Description
The GEn-RP experiment is among various form factor experiments with the Super-Bigbite Spectrometer (SBS) setup at Hall-A, Jefferson Lab and measures the ratio of electric to magnetic elastic form factors of the neutron, GEn/GMn using recoil polarimetry techniques at Q2=4.3GeVc2 in quasi-elastic electron-neutron scattering from a deuterium target. The ratio of these form factors is measured from the ratio of the transverse Px and the longitudinal Pz components of the spin polarization, that is transferred to the recoiling neutron from the incident, longitudinally polarized electron beam. Both high-momentum, small-angle neutrons 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 after precessing through known magnetic fields. In addition, low momentum, large-angle protons produced during np→np elastic scattering in active analyzer are detected, as a proof-of-principle measurement of the analyzing power. To detect large-angle protons which is recoiling protons and forward neutrons we have one pair of side GEMs setup, a hodoscope, Active analyzer is aligned near rear inline GEMs and Hardon Calorimeter, to detect forward neutron.
This experiment will yield GEn/GMn at kinematic point the three times higher Q2 yet published with recoil polarization and the experimental figure-of-merit information on the polarimetry along with the analyzing power will be used to optimize the future measurements of GEn/GMn to reach higher Q2 values using recoil polarimetry techniques. Ongoing work focuses on the analysis of large-angle recoil protons to extract the GEn and analyzing power, with results expected soon.
*This work has been supported by the Department of Energy under award DE-SC0013941 and by Jefferson Science Associates, LLC (JSA).