Indication of electron neutrino appearance from an accelerator-produced off-axis muon neutrino beam.

T2K (Tokai to Kamioka) is a long baseline neutrino experiment with the primary goal of measuring the neutrino mixing angle 13. It uses a muon neutrino beam, produced at the J-PARC accelerator facility in Tokai, sent through a near detector complex on its way to the far detector, Super-Kamiokande. Appearance of electron neutrinos at the far detector due to oscillation is used to measure the value of 13. This dissertation describes the experimental setup, analysis methods, and results from the analysis of T2K data taken from January 2010 through March 2011. Six signal candidate events were observed on an expected background of 1:5 0:3. The probability to see six or more such events is 0.7% under the 13 = 0 hypothesis. This is the first experiment to exclude 13 = 0 at the 90% confidence level. The 90% confidence level allowed region is 0:03p0:04q   sin2 2 13   0:28p0:34q with a best fit point of sin2 2 13 = 0:11p0:14q for CP = 0 and | m2 32| = 2:4 x 10-3 eV2 in the normal (inverted) hierarchy.