Diffractive Photoproduction of High pT Photons at HERA

The process γp → γY , in which the outgoing photon has transverse momentum pγT > 2 GeV and there is a large rapidity gap between the proton dissociative system Y and the outgoing photon, is studied, using the H1 detector at HERA, for the first time. The measurement is based on 47.6 pb−1 of data collected in the 1999– 2000 running period. Cross sections are measured differentially in the squared four momentum transfer at the proton vertex, t −(pT ), and xIP = (E + pz)γ/2Ep, where Ep is the incoming proton energy. All cross sections are consistent with a perturbative QCD model calculated using the leading logarithmic approximation of BFKL. A fit of the form A(1/W )(1/xIP ) n performed on the xIP cross section yields a pomeron intercept of α(0) = 1.50± 0.12(stat.) ± 0.01(sys.) and a fit of the form A |t|−n performed on the t cross section yields n = 2.14± 0.41(stat.)± 0.22(sys.).