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Abstract:: The electric form factor of the neutron G E,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q 2= 0.15 (GeV/c)2 in a measurement of the recoil polarisation ratio P x/Pz in the quasifree reaction D(e,e′n)p. At this Q 2 the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively by a model of Arenhövel et al.. After the corresponding corrections a value of G E,n(0.15 (GeV/c)2) = 0.0481±0.0065stat±0.0053syst is obtained.

Abstract:: The electric form factor of the neutron GEn has been determined in double polarized exclusive 3 He(e,e'n) scattering in quasi–elastic kinematics by measuring asymmetries A ⊥, A ∥ of the cross section with respect to helicity reversal of the electron, with the nuclear spin being oriented perpendicular to the momentum transfer q in case of A⊥ and parallel in case of A∥. The experiment was performed at the 855 MeV c. w. microtron MAMI at Mainz. The degree of polarization of the electron beam and of the gaseous 3 He target were each about 50%. Scattered electrons and neutrons were detected in coincidence by detector arrays covering large solid angles. Quasi–elastic scattering events were reconstructed from the measured electron scattering angles ϑe, φe and the neutron momentum vector p n′ in the plane wave impulse approximation. We obtain the result En>(0.27 < Q2c2/GeV2 < 0.5)= 0.0334 ± 0.0033stat± 0.0028syst which is averaged over the indicated range of Q 2, the squared momentum transfer. This G En value is significantly smaller than measured from the D(e,e'n) reaction under similar kinematical conditions. To what extent final state interactions in 3He quench the G En result is subject of calculations currently in progress elsewhere.