Search for the rare decay mü ---> eee with a high rate experiment based on thin Monolithic Active Pixel Sensors

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The standard model of elementary particle physics encompasses three electron-like particles (the electron, the muon and the tau) and three neutrinos, together known as leptons. It was long believed that the number of leptons of each kind (flavour ) is conserved. Since the discovery of neutrino oscillations it is known that this is not the case; transitions violating charged lepton flavour have however so far eluded detection. The mechanism for and size of lepton flavour violating interactions are of great interest, as they are linked to the generation of neutrino masses, CP violation and new physics beyond the standard model. This project is for an experiment searching for the lepton flavour violating transition μ+ → e+e−e+ with a sensitivity of one in 1016 μ decays. In order to reach that sensitivity, the momenta of the decay electrons from up to a billion μ decays per second have to be precisely reconstructed by a detector built from thin silicon high-voltage monolithic active pixel sensors (HV-MAPS). This project encompasses the design, construction and operation of such a detector (the first of its kind), with a focus on the associated electronics and on-line track reconstruction methods implemented on powerful electronics components such as Field Programmable Gate Arrays (FPGAs) and Graphics Processing Units (GPUs).