Low-energy Compton scattering and the polarizabilities of the proton

Differential cross-sections for Compton scattering from the proton hal e be en measured at the MAMI tagged photon facility using the TAPS setup. The da ta cover an angular range of theta (lab)(gamma) = 59 degrees -155 degrees a nd 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 determine d to be <(<alpha>)over bar> = [11.9 +/- 0.5(stat.) -/+ 1.3(syst.) +/- 0.3(m od.)] (.) 10(-4) fm(3) and <(<beta>)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 <(<alpha>)over bar> + <(<beta>)over b ar> = [13.8 +/- 0.4] 10(-4) fm(3). We can also conclude that there is no si gnificant additional asymptotic contribution to the backward spin polarizab ility gamma (pi) beyond the t-channel pi (0)-exchange.