Scattering of photons by the proton through theta(cms)=90 degrees in the Delta-resonance region

The differential cross section for the scattering of photons by the proton was measured in the energy range E(gamma) = 250-500 MeV at the scattering angle theta(cms) = 90 degrees +/- 3 degrees. The tagged photon beam of the MAMI accelerator was used and both the scattered photon and the recoil proton were detected. The data essentially are consistent with dispersion theories, and remove the discrepancy that has existed above 290 MeV between theory and earlier published experimental results

Compton scattering by the proton through theta(cms)=75 degrees and 90 degrees in the Delta-resonance region

Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of theta(cms) = 75 degrees and theta(cms) = 90 degrees using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Delta-range is concerned. However, there is evidence that a scaling down of the resonance part of the M-1+(3/2) photo-meson amplitude by (2.8+/-0.9)% is required in comparison with the VPI analysis. The deduced value of the M-1+(3/2)-photoproduction amplitude at the resonance energy of 320 MeV is: M-1+(3/2) = (39.6+/-0.4) x 10(-3) m(pi+)(-1). (C) 1997 Elsevier Science B.V

Compton scattering from the free and bound proton at backward angles above π-threshold

Differential cross sections for Compton scattering from the free proton at Theta(gamma)(lab) = 130.7 degrees in the energy region from 200 MeV to 410 MeV and far quasi-free Compton scattering from the proton bound in the deuteron at Theta(gamma)(lab) = 148.8 degrees in the energy region from 200 MeV to 290 MeV have been measured. The free proton data are in agreement with dispersion-theory predictions based on standard parameters. The difference of the proton polarizabilities has been extracted from the quasi-free data. Our result, - = [9.1 +/- 1.7(stat + syst) +/- 1.2(mod)] x 10(-4) fm(3), is in reasonable agreement with the world average of the free proton data if the backward spin polarizability gamma(pi) is taken to be -37.6 x 10(-4) fm(4) as predicted by dispersion theory in agreement with many theoretical calculations. This implies that quasi-free Compton scattering may also be used to determine the electromagnetic polarizabilities of the neutron. No indication has been found of a recently suggested new contribution to gamma(pi)

Compton scattering from the free and bound proton above pi-threshold

The differential cross sections for Compton scattering from the proton have been measured at MAMI with three different detector setups. There is a good agreement among all the results. The theoretical calculation based on dispersion relations shows that there is no drastic change necessary in the parameters of this approach