Low-energy Compton scattering and the polarizabilities of the proton

Differential cross-sections for Compton scattering from the proton hal e been measured at the MAMI tagged photon facility using the TAPS setup. The data cover an angular range of theta (lab)(gamma) = 59 degrees -155 degrees and photon energies ranging from 55 MeV to 165 MeV. Our results are in good agreement with those from previous experiments, but yield higher precision. Using dispersion relations the proton polarizabilities have been determined to be <()over bar> = [11.9 +/- 0.5(stat.) -/+ 1.3(syst.) +/- 0.3(mod.)] (.) 10(-4) fm(3) and <()over bar> = [1.2 +/- 0.7(stat.) +/- 0.3(syst). +/- 0.4(mod.))] (.) 10(-4) fm(3). These results confirm the Baldin sum rule which was re-evaluated to be <()over bar> + <()over bar> = [13.8 +/- 0.4] 10(-4) fm(3). We can also conclude that there is no significant additional asymptotic contribution to the backward spin polarizability gamma (pi) beyond the t-channel pi (0)-exchange.