Ultra-low material pixel layers for the Mu3e experiment

TL;DR

This paper presents a low-material-budget pixel detector design for the Mu3e experiment, utilizing advanced thin sensors, flexible circuits, and helium cooling to achieve minimal radiation length.

Contribution

It introduces a novel combination of thinned HV-CMOS sensors, ultra-thin flexible circuits, and helium cooling to meet strict material budget requirements.

Findings

Achieved approximately 0.1% radiation length per pixel layer.

Demonstrated feasibility of using HV-CMOS technology for low-mass detectors.

Developed a cooling solution based on helium gas for minimal material impact.

Abstract

The upcoming Mu3e experiment will search for the charged lepton flavour violating decay of a muon at rest into three electrons. The maximal energy of the electrons is 53 MeV, hence a low material budget is a key performance requirement for the tracking detector. In this paper we summarize our approach to meet the requirement of about 0.1 % of a radiation length per pixel detector layer. This includes the choice of thinned active monolithic pixel sensors in HV-CMOS technology, ultra-thin flexible printed circuits, and helium gas cooling.