Diffractive deep-inelastic scattering with a leading proton at HERA

Abstract

The cross section for the diffractive deep-inelastic scattering process ep → eXp is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data analysed cover the range x IP < 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 < Q 2 < 50 GeV 2 in photon virtuality and 0.004 < β = x/x IP < 1, where x is the Bjorken scaling variable. For x IP < ∼ 10 −2 , the differential cross section has a dependence of approximately dσ/dt ∝ e 6t , independently of x IP , β and Q 2 within uncertainties. The cross section is also measured triple differentially in x IP , β and Q 2 . The x IP dependence is interpreted in terms of an effective pomeron trajectory with intercept α IP (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 Q 2 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.

Nuclear effects in the Glauber-Gribov model

“…The gluon distribution is almost a factor of 10 bigger than the quark distribution at the same Q 2 for a broad region of β [19,20]. Therefore, in the relevant kinematical range for hadron-nucleus and nucleus-nucleus collisions at RHIC and LHC, the gluon density dominates.…”

“…In particular, the diffractive gluon density was affected by large uncertainty since it is not measured directly in experiment. Results of new high-precision measurements of the diffractive parton distribution functions (DPDFs) presented by the H1 Collaboration [19,20] give important constraints to our model of shadowing. Due to the indirect extraction of the diffractive gluon density, β g D (β , Q 2 ), from experimental data, two fits were presented, FIT A and FIT B, reflecting the systematic uncertainty of the procedure.…”

“…For completeness, we also compare the new results with the old H1 parameterization [22] presented in 2002. For details on extracted DPDFs and corresponding Pomeron parameters, α I P (0) and α ′ I P , we refer the reader to the experimental papers [19,20].…”

Diffractive dijet photoproduction in ultraperipheral collisions at the LHC in next-to-leading order QCD

“…The QCD collinear factorization theorem for hard inclusive diffraction [41] allows one to introduce universal diffractive PDFs f D (4) b/p (x P , z P , t, µ 2 ) and to determine them by fitting to the measured diffractive structure functions [42][43][44]. The analysis also shows that for small values of x P , f D (4) b/p (x P , z P , t, µ 2 ) can be written as the product of two factors [45]:…”

“…Second, while the general trends of the dependence on various variables are similar in the pp UPC and ep cases, the former allows to probe values of W exceeding those achieved in the ep case by at least a factor of ten and to produce dijets with the significantly larger M 12 and M X . In addition, the contribution of the low-z jets P region is much more important in the pp UPC case than in the ep case, which signals the enhanced sensitivity to the proton diffractive PDFs f D (4) b/p (x P , z P , t, µ 2 ) at small z P , where they are poorly constrained [42][43][44].…”