Speaker
Description
Recent results on diffraction from the H1 and ZEUS experiments at HERA are presented. Measurement of open charm production in diffractive DIS has been performed by the H1 experiment using the event topology, given by ep→eXY, where the system X, containing at least one D*(2010) meson, is separated from a leading low-mass proton dissociative system Y by a large rapidity gap. The kinematics of D∗ candidates are fully reconstructed in the D∗→Kππ decay channel. The measured cross sections are compared at the level of stable hadrons with NLO QCD predictions obtained in the massive scheme, where the charm quark is produced via the boson-gluon fusion. The calculations rely on the collinear factorization theorem and are based on diffractive parton densities previously obtained by H1 from fits of the inclusive diffractive cross sections. The measured data are further used to estimate the ratio of diffractive to inclusive open charm production in deep inelastic scattering. The photoproduction of isolated photons is measured using diffractive events recorded by the ZEUS experiment. Cross sections are evaluated in the photon transverse-energy and pseudorapidity ranges 5 < EγT < 15 GeV and −0.7 < ηγ < 0.9, inclusively and with a jet with transverse-energy and pseudorapidity in the ranges 4 < EjetT < 35 GeV and −1.5 < ηjet < 1.8. A number of kinematic variables are studied and compared to predictions from the RAPGAP Monte Carlo model. In considering the fraction of the energy of the colourless (Pomeron) exchange that is transferred to the photon-jet final state, zP, it is found that the data lie above the RAPGAP predictions for zP > 0.9, giving evidence for direct-Pomeron interactions. The shapes of the kinematic distributions of events below and above this value of zP are separately well described by RAPGAP. This and other features provide evidence for a universal set of parton distribution functions in the Pomeron. The exclusive deep inelastic electroproduction and photoproduction of ψ(2S) and J/ψ(1S) has been studied by ZEUS. The cross-section ratio σ(ψ(2S))/σ(J/ψ(1S)) has been measured by ZUES as a function of Q2, W and t. The results are compared to many predictions of QCD-inspired models, providing tests of the models in a region of soft to hard diffraction.
| Topic: | Topic: High Energy Particle Physics |
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