| Abstract: | The T2K collaboration reports a precision measurement of muon neutrino
disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV.
Near detector measurements are used to constrain the neutrino flux and cross
section parameters. The Super-Kamiokande far detector, which is 295 km
downstream of the neutrino production target, collected data corresponding to
$3.01 imes 10^{20}$ protons on target. In the absence of neutrino
oscillations, $205 pm 17$ (syst.) events are expected to be detected and only
58 muon neutrino event candidates are observed. A fit to the neutrino rate and
energy spectrum assuming three neutrino flavors, normal mass hierarchy and
$ heta_{23}leq pi/4$ yields a best-fit mixing angle
$sin^2(2 heta_{23})=1.000$ and mass splitting $|Delta m^2_{32}| =2.44 imes
10^{-3}$ eV$^2$/c$^4$. If $ heta_{23}geq pi/4$ is assumed, the best-fit
mixing angle changes to $sin^2(2 heta_{23})=0.999$ and the mass splitting
remains unchanged. |
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