Speaker
Description
Nucleon elastic form factors encode crucial information about its charge and magnetization distributions. For many decades, nucleon form factors were studied by using unpolarized electron-nucleon cross section measurements. The advent of electron beams with higher luminosities and beam polarization coupled with large acceptance detectors, polarized targets and recoil polarimeters enabled a wealth of information on nucleon form factors over a broad range of momentum transfer ($Q^2$). While plenty of information is available on the proton, no data above $Q^2$ = 3.5 GeV$^2$ is available on the neutron electric form factor. Pushing the data to a higher $Q^2$ allows constraining spin flip GPDs and serves as a benchmark for various theoretical models. Using quasi-elastic scattering of a polarized electron beam on a polarized $^3$He target, one can extract the $G_E^n$ term which is proportional to the measured asymmetry from opposite electron beam helicity.
The goal of the SBS (Super Bigbite Spectrometer) physics program in Hall A at Jefferson Lab is to conduct a series of experiments to measure the electric and magnetic form factors of the proton and the neutron at an unprecedentedly high $Q^2$. One of the experiments, GEn-II (E12-09-016) is aimed at measuring the neutron electric form factor using the double-polarization technique with both a polarized electron beam and a polarized $^3$He target. This experiment finished taking data at three out of four kinematic settings and is scheduled for completion in the Fall of this year. The physics motivation and status of the experiment will be discussed in this talk. This work was supported in part by DOE grant DE-FG02-96ER41003.
