Abstract
T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beams. The data include all runs from January 2010 to May 2016 and comprise 7.482×10^{20} protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 μ-like events, and 7.471×10^{20} protons on target in antineutrino mode, which yielded 4 e-like and 66 μ-like events. Reactor measurements of sin^{2}2θ_{13} have been used as an additional constraint. The one-dimensional confidence interval at 90% for the phase δ_{CP} spans the range (-3.13, -0.39) for normal mass ordering. The CP conservation hypothesis (δ_{CP}=0, π) is excluded at 90%C.L.
Highlights
Events/0.5 GeVReconstructed neutrino energy (GeV)Reconstructed neutrino energy (GeV)Unoscillated predictionBest-fit spectrum0 0 0.2 0.4 0.6 0.8 1 1.2 Reconstructed neutrino energy (GeV)sin2 θ23 1⁄4 0.528
The mixing of neutrinos in the three-flavor framework is represented by the unitary PMNS matrix, parameterized by three mixing angles, θ12, θ13, and θ23, and a CP-violating phase δCP [8]
Fit to near-detector data.—The systematic parameters in the neutrino flux and interaction models are constrained by a fit to charged current (CC) candidate samples in the ND280 [10] near detector
Summary
T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beams. The mixing of neutrinos in the three-flavor framework is represented by the unitary PMNS matrix, parameterized by three mixing angles, θ12, θ13, and θ23, and a CP-violating phase δCP [8]. Appearance probabilities allows a direct measurement of CP violation at T2K. At the flux peak energy, ACP can be as large as 0.4, including a contribution of around 0.1 due to matter effects. Depending on the polarity of the horn current, either positively or negatively charged mesons are focused, resulting in a beam largely composed of muon neutrinos or antineutrinos.
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