1. Two-photon Exchange as a Laboratory for Nucleon Structure Studies The entire response of the nucleon is contained in the two-photon box. A y : Measure the target SSA using quasi-elastic scattering from vertically polarized 3 He. E05-015, A y n can only be non-zero through two- photon exchange. GPDs predict A y n ~ -2% at Q 2 =1 GeV 2. E08-005, A y n ~ 50% expected at Q 2 ~ 0.2 GeV 2 due to nuclear FSI. T. Averett, J. P. Chen, D. Higinbotham, X. Jiang, V. Sulkosky The Hall A and Polarized 3 He Collaborations, Thesis students: Yawei Zhang, Ellie Long γ γ

2. Data Quality (from Yawei Zhang) Q 2 =0.13 GeV 2 Q 2 =0.46 GeV 2 Q 2 =0.97 GeV 2 Pion rejector2 Pion rejector1 Cerenkov ADC channels

3. Raw asymmetries are consistent between LHRS and RHRS Left armRight arm Q 2 =0.96 (GeV/c) 2 A y raw = 0.108% +/-0.012%A y raw = -0.107% +/-0.012%

4. E07-013 A y in the Deep-Inelastic Region Inclusive DIS: Measure the target SSA using deep- inelastic scattering from vertically polarized 3 He (neutron). A y DIS vanishes in the Born approximation. Two-photon exchange produces a small, but non-zero asymmetry in the constituent quark and other partonic models Unlike QE, the DIS asymmetry is expected to be ~10 -4 (Afanasev, Strikman, Weiss, PRD) due to contributions beyond leading-twist. Proton measurement at SLAC found zero asymmetry with uncertainty of 10 -2. JLab E07-013 measured 2 points at Q 2 =1-3 GeV 2 to the 10 -3 level; a factor of 10 improvement in uncertainty. Large backgrounds and small number of photoelectrons in BigBite cerenkov detector prevented having a clean trigger and higher statistics. T. Averett, R. Gilman, T. Holmstrom, X. Jiang The Hall A and Polarized 3 He Collaborations, Thesis student: Joseph Katich William and Mary