Measurements of the Generalized Electric and Magnetic Polarizabilities of the Proton at Low Q{sup 2} 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{sup 2}=0.057 GeV{sup 2}/c{sup 2} are in agreement with O(p{sup 3}) heavy baryon chiral perturbation theory. The data support the dominance of mesonic effects in the polarizabilities.