Figure 3
Fig. 3. Measurement by PHENIX of the ratio of photons detected to those expected from meson decays in the most central gold-gold collisions at RHIC. If all observed photons came from decays of hadrons, then the ratio would be 1. The direct photon yield agrees with perturbative QCD calculations, shown by the red curve; the purple curves show the theoretical uncertainties. The blue curve is the expectation assuming that there is no suppression of high-pT mesons.