Measurement of the electric and magnetic polarizabilities of the proton

Abstract

The Compton scattering cross section on the proton has been measured at laboratory angles of 90° and 135° using tagged photons in the energy range 70–100 MeV and simultaneously using untagged photons in the range 100–148 MeV. With the aid of dispersion relations, these cross sections were used to extract the electric and magnetic polarizabilities, α¯ and β¯ respectively, of the proton. We find α¯+β¯=(15.0 ±2.9±1.1±0.4)×10−4 fm3, in agreement with a model-independent dispersion sum rule, and α¯ -β¯ =(10.8±1.1±1.4±1.0)×10−4 fm3, where the errors shown are statistical, systematic, and model-dependent, respectively. A comparison with previous experiments is given and global values for the polarizabilities are extracted.