We report measurements by the T2K experiment of the parameters θ23 and Δm322 governing the disappearance of muon neutrinos and antineutrinos in the three-flavor neutrino oscillation model. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, the parameters are measured separately for neutrinos and antineutrinos. Using 7.482×1020 POT in neutrino running mode and 7.471×1020 POT in antineutrino mode, T2K obtained sin2(θ23)=0.51-0.07+0.08 and Δm322=2.53-0.13+0.15×10-3 eV2/c4 for neutrinos, and sin2(θ-23)=0.42-0.07+0.25 and Δm-232=2.55-0.27+0.33×10-3 eV2/c4 for antineutrinos (assuming normal mass ordering). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed.
Abe, K., Amey, J., Andreopoulos, C., Antonova, M., Aoki, S., Ariga, A., … Żmuda, J. (2017). Updated T2K measurements of muon neutrino and antineutrino disappearance using 1.5×1021 protons on target. Physical Review D, 96(1). https://doi.org/10.1103/PhysRevD.96.011102