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One of the most surprising discoveries made at Jefferson Lab has been thediscrepancy in the determinations of the proton's form factor ratio $\mu_pG_E^p/G_M^p$ between unpolarized cross section measurements and thepolarization transfer technique. Over two decades later, the discrepancy notonly persists but has been confirmed at higher momentum transfers nowaccessible in the 12-GeV era. The leading hypothesis for the cause of thisdiscrepancy, a non-negligible contribution from hard two-photon exchange, hasneither been conclusively proven or disproven. This state of uncertainty notonly clouds our knowledge of one-dimensional nucleon structure but also poses amajor concern for our field's efforts to map out the three-dimensional nuclearstructure. A better understanding of multi-photon exchange over a wide phasespace is needed. We propose making comprehensive measurements of two-photonexchange over a wide range in momentum transfer and scattering angle using theCLAS12 detector. Specifically, we will measure the ratio of positron-proton toelectron-proton elastic scattering cross sections, using the proposed positronbeam upgrade for CEBAF. The experiment will use 2.2, 4.4, and 6.6 GeV leptonbeams incident on the standard CLAS12 unpolarized hydrogen target. Data will becollected by the CLAS12 detector in its standard configuration, except for amodified trigger to allow the recording of events with beam leptons scatteredinto the CLAS12 central detector. The sign of the beam charge, as well as thepolarity of the CLAS12 solenoid and toroid, will be reversed several times inorder to suppress systematics associated with local detector efficiency andtime-dependent detector performance. The proposed high-precision determinationof two-photon effects will be...

A Direct Measurement of Hard Two-Photon Exchange with Electrons and Positrons at CLAS12