A study of atmospheric neutrino oscillations in the MINOS far detector

Thesis/Dissertation · Mon Aug 01 00:00:00 EDT 2005

DOI:https://doi.org/10.2172/892420· OSTI ID:892420

Blake, Andrew ^[1]

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1. Univ. of Cambridge (United Kingdom)

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 flavors. This would imply that neutrinos possess mass and that neutrino flavors 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 v_μ and $$\bar{v}$$_μ 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 at anti-neutrinos. This represents the first direct observation of atmospheric v_μ and $$\bar{v}$$_μ charged current interactions. A maximum likelihood analysis us used to determine the allowed region for the oscillation parameters Δm$$2\atop{23}$$ and sin²2θ₂₃. This disfavors the null oscillation hypothesis at the 79% confidence level. With the current low statistics, the sensitivity of the analysis is limited. The expected future sensitivity of the atmospheric neutrino analysis is discussed.

• Research Organization: Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-76CH03000
• OSTI ID: 892420
• Report Number(s): FERMILAB-THESIS-2005-77; TRN: US0701350
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CALORIMETERS
CHARGED-CURRENT INTERACTIONS
COSMIC MUONS
HYPOTHESIS
MAGNETIC FIELDS
MINNESOTA
NEUTRINO OSCILLATION
NEUTRINOS
OSCILLATIONS
SAMPLING
SENSITIVITY
STANDARD MODEL
STATISTICS
WEAK INTERACTIONS
Astrophysics
Experiment-HEP