Measurement of the generalized polarizabilities of the proton in virtual Compton scattering at Q2=0.92 and 1.76 GeV2 -: art. no. 122001

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P-LL-P-TT/epsilon and P-LT, and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q(2)) and beta(M)(Q(2)) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q(2), and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q(2), compensated at higher Q(2) by a paramagnetic contribution from piN intermediate states.