Research

The main goal of the Mu3e experiment  at PSI  is to search for the Lepton-Flavour-Number violating decay  of positively charged muons to a positron and an electron/positron pair. This decay is "forbidden" in the Standard Model of Particle Physics (with a predicted branching fraction of the order of 10^-54). Its experimental observation would therefore provide unequivocal proof of physics Beyond the Standard Model (BSM). The non-observation of a signal should allow Mu3e to significantly improve on existing experimental limits and thereby put constraints on a variety of BSM models. The currently best upper experimental  limit on the Branching Fraction for this decay (10^-12 at 90% confidence level) was established by the SINDRUM experiment at PSI more than 35 years ago in a measurement in which a team  from UZH played a prominent role. Using the existing Compact Muon Beam Line at PSI, Mu3e aims to improve this limit by three  orders of magnitude. Using a new High Intensity Muon Beam (HiMB) and a phase-2 detector, a further improvement by another order of magnitude could be possible. The measurement presents significant experimental challenges. One of the biggest of these is due to the very low momentum of the electrons and positrons produced in decays of muons at rest. Very low-mass solutions for detectors and detector services need to be employed to limit energy loss and  multiple scattering of these low-momentum particles such that their  trajectories and  momenta can be measured with the required precision. These stringent requirements have led to the development of a tracking system based on a novel detector technology, Monolithic Active Pixel Sensors designed in a High-Voltage tolerant CMOS process (HV-MAPS). The tracking system consists of a vertex detector and so-called outer tracking layers. Our group contributes to the construction  and commissioning of the veretx detector surrounding the Mu3e target.

Initially, it was a small group under the leadership of Prof. Ulrich (Ueli) Straumann who joined the Mu3e experiment at PSI. Their contribution to the experiment culminated in the PhD thesis  of Dr. Roman Gredig, with the title "Scintillating Fibre Detector for the Mu3e Experiment". After an intermission following Ueli Straumann's retirement, a group led by Profs. Nicola Serra and Olaf Steinkamp revived the Mu3e activities at UZH, now contributing to the HV-MAPS based vertex detector of the experiment. Thomas Senger (PhD student) and Vadym Denysenko (PostDoc) make significant contributions to the construction and quality assurance of the first detector modules, the assembly of the detector and preparations for a commissioning run using cosmics.

If you are interested in joining our effort for your Bachelor or Master thesis, please do not hesitate to contact one of us.