Indication of Electron Neutrino Appearance in an Accelerator-Produced Muon Neutrino Beam

Abstract

<p>T2K (Tokai to Kamioka) is a long baseline neutrino experiment with the primary goal of measuring the</p><p>neutrino mixing angle $\theta_{13}$. It uses a muon neutrino beam, produced at the J-PARC</p><p>accelerator facility in Tokai, sent through a near detector complex on its way to the far detector,</p><p>Super-Kamiokande. Appearance of electron neutrinos at the far detector due to oscillation is used to</p><p>measure the value of $\theta_{13}$.</p><p>This dissertation describes the experimental setup, analysis methods, </p><p>and results from the analysis of T2K</p><p>data taken from January 2010 through March 2011. Six signal candidate events were observed on</p><p>an expected background of $1.5\pm0.3$. The probability to see six or more such events is </p><p>0.7\% under the $\theta_{13}=0$ hypothesis. This is the first experiment to exclude </p><p>$\theta_{13}=0$ at the 90\% confidence level.</p><p>The 90\% confidence level allowed region is</p><p>$0.03 (0.04) < \mmssttot < 0.28 (0.34)$ with a best fit point of $\mmssttot = 0.11 (0.14)$ for</p><p>$\delta_{\textrm{CP}} = 0$ and $|\Delta m^{2}_{32}| = 2.4\times10^{-3}$~eV$^{2}$~in the</p><p>normal (inverted) hierarchy.</p>