Results from T2K: A joint analysis of neutrino and antineutrino data

Abstract

We report the results of a joint analysis of neutrino and antineutrino oscillations at T2K with the disappearance and appearance channels. The disappearance channel is primarily sensitive to sin2 2θ23 and the mass splitting , while νμ → νe is sensitive to sin2 θ23 and sin2 2θ13, with the CP violating phase δCP and matter effects inducing asymmetries in the oscillation probabilities between the CP conjugate channels. Since the Neutrino 2016 conference, a small increment of data has been added to the analysis, so that the accumulated protons-on-target are 7.48 × 1020 in ν-mode and 7.47 × 1020 in mode. The data continue to favor maximal mixing in θ23 with a 1 σ confidence interval of [0.464, 0.578] for sin2 θ23, while the large νe appearance observed in the data favors δCP ∼ −π/2 with a 90% confidence interval of [-3.13, -0.39] in normal hierarchy and [-2.09, -0.74] in inverted hierarchy. We comment briefly on the future prospects for T2K, including a proposal for extended running to accumulate 20 × 1021 protons-on-target, nearly three times the currently approved amount by 2026, to gain substantial sensitivity to CP violating effects in oscillations if parameters are favorable.