Ann-Kathrin Perrevoort

Overview of HVCMOS pixel sensors

High voltage CMOS (HVCMOS) sensors are presently considered for the use in Mu3e experiment, ATLAS and CLIC. These sensors can be implemented in commercial HVCMOS processes. HVCMOS sensors feature fast charge collection by drift and high radiation tolerance. The sensor element is an n-well/p-type diode. This proceeding-paper gives an overview of HVCMOS projects and the recent results.

A Tracker for the Mu3e Experiment based on High-Voltage Monolithic Active Pixel Sensors

The Mu3e experiment searches for the lepton flavour violating decay + ! e + e e + , aiming for a branching fraction sensitivity of 10 16 . This requires an excellent momentum resolution for low energy electrons, high rate capability and a large acceptance. In order to minimize multiple scattering, the amount of material has to be as small as possible. These challenges can be met with a tracker built from high-voltage monolithic active pixel sensors (HV-MAPS), which can be thinned to 50 µm and which incorporate the complete read-out electronics on the sensor chip. To further minimise material, the sensors are supported by a mechanical structure built from 25 m thick Kapton foil and cooled with gaseous helium.

Status of the Mu3e Experiment at PSI

The Mu3e experiment aims to search for the lepton-flavour violating decay μ → e+e+e− with a sensitivity to one signal decay in 1016 muon decays at a muon stopping rate of 2 × 109 muons/s. With currently available rates of 108 muons/s, a sensitivity on the branching ratio of 10−15 is the aim of the first phase. This will allow for tests of new physics models with enhanced branching ratios for lepton-flavour violating processes with an unprecedented precision. The experiment must be operated at very high muon rates all the while suppressing the background of the decay μ → e+e−e+νμνe and accidental electron-positron combinations. Therefore, a tracking detector made of thin pixel sensors with additional scintillating fibres and tiles for precise time measurement will be built. The development of the subdetectors is ongoing while detector construction is still in preparation.

The MuPix Telescope: A Thin, High-Rate Tracking Telescope

The MuPix Telescope is a particle tracking telescope, optimized for tracking low momentum particles at high rates. It is based on the novel High-Voltage Monolithic Active Pixel Sensors (HV-MAPS), designed for the Mu3e tracking detector. The telescope represents a first application of the HV-MAPS technology and also serves as test bed of the Mu3e readout chain. The telescope consists of up to eight layers of the newest prototypes, the MuPix7 sensors, which send self-triggered data via fast serial links to FPGAs, where the data is time-ordered and sent to the PC. A particle hit rate of 1 MHz per layer could be processed. Online tracking is performed with a subset of the incoming data. The general concept of the telescope, chip architecture, readout concept and online reconstruction are described. The performance of the sensor and of the telescope during test beam measurements are presented.

MuPix7—A fast monolithic HV-CMOS pixel chip for Mu3e

The MuPix7 chip is a monolithic HV-CMOS pixel chip, thinned down to 50 \mu m. It provides continuous self-triggered, non-shuttered readout at rates up to 30 Mhits/chip of 3x3 mm^2 active area and a pixel size of 103x80 \mu m^2. The hit efficiency depends on the chosen working point. Settings with a power consumption of 300 mW/cm^2 allow for a hit efficiency >99.5%. A time resolution of 14.2 ns (Gaussian sigma) is achieved. Latest results from 2016 test beam campaigns are shown.

Readout Electronics for the First Large HV-MAPS Chip for Mu3e

Mu3e is an upcoming experiment searching for charged lepton flavour violation in the rare decay μ+->e+e-e+. A silicon pixel tracker based on 50 μm thin High-Voltage Monolithic Active Pixel Sensors in a 1T magnetic field will deliver precise vertex and momentum information. The MuPix High-Voltage Monolithic Active Pixel Sensor combines pixel sensor cells with integrated analogue electronics and a complete digital readout. For the characterization of the first large MuPix system-on-chip a dedicated readout system was developed. The readout chain and the first results from the characterization of the large scale MuPix8 prototype are presented.