Physics with a Positron Beam at Jefferson Lab

Positron scattering from hadronic targets can provide new information that cannot be accessed with electron scattering alone. The asymmetry in deeply virtual Compton scattering cross sections between positrons and electrons can provide a critical handle on the Bethe-Heitler background process. A similar asymmetry in elastic scattering can reveal the contribution from two-photon exchange, which has been suggested as a possible explanation for the puzzling discrepancy in measurements of the proton's form factors at high momentum transfer. Positron capture and annihilation offer new ways to measure axial form factors, search for light dark matter, and probe fundamental symmetries. For these reasons, the Jefferson Lab Positron Working Group is working to bring positron capabilities to Jefferson Lab. Here, I present the design concept for producing and injecting polarized positrons into CEBAF, and review the range of experiments that would be made possible with positrons at Jefferson Lab.