# Performance of the large scale HV-CMOS pixel sensor MuPix8

## TL;DR

The MuPix8 HV-CMOS pixel sensor demonstrates high efficiency and sub-10 nanosecond time resolution, validating its scalability for large-scale particle physics experiments like Mu3e.

## Contribution

This paper presents the first large-scale prototype of HV-MAPS technology, showing its high efficiency and fast timing capabilities for particle detection.

## Key findings

- Efficiency >99.6% in laboratory tests
- Time resolution better than 10 ns after correction
- Scalability of HV-MAPS technology proven

## Abstract

The Mu3e experiment is searching for the charged lepton flavour violating decay $ \mu^+\rightarrow e^+ e^- e^+ $, aiming for an ultimate sensitivity of one in $10^{16}$ decays. In an environment of up to $10^9$ muon decays per second the detector needs to provide precise vertex, time and momentum information to suppress accidental and physics background. The detector consists of cylindrical layers of $50\, \mu\text{m}$ thin High Voltage Monolithic Active Pixel Sensors (HV-MAPS) placed in a $1\,\text{T}$ magnetic field. The measurement of the trajectories of the decay particles allows for a precise vertex and momentum reconstruction. Additional layers of fast scintillating fibre and tile detectors provide sub-nanosecond time resolution. The MuPix8 chip is the first large scale prototype, proving the scalability of the HV-MAPS technology. It is produced in the AMS aH18 $180\, \text{nm}$ HV-CMOS process. It consists of three sub-matrices, each providing an untriggered datastream of more than $10\,\text{MHits}/\text{s}$. The latest results from laboratory and testbeam characterisation are presented, showing an excellent performance with efficiencies $>99.6\,\text{\%}$ and a time resolution better than $10\, \text{ns}$ achieved with time walk correction.