New Insight in the Q2 Dependence of Proton Generalized Polarizabilities

Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer Q(2): 0.10, 0.20, and 0.45 GeV2, at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion relations allowed the extraction of the structure functions P-LL - P-TT/epsilon and P-LT, as well as the electric and magnetic generalized polarizabilities alpha(E1)(Q(2)) and beta(M1)(Q(2)). These new results show a smooth and rapid falloff of alpha(E1)(Q(2)), in contrast to previous measurements at Q(2) = 0.33 GeV2, and provide for the first time a precise mapping of beta(M1)(Q(2)) in the low-Q(2) region.