Two-Photon Exchange Contributions to the $e-n$ Elastic Scattering Cross-section and Related GEM Detectors

The nTPE experiment ran as part of the first segment of JLab's SBS program. nTPE is a measurement of the two-photon exchange contribution to the electron-neutron elastic scattering cross section at a four-momentum transfer of $Q^2 = 4.5$,(GeV/c)$^2$. Comparisons of nucleon form factor measurements acquired through polarization transfer and the Rosenbluth technique show discrepancies as the four-momentum transfer, $Q^{2}$, increases. Two photon exchange is strongly favored as the reason for this discrepancy and this experiment assesses the contribution of two-photon exchange in $e$-$N$ elastic scattering processes by elastically scattering electrons off neutrons in a deuterium target. The scattered electrons were detected in the BigBite spectrometer --- which is equipped with a Gas Electron Multiplier (GEM) detector-based tracker --- while the scattered nucleons were detected in a hadron calorimeter located behind the SBS magnet. High background rates (100 kHz/cm$^{2}$) were present during the experiment and require rejection and clean-track reconstruction techniques for proper extraction of physics results. This talk will discuss the nTPE experiment, GEM detector background rejection techniques, and some preliminary analysis results.