The first measurements of elastic electron nucleon scattering with polarization transfer, allowing to separate the electric and magnetic nucleon form factors, showed a significant discrepancy with Rosenbluth measurement of the cross section of the same process. The two-photon exchange, suspected to be the cause of this observation, got a major focus since then. The two-photon exchange is expected to depend on the charge of the lepton, meaning that the ratio of positron-nucleon to electron-nucleon measurements should clarify the role of the two photon exchange in the aforementioned discrepancy.
We propose measurements of the quasi-elastic positron-neutron and electron-neutron at Q2 = 3.0 (GeV/c)2, 4.5 (GeV/c)2 and 6 (GeV/c)^2, combined with Rosenbluth measurements at these kinematics. These measurements purport to complete and extend the measurement of the two-photon exchange in electron-neutron scattering submitted to and approved by PAC48 in 2020, and recorded in 2022 (experiment E12-20-010 currently under analysis). It would be performed with the Super BigBite Spectrometer installed in Hall C and will measure simultaneously positron-proton and
positron-neutron scattering off deuterium.
I will present the motivations and details of the proposed measurement, and provide a few aspects of the ongoing analysis of experiment E12-20-010 relevant to this new measurement.
