Measurement of the single-spin asymmetry A_y ⁰ in quasi-elastic ³He^↑(e,e′n) scattering at 0.4 < Q² < 1.0 GeV/c²

Due to the lack of free neutron targets, studies of the structure of the neutron are typically made by scattering electrons from either ²H or ³He targets. In order to extract useful neutron information from a ³He target, one must understand how the neutron in a ³He system differs from a free neutron by taking into account nuclear effects such as final state interactions and meson exchange currents. The target single spin asymmetry A_y ⁰ is an ideal probe of such effects, as any deviation from zero indicates effects beyond plane wave impulse approximation. New measurements of the target single spin asymmetry A_y ⁰ at Q² of 0.46 and 0.96 (GeV/c)² were made at Jefferson Lab using the quasi-elastic He↑3(e,e^′n) reaction. Our measured asymmetry decreases rapidly, from >20% at Q²=0.46 (GeV/c)² to nearly zero at Q²=0.96 (GeV/c)², demonstrating the fall-off of the reaction mechanism effects as Q² increases. We also observed a small ϵ-dependent increase in A_y ⁰ compared to previous measurements, particularly at moderate Q². This indicates that upcoming high Q² measurements from the Jefferson Lab 12 GeV program can cleanly probe neutron structure from polarized ³He using plane wave impulse approximation.