Measurements of neutrino oscillation in appearance and disappearance channels by the T2K experiment with 6.6×10 20 protons on target

Abstract

We report on measurements of neutrino oscillation using data from the T2K long-baseline neutrino experiment collected between 2010 and 2013. In an analysis of muon neutrino disappearance alone, we find the following estimates and 68% confidence intervals for the two possible mass hierarchies: normal hierarchy∶ sin2θ23 ¼ 0.514þ0.055 −0.056 and Δm2 32 ¼ ð2.51 0.10Þ × 10−3 eV2=c4 and inverted hierarchy∶ sin2θ23 ¼ 0.511 0.055 and Δm2 13 ¼ ð2.48 0.10Þ × 10−3 eV2=c4. The analysis accounts for multinucleon mechanisms in neutrino interactions which were found to introduce negligible bias. We describe our first analyses that combine measurements of muon neutrino disappearance and electron neutrino appearance to estimate four oscillation parameters, jΔm2j, sin2 θ23, sin2 θ13, δCP, and the mass hierarchy. Frequentist and Bayesian intervals are presented for combinations of these parameters, with and without including recent reactor measurements. At 90% confidence level and including reactor measurements, we exclude the region δCP ¼ ½0.15; 0.83 π for normal hierarchy and δCP ¼ ½−0.08; 1.09 π for inverted hierarchy. The T2K and reactor data weakly favor the normal hierarchy with a Bayes factor of 2.2. The most probable values and 68% one-dimensional credible intervals for the other oscillation parameters, when reactor data are included, are sin2θ23 ¼ 0.528þ0.055 −0.038 and jΔm2 32j ¼ ð2.51 0.11Þ × 10−3 eV2=c4.