# Technical design of the phase I Mu3e experiment

Arndt, K, Augustin, H, Baesso, P, Berger, N, Berg, F, Betancourt, C, Bortoletto, D, Bravar, A, Briggl, K, Bruch, D vom
et al (show 95 more authors) Technical design of the phase I Mu3e experiment. Nuclear Instruments and Methods in Physics Research Section A:, 1014. 2021 - ?.

The Mu3e experiment aims to find or exclude the lepton flavour violating decay $\mu \rightarrow eee$ at branching fractions above $10^{-16}$. A first phase of the experiment using an existing beamline at the Paul Scherrer Institute (PSI) is designed to reach a single event sensitivity of $2\cdot 10^{-15}$. We present an overview of all aspects of the technical design and expected performance of the phase~I Mu3e detector. The high rate of up to $10^{8}$ muon decays per second and the low momenta of the decay electrons and positrons pose a unique set of challenges, which we tackle using an ultra thin tracking detector based on high-voltage monolithic active pixel sensors combined with scintillating fibres and tiles for precise timing measurements.