T2K measurements of muon neutrino and antineutrino disappearance using 3.13 x 10(21) protons on target

Abstract

We report measurements by the T2K experiment of the parameters θ 23 and Δ m 2 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 × 10 21 protons on target (POT) in neutrino mode and 1.64 × 10 21 POT in antineutrino mode are used. The best-fit values obtained by T2K were sin 2 ( θ 23 ) = 0.51 + 0.06 − 0.07 ( 0.43 + 0.21 − 0.05 ) and Δ m 2 32 = 2.47 + 0.08 − 0.09 ( 2.50 + 0.18 − 0.13 ) × 10 − 3 eV 2 / c 4 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.