Inclusive direct photon invariant cross sections have been measured in both ppBAR and pp collisions at square-root s = 24.3 GeV at the CERN SPS, permitting the first measurement of the difference of the ppBAR and pp cross sections. The direct photon cross section in ppBAR collisions has been found to be systematically larger than that in pp collisions, which indicates a significant contribution of the qqBAR annihilation term as predicted by theoretical calculations.
