A Sterile-Neutrino Search with the MINOS Experiment

Abstract

The MINOS experiment is a long-baseline neutrino oscillation experiment in the the NuMI beamline at Fermilab, USA. Using a near detector at 1 km distance from the neutrino production target, and a far detector at 735 km from the target, it is designed primarily to measure the disappearance of muon neutrinos. This thesis presents an analysis using MINOS data of the possibility of oscil- lation of the neutrinos in the NuMI beam to a hypothetical sterile flavour, which would have no Standard Model couplings. Such oscillations would result in a deficit in the neutral current interaction rate in the MINOS far detector relative to the expectation derived from the near detector data. The method used to identify neutral current and charged current events in the MINOS detectors is described and a new method of predicting and fitting the far detector spectrum presented, along with the effects of systematic uncertainties on the sterile neutrino oscillation analysis. Using this analysis, the fraction f{sub s} of the disappearing neutrinos that go to steriles is constrained to be below 0.15 at the 90% confidence level in the absence of electron neutrino appearance in the NuMI beam. With electron appearance at the CHOOZ limit, f{sub s} < 0.41 at 90% C.L.