Search

A physically motivated parameterization of the chiral-even generalized parton distributions (GPDs) has been obtained from a global analysis using available experimental data including nucleon electromagnetic form factors, deep inelastic scattering and DVCS. Additional information provided by lattice calculations of the higher moments of GPDs is also considered. Recently extracted observables from DVCS at JLab and Hermes are reproduced by our fit and predictions are made for higher energy regimes. Our scheme uses a Reggeized diquark model and concomitant helicity amplitude relations, which allow the extension to the chiral-odd sector. Having obtained the chiral-odd GPDs, we are able to explain the features of exclusive neutral meson electroproduction. Our analysis is applied to existing and forthcoming spin-dependent π0 and η data in the kinematical region of intermediate Bjorken x and Q2 in the multi-GeV region, accessible at present and currently planned facilities. [ABSTRACT FROM AUTHOR]

We discuss the extension of a systematic perturbative QCD based analysis to the x → 1 region. After subtracting a number of effects that transcend NLO pQCD evolution, such as target mass corrections and large x resummation effects, the remaining power corrections can be interpreted as dynamical higher twists. The quantitative outcome of the analysis is dominated by the interplay between the value of αS in the infrared region and the higher twists. We uncover a dual role played by αS at large Bjorken x that can be used to experimentally extract its value in the non-perturbative regime. [ABSTRACT FROM AUTHOR]

Exclusive pi0 electroproduction from nucleons at large photon virtuality can be described in terms of Generalized Parton Distributions, particularly the chiral odd subset. Chiral odd GPDs are related to transversity and can be accessed experimentally for various special choices of observables. This is accomplished by choosing C-parity odd and chiral odd combinations of t-channel exchange quantum numbers. These GPDs are calculated in a spectator model, and are constrained by boundary functions. Alternatively, the production amplitudes correspond to C-odd Regge exchanges with final state interactions. The helicity structure of the virtual photoproduction amplitudes provides relations between the partonic description via GPDs and the hadronic, Regge description of C-odd processes, all via quark helicity flip. GPDs, in general, are analytic functions of energy variables. Their integrals over unobservable parton momenta thereby satisfy Dispersion Relations (DR). Using DR’s could allow the real part of the amplitudes, the integrated GPDs, to be extracted from the more easily measured imaginary parts. However, at non-zero momentum transfer DRs require integration over unphysical regions of the variables. We show that the relevant unphysical region of the non-forward DRs is considerable. This will vitiate the efforts to avoid the actual measurement of the real parts more directly. [ABSTRACT FROM AUTHOR]

In most experiments aimed at determining the masses and mixing parameters for neutrino oscillations in different energy regimes there are strong backgrounds to neutrino interactions with matter that can confuse the expected small signals. One particular set of backgrounds is due to neutrino production of mesons, particularly pions, from nucleon or nuclear targets. It is especially important and theoretically interesting in itself to study coherent neutrino production of pions, i.e. wherein the target does not break up. Preserving the target requires that the meson produced in the reaction will be charged for Charged Current (CC) interactions or neutral for Neutral Current (NC) interactions. Coherent scattering is the weak analog of exclusive neutral meson electroproduction for which considerable progress has been made in understanding the intermediate energy, small momentum transfer region by applying the Generalized Parton Distribution (GPD) phenomenology. The GPD perspective will be explained with emphasis on how the understanding gained from electroproduction of neutral pions can carry over to the neutrino processes. [ABSTRACT FROM AUTHOR]