Proton Compton effect: A measurement of the electric and magnetic polarizabilities of the proton

We have measured the Compton-scattering cross section on hydrogen at 60^∘{} and 135^∘{} using monochromatic tagged photons spanning the energy between 32 and 72 MeV. These data, when analyzed with a low-energy expansion of the scattering cross-section formula, provides a determination of values for the electric and magnetic polarizabilities of the proton. We find, respectively, {α}{}=(10.9±{}2.2±{}1.3)×{}10^-4 fm³ and {β}{}=(3.3{∓}2.2{∓}1.3)×{}10^-4 fm³, assuming the model-independent constraint {α}{}+{β}{}=14.2×{}10^-4 fm³.