Neutron Elastic Form Factor Ratio from Recoil Polarization*

The GEn-RP experiment is among various form factor experiments with the Super-Bigbite Spectrometer setup at Hall-A, Jefferson Lab and measures the ratio of electric to magnetic elastic form factors of the neutron, GEn/GMn using two recoil polarimetry techniques at Q² = 4.5 (GeV/c)² in quasi-elastic electron-neutron scattering from a deuterium target.

The ratio of the above-mentioned form factors is measured from the ratio of the transverse (P_x) and the longitudinal (P_z) components of the spin polarization, that is transferred to the recoiling neutron from an incident, longitudinally polarized electron beam. Both low-momentum, large-angle protons produced during np → np 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.

This experiment will yield GEn /GMn at the highest Q² kinematic point yet recorded and the experimental figure-of-merit information on the polarimetry along with the analyzing powers will be used to optimize future measurements of GEn/GMn to reach higher Q² values using recoil polarimetry techniques.