  The T2K collaboration: reports evidence for electron neutrino appearance at
the atmospheric mass splitting, |\Delta m_{32}^2|=2.4x10^{-3} eV^2. An excess
of electron neutrino interactions over background is observed from a muon
neutrino beam with a peak energy of 0.6 GeV at the Super-Kamiokande (SK)
detector 295 km from the beam's origin. Signal and background predictions are
constrained by data from near detectors located 280 m from the neutrino
production target. We observe 11 electron neutrino candidate events at the SK
detector when a background of 3.3\pm0.4(syst.) events is expected. The
background-only hypothesis is rejected with a p-value of 0.0009 (3.1\sigma),
and a fit assuming \nu_{\mu}->\nu_e oscillations with sin^2(2\theta_{23})=1,
\delta_{CP}=0 and |\Delta m_{32}^2|=2.4x10^{-3} eV^2 yields
sin^2(2\theta_{13})=0.088^{+0.049}_{-0.039}(stat.+syst.).
