Exclusive Deeply Inelastic Electroproduction at Hermes

Asymmetries in beam charge, beam helicity and target polarization have been measured for hard exclusive electroproduction of photons, ρ° and π⁺ in HERMES. The asymmetries appear in the distribution of the photons or mesons in the azimuthal angle around the virtual photon direction, relative to the lepton scattering plane. Such asymmetries can constrain the Generalized Parton Distributions (GPDs) of the nucleon or nucleus. The experiment is performed at the DESY laboratory in Hamburg Germany, using 27.5 GeV positrons and electrons incident on hydrogen, deuterium and neon targets.