Neutron Elastic Form Factor Ratio from Recoil Polarization

The GEn-RP experiment with the Super-Bigbite Spectrometer (SBS) setup at Hall-A, Jefferson Lab, measures the ratio of electric to magnetic elastic form factors of the neutron, G_Eⁿ/G_Mⁿ using two recoil polarimetry techniques at Q²= 4.5 (Gev/c)² in quasi-elastic electron-deuterium scattering. Both high-momentum, small-angle neutrons produced during elastic scattering and high-momentum, small-angle protons produced by np-pn (charge exchange) are used to analyze the neutron polarization components upon precessing through a known magnetic field. In addition, low-momentum, large-angle protons produced during np-np elastic scattering are detected, as a proof-of-principle measurement of the analyzing power. This experiment will yield G_Eⁿ/G_Mⁿ at the highest kinematic point yet recorded with recoil polarization and the experimental figure-of-merit information on the polarimetry along with the analyzing powers will be used to optimize future measurements of G_Eⁿ/G_Mⁿ to reach higher Q² values using recoil polarimetry techniques.