Measurement of Atmospheric Neutrino Oscillation Parameters Using Three Years of IceCube-DeepCore Data

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The story of neutrinos began in 1930 when Pauli proposed a hypothesized particle

as a ``desperate remedy" to rescue quantum theory. Although Pauli was pessimistic

about the detectability of his new particle, Reins and Cowan first discovered (anti)

neutrinos in 1956. Soon after, neutrinos became a puzzle for particle physicists due

to a persistent deficit in observed rates by multiple experiments. This mystery was

partly answered by Pontecorvo who first proposed the idea of neutrino oscillations

in 1957. In 1998, the Super-Kamiokande (SK) collaboration provided the first definitive

evidence of neutrino oscillations, for which both the SK and the Sudbury Neutrino

Observatory (SNO) collaborations were awarded the Nobel Prize in Physics 2015.

While measuring oscillation parameters has long been a focus for numerous

neutrino experiments, the IceCube Neutrino Observatory with DeepCore provides

a unique window to measure atmospheric oscillation parameters. With an effective

volume $\sim$ 300 times larger than SK, DeepCore can detect atmospheric

neutrinos between a few and 100 GeV. In addition, IceCube acts as a thick veto

shield for DeepCore to better identify atmospheric muon backgrounds. Given that

the amplitude of atmospheric neutrino oscillations is expected to be maximal at

$\sim$ 25 GeV, IceCube-DeepCore is well suited for studying atmospheric neutrino

oscillations by probing this energy window for the first time.

Using three years of IceCube-DeepCore data from 2012 to 2014, this work measures

atmospheric neutrino oscillation parameters from the disappearance

of muon neutrinos. The standard three neutrino mixing and matter

effect due to Earth are considered. Under the assumption of a unitary mixing matrix,

a binned analysis using a modified $\chi^2$ is performed, and sixteen systematics

are taken into account. Preferring a normal neutrino mass ordering, this analysis

measures the mass squared difference, $\Delta$m$^2_{23} = 2.55^{+0.12}_{-0.11}

\times 10^{-3}$ eV$^2$, and the mixing angle, sin$^2 \theta_{23} = 0.58^{+0.04}_{-0.13}$.

The measurement from this work is comparable to the latest measurements from other

long baseline neutrino experiments.