Spin density matrix elements in vector meson leptoproduction

It is reported on an analysis of vector meson leptoproduction at small Bjorken-$x$ and large photon virtuality within an approach that bases on generalized parton distributions (GPDs). This approach leads to results for cross sections and spin density matrix elements for $\rho$ and $\phi$ leptoproduction in fair agreement with experiment.Comment: Report at Spin 2004 Symposium, October 10-16, Trieste, Ital

Transversity in exclusive vector-meson leptoproduction

The role of transversity or helicity-flip generalized parton distributions (GPDs) in leptoproduction of vector mesons is investigated within the framework of the handbag approach. The transversity GPDs in combination with twist-3 meson wave functions, occur in the amplitudes for transitions from a transversely polarized virtual photon to a longitudinal polarized vector meson. The importance of the transversity GPDs can be examined in some of the spin density matrix elements and in transverse target spin asymmetries. Using suitable parametrizations of both helicity-flip and non-flip GPDs, which are essentially taken from our previous papers, we estimate these observables and compare the results with available data.Comment: 30 pages, 19 figure

The pion pole in hard exclusive vector-meson leptoproduction

Exploiting a set of generalized parton distributions (GPDs) derived from analyses of hard exclusive leptoproduction of rho0, phi and pi+ mesons, we investigate the omega spin density matrix elements (SDMEs) recently measured by the HERMES collaboration. It turns out from our study that the pion pole is an important contribution to omega production. It will be treated as a one-particle exchange since its evaluation from the GPD E-tilde considerably underestimates its contribution. As an intermediate step of our analysis we extract the pi-omega transition form factor for photon virtualities less than 4 GeV^2. From our approach we achieve results for the omega SDMEs in good agreement with the HERMES data. The role of the pion pole in exclusive rho0 and phi leptoproduction is discussed too.Comment: 27 pages, 33 figure

The exclusive limit of the pion-induced Drell-Yan process

Based on previous studies of hard exclusive leptoproduction of pions in which the essential role of the pion pole and the transversity generalized parton distributions has been pointed out, we present predictions for the four partial cross sections of the exclusive Drell-Yan process, pi^-p -> l^-l^+n.Comment: 14 pages, 6 figure

Ising magnets with mobile defects

Motivated by recent experiments on cuprates with low-dimensional magnetic interactions, a new class of two-dimensional Ising models with short-range interactions and mobile defects is introduced and studied. The non-magnetic defects form lines, which, as temperature increases, first meander and then become unstable. Using Monte Carlo simulations and analytical low- and high-temperature considerations, the instability of the defect stripes is monitored for various microscopic and thermodynamic quantities in detail for a minimal model, assuming some of the couplings to be indefinitely strong. The robustness of the findings against weakening the interactions is discussed as well

Aperture judgement in fire-appliance drivers

Low-speed collisions are a common occurrence for UK Fire and Rescue Services, with frequent bumps and scrapes adding up to create a significant drain on emergency service budgets, and damaging public faith in the service. We hypothesised that the decision to drive through a gap, or aperture, created by other vehicles and/or road furniture, may be related to driver experience and risk-level. To create a test to assess this skill, video clips were recorded from a fire appliance on bluelight training runs. Eighteen clips were selected on the basis that they culminated in a narrow aperture that the film-driver either navigated through, or stopped and waited for other vehicles to move and the gap to widen. Drivers were required to watch these clips, which paused at the point that the film-driver made the decision to either go though, or to wait. The participants rated their belief that the appliance would fit through the gap, and how confident they would be to drive through that aperture themselves (on a 1-8 scale). Novice fire-appliance drivers were less accurate in deciding whether to proceed or not, though their criterion threshold did not differ to that of more experienced drivers. All drivers favoured looking at the right edge of the aperture (either a vehicle or road furniture), but low-risk, experienced fire appliance drivers had the shortest fixations on this area. The results suggest that a video-based test of aperture judgement can differentiate between fire-appliance driver groups based on experience, opening the way for future testing and training tools using this methodology