Diffractive photoproduction of jets with a direct pomeron coupling at HERA

We investigate in detail the effect of a direct pomeron coupling to quarks on the production of jets inep scattering with almost real photons. Jet production via a direct pomeron coupling is compared with the resolved-pomeron mechanism. We consider both direct and resolved photoproduction. Rapidity and transverse momentum distributions are calculated and compared with preliminary H1 and ZEUS data.     

Intermediate mass distribution of the dual resonance pomeron

We determine the intermediate mass distribution of the dual resonance pomeron at the one-loop level and we show that the mass distribution obtained is remarkably similar to a suitably defined mass distribution in the dual multiperipheral model. Thus it is suggestive to identify the intermediate states of the dual resonance pomeron with multipheripheral processes.     

Diffractive production and hadron structure

Analysis of diffractive production on nuclei implied cross sections of the diffractively produced system on nucleons which are smaller than the corresponding projectile nucleon cross sections. We provide a natural explanation for this feature in the Good-Walker coherent production formalism. A specific realization of the Good-Walker formalism stated in terms of quarks and connecting electric flux tubes and some ensuing consequences are also discussed briefly.     

Particle production in the double dual pomeron region

By an indirect method we calculate the missing mass discontiniuty of the dual two-loop graph in the double-pomeron region. We confirm the central region scaling and determine the P_⊥ dependence.     

Cluster production and the pomeron in meson-baryon and baryon-baryon collisions

The bare pomeron in models based on duality diagrams is found to contribute very differently at low energies to pp and Kp total cross-sections. A simple quantitative comparison of these cross-sections is found to be consistent with phenomenological cluster production models.     

Triple pomeron vertex and complex pomeron trajectories

Complex Pomeron trajectories can give rise to (log s)²-shrinkage of the diffraction peak. With factorization, one obtains consistency with the energy momentum sum rule in the triple-Regge limit provided the total cross section approaches a constant or increases less fast than $\text{(}\text{log}\text{s)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$.     

Diffractive neutrino production of vector mesons

Using the diffractive vector dominance, we predict an event rate for charged vector mesons which is within the experimental bounds measured at Fermilab. Due to the very limited statistics no firm conclusion can be drawn on the structure of the neutral current. Similar estimations have been done for the Gargamelle experiment.     

Dijet production by double pomeron exchange at the fermilab tevatron

We report the first observation of dijet events with a double Pomeron exchange topology produced in &pmacr;p collisions at sqrt[s] = 1800 GeV. The events are characterized by a leading antiproton, two jets in the central pseudorapidity region, and a large rapidity gap on the outgoing proton side. We present results on jet kinematics and production rates, compare them with corresponding results from single diffractive and inclusive dijet production, and test factorization.     

Diffractive production of dijets at HERA

We investigate the production of a quark-antiquark pair in diffractive photon-proton scattering, approximating soft pomeron exchange by the exchange of two nonperturbative gluons. In deep inelastic scattering at HERA, events with two jets and the scattered proton in the final state are predicted to be observable, with an important contribution from charm production. For photoproduction of light quark jets with high transverse momentum we find that both exchanged gluons must have a large invariant mass, so that the cross section is very small, whereas for charm quarks it is quite appreciable. From our calculation we also extract the quark structure function of the pomeron for the scaling variablez no too close to 0 or 1, finding a strong flavour dependence and a behaviour somewhat harder thanz(1?z) for light quarks.     

Particle production at high energies in the Cardy pomeron model

Particle production at very high energies inhh, hA andAB collisions is studied in the framework of the pomeron model with a strong self-interaction proposed by Cardy. It is shown that the interaction between pomerons substancially damps the production rate one nuclei, the multiplicities forhA collisions becomingA-independent.     

Diffractive Higgs production: myths and reality

A critical comparison is made between recent predictions of the cross sections for diffractive Higgs production at the Tevatron and the LHC. We show that the huge spread of the predictions arises either because different diffractive processes are studied or because important effects are overlooked. Exclusive production offers a reliable, viable Higgs signal at the LHC provided that proton taggers are installed. Received: 13 August 2002 / Revised version: 24 September 2002 / Published online: 18 October 2002     

Diffractive and non-diffractive pion production on deuterons

We present an ensemble of formulae for the calculation of the Glauber correction to incoherent production on deuterons. The formulae are written in terms of phases, slopes and integrated cross sections and both the diffractive and non-diffractive case are considered. It is shown in the case K⁺ → K⁰π⁺, that only if the analysis is done in such a way that the final set of states is complete, is there agreement between theory and experiment.     

Diffractive particle production and anisotropic fireball decay

A model is considered for the diffractive component of particle production with anisotropically decaying fireballs. Application of this model to recent data on diffractive proton production gives favourable results. For these data the fragmentation model with isotropically decaying fireballs cannot account. The behaviour of inclusive single particle, two-particle and multiplicity distributions are studied.     

Diffractive heavy flavour production at the Tevatron and the LHC

We give predictions for diffractive heavy flavour production at the Tevatron and the LHC in leading-order approximation. In the framework of these studies we use three different models for the partonic structure of the Pomeron recently proposed by Stirling and Kunszt. These Pomeron models are, despite being fitted to the same diffractive deep inelastic HERA data, very different in their parton content and taken together provide a powerful tool to probe the structure of the Pomeron. All models satisfy GLAP evolution and show a significant Q₂ dependence. We give numerical predictions for single as well as double diffractive cross sections assuming a Donnachie-Landshoff-type Pomeron flux factor.     

Diffractive open charm production at HERA

We use perturbative QCD to calculate the cross sections σ^LT for the diffractive production of open charm (cc) from longitudinally and transversely polarised photons (of virtuality Q2) incident at high energy (√S) on a proton target. We study both the Q ² and M ² dependence of the cross sections, where M is the invariant mass of the cc pair. Surprisingly, the result for σ^T, as well as for σ^L, is perturbatively stable. We estimate higher-order corrections and find a sizeable enhancement of the cross sections. The cross sections depend on the square of the gluon density g(x, K²), and we show that the observation of open charm at the HERA electron-proton collider can act as a sensitive probe of the gluon distribution for x = (Q ² + M ²)/s and scale K2 = (M ²c + )(1 + Q ²/M ²) where the average quark transverse momentum squared 〈k ₂ ^t ~ (M ²c . As compared to diffractive J/#x03C8; production, open charm has the advantage that it is independent of the non-perturbative ambiguities arising from the J/#x03C8; wave function. We estimate the fraction of diffractive events that arise from cc¯ production.     

Diffractive elastic neutrino production of vector mesons

The diffractive elastic neutrino production of vector mesons has been studied in detail. The results of this analysis encourage experimental effort which may provide useful information concerning the nature of neutral currents and of the recently discovered new particles.