Two-Photon Exchange Measurement on Neutron with Super BigBite Spectrometer

The nucleon form factors are one of the most fundamental aspects of the nucleon structure. At high Q2, they are linked to the generalized parton distributions which provide information on the nucleon spin. The Super Bigbite Spectrometer (SBS) in Hall A at Jefferson Lab is dedicated to measure the form factors at high Q2, and has started taking data during Fall of 2021.

Among those experiments, nTPE measures the two-photon exchange contribution in elastic electron-neutron scattering at a four-momentum transfer Q2= 4.0 GeV2. The two-photon exchange is suspected to be the root cause of the discrepancies between the form factor Rosenbluth measurements and polarization transfer measurements on the proton, but it has never been measured on the neutron. Specifically, nTPE measures the ratio of quasi-elastic en over ep cross sections off deuterium at the aforementioned value of Q2 and two beam energies, 4.03 and 6.00 GeV. The comparison between the obtained experimental Rosenbluth slope and the current estimation of GEn will provide an experimental estimation of the two-photon exchange contribution.

In this presentation we provide a very brief overview of the SBS neutron form factor measurements with an emphasis on nTPE, its experimental analysis method, and the progress of the data analysis.