Steven Boi, supervised by E. Craig Dukes, passes his thesis defense!

Design and Fabrication of a Novel Large-area, High-efficiency Cosmic Ray Veto Detector for the Mu2e Experiment


I present the first Dark Matter search results using the full data set collected with the upward-going muon trigger in NOvA.

The Muon to Electron Conversion (Mu2e) experiment is a high-precision experiment being mounted at Fermilab, which will search for coherent, neutrino-less muon-to-electron conversion in the presence of an atomic nucleus. Such a process would exhibit charged lepton flavor violation (CLFV), which has not yet been observed. Mu2e is designed to improve the sensitivity by four orders of magnitude over the present limits. In the search for beyond the standard model (BSM) physics, Mu2e is uniquely sensitive to a wide range of models and indirectly probes mass scales up to the energy scale of 10^4 TeV. By design, the backgrounds for the experiment will be well understood and kept at a sub-event level, which in the event of the observation of muon-to-electron conversion, will be direct confirmation of BSM physics.

A significant background comes from processes initiated by cosmic-ray muons, which will produce approximately one CLFV-like event per day. In order to reduce this rate to less than one event over the lifetime of the experiment, a large and highly efficient cosmic-ray veto (CRV) detector is needed. The overall efficiency must be no less than 99:99%, a requirement that must be maintained in the presence of intense backgrounds produced by proton and muon beams. A novel detector was designed that employs long scintillator strips with embedded wavelength shifting fibers, read out using silicon photomultipliers. The combination of a high-light yield scintillator and state-of-the-art photosensors results in a compact, highly efficient detector that is easy to manufacture and whose design is being used or considered for use in a host of other planned experiments. The design, fabrication, and performance of the CRV is presented.

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