Measurement of diffractive scattering of photons with large momentum transfer at HERA

The first measurement of diffractive scattering of quasi-real photons with large momentum transfer γ p → γ Y , where Y is the proton dissociative system, is made using the H1 detector at HERA. The measurement is performed for initial photon virtualities Q 2 < 0.01 GeV 2 . Single differential cross sections are measured as a function of W , the incident photon–proton centre of mass energy, and t , the square of the four-momentum transferred at the proton vertex, in the range 175 < W < 247 GeV and 4 < | t | < 36 GeV 2 . The W dependence is well described by a model based on perturbative QCD using a leading logarithmic approximation of the BFKL evolution. The measured | t | dependence is harder than that predicted by the model and those observed in exclusive vector meson production.