Demonstration of a novel technique to measure two-photon exchange effects in elastic $e^\pm p$ scattering

Understand

The discrepancy between proton electromagnetic form factors extracted using unpolarized and polarized scattering data is believed to be a consequence of two-photon exchange (TPE) effects.

• However, the calculations of TPE corrections have significant model dependence, and there is limited direct experimental evidence for such corrections.
• We present the results of a new experimental technique for making direct $e^\pm p$ comparisons, which has the potential to make precise measurements over a broad range in $Q^2$ and scattering angles.
• We use the Jefferson Lab electron beam and the Hall B photon tagger to generate a clean but untagged photon beam.