Measurements of the generalized electric and magnetic polarizabilities of the proton at low Q2 using the virtual-compton-scattering reaction

The mean square polarizability radii of the proton have been measured for the first time in a virtual-Compton-scattering experiment performed at the MIT-Bates out-of-plane scattering facility. Response functions and polarizabilities obtained from a dispersion analysis of the data at Q(2)=0.057 GeV2/c(2) are in agreement with O(p(3)) heavy baryon chiral perturbation theory. The data support the dominance of mesonic effects in the polarizabilities.