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

Abstract

We have measured the Compton-scattering cross section on hydrogen at 60\ifmmode^\circ\else\textdegree\fi{} and 135\ifmmode^\circ\else\textdegree\fi{} 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, \ensuremath{\alpha}\ifmmode\bar\else\textasciimacron\fi{}=(10.9\ifmmode\pm\else\textpm\fi{}2.2\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{fm}}^{3}$ and \ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{}=(3.3\ensuremath{\mp}2.2\ensuremath{\mp}1.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{fm}}^{3}$, assuming the model-independent constraint \ensuremath{\alpha}\ifmmode\bar\else\textasciimacron\fi{}+\ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{}=14.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{fm}}^{3}$.