Speaker
Description
The Mu3e experiment at the Paul Scherrer Institute (PSI) will search for the charged lepton flavour violating decay µ⁺ → e⁺e⁻e⁺, improving the current best limit set by the SINDRUM experiment by four orders of magnitude.
Mu3e will be conducted in two phases. Phase I, currently under construction at the πE5 beamline at PSI, will utilise an intense DC surface muon beam of 10⁸ µ⁺/s to reach a single event sensitivity of 2 × 10⁻¹⁵. Phase II will exploit the future High-Intensity Muon Beam to push the sensitivity further to the 10⁻¹⁶ level.
Such an improvement in sensitivity is enabled by several key aspects of the experiment design: the availability of high-intensity muon beams, a low-material-budget tracking system consisting of the ultra-thin HV-MAPS silicon pixel detectors combined with scintillating fibre and tile detectors providing sub-ns timing resolution to reduce multiple scattering, and a high-rate data acquisition system capable of handling the large data volume produced by the detector at high beam rates. The detector system, specifically optimised for the µ⁺ → e⁺e⁻e⁺ signature, operates under a 1 T solenoidal magnetic field, enabling precise reconstruction of the decay vertex and invariant mass of the three final-state particles.
Preparations for Phase I data-taking are actively ongoing at the PSI πE5 beamline. A recent beamtime campaign in June 2025 validated key detector components - including vertex, scintillating fibre, and tile modules - and their integration with the high-intensity muon beamline under a 1 T magnetic field, marking a significant milestone in commissioning.
This contribution will present the status of the experiment, the first results from the recent beamtime campaign at PSI, and future prospects.
