Test Beams for a Proposed Two-Photon Exchange Experiment (TPEX) at DESY*

Recent elastic lepton-proton measurements of the proton form factor ratio, $\mu^{p} G^{p}_{E}/G^{p}_{M}$, have yielded dramatically different results using polarized and unpolarized techniques. The leading explanation for this discrepancy is the contribution of the hard two-photon exchange corrections. A proposed experiment at DESY aims to measure this contribution by measuring the ratio of positron-proton to electron-proton elastic scattering at lepton energies of 2 and 3 GeV. This talk will focus on test beams conducted in Fall 2019 and Fall 2021 at the DESY II synchrotron, which tested the performance of the PbWO$_{4}$ calorimeters, as well as triggered and streaming readout data acquisition systems.