Diffractive deep-inelastic scattering with a leading proton at HERA

The cross section for the diffractive deep-inelastic scattering process ep →e X p is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data analysed cover the range xP<0.1 in fractional proton longitudinal momentum loss, 0.08<t<0.5 GeV-2 in squared four-momentum transfer at the proton vertex, 2<Q2<50 GeV2 in photon virtuality and 0.004<β=x /xP<1, where x is the Bjorken scaling variable. For xP<or ∼ 10-2, the differential cross section has a dependence of approximately dσ/ d t∝e6t, independently of xP, β and Q2 within uncertainties. The cross section is also measured triple differentially in xP, β and Q2. The xP dependence is interpreted in terms of an effective pomeron trajectory with intercept αP(0)=1.114 ±0.018 (stat.) ±0.012 (syst.) +0.040-0.020 (model) and a sub-leading exchange. The data are in good agreement with an H1 measurement for which the event selection is based on a large gap in the rapidity distribution of the final state hadrons, after accounting for proton dissociation contributions in the latter. Within uncertainties, the dependence of the cross section on x and Q2 can thus be factorised from the dependences on all studied variables which characterise the proton vertex, for both the pomeron and the sub-leading exchange. (Orig.)