N. Berger

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.

The High-Voltage Monolithic Active Pixel Sensor for the Mu3e Experiment

Mu3e is a novel experiment searching for charged lepton flavor violation in the rare decay μ → eee. In order to reduce background by up to 16 orders of magnitude, decay vertex position, decay time and particle momenta have to be measured precisely. A pixel tracker based on 50 μm thin high voltage monolithic active pixel sensors (HV-MAPS) in a magnetic field will deliver precise vertex and momentum information. Test beam results like an excellent efficiency of >99.5% and a time resolution of better than 16.6 ns obtained with the MuPix HV-MAPS chip developed for the Mu3e pixel tracker are presented.

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.

The proposed trigger-less TBit/s readout for the Mu3e experiment

The Mu3e experiment searches for charged lepton flavor violation in the rare decay μ→eee with a projected sensitivity of 10−16. A precise measurement of the decay product momenta, decay vertex and time is necessary for background suppression at rates of 109 muons/s. This can be achieved by combining an ultra-lightweight pixel tracker based on HV-MAPS with two timing systems. The trigger-less readout of the detector with three stages of FPGA-boards over multi GBit/s optical links into a GPU filter farm is presented. In this scheme data from all sub-detectors is merged and distributed in time slices to the filter farm.

A novel experiment searching for the lepton flavour violating decay μ → eee

Since the discovery of neutrino oscillations it is known that lepton flavour is not conserved. Lepton flavour violating processes in the charged lepton sector have so far however eluded detection; as they are heavily suppressed in the standard model of particle physics, an observation would be a clear signal for new physics and help to understand the source of neutrino masses and CP violation. We propose a novel experiment searching for the decay μ → eee with the aim of ultimately reaching a sensitivity of 10−16, an improvement by four orders of magnitude compared to previous experiments. The technologies enabling this step are thin high-voltage monolithic active pixel sensors for precise tracking at high rates with a minimum of material and scintillating fibres for high resolution time measurements.

First results from the first level of the H1 fast track trigger

The H1 experiment at the electron-proton collider HERA has built a new fast track trigger to increase the selectivity for exclusive final states and to cope with the higher background rates after the HERA luminosity upgrade. Hits measured in the central jet chamber of H1 are combined to track segments by performing 5times1012 mask comparisons per second using content addressable memories (CAMs). These segments are collected and transmitted via 5 Gbit/s LVDS links to custom made multi-purpose boards and linked to tracks. The latency of the fully pipelined processing chain implemented in programmable logic (FPGAs) is 0.72 mus. During the summer 2004 running period, the FTT level one system delivered first physics triggers from which performance figures were extracted. A single hit efficiency of more than 95% was achieved, and first studies on the pT resolution of tracks were performed using triggered rho meson candidates.

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.

Multiple Coulomb scattering in thin silicon

We present a measurement of multiple Coulomb scattering of 1 to 6 GeV/c electrons in thin (50–140 μm) silicon targets. The data were obtained with the EUDET telescope Aconite at DESY and are compared to parametrisations as used in the Geant4 software package. We find good agreement between data and simulation in the scattering distribution width but large deviations in the shape of the distribution. In order to achieve a better description of the shape, a new scattering model based on a Students t distribution is developed and compared to the data.

Ultra-low material pixel layers for the Mu3e experiment

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.

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.