Measurement of the Generalized Polarizabilities of the Proton in Virtual Compton Scattering at Q² = 0.92 and 1.76 GeV²

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions PLL–PTT/and PLT, and the electric and magnetic generalized polarizabilities (GPs) E(Q2) and M(Q2) at momentum transfer Q2=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, 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 Q2, compensated at higher Q2 by a paramagnetic contribution from N intermediate states.