Measurement of the Neutron Electromagnetic Form Factor at High Q²

The neutron electromagnetic form factors, Gⁿ_E and Gⁿ_M, give important insights into the neutron structure. In previous experiments the proton electromagnetic form factors, G^p_E , was measured up to Q² = 8.5 GeV², and G^p_M was measured up to Q² = 30 GeV², while Gⁿ_E has only been measured up to Q² = 3.4 GeV². The flavor decomposed form factors showed an unexpected Q² scaling for the u and d quarks, but higher Q² data is needed for the neutron. The Super BigBite Spectrometer (SBS) program at JLab plans to measure the neutron from factor ratio, Gⁿ_E/Gⁿ_M , at Q² values of 1.5, 3.8, 6.8, and 10.2 GeV² by colliding a polarized electron beam with a polarized ³He target, used here as an effective polarized neutron target, and measuring the transverse asymmetry of the cross section. This can then be used to extract the Gⁿ_E values using Gⁿ_M data from a companion experiment. Scattered electrons will be measured in the BigBite spectrometer while scattered neutrons will be magnetically separated from scattered protons and detected in a segmented hadron calorimeter. At the highest Q² point the form factor ratio should be calculated with an accuracy better than ∆Gⁿ_E = 3 × 10^-4 , with accurate measurements of Gⁿ_M.