Nucleon Form Factors

Measurements of the electric and magnetic form factors have been carried out by means of scattering of polarized electrons from vector-polarized hydrogen and deuterium. The experiment used the longitudinally polarized stored electron beam of the MIT-Bates South Hall Ring along with an isotopically pure, highly vector-polarized internal atomic hydrogen and deuterium target provided by an atomic beam source, and the symmetric Bates Large Acceptance Spectrometer Toroid (BLAST) with enhanced neutron detection capability. The measurements are at low momentum transfers (Q < 1 (Gev/c)) and results are presented for the proton form factor ratio GE/GM and for the electric form factor of the neutron, GE. To quantify the effect of multiple photon exchange and to address the puzzle of the proton form factor ratio at Q > 1 (GeV/c), an experiment under development using BLAST and an unpolarized internal hydrogen target will measure electron-proton and positron-proton elastic scattering.