Diffractive production of high pt photons at HERA

We study the diffractive production of high pt photons at HERA. We have implemented the process as a new hard sub-process in the HERWIG event generator in order to prepare the ground for a future measurement.Comment: 4 pages, 4 figures. Contribution to the 1999 UK Phenomenology Workshop on Collider Physics, Durham, U

Observing a Light CP-Violating Higgs Boson in Diffraction

Light CP-violating Higgs bosons with mass lower than 70 GeV might have escaped detection in direct searches at the LEP collider. They may remain undetected in conventional search channels at the Tevatron and LHC. In this Letter we show that exclusive diffractive reactions may be able to probe for the existence of these otherwise elusive Higgs particles. As a prototype example, we calculate diffractive production cross-sections of the lightest Higgs boson within the framework of the Minimal Supersymmetric Standard Model with explicit CP violation. Our analysis shows that the challenging regions of parameter space corresponding to a light CP-violating Higgs boson might be accessible at the LHC provided suitable proton tagging detectors are installed.Comment: 9 pages, LaTeX, 2 figures, version as to appear in Phys. Rev.

Diffractive vector boson production at the Tevatron

The diffractive production of vector bosons at the Tevatron is studied. We take a hard pomeron flux and use the H1 parton density functions extracted from their measurement of F_2^{D(3)}. To this we add a reggeon exchange contribution. We find that the ratio of diffractive to non-diffractive W boson production is in good agreement with the CDF data. We note that the poorly understood reggeon contribution might be as large as the pomeron contribution in the kinematic range of the data. We also note that our pomeron exchange contribution is much smaller than earlier predictions due to our use of a hard pomeron flux. All our results have been obtained using the lowest order matrix elements and we have compared to the results obtained using a modified version of Herwig which is capable of generating a wide variety of diffractive scattering processes. Gap survival is estimated using Pythia and is found to be around 60%. We make predictions which could be compared to future measurements of diffractive Drell-Yan production.Comment: 11 pages, 4 figure

Soft gluons in Higgs plus two jet production

We investigate the effects of an all order QCD resummation of soft gluon emissions for Higgs boson production in association with two hard jets. We consider both the gluon-gluon fusion and weak boson fusion processes and show how to resum a large part of the leading logarithms in the jet veto scale. Our resummation improves on previous analyses which also aim to include the effects of multiple soft gluon radiation. In addition we calculate the interference between weak boson fusion and gluon-gluon fusion and find that it is small.Comment: 15 pages and 5 figure

Interpretation of the Flavor Dependence of Nucleon Form Factors in a Generalized Parton Distribution Model

We give an interpretation of the $u$ and $d$ quarks contributions to the nucleon electromagnetic form factors for values of the four-momentum transfer in the multi-GeV region where flavor separated data have been recently made available. The data show, in particular, a suppression of $d$ quarks with respect to $u$ quarks at large momentum transfer. %and constant ratios of the flavor dependent Pauli to Dirac form factors ratios. This trend can be explained using a reggeized diquark model calculation of generalized parton distributions, thus providing a correlation between momentum and coordinate spaces, both of which are necessary in order to interpret the partonic substructure of the form factors. We extend our discussion to the second moments of generalized parton distributions which are believed to contribute to partonic angular momentum.Comment: 22 pages, 19 figures; results and figures added and changed, tables added, formulae added, major rewriting of tex

Vector Meson Photoproduction from the BFKL Equation II: Phenomenology

Diffractive vector meson photoproduction accompanied by proton dissociation is studied for large momentum transfer. The process is described by the non-forward BFKL equation which we use to compare to data collected at the HERA collider.Comment: 39 pages, 29 figure

Gaps between Jets in the High Energy Limit

We use perturbative QCD to calculate the parton level cross section for the production of two jets that are far apart in rapidity, subject to a limitation on the total transverse momentum Q0 in the interjet region. We specifically address the question of how to combine the approach which sums all leading logarithms in Q/Q0 (where Q is the jet transverse momentum) with the BFKL approach, in which leading logarithms of the scattering energy are summed. This paper constitutes progress towards the simultaneous summation of all important logarithms. Using an "all orders" matching, we are able to obtain results for the cross section which correctly reproduce the two approaches in the appropriate limits.Comment: 29 pages, 9 figures, minor corrections to text and improved figure

Jet vetoing at the LHC

We study the effect of a veto on additional jets in the rapidity region between a pair of high transverse momentum jets at the LHC. We aim to sum the most important logarithms in the ratio of the jet transverse momentum to the veto scale and to that end we attempt to assess the significance of the super-leading logarithms that appear at high orders in the perturbative expansion. We also compare our results to those of HERWIG++, in an attempt to ascertain the accuracy of the angular ordered parton shower. We find that there are large corrections that arise for large enough jet transverse momenta as a consequence of Coulomb gluon exchanges.Comment: 25 page

Testing the dynamics of high energy scattering using vector meson production

I review work on diffractive vector meson production in photon-proton collisions at high energy and large momentum transfer, accompanied by proton dissociation and a large rapidity gap. This process provides a test of the high energy scattering dynamics, but is also sensitive to the details of the treatment of the vector meson vertex. The emphasis is on the description of the process by a solution of the non-forward BFKL equation, i.e. the equation describing the evolution of scattering amplitudes in the high-energy limit of QCD. The formation of the vector meson and the non-perturbative modeling needed is also briefly discussed.Comment: 17 pages, 8 figures. Brief review to appear in Mod. Phys. Lett.