Abe, K.Andreopoulos, C.Antonova, M.Aoki, S.Ariga, A.Assylbekov, S.Autiero, D.Barbi, M.Barker, G.J.Barr, G.Bartet-Friburg, P.Batkiewicz, M.Bay, F.Berardi, V.Berkman, S.Bhadra, S.Blondel, A.Bolognesi, S.Karlen, Deanet al.2021-05-112021-05-1120162016Abe, K., Andreopoulos, C., Antonova, M., Aoki, S., Ariga, A., Karlen, D., … Żmuda, A. (2016). Measurement of Muon Antineutrino Oscillations with an Accelerator-Produced Off-Axis Beam. Physical Review Letters, 116(18), 1-8. https://doi.org/10.1103/PhysRevLett.116.181801.https://doi.org/10.1103/PhysRevLett.116.181801http://hdl.handle.net/1828/12970T2K reports its first measurements of the parameters governing the disappearance of ¯ ν μ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic ¯ ν μ beam, produced with a peak energy of 0.6 GeV at J-PARC, is observed at the far detector Super-Kamiokande, 295 km away, where the ¯ ν μ survival probability is expected to be minimal. Using a data set corresponding to 4.01 × 10 20 protons on target, 34 fully contained μ -like events were observed. The best-fit oscillation parameters are sin 2 ( ¯ θ 23 ) = 0.45 and | Δ ¯ m 2 32 | = 2.51 × 10 − 3     eV 2 with 68% confidence intervals of 0.38 – 0.64 and 2.26 – 2.80 × 10 − 3     eV 2 , respectively. These results are in agreement with existing antineutrino parameter measurements and also with the ν μ disappearance parameters measured by T2K.enArticle