Evidence of Electron Neutrino Appearance in a Muon Neutrino Beam

The T2K collaboration reports evidence for electron neutrino appearance at the atmospheric mass splitting, |Δm₃₂²|=2.4×10^-3 eV². 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±0.4(syst.) events is expected. The background-only hypothesis is rejected with a p-value of 0.0009 (3.1σ), and a fit assuming ν_μ→ν_e oscillations with sin²(2θ₂₃)=1, δ_CP=0 and |Δm₃₂²|=2.4×10^-3 eV² yields sin²(2θ₁₃)=0.088^+0.049_-0.039(stat.+syst.).

Data release

• arXiv preprint: https://arxiv.org/abs/1304.0841
• Reference: Phys. Rev. D 88, 032002 (2013)
• DOI: https://doi.org/10.1103/PhysRevD.88.032002