Improved constraints on neutrino mixing from the T2K experiment with 3.13×1021 protons on target

Abstract

The T2K experiment reports updated measurements of neutrino and antineutrino oscillations using both appearance and disappearance channels. This result comes from an exposure of 14.9 ( 16.4 ) × 1 0 20 protons on target in neutrino (antineutrino) mode. Significant improvements have been made to the neutrino interaction model and far detector reconstruction. An extensive set of simulated data studies have also been performed to quantify the effect interaction model uncertainties have on the T2K oscillation parameter sensitivity. T2K performs multiple oscillation analyses that present both frequentist and Bayesian intervals for the Pontecorvo-Maki-Nakagawa-Sakata parameters. For fits including a constraint on sin 2 θ 13 from reactor data and assuming normal mass ordering T2K measures sin 2 θ 23 = 0.53 + 0.03 − 0.04 and Δ m 2 32 = ( 2.45 ± 0.07 ) × 10 − 3 eV 2 c − 4 . The Bayesian analyses show a weak preference for normal mass ordering (89% posterior probability) and the upper sin 2 θ 23 octant (80% posterior probability), with a uniform prior probability assumed in both cases. The T2K data exclude CP conservation in neutrino oscillations at the 2 σ level.