A study of atmospheric neutrino oscillations in the MINOS far detector Page: 2 of 257
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A Study of Atmospheric Neutrino Oscillations
in the MINOS Far Detector
In recent years, neutrino experiments have begun to challenge the Standard Model as-
sumption that neutrinos are massless. There is now firm evidence that neutrinos undergo
quantum mechanical oscillations between flavours. This would imply that neutrinos pos-
sess 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 under-
ground (2100 in 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,, and Fu 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 sep-
aration 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 identi-
fied charge, with 27 events tagged as neutrinos and 13 events tagged as anti-neutrinos.
This represents the first direct observation of atmospheric v, and F, charged current
interactions. A maximum likelihood analysis is used to determine the allowed region
for the oscillation parameters Am', and sin22023. This disfavours 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.
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Blake, Andrew & U., /Cambridge. A study of atmospheric neutrino oscillations in the MINOS far detector, thesis or dissertation, August 1, 2005; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc884341/m1/2/: accessed November 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.