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 in ep 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 of x IP , the momentum fraction lost by the proton, of β, the momentum fraction of the struck quark with respect to x IP , and of Q 2 . The x IP dependence is consistent with the form (1/x IP ) a where a = 1.30 ± 0.08 (stat) + 0.08 − 0.14 (sys) in all bins of β and Q 2 . In the measured Q 2 range, the diffractive structure function approximately scales with Q 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.

$ J/\psi +{\mathrm{jet}} $ diffractive production in the direct photon process at HERA

“…The diffractive parton densities (the primary non-perturbative quantities in hard diffraction) obey exactly the same DGLAP evolution equations as ordinary parton densities, and have been extracted from HERA data on DDIS and on diffractive photonproduction of jets [16]. This factorization theorem also establishes the universality of the diffractive parton distrubutions for those processes to which the theorem applies, hence justifies, from fundamental principles, the analysis of ZEUS and H1 Collaboration [6,5] on hard diffraction, provided the term " Pomeron " used in these analyses is as a label for a particular kind of parametrization for diffractive parton densities, and an indication of the vacuum quantum numbers to be exchanged. In the light of hard diffractive factorization proven by Collins [13], the Ingelman-Schlein model for hard diffraction assumed further the factorization of diffractive parton densities into a universal Pomeron flux and a Pomeron parton densities, but such further factorization is unjustifiable.…”

“…Events containing rapidity gap and jets were first observed by UA8 Collaboration at CERN [3], opening the field of hard diffraction. The hard diffraction is also observed and studied by various experiments [4][5][6][7][8]. Although it is still difficult to understand the soft diffractive scattering in the framework of QCD, much progresses in understanding the nature of hard diffraction are made in the light of great theoritical and experimental efforts [9].…”

Inclusive measurement of diffractive deep-inelastic scattering at HERA

“…3 Fig. 5 The β dependence of the reduced diffractive cross section, multiplied by x P , at a fixed value of x P = 0.003, resulting from the combination of all data samples. Details are explained in the caption of Fig.…”

“…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]. In contrast to the standard deep inelastic scattering (DIS) process ep → eX (Fig.…”

AssociatedJ/ψ+γdiffractive production: The nature of the Pomeron and a test of hard diffractive factorization

“…The DDIS and dijet photoproduction experiments at HERA have shed light on the partonic structure of the Pomeron. Combining the measurements of the diffractive structure function in DDIS and the photoproduction jet cross sections, the ZEUS Collaboration gives the first experimental evidence for the gluon content of the Pomeron and determines that the hard gluon fraction of the pomeron f g is in the range 0.3 < f g < 0.8, independent of the validity of the momentum sum rule for the Pomeron and the normalization of the flux of Pomeron from the proton [6] . The H1 Collaboration also determines the fraction of the momentum of the Pomeron carried by the hard gluon, which is f g ∼ 0.9 at Q 2 = 4.5 GeV 2 and f g ∼ 0.8 at Q 2 = 75 GeV 2 [7] .…”