Projections for Dark Photon Searches at Mu3e

We show that dark photons (A') with masses ~10-80 MeV can be probed in the decay $\mu^+\to e^+ \nu_e \bar{\nu}_\mu A'$, $A' \to e^+e^-$, with the upcoming Mu3e experiment at the Paul Scherrer Institute (PSI) in Switzerland. With an expected $10^{15}$ ($5.5\times 10^{16}$) muon decays in 2015-2016 (2018 and beyond), Mu3e has the exciting opportunity to probe a substantial fraction of currently unexplored dark photon parameter space, probing kinetic-mixing parameter, $\epsilon$, as low as $\epsilon^2 \sim 10^{-7}~(10^{-8})$. No modifications of the existing Mu3e setup are required.