Measurement of the cross section for diffractive deep-inelastic scattering with a leading proton at HERA

The cross section for the diffractive deep-inelastic scattering process ep - GT eXp is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data sample covers the range x(P) LT 0.1 in fractional proton longitudinal momentum loss, 0.1 LT vertical bar t vertical bar LT 0.7 GeV2 in squared four-momentum transfer at the proton vertex and 4 LT Q(2) LT 700 GeV2 in photon virtuality. The cross section is measured four-fold differentially in t, x(P), Q2 and beta = x/x(P), where x is the Bjorken scaling variable. The t and x(P) dependences are interpreted in terms of an effective pomeron trajectory and a sub-leading exchange. The data are compared with perturbative QCD predictions at next-to-leading order based on diffractive parton distribution functions previously extracted from complementary measurements of inclusive diffractive deep-inelastic scattering. The ratio of the diffractive to the inclusive ep cross section is studied as a function of Q(2), beta and x(P)