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

Abstract

We report a Virtual Compton Scattering study of the proton at low CM energies. We have determined the structure functions $P_{LL}-P_{TT}/ε$ and $P_{LT}$, and the electric and magnetic Generalized Polarizabilities (GPs) $α_E(Q2)$ and $β_M(Q2)$ at momentum transfer Q2= 0.92 and 1.76 GeV2. The electric GP shows a strong fall-off with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a fall-off; 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 $πN$ intermediate states.

4 pages, 2 Figs. Version for PRL after PRL cancelled their request for reducing length of paper