Pixel Sensor Evaluation and Track Fitting for the Mu3e Experiment

Mu3e is a proposed new experiment that searches for the lepton flavour changing muon decay µ⁺ → e⁺e⁻e⁺ with a projected sensitivity of 1 in 10¹⁶ decays. This decay is extremely suppressed in the Standard Model and an observation would be a clear sign of new physics. The muons are stopped on a target and decay electrons are measured in a magnetic spectrometer with a pixel detector. A low material budget and special algorithms are required to reconstruct the low momentum, strongly curved tracks with high precision at high rates. In this work, I present the first systematic performance evaluation of the Mu3e high voltage monolithic active pixel sensor prototypes using test beam measurements at DESY. I showed that this novel technology allows sensor efficiencies above 99%. In addition, I characterized a new track fit based on hit triplets. This fast fit is optimized to reconstruct multiple scattering dominated tracks and is suitable for Mu3e online tracking. For a precise offline reconstruction, I adapted the advanced general broken lines fit. It allows an increase in momentum resolution of up to 20% compared to the best fast algorithm. The systematic pixel sensor and track fit evaluation with the corresponding software development is a cornerstone for Mu3e tracking

Efficiency and timing performance of the MuPix7 high-voltage monolithic active pixel sensor

The MuPix7 is a prototype high voltage monolithic active pixel sensor with 103 times 80 um2 pixels thinned to 64 um and incorporating the complete read-out circuitry including a 1.25 Gbit/s differential data link. Using data taken at the DESY electron test beam, we demonstrate an efficiency of 99.3% and a time resolution of 14 ns. The efficiency and time resolution are studied with sub-pixel resolution and reproduced in simulations.Comment: 7 pages, 13 figures, submitted to Nucl.Instr.Meth.

TrackML high-energy physics tracking challenge on Kaggle

The High-Luminosity LHC (HL-LHC) is expected to reach unprecedented collision intensities, which in turn will greatly increase the complexity of tracking within the event reconstruction. To reach out to computer science specialists, a tracking machine learning challenge (TrackML) was set up on Kaggle by a team of ATLAS, CMS, and LHCb physicists tracking experts and computer scientists building on the experience of the successful Higgs Machine Learning challenge in 2014. A training dataset based on a simulation of a generic HL-LHC experiment tracker has been created, listing for each event the measured 3D points, and the list of 3D points associated to a true track.The participants to the challenge should find the tracks in the test dataset, which means building the list of 3D points belonging to each track.The emphasis is to expose innovative approaches, rather than hyper-optimising known approaches. A metric reflecting the accuracy of a model at finding the proper associations that matter most to physics analysis will allow to select good candidates to augment or replace existing algorithms

MuPix & ATLASpix: Architectures and Results

High Voltage Monolithic Active Pixel Sensors (HV-MAPS) are based ona commercial High Voltage CMOS process and collect charge by driftinside a reversely biased diode. HV-MAPS represent a promising technology for future pixel tracking detectors. Two recent developments are presented. The MuPix has a continuous readout and is being developed for the Mu3e experiment whereas the ATLASPix is being developed for LHC applications with a triggered readout. Both variants have a fully monolithic design including state machines, clock circuitries and serial drivers. Several prototypes and design variants were characterised in the lab and in testbeam campaigns to measure efficiencies, noise, time resolution and radiation tolerance. Results from recent MuPix and ATLASPix prototypes are presented and prospects for future improvements are discussed.High Voltage Monolithic Active Pixel Sensors (HV-MAPS) are based on a commercial High Voltage CMOS process and collect charge by drift inside a reversely biased diode. HV-MAPS represent a promising technology for future pixel tracking detectors. Two recent developments are presented. The MuPix has a continuous readout and is being developed for the Mu3e experiment whereas the ATLASPix is being developed for LHC applications with a triggered readout. Both variants have a fully monolithic design including state machines, clock circuitries and serial drivers. Several prototypes and design variants were characterised in the lab and in testbeam campaigns to measure efficiencies, noise, time resolution and radiation tolerance. Results from recent MuPix and ATLASPix prototypes are presented and prospects for future improvements are discussed