Photoproduction

Some selected topics in photoproduction are reviewed. In particular, the focus is on quasi-real photon-proton scattering as measured at HERA. Single & dijet rates and jet profiles are discussed, as are open charm production and inelastic charmonium production. The many intriguing theoretical issues which can be addressed through study of these processes are highlighted.Comment: 17 pages. Talk given at DIS97, Chicago, 14-18 April 199

Low x saturation at HERA ?

We compare the predictions of two distinct dipole models for inclusive and exclusive diffractive processes. While only one of these dipole models contains perturbative saturation dynamics, we show that the predictions of both models are fully consistent with the available HERA data, indicating no compelling evidence for saturation at present HERA energies.Comment: 8 pages, 4 figures, presented at the 26th Montreal-Rochester-Syracuse-Toronto (MRST) conference held at Concordia University, Montreal, Canada, 12th-14th May 2004. To appear in the proceeding

Soft gluons and superleading logarithms in QCD

After a brief introduction to the physics of soft gluons in QCD we present a surprising prediction. Dijet production in hadron-hadron collisions provides the paradigm, i.e. h_1 +h_2 \to jj+X. In particular, we look at the case where there is a restriction placed on the emission of any further jets in the region in between the primary (highest p_T) dijets. Logarithms in the ratio of the jet scale to the veto scale can be summed to all orders in the strong coupling. Surprisingly, factorization of collinear emissions fails at scales above the veto scale and triggers the appearance of double logarithms in the hard sub-process. The effect appears first at fourth order relative to the leading order prediction and is subleading in the number of colours.Comment: Talk presented at the workshop "New Trends in HERA Physics", Ringberg Castle, Tegernsee, 5-10 October 200

Photon '97: Theory Summary

Some recent developments in the physics of photon induced reactions are discussed. My presentation is biased towards HERA physics with the other summary talk (of David Miller) being biased towards the gamma-gamma topics. Within the context of the data which were presented, I concentrate upon the the following topics: diffraction; jets; prompt photons; open charm and charmonium.Comment: 15 pages. To appear in the proceedings of the "Photon '97" conference, Egmond aan Zee, The Netherlands, May 199

Diffractive Higgs production

Instrumenting the LHC to measure the outgoing protons in the process pp -> p+X+p opens up new possibilities for physics studies in the Standard Model and beyond. In this talk I first present an overview of the underlying QCD calculation and its uncertainties. I then move on to present a variety of new physics scenarios which one would want to explore via this unique channel. There is a short discussion of the recent CDF data which may provide evidence for the existence of central exclusive jet production at the Tevatron.Comment: 8 pages. Talk presented at "Diffraction 2006

Diffractive Higgs production: theory

We review the calculation for Higgs production via the exclusive reaction pp -> p+H+p. In the first part we review in some detail the calculation of the Durham group and emphasise the main areas of uncertainty. Afterwards, we comment upon other calculations.Comment: 19 pages. 11 figures. Contribution to the workshop "HERA and the LHC

Probing the theoretical description of central exclusive production

We investigate the theoretical description of the central exclusive production process, $h_1 + h_2 \to h_1+X+h_2$. Taking Higgs production as an example, we compute the subset of next-to-leading order corrections sensitive to the Sudakov factor appearing in the process. Our results agree with those originally presented by Khoze, Martin and Ryskin except that the scale appearing in the Sudakov factor, $\mu=0.62 \sqrt{\hat{s}}$, should be replaced with $\mu=\sqrt{\hat{s}}$, where $\sqrt{\hat{s}}$ is the invariant mass of the centrally produced system. We show that the replacement leads to approximately a factor 2 suppression in the cross-section for central system masses in the range 100--500GeV.Comment: 5 pages, 2 figures; to appear in the proceedings of DIS201

Diffractive vector meson production at HERA using holographic AdS/QCD wavefunctions

We demonstrate another success of the AdS/QCD correspondence by showing that an AdS/QCD holographic light-front wavefunction for the $\rho$ meson generates predictions for the cross-sections of diffractive $\rho$ production that are in agreement with data collected at the HERA electron-proton collider.Comment: Proceedings Contribution to the XXI International Workshop on Deep-Inelastic Scattering and Related Subjects, 22-26 April, 2013, Marseilles, France. 5 pages, 1 figur

Phenomenology of Distribution Amplitudes for the rho meson

We report on a successful extraction of the twist-2 and twist-3 Distribution Amplitudes (DAs) of the rho meson using the HERA data on diffractive rho photoproduction. We extract these DAs using several Colour Glass Condensate (CGC) inspired and a Regge inspired dipole models. All our extracted DAs are consistent with Sum Rules and lattice predictions.Comment: 4 pages, 2 figures, presented at the 19th International Workshop on Deep Inelastic Scattering and Related Subjects (DIS 2011), Jefferson Lab, Newport News, April 2011. To appear in the Proceeding