Current status of the T2K experiment

Abstract

The T2K long-baseline neutrino-oscillationexperiment was started in January 2010 for the purpose of physics data-taking. Until the massive earthquake on March 11, 2011 in Japan, $1.43\times 10^{20}$ pot data were accumulated. In this data, 6 possible $\nu_{e}$ appearance candidates are found forexpected background of 1.5$\pm$0.3(syst.)if $\sin^{2}2\theta_{13}=0$ is assumed.The probability that 6 or more events can be observed for1.5$\pm$0.3 expected events is 7$\times10^{-3}$,equivalent to 2.5$\sigma$ significance. This is the first indication of a $\nu_{e}$ appearance or, in other words, the first indication of a non-zero $\sin^{2}2\theta_{13}$.