The Mu3e experiment aims to find or exclude the lepton flavour violating
decay μ→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⋅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
108 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.Comment: 114 pages, 185 figures. Submitted to Nuclear Instruments and Methods
A. Edited by Frank Meier Aeschbacher This version has many enhancements for
better readability and more detail