Compton scattering from the proton

The proton Compton effect has been studied in the region between the threshold for pion photoproduction and the Δ(1232). The measurements were performed using bremmstrahlung from the high duty-factor electron beam available at the Saskatchewan Accelerator Laboratory. Elastically scattered photons were detected with an energy resolution of approximately 1.5% using a large NaI total absorption scintillation detector. Differential cross sections were measured for photon energies in the range 136 MeV≤Eγ≤289 MeV and for angles in the range 25 degree <θlab<135 degree. The angular distributions and the excitation functions derived from these data are in agreement with recent theoretical analyses. The results were interpreted within a formalism based in part on dispersion relations to obtain model-dependent estimates of the electric and magnetic polarizabilities, bar α and bar β. We find, subject to the dispersion sum rule constraint bar α+bar β=(14.2±0.5)x10-4 fm3, that bar α=(9.8±0.4±1.1)x10-4 fm3 and bar β=(4.4 minus-plus 0.4 minus-plus 1.1)x10-4 fm3, which are consistent with the best previous measurements