Virtual Compton scattering measurements in the nucleon resonance region

Abstract

Abstract. We report on new measurements of the electric Generalized Polarizability (GP) of the proton $ \alpha_{E}$αE in a kinematic region where a puzzling dependence on momentum transfer has been observed, and we have found that $ \alpha_E = (5.3 \pm 0.6_{stat} \pm 1.3_{sys}) 10^{-4}$αE=(5.3±0.6stat±1.3sys)10-4 fm3 at $ Q^{2}=0.20$Q2=0.20 (GeV/c)2. The new measurements, when considered along with the rest of the world data, suggest that $ \alpha_E$αE can be described by either a local plateau or by an enhancement in the region $ Q^2=0.20$Q2=0.20 (GeV/c)2 to 0.33 (GeV/c)2. The experiment also provides the first measurement of the Coulomb quadrupole amplitude in the $ N \rightarrow \Delta$N→Δ transition through the exploration of the $ p(e,e'p)\gamma$p(e,ep)γ reaction. The new measurement gives $ CMR = (-4.4 \pm 0.8_{stat} \pm 0.6_{sys})\%$CMR=(-4.4±0.8stat±0.6sys)% at $ Q^2=0.20$Q2=0.20 (GeV/c)2 and is consistent with the results from the pion electroproduction world data. It has been obtained using a completely different extraction method, and therefore represents a strong validation test of the world data model uncertainties.