Evidence of Electron Neutrino Appearance in a Muon Neutrino Beam

TL;DR

The T2K experiment provides evidence for electron neutrino appearance in a muon neutrino beam, supporting neutrino oscillation phenomena and measuring the mixing angle _{13}.

Contribution

This work presents the first statistically significant evidence of  neutrino appearance at the atmospheric mass splitting, using data from the T2K experiment.

Findings

Observed 11 electron neutrino events at Super-Kamiokande.

Background-only hypothesis rejected with 3.1c sigma significance.

Measured _{13} mixing angle as approximately 0.088.

Abstract

The T2K collaboration: reports evidence for electron neutrino appearance at the atmospheric mass splitting, |\Delta m_{32}^2|=2.4x10^{-3} eV^2. An excess of electron neutrino interactions over background is observed from a muon neutrino beam with a peak energy of 0.6 GeV at the Super-Kamiokande (SK) detector 295 km from the beam's origin. Signal and background predictions are constrained by data from near detectors located 280 m from the neutrino production target. We observe 11 electron neutrino candidate events at the SK detector when a background of 3.3\pm0.4(syst.) events is expected. The background-only hypothesis is rejected with a p-value of 0.0009 (3.1\sigma), and a fit assuming \nu_{\mu}->\nu_e oscillations with sin^2(2\theta_{23})=1, \delta_{CP}=0 and |\Delta m_{32}^2|=2.4x10^{-3} eV^2 yields sin^2(2\theta_{13})=0.088^{+0.049}_{-0.039}(stat.+syst.).