The Mu3e Experiment at PSI

Abstract

The Mu3e experiment will search for lepton flavor violation in the neutrinoless muon decay $\mu^+ \rightarrow e^+ e^- e^+$ with a sensitivity down to $10^{-16}$(90% C.L.) using the world most intense muon beam at the Paul Scherrer Institute. This represents a four order of magnitude improvement w.r.t. previous measurements. The $\mu^+ \rightarrow e^+ e^- e^+$ decay is strongly suppressed in the Standard Model whilst several Beyond the SM models predict observable effects accessible to the new generation of LFV experiments. The search for the $\mu^+ \rightarrow e^+ e^- e^+$ decay requires a large acceptance detector capable of measuring up to $2 \times 10^9$ decays of stopped muons per second with excellent momentum, space, and time resolution to suppress backgrounds below the $10^{16}$ level. The required Mu3e detector performance is possible thanks to tracking detectors based on thin monolithic active silicon pixel sensors (HV-MAPS) and very precise timing measurements using scintillating fibers and tiles both coupled to silicon photo-multipliers. The first phase of the Mu3e experiment aiming to a sensitivity of $10^{-15}$ has been recently approved. Following an intense R&D program the collaboration is preparing for detector construction. First data taking is expected in 2019.