Measurements of soft and intermediate $p_T$ photons from hot and dense matter at RHIC-PHENIX

Abstract

The measurements of direct photons in $1.0<p_T<5.0$GeV/$c$ for p+p and Au+Au collisions have been made through the virtual photon method at PHENIX. The fraction of the virtual direct photon component to the inclusive $e^{+}{e}^{-}$ yield is determined by a shape analysis using the $e^{+}{e}^{-}$ mass spectra in $m_{ee}<300$MeV/$c^2$ for $1.0<p_T<5.0$GeV/$c$. The real direct photon spectra in p+p and Au+Au collisions are obtained from the virtual direct photon fractions, and a significant excess over a binary-scaled p+p result is seen in Au+Au collisions. Hydrodynamical models which reproduce the Au+Au result indicate the initial temperature of the matter is higher than the critical temperature of QGP. The d+Au data taken in 2008 are promising to evaluate the contribution of the nuclear effects because of its large statistics.

4 pages, 3 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee

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