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Title: A study of atmospheric neutrino oscillations in the MINOS Far Detector
Author: Blake, A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2005
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In recent years neutrino experiments have begun to challenge the Standard Model assumption that neutrinos are massless. There is now firm evidence that neutrinos undergo quantum mechanical oscillations between flavours. This would imply that neutrinos possess mass and that neutrino flavours are mixed by the weak interaction. Atmospheric neutrinos, produced by the interactions of cosmic rays in the earth’s atmosphere, can be used to study these oscillations. The MINOS Far Detector has been collecting atmospheric neutrino data since 1st August 2003 using a 5.4 kT steel-scintillator sampling calorimeter located 700 m underground (2100 m water-equivalent) at the Soudan Underground Laboratory, Minnesota. The Far Detector is the first massive underground detector to possess a magnetic field. This makes the separation of atmospheric vμ and vμ charged current interactions possible for the first time. This thesis presents a study of atmospheric neutrino oscillations in the Far Detector, based on a total detector exposure of 316 days (3.3 kT-Yrs fiducial exposure). The separation of atmospheric neutrinos from the high background of cosmic muons is outlined. A total of 82 candidate events are observed, with an expectation of 109.9± 21.4 events in the absence of oscillations. Of the selected events, 40 events have a clearly identified charge, with 27 events tagged as neutrinos and 13 events tagged as anti-neutrinos. This represents the first direct observation of atmospheric vμ and v̄μ charged current interactions. A maximum likelihood analysis is used to determine the allowed region for the oscillation parameters Δm223 and sin223. This disfavours the null oscillation hypothesis at the 79% confidence level. With current low statistics, the sensitivity of the analysis is limited. The expected future sensitivity of the atmospheric neutrino analysis is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available