Inclusive Photon Production in Hadronic Collisions

High statistics fixed target and ISR inclusive photon production data are compared to next-to-leading order (NLO) QCD calculations. The dependence of the theoretical predictions on the structure functions, and on the theoretical scales is investigated. It is shown that the data cannot be simultaneously fitted with a single set of structure functions and scales. However, it is argued that as long as one restricts the data/theory comparison to the xT range where the theory is reliable, i.e. stable with respect to the scale variation, there is no need to introduce an additional primordial kT dependence except for Be data. Finally a precise determination of the strong coupling constant, alpha_s, is performed from the direct photon production cross sections obtained in high statistics pbar p and pp collisions at the CERN SPS (UA6) by a NLO QCD analysis.