Abstract
The diffractive process ep \rightarrow eXY, where Y denotes a proton or its low mass excitation with MY < 1.6 GeV, is studied with the H1 experiment at HERA. The analysis is restricted to the phase space region of the photon virtuality 3 \leq Q2 \leq 1600 GeV2, the square of the four-momentum transfer at the proton vertex |t| < 1.0 GeV2 and the longitudinal momentum fraction of the incident proton carried by the colourless exchange xIP < 0.05. Triple differential cross sections are measured as a function of xIP, Q2 and beta = x/xIP where x is the Bjorken scaling variable. These measurements are made after selecting diffractive events by demanding a large empty rapidity interval separating the final state hadronic systems X and Y . High statistics measurements covering the data taking periods 1999-2000 and 2004-2007 are combined with previously published results in order to provide a single set of diffractive cross sections from the H1 experiment using the large rapidity gap selection method. The combined data represent a factor between three and thirty increase in statistics with respect to the previously published results. The measurements are compared with predictions from NLO QCD calculations based on diffractive parton densities and from a dipole model. The proton vertex factorisation hypothesis is tested.
Highlights
At HERA a substantial fraction of up to 10 % of ep interactions proceed via the diffractive scattering process initiated by a highly virtual photon [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
The dependence of the diffractive parton distribution functions (DPDFs) on the kinematic variables related to the proton vertex can be parametrised conveniently using Regge formalism, which amounts to a description of diffraction in terms of the exchange of a factorisable Pomeron (P) [21, 22] with universal parton densities
The cross section measurements are corrected to fixed values of Q2, β and xP for each bin using predictions from the H1 2006 DPDF Fit B
Summary
At HERA a substantial fraction of up to 10 % of ep interactions proceed via the diffractive scattering process initiated by a highly virtual photon [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. A general theoretical framework is provided by the QCD collinear factorisation theorem for semi-inclusive DIS cross sections such as that for ep → eXp [17, 18]. This implies that the concept of diffractive parton distribution functions (DPDFs) may be introduced, representing conditional proton parton probability distributions under the constraint of a leading final state proton with a particular four-momentum. At larger xP (xP > 0.1), a separately factorisable sub-leading Reggeon exchange (R), with a different xP dependence and partonic composition, is usually included to maintain a good description
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