Jlab User Group

We propose a measurement of the neutron electric form factor GEn at high four– momentum transfer values of Q = 1.3, 2.4, and 3.4 (GeV/c) in double polarized semi-exclusive 3 He( e, e′n) scattering in quasi–elastic kinematics by measuring the asymmetry AT of the cross section. Results from the recent JLab experiment E93-027 for elastic electron-proton scattering, using a recoil polarization technique, show remarkable features for the proton electric form factor at these momentum transfers, whereas no accurate data on GEn are available. The recently developed approach for calculations of exclusive reactions in the Q-range between 1 and 10 (GeV/c) using generalized parton distributions (GPD) relates these elastic form factors to the results from deep inelastic scattering and from Compton scattering. Data for GEn at high Q 2 are necessary, in particular, to constrain spin-flip GPDs. The experiment utilizes the polarized He target and the polarized CEBAF beam at moderate beam energies of 1.644, 2.444, and 3.244 GeV. The electrons will be detected in the BigBite spectrometer, the neutrons in an array of scintillators. Because of the high kinetic energy of the neutrons, a high neutron detection efficiency with an excellent background suppression can be achieved. Within 768 hours of beamtime GEn can be measured to a statistical accuracy of ∆GEn/GEn= 0.14 for these three values of Q . Such a measurement would significantly increase our knowledge about a fundamental property of the neutron in a region where no accurate data are yet available.