Compton scattering by the proton using a large-acceptance arrangement

Compton scattering by the proton has been measured over a wide range covering photon energies 250MeV <or∼Eγ <or∼ 800MeV and photon scattering angles 30 <or∼labγ <or∼150 , using the tagged-photon facility at MAMI (Mainz) and the large-acceptance arrangement LARA. The previously existing data base on proton Compton scattering is greatly enlarged by more than 700 new data points. The new data are interpreted in terms of dispersion theory based on the SAID-SM99K parametrization of photo-meson amplitudes. It is found that two-pion exchange in the t-channel is needed for a description of the data in the second resonance region. The data are well represented if this channel is modeled by a single pole with the mass parameter mσ∼ 600 MeV. The asymptotic part of the spin-dependent amplitude is found to be well represented by π0 exchange in the t-channel. No indications of additional effects were found. (orig.)