Measurement of the diffractive structure function in deep inelastic scattering at HERA

Abstract

This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced inep interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function ofx _ℙ, the momentum fraction lost by the proton, of β, the momentum fraction of the struck quark with respect tox _ℙ, and ofQ ² in the range 6.3·10⁻⁴<x _ℙ <10⁻², 0.1<β<0.8 and 8<Q ²<100 GeV². The dependence is consistent with the formx _ℙ wherea=1.30±0.08(stat) ^+0.08_−0.14 (sys) in all bins of β andQ ². In the measuredQ ² range, the diffractive structure function approximately scales withQ ² at fixed β. In an Ingelman-Schlein type model, where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule.