Technical design of the phase I Mu3e experiment

TL;DR

The paper details the technical design and expected performance of the phase I Mu3e detector, aimed at detecting rare muon decay events with high sensitivity using advanced tracking and timing technologies.

Contribution

It provides a comprehensive overview of the technical design and innovative solutions for the Mu3e phase I detector to achieve high sensitivity in rare decay searches.

Findings

Design achieves a sensitivity of 2×10^{-15} for muon decay

Detector handles high muon decay rates up to 10^8 per second

Utilizes ultra thin sensors and scintillating fibers for precise measurements

Abstract

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.