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Register a new userScale Dependent Pomeron Intercept in Electromagnetic Diffractive Processes
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We test the hypothesis that diffractive scattering in the perturbative and non-perturbative domain is determined by the exchange of a single pomeron with a scale dependent trajectory. Present data on diffractive vector meson production are well compatible with this model and recent results for $J/psi$ photoproduction at LHC strongly support it. The model is inspired by concepts of gauge/string duality applied to the pomeron.
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The energy dependence of the cross sections for electromagnetic diffractive processes can be well described by a single power, $W^delta$. For $J/psi$ photoproduction this holds in the range from 20 GeV to 2 TeV. This feature is most easily explained by a single pole in the angular momentum plane which depends on the scale of the process, at least in a certain range of values of the momentum transfer. It is shown that this assumption allows a unified description of all electromagnetic elastic diffractive processes. We also discuss an alternative model with an energy dependent dipole cross section, which is compatible with the data up to 2 TeV and which shows an energy behaviour typical for a cut in the angular momentum plane.
In the framework of semihard (k$_T$ factorization) QCD approach, we consider the differential cross sections of $D^{*pm}$ meson production at HERA. The consideration is based on BFKL and CCFM gluon distributions. We find that in the case of BFKL LO gluon distribution the theoretical results are sensitive to the Pomeron intercept parameter $Delta$. We present a comparison of the theoretical results with available ZEUS experimental data.
We have recently studied the QCD pomeron loop evolution equations in zero transverse dimensions [Shoshi:2005pf]. Using the techniques developed in [Shoshi:2005pf] together with the AGK cutting rules, we present a calculation of single, double and central diffractive cross sections (for large diffractive masses and large rapidity gaps) in zero transverse dimensions in which all dominant pomeron loop graphs are consistently summed. We find that the diffractive cross sections unitarise at asymptotic energies and that they are suppressed by powers of alpha_s. Our calculation is expected to expose some of the diffractive physics in hadron-hadron collisions at high energy.
Central diffractive production of heavy states (massive dijets, Higgs boson) is studied in the exclusive mode using a new Hybrid Pomeron Model (HPM). Built from Hybrid Pomerons defined by the combination of one hard and one soft color exchanges, the model describes well the centrally produced diffractive dijet data at the Tevatron. Predictions for the Higgs boson and dijet exclusive production at the LHC are presented.
We review the evolution of the studies of diffractive processes in the strong interaction over the last 60 years. First, we briefly outline the early developments of the theory based on analyticity and unitarity of the S-matrix, including the derivation and exploration of the Regge trajectories and related moving cuts. Special attention is paid to the concept of the Pomeron trajectory introduced for description of total, elastic and diffractive cross sections at high energies and to the emergence of the dynamics of multi-Pomeron interactions.The role of large longitudinal distances and color coherent phenomena for the understanding of inelastic diffraction in hadron-hadron scattering and deep inelastic scattering is emphasized. The connection of these phenomena to the cancellation of the contribution of the Glauber approximation in hadron-nucleus collisions and to the understanding of the Gribov-Glauber approximation is explained. The presence of different scales in perturbative QCD due to masses of heavy quarks has led to the emergence of numerous new phenomena including non-universality of the slopes of Regge trajectories made of light and heavy quarks and non-universal energy dependence of elastic cross sections. The application of the perturbative QCD techniques allowed us to calculate from the first principles the interaction of small transverse size color singlets with hadrons leading to the development of the quantitative theory of hard exclusive reactions and to the successful prediction of many regularities in hard large mass diffraction. It also led to the prediction of the phenomenon of complete transparency of nuclear matter in QCD in special processes. The conflict of perturbative QCD with probability conservation for high energy processes of virtual photon-nucleon scattering is explained. Some properties of the new QCD regime are outlined.
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