  The T2K experiment has observed electron neutrino appearance in a muon
neutrino beam produced 295 km from the Super-Kamiokande detector with a peak
energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an
energy distribution consistent with an appearance signal, corresponding to a
significance of 7.3$\sigma$ when compared to 4.92 $\pm$ 0.55 expected
background events. In the PMNS mixing model, the electron neutrino appearance
signal depends on several parameters including three mixing angles
$\theta_{12}$, $\theta_{23}$, $\theta_{13}$, a mass difference $\Delta
m^2_{32}$ and a CP violating phase $\delta_{\mathrm{CP}}$. In this neutrino
oscillation scenario, assuming $|\Delta m^2_{32}| = 2.4 \times 10^{-3}$ $\rm
eV^2$, $\sin^2 \theta_{23} = 0.5$, and $\Delta m^2_{32} >0$ ($\Delta m^2_{32}
<0$), a best-fit value of $\sin^2 2 \theta_{13}$ = $0.140^{+0.038}_{-0.032}$
($0.170^{+0.045}_{-0.037}$) is obtained at $\delta_{\mathrm{CP}}=0$. When
combining the result with the current best knowledge of oscillation parameters
including the world average value of $\theta_{13}$ from reactor experiments,
some values of $\delta_{\mathrm{CP}}$ are disfavored at the 90% CL.
