Inclusive measurement of diffractive deep-inelastic ep scattering

Abstract

A measurement is made of the cross section for the process ep → eXY in deep-inelastic scattering with the H1 detector at HERA. The cross section is presented in terms of a differential structure function F ₂ ^D(3) (x _P, β,Q ²) of the proton over the kinematic range 4.5 < Q ² < 75 GeV². The dependence of F ₂ ^D(3) on x _P is found to vary with β, demonstrating that a factorisation of F ₂ ^D(3) with a single diffractive flux independent of β and Q ² is not tenable. An interpretation in which a leading diffractive exchange and a subleading reggeon contribute to F ₂ ^D(3) reproduces well the x _P dependence of F ₂ ^D(3) with values for the pomeron and subleading reggeon intercepts of α_P (0) = 1.203±0.020(stat.)±0.013(sys.) ^+0.030_-0.035 (model) and α _R (0) = 0.50 ± 0.11(stat.) ± 0.11(sys.) ^+0.09_-0.10 (model), respectively. A fit is performed of the data using a QCD motivated model, in which parton distributions are assigned to the leading and subleading exchanges. In this model, the majority of the momentum of the pomeron must be carried by gluons in order for the data to be well described.