Measurement of neutrino and antineutrino oscillations by the T2K experiment, including a new additional sample of electron neutrino interactions in the far detector

September 13, 2017

The T2K experiment reports an updated analysis of neutrino and antineutrino oscillations in appearance and disappearance channels.  A sample of electron neutrino candidates at Super-Kamiokande in which a pion decay has been tagged is added to the four single-ring samples used in previous T2K oscillation analyses.  Through combined analyses of these five samples, simultaneous measurements of four oscillation parameters, |Δm232|, sin223), sin213) and δCP, and of the mass ordering are made.  A set of studies of simulated data indicates that the sensitivity to the oscillation parameters is not limited by neutrino interaction model uncertainty.  Multiple oscillation analyses are performed, and frequentist and Bayesian intervals are presented for combinations of the oscillation parameters with and without the inclusion of reactor constraints on sin213).  When combined with reactor measurements, the hypothesis of CP conservation (δCP = 0 or π) is excluded at the 90% confidence level.  The 90% confidence region for δCP is [–2.95,–0.44] ([–1.47,–1.27]) for normal (inverted) ordering.  The central values and 68% confidence intervals for the other oscillation parameters for normal (inverted) ordering are |Δm232| = 2.54 ± 0.08 (2.51 ± 0.08) × 10–3 eV2/c4 and sin223) = 0.55–0.09+0.05 (0.55–0.08+0.05), compatible with maximal mixing.  In the Bayesian analysis, the data weakly prefer normal ordering (Bayes factor 3.7) and the upper octant for sin223) (Bayes factor 2.4).

ArXiv preprint: 1707.01048 [hep-ex]