Neutrino have been known to oscillate between the three flavors since the first
discoveries two decades ago. Over that time, our knowledge of the parameters which
govern these oscillations has improved significantly. The largest remaining uncertainties
in the measurement of neutrino oscillations are those that govern the tau neutrino. In this
thesis, a direct measurement of tau neutrino oscillations is performed with the IceCube
Neutrino Observatory located in the ice deep beneath the South Pole.
The measurement of atmospheric tau neutrino appearance requires a precise understanding
of backgrounds. In order to perform the measurement, improvements to the
modeling of the detector noise have been performed, reducing the uncertainties in the
noise model used in IceCube significantly. Additional improvements to the simulation
efficiency investigated during this thesis reduce the computational requirements of atmospheric
muon background events by more than three orders of magnitude. These
improvements allow, for the first time, the use of simulation of background events in
oscillation measurements performed by IceCube.
Using the DeepCore detector, a densely instrumented infill of IceCube located in the
clearest ice of the Antarctic glacier, a new selection of events has been created in the search
for tau neutrino appearance from atmospheric oscillations. Tau neutrino appearance
and muon neutrino disappearance were measured simultaneously with the new sample
from 5.6 to 56 GeV from data collected over a period of 968 days. The best fit values,
NCC
= 0.566+0.356
−0.303 for the charged current exclusive channel and NNC+CC
= 0.733+0.305
−0.243
for the neutral current inclusive channel, improve upon previous measurements set by
other experiments