T2K (Tokai to Kamiokande) is a long baseline neutrino experiment located in Japan. It uses a 30 GeV proton beam at the J-PARC accelerator in Tokai to produce an intense off-axis muon neutrino beam that travels 295 km through the Earth to Super-Kamiokande. One of its primary goals is to measure neutrino oscillation parameters by directly detecting ν_e at Super-Kamiokande that have oscillated from the ν_μ beam. The measurement of ν_μ → ν_e oscillations are of a particular interest because this mode is sensitive to both mixing angle &thetas; ₁₃ and CP phase δ_CP of the PMNS matrix. Precise measurement of ν_μ → ν_e allows us to explore the possibility of CP violation in the lepton sector.

This dissertation will describe the recent 2013 ν_e appearance oscillation analysis using the reconstructed neutrino energy spectrum by means of a maximum likelihood fit. The data used for this analysis corresponds to 6.57 × 10²⁰ POT. A total of 28 ν _e candidate events were observed, corresponding to a 7.2 σ significance of ν_e appearance by non-zero &thetas;₁₃. These results are then combined with the world average value of &thetas;₁₃ from reactor experiments and some values of δ_CP are disfavored at the 90% CL.