Mu3e

Mu3e is a particle physics experiment at the Paul Scherrer Institute, searching for decays of anti-muons (Mu) to an electron and two positrons (3e). This decay is extremely unlikely in the Standard Model of particle physics, as it changes the lepton number. Several new theories, especially supersymmetric ones, predict a much more frequent decay. Searching for this decay allows a test of these theories, even if they cannot be tested directly in other experiments like at the LHC.

Mu3e is constructed at the Paul Scherrer Institute, as it provides the world's most intense muon beam. More than one billion decays per second can be analyzed. This rate is necessary to study more than 10¹⁶ muon decays in total. Important backgrounds are the decays ${\displaystyle \mu ^{+}\to e^{+}e^{-}e^{+}{\bar {\nu _{\mu }}}\nu _{e}}$ and ${\displaystyle \mu ^{+}\to e^{+}{\bar {\nu _{\mu }}}\nu _{e}}$. To distinguish between signal and background, the detector has a spatial resolution better than 200 µm, a time resolution better than 100 ps and an energy resolution better than 0,5 MeV for the individual electrons. To minimize multiple scattering, the detector is built as light as possible. Semiconductor detectors are used for the spatial and energy resolution, scintillator fibers provide a good timing resolution. The whole experiment is in a magnetic field of 1 Tesla to determine the energy of the particles based on their curvature radius.

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