$K^{0}_{L}\rightarrow \pi^{0} \nu \bar{\nu}$ at KOTO

Abstract

The KOTO experiment aims to discover the rare decay $K^{0}_{L}\rightarrow \pi^{0} \nu \bar{\nu}$ at J-PARC. This mode breaks the CP symmetry directly and is highly suppressed in the Standard Model. Thus the mode is sensitive to new physics, in particular to the models related to CP violation. We performed the first physics run in May 2013. Although the data taking was terminated after 100 hours due to an accident, the single event sensitivity for the $K^{0}_{L}\rightarrow \pi^{0} \nu \bar{\nu}$ decay reached $1.29\times10^{-8}$, which was comparable to the sensitivity of the prior experiment. We observed one candidate event while $0.36\pm0.16$ background events were expected.