Type: Article
Publication Date: 2012-02-22
Citations: 100
DOI: https://doi.org/10.1103/physrevd.85.031103
We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to $1.43\ifmmode\times\else\texttimes\fi{}{10}^{20}$ protons on target, we observe 31 fully-contained single $\ensuremath{\mu}$-like ring events in Super-Kamiokande, compared with an expectation of $104\ifmmode\pm\else\textpm\fi{}14\text{ }(\mathrm{syst})$ events without neutrino oscillations. The best-fit point for two-flavor ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ oscillations is ${sin}^{2}(2{\ensuremath{\theta}}_{23})=0.98$ and $|\ensuremath{\Delta}{m}_{32}^{2}|=2.65\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{eV}}^{2}$. The boundary of the 90% confidence region includes the points $({sin}^{2}(2{\ensuremath{\theta}}_{23}),|\ensuremath{\Delta}{m}_{32}^{2}|)=(1.0,3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{eV}}^{2})$, (0.84, $2.65\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{eV}}^{2}$) and (1.0, $2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{eV}}^{2}$).