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
σ
when compared to
4.92
±
0.55
expected background events. In the Pontecorvo-Maki-Nakagawa-Sakata mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles
θ
12
,
θ
23
,
θ
13
, a mass difference
Δ
m
2
32
and a
C
P
violating phase
δ
C
P
. In this neutrino oscillation scenario, assuming
|
Δ
m
2
32
|
=
2.4
×
10
−
3
 
 
eV
2
,
sin
2
θ
23
=
0.5
, and
Δ
m
2
32
>
0
(
Δ
m
2
32
<
0
), a best-fit value of
sin
2
2
θ
13
=
0.14
0
+
0.038
−
0.032
(
0.17
0
+
0.045
−
0.037
) is obtained at
δ
C
P
=
0
. When combining the result with the current best knowledge of oscillation parameters including the world average value of
θ
13
from reactor experiments, some values of
δ
C
P
are disfavored at the 90% C.L