Abstract
An analysis of atmospheric neutrino data from all four run periods of \superk optimized for sensitivity to the neutrino mass hierarchy is presented. Confidence intervals for $\Delta m^2_{32}$, $\sin^2 \theta_{23}$, $\sin^2 \theta_{13}$ and $\delta_{CP}$ are presented for normal neutrino mass hierarchy and inverted neutrino mass hierarchy hypotheses based on atmospheric neutrino data alone. Additional constraints from reactor data on $\theta_{13}$ and from published binned T2K data on muon neutrino disappearance and electron neutrino appearance are added to the atmospheric neutrino fit to give enhanced constraints on the above parameters. Over the range of parameters allowed at 90% confidence level, the normal mass hierarchy is favored by between 91.5% and 94.5% based on the combined result.
Highlights
INTRODUCTIONParadigm based on the Pontecorvo-Maki-NakagawaSakata (PMNS) matrix [1,2]
There remain unknown parameters in the PMNS formalism, most notably the ordering of the mass states with the largest splitting, which is mathematically expressed as the sign of Δm231, and ATMOSPHERIC NEUTRINO OSCILLATION ANALYSIS
The total systematic error is assigned taking this value summed in quadrature with the time variation of the energy scale, which is measured using the variation in the average reconstructed momentum of Michel electrons and the variation in the stopping muon momentum divided by range
Summary
Paradigm based on the Pontecorvo-Maki-NakagawaSakata (PMNS) matrix [1,2] This paradigm is characterized by three mixing angles, two mass splittings, and one CP-violating phase. With all three neutrino flavors and mass states mixing, it is possible to measure the unknown CP-violating phase δCP and perhaps conclude that neutrinos and antineutrinos have different oscillation probabilities, if it is found that δCP is neither 0 nor π. Due to the presence of neutrinos and antineutrinos, the effects of matter on neutrino oscillations, and the wide variety of energies and pathlengths spanned, atmospheric neutrinos are sensitive to the unknown parameters of the PMNS formalism. Determining the mass hierarchy and measuring θ23 play an important role in interpreting any neutrino versus antineutrino oscillation difference and thereby establishing CP violation.
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