1ST MEASUREMENT OF THE ELECTRIC FORMFACTOR OF THE NEUTRON IN THE EXCLUSIVE QUASI-ELASTIC SCATTERING OF POLARIZED ELECTRONS FROM POLARIZED HE-3

A first measurement of the asymmetry in quasielastic scattering of lon gitudinally polarized electrons from a polarized He-3 gas target in co incidence with the knocked out neutron is reported. This measurement w as made feasible by the cw beam of the 855 MeV Mainz Microtron MAMI. I t allows a determination of the electric formfactor of the neutron G(E )n independent of binding effects a to first order. At Q2BAR = 0.31 (G eV/c)2 two asymmetries ABAR(parallel-to) (S(He) parallel-to q) and ABA R(perpendicular-to) (S(He) perpendicular-to q) have been measured givi ng ABAR(parallel-to) = (-7.40 +/- 0.73)% and ABAR(perpendicular-to) = (0.89 +/- 0.30)%. The ratio ABAR(perpendicular-to)/ABAR(parallel-to) i s independent of the absolute value of the electron and target polariz ation and yields G(E)n = 0.035 +/- 0.012 +/- 0.005.