Abstract
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(2þeta_23)=1,
\delta_CP=0 and |\Delta m_32^2|=2.4x10^-3 eV^2 yields
sin^2(2þeta_13)=0.088^+0.049_-0.039(stat.+syst.).
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