Abstract:
The T2K experiment observes indications of ! e appearance in data accumulated with
1:43 1020 protons on target. Six events pass all selection criteria at the far detector. In a three-
avor neutrino oscillation scenario with j m2
23j = 2:4 103 eV2, sin2 2 23 = 1 and sin2 2 13 = 0,
the expected number of such events is 1.5 0.3(syst.). Under this hypothesis, the probability to
observe six or more candidate events is 7 103, equivalent to 2.5 signi cance. At 90% C.L.,
the data are consistent with 0.03(0.04)< sin2 2 13 < 0.28(0.34) for CP = 0 and normal (inverted)
hierarchy.