The Mu3e experiment is designed to search for the rare charged lepton flavor violating muon decay μ+ → e+e−e+. The goal is to observe this decay, if its branching fraction is larger than 10−16, or to exclude it. Since this process is heavily suppressed in the Standard Model of particle physics, observing this decay would be a clear indication of new physics. The experiment, located at the Paul Scherrer Institute (PSI) in Villigen (Switzerland), will use the most intense continuous surface muon beam in the world to produce the muons at a rate of 108 muons per second. To achieve this goal, the detector requires wide acceptance, good momemtum and vertex resolution, as well as precise timing information. This experiment is based on thin high-voltage monolithic active silicon pixel sensors (HV-MAPS) for precise tracking in conjuction with a scintillating fiber (SciFi) and a tile detector for precise timing information.
This thesis presents the work done in the development of the SciFi detector, one of the timing detectors of the Mu3e experiment. Different 250μm diameter round scintillating fibers have been studied and compared, with a primary focus on their timing performances. The NOL-11 fiber has the best timing with a time resolution of ≃250 ps. Additionally, the importance of maximizing the number of detected photons to enhance the timing performance of the fibers is discussed. The mean time analysis further demonstrated as a reliable time measurement observable, independent of the particle’s crossing point.
Next, the performance of the SciFi detector with different scintillating fiber ribbons and configurations has been studied. In the study, a time resolution of 245 ps with an efficiency of 97% has been achieved with a 3-layer ribbon using SCSF-78 fibers assembled with black epoxy. Further studies have shown that the addition of a fourth layer of fibers to the ribbon improved the time resolution by around 15%. Other studies are also presented, such as the effect on the time resolution and the efficiency when the number of fiber layers or the crossing angle change.
Moreover the development of the latest SciFi readout board, SciFi Module Board (SMB), is presented. The SMB is designed to host 4 MuTRiGv3 ASICs within a compact size due to space limitations in the Mu3e experiment. A description of the design, components and integration process of the SMB into the SciFi detector are provided. A description of the calibration and verification procedures to ensure the proper functioning of the SMB are also outlined. The MuTRiG ASICs are also detailed and characterized with additional studies.
In summary, this thesis significantly contributes to understanding the potential of the SciFi detector in high-precision, high-rate particle physics experiments like the Mu3e experiment. It identifies key areas for optimization in scintillating fibers and detectors, setting a basis for future enhancements.
