Direct photons from Au+Au collisions at RHIC: QGP vs. hot hadronic gas
  We have analysed the preliminary PHENIX data on the transverse momentum distribution of direct photons in 0-20% centrality Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. In ideal hydrodynamics, data are explained if Au+Au collision produces Quark-Gluon-Plasma at the temperature $T_i$=400 MeV, at an initial time $\tau_i$=0.6 fm. PHENIX data are not explained in the alternate scenario when Au+Au collisions produces hot hadronic gas with initial temperature within physically acceptable limit. 
A. K. Chaudhuri