Searching e⁺e^- Final States for New Physics With an Invariant Mass of 10-20 MeV at the ARIEL Electron Accelerator

Reported anomalies in ⁴He and ⁸Be transitions, along with the disagreement between calculated and measured values of muonic g-2, which has been recently reiterated by the Fermliab g-2 experiment, have heightened interest in a potential new particle near 17 MeV. To evade current limits, this particle would need to be proto-phobic, and hence suppressed in hadronic production. Leptonic searches, such as production and decay in electron-nucleus scattering, eX → eXA' → eXee⁺, can test leptonic couplings directly. The DarkLight collaboration of US and Canadian institutions has recently been approved to mount such a search at TRIUMF's ARIEL accelerator, using magnetic spectrometers to reconstruct candidate e⁺e^- pairs in electron scattering from tantalum. Initial data is expected to take place with a 31 MeV, 150 µA beam, with higher beam energies expected to be available in the future. A brief review of the physics involved will be presented, as will the details of the planned experiment and its expected sensitivities to new physics.