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

Abstract

The first measurement of diffractive scattering of quasi-real photons with large momentum transfer $\gamma p\to \gamma Y$, where Y is the proton dissociative system, is made using the H1 detector at HERA. The measurement is performed for initial photon virtualities $Q^2<0.01{\text{GeV}}^2$. 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 $175<W<247\text{GeV}$ and $4<|t|<36{\text{GeV}}^2$. 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.