Compton scattering from the proton below pion threshold: A measurement of the electric and magnetic polarizabilities of the proton

The Compton scattering cross section on the proton was measured at laboratory angles of 90$\sp\circ$ and 135$\sp\circ$, using 70-100 MeV tagged photons, and simultaneously using 100-150 MeV untagged photons, in order to determine the electric and magnetic polarizabilities. The 135$\sp\circ$ cross section is sensitive to the difference of the electric and magnetic polarizabilities, $\bar \alpha - \bar\beta$, while the 90$\sp\circ$ cross section is sensitive to the electric polarizability $\bar \alpha$. Using the model independent sum rule constraint for $\bar \alpha$ + $\bar \beta$ and a model dependent dispersion relation calculation, the values for the polarizabilities extracted from the cross sections are:$$\bar \alpha = (12.5 \pm 0.6 \pm 0.8 \pm 0.6) \times 10\sp{-4} fm\sp3\cr \bar \beta = (1.8 \mp 0.6 \mp 0.8 \mp 0.6) \times 10\sp{-4} fm\sp3$$where the errors shown are statistical, systematic, and model, respectively.U of I OnlyETDs are only available to UIUC Users without author permissio