Isolated prompt photon production at DESY HERA

Abstract

We study in detail the effects of isolation requirements on expectations for prompt photon production rates at DESY HERA in the first fully consistent study performed completely in next-to-leading order of QCD. In particular we examine whether the isolated cross section will give useful information on the gluon content of the photon and proton. We find that the cross section turns out to be hardly sensitive to the gluon distribution of the photon in the kinematically accessible range, but that it depends significantly on the quark content of the photon in some regions of the kinematical variables. We show furthermore that the present knowledge of the proton's parton distributions, in particular, its gluon distribution, has to be improved in order to determine the photonic structure functions in this process.