New Results from the T2K Experiment: Observation of $\nu_e$ Appearance in a $\nu_\mu$ Beam

Abstract

The T2K Experiment has observed the appearance of electron neutrinos in a muon-neutrino beam. Twenty eight neutrino candidates pass the selection cuts with a predicted background of $4.64 \pm 0.53$ events, which corresponds to a 6.8$\sigma$ exclusion of $\theta_{13} = 0$. When comparing the $\theta_{13} = 0$ hypothesis to the best fit of the full electron momentum and angle distribution, $\theta_{13} = 0$ is excluded at 7.5$\sigma$ for $\sin^2 2\theta_{23} = 1$ and $\delta_{CP} = 0$. In addition, results from the T2K $\nu_\mu$ disappearance analysis have also been updated to improve the treatment of full 3-flavor oscillations.