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

Abstract

The Compton scattering cross section on hydrogen was measured at 60$\sp\circ$ and 135$\sp\circ$ in order to determine the largely unknown electric and magnetic polarizabilities of the proton. The cross sections were measured using tagged photons spanning 32 through 72 MeV in energy. In this energy range, the forward scattering cross section is well constrained by model-independent theory and was measured to check the systematics of our experimental and data reduction procedures. Within the statistical errors, the measured forward cross section agrees with theory. The following values for the polarizabilities are extracted from the measured cross sections: $\bar\alpha = (10.1 \pm 2.2 \pm 1.4)\cdot 10\sp{-4}fm\sp3$ and $\bar\beta = (4.1 \mp 2.2 \mp 1.4)\cdot 10\sp{-4}fm\sp3$, where the errors shown are statistical and systematic, respectively.