The Mu3e experiment: Toward the construction of an HV-MAPS vertex detector

TL;DR

The Mu3e experiment aims to detect rare muon decays by developing ultra-thin HV-MAPS sensors and helium cooling, with recent prototypes demonstrating promising performance for future high-sensitivity measurements.

Contribution

This paper presents recent advancements in HV-MAPS sensor prototypes, helium cooling systems, and module design for the Mu3e experiment's vertex detector.

Findings

MuPix10 chip shows high efficiency and good time resolution

Helium cooling system verified with a full-scale prototype

Prototype with MuPix10 will be tested in Mu3e magnet in summer 2021

Abstract

The Mu3e experiment searches for the lepton flavor violating decay $\mu^+~\rightarrow~e^+~e^+~e^-$ with an ultimate aimed sensitivity of 1 event in $10^{16}$ decays. This goal can only be achieved by reducing the material budget per tracking layer to $X/X_0 \approx 0.1 \%$. High-Voltage Monolithic Active Pixel Sensors (HV-MAPS) which are thinned to $50\ \mu m$ serve as sensors. Gaseous helium is chosen as coolant. Results of recent studies related to the sensor prototypes, the helium cooling, and module prototyping are presented. The recent chip submission MuPix10 has proven its functionality regarding efficiency and time resolution. The helium cooling system for the inner tracker could be verified using a full-scale prototype. A complete prototype equipped with MuPix10 chips will be tested inside the Mu3e magnet in summer 2021.