A measurement of two-photon exchange in Super-Rosenbluth separations with positron beams

The proton electric and magnetic form factors, G_E and G_M , are intrinsically connected to the spatial distribution of charge and magnetization in the proton. For decades, Rosenbluth separation measurements of the angular dependence of elastic e ^- -p scattering were used to extract G_E and G_M . More recently, polarized electron scattering measurements, aiming to improve the precision of G_E extractions, showed significant disagreement with Rosenbluth measurements at large momentum transfers ( Q^2 ). This discrepancy is generally attributed to neglected two-photon exchange (TPE) corrections. At larger Q^2 values, a new ‘Super-Rosenbluth’ technique was used to improve the precision of the Rosenbluth extraction, allowing for a better quantification of the discrepancy, while comparisons of e ^+ -p and e ^- -p scattering indicated the presence of TPE corrections, but at Q^2 values below where a clear discrepancy is observed. In this work, we demonstrate the significant benefits to combining the Super-Rosenbluth technique with positron beam measurements. This approach provides a greater kinematic reach and is insensitive to some of the key systematic uncertainties in previous positron measurements.