Structure of the nucleon investigated by Compton scattering

Experimental differential cross sections for Compton scattering by the proton measured with the LARge Acceptance arrangement at the tagged-photon facility MAMI (Mainz) are interpreted in terms of the nonsubtracted dispersion theory based on the SAID-SM99K parameterization of photo-meson amplitudes. Using the new global average for the difference of electric and magnetic polarizabilities of the proton α β= (10:5 0:9stat+syst 0:7model) 10 4fm3 a backward spin-polarizability of γπ = ( 37:1 0:6stat+syst 3:5model) 10 4fm4 and a E2/M1 ratio of EMR(340 MeV)=( 1:7 0:4stat+syst 0:2model) % have been obtained.