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[subscript]μ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic ¯ν[subscript]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[subscript]μ survival probability is expected to be minimal. Using a data set corresponding to 4.01 × 10[superscript]20 protons on target, 34 fully contained μ-like events were observed. The best-fit oscillation parameters are sin[superscript]2(¯θ[subscript]23) = 0.45 and |Δ¯m[subscript]232| = 2.51 × 10[superscript]−3 eV[superscript]2 with 68% confidence intervals of 0.38–0.64 and 2.26–2.80 × 10[superscript]−3 eV[superscript]2, respectively. These results are in agreement with existing antineutrino parameter measurements and also with the ν[subscript]μ disappearance parameters measured by T2K.enArticleDepartment of Physics and Astronomy