Indication of Electron Neutrino Appearance from an Accelerator-produced Off-axis Muon Neutrino Beam

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 10����3 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 10����3, 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.