The proton form factor puzzle began in 2007 when an electron-proton polarization transfer measurement at JLab found a difference in the electric and magnetic form factor ratios of the proton. The polarization measurements found that the form factor ratios decreased with increasing Q^2, in contrast with the standard Rosenbluth separation measurements of the form factor ratios, which are constant. The proposed explanation for this discrepancy, the two-photon exchange, has been measured by several recent experiments. However, these results have been limited in their Q^2 range. TPEX, which is proposed to run at DESY (https://www.desy.de/), aims to measure the two-photon effect from 3 – 4.6 (GeV/c)^2, to provide additional data on the proton form factor puzzle.

The TPEX proposal will be submitted to the next DESY PAC, and will be placed here when it is publicly available.