T2K measurements of muon neutrino and antineutrino disappearance using 3.13×1021 protons on target

Abstract

We report measurements by the T2K experiment of the parameters θ23 and Δm2 32, which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNS neutrino oscillation model at T2K’s neutrino energy and propagation distance. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, muon-like events from each beam mode are used to measure these parameters separately for neutrino and antineutrino oscillations. Data taken from 1.49 × 1021 protons on target (POT) in neutrino mode and 1.64 × 1021 POT in antineutrino mode are used. The best-fit values obtained by T2K were sin2ðθ23 Þ ¼ 0.51 þ0.06 −0.07 ð0.43 þ0.21 −0.05 Þ and Δm2 32 ¼ 2.47 þ0.08 −0.09 ð2.50 þ0.18 −0.13 Þ × 10−3 eV2=c4 for neutrinos (antineutrinos). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed. An analysis using an effective two-flavor neutrino oscillation model where the sine of the mixing angle is allowed to take nonphysical values larger than 1 is also performed to check the consistency of our data with the three-flavor model. Our data were found to be consistent with a physical value for the mixing angle.