Abe, K.Akutsu, K.Ali, A.Alt, C.Andreopoulos, C.Anthony, L.Antonova, M.Aoki, S.Ariga, A.Asada, Y.Ashida, Y.Atkin, E.T.Awataguchi, Y.Ban, S.Barbi, M.Barker, G.J.Barr, G.Barrow, D.Karlen, Deanet al.2021-05-062021-05-0620202020Abe, K., Akutsu, R., Ali, A., Alt, C., Andreopoulos, C., Karlen, D., … Zykova, A. (2020). Search for Electron Antineutrino Appearance in a Long-Baseline Muon Antineutrino Beam. Physical Review Letters, 124, 1-8. https://doi.org/10.1103/PhysRevLett.124.161802.https://doi.org/10.1103/PhysRevLett.124.161802http://hdl.handle.net/1828/12950Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40 σ and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions.enArticleDepartment of Physics and Astronomy