Measurement of Muon Antineutrino Oscillations with an Accelerator-Produced Off-Axis Beam
hep-ex
/ Authors
T2K collaboration, K. Abe, C. Andreopoulos, M. Antonova, S. Aoki, A. Ariga, S. Assylbekov, D. Autiero, M. Barbi, G. J. Barker
and 319 more authors
G. Barr, P. Bartet-Friburg, M. Batkiewicz, F. Bay, V. Berardi, S. Berkman, S. Bhadra, A. Blondel, S. Bolognesi, S. Bordoni, S. B. Boyd, D. Brailsford, A. Bravar, C. Bronner, M. Buizza Avanzini, R. G. Calland, S. Cao, J. Caravaca Rodríguez, S. L. Cartwright, R. Castillo, M. G. Catanesi, A. Cervera, D. Cherdack, N. Chikuma
/ Abstract
T2K reports its first measurements of the parameters governing the disappearance of $\barν_μ$ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic $\barν_μ$ 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 $\barν_μ$ survival probability is expected to be minimal. Using a dataset corresponding to $4.01 \times 10^{20}$ protons on target, $34$ fully contained $μ$-like events were observed. The best-fit oscillation parameters are $\sin^2 (\barθ_{23}) = 0.45$ and $|Δ\bar{m}^2_{32}| = 2.51 \times 10^{-3}$ eV$^2$ with 68% confidence intervals of 0.38 - 0.64 and 2.26 - 2.80 $\times 10^{-3}$ eV$^2$ respectively. These results are in agreement with existing antineutrino parameter measurements and also with the $ν_μ$ disappearance parameters measured by T2K.