Search for Electron Antineutrino Appearance in a Long-baseline Muon Antineutrino Beam

Brailsford, D. and Dealtry, T. and Doyle, T. A. and Finch, A. J. and Knox, A. and Kormos, L. L. and Lawe, M. and Nowak, J. and O'Keeffe, H. M. and Ratoff, P. N. and Walsh, J. G. (2020) Search for Electron Antineutrino Appearance in a Long-baseline Muon Antineutrino Beam. Physical review letters, 124: 161802. ISSN 1079-7114

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Abstract

Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the 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{\sigma} 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.