Abstract: Peter Kroll

Generalized parton distributions from meson electroproduction

The analysis of exclusive electroproduction of light mesons at small Bjorken-x within the handbag approach will be reviewed. The required GPDs are constructed from double distributions using suitable parametrizations of the latter. Constraints from parton distributions, sum rules and positivity bounds are taken into account and the remaining free parameters are fitted to experiment. What has been learned about the GPDs from the analysis of meson electroproduction will be summarized. As an application the set of extracted GPDs has been used in a parameter-free calculation of DVCS. It will be shown that good agreement with HERMES and HERA DVCS data is obtained. The present knowledge of the GPD E which is required for an evaluation of Ji's sum rule, will be discussed in some detail. It turned out that transversally polarized photons play an important role. Electroproduction of pseudoscalar mesons seem to be dominated by such contributions which, within the handbag approach, are to be modelled by transversity (helicity flip) GPDs and twist-3 meson wave functions. Finally, it will be commented on exclusive photo- and electroproduction of the J/Psi meson.