Projections for Dark Photon Searches at Mu3e

TL;DR

This paper proposes that the upcoming Mu3e experiment can effectively search for dark photons in muon decays, exploring new parameter space without modifications to the existing setup.

Contribution

It demonstrates the potential of Mu3e to probe unexplored dark photon parameter space through muon decay channels, with significant sensitivity.

Findings

Mu3e can probe kinetic-mixing parameter epsilon^2 down to 10^{-7} and 10^{-8}.

The experiment can explore a large fraction of currently unexplored dark photon parameter space.

No modifications to the existing Mu3e setup are needed.

Abstract

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 x 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 ~ 10^{-7} (10^{-8}). No modifications of the existing Mu3e setup are required.