81.034911
©2010 American Physical Society
Viewpoint
Taking the temperature of extreme matter
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