Münster 2002 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 19: Electromagnetic and Hadronic Probes II

HK 19.3: Talk

Tuesday, March 12, 2002, 17:45–18:00, D

Hard exclusive electroproduction of real photons and π⁺ on the proton at HERMES — •Björn Seitz — II. Physikalisches Insitut, Justus–Liebig Universität Giessen, Heinrich–Buff Ring 16, 35392 Giessen, F.R.G.

The production of mesons (or photons) in deep–inelastic lepton scattering gives access to information on the structure of hadrons that is otherwise hard to obtain. When the production process involves at least on hard scale and is exclusive, the data can be interpreted in terms of the recently introduced generalized parton distributions (GPDs). These GPDs provide a unified description of hadronic structure, which can be applied to many different reactions.

Single Spin Asymmetries in the hard, exclusive electroproduction of real photons (DVCS) and π⁺ on the proton have been measured for the first time by HERMES. Sizeable asymmetries for DVCS using a polarized beam and unpolarized target have been observed. A large asymmetry using an unpolarized beam and a longitudinal polarized target has been observed in the exclusive electroproduction of π⁺. These data provide a first testing ground for the GPD formalism.