Search for Nucleon Decay intoμ+K0andνK0

Abstract

Observations have been made 1570 m (water equivalent) underground with an 8000-metric-ton water Cherenkov detector. During a live time of 132 days, events consistent with the decay modes $p\to {\mu }^{+}{K}^0$ and $n\to \nu K^0$ were searched for in a fiducial mass of 3300 metric tons. It is concluded that the limit on the lifetime for bound plus free protons divided by the ${\mu }^{+}{K}^0$ branching ratio is $\frac{\tau }{B}>2.6\mathrm{}\times {10}^{31}$ yr. For bound neutrons decaying into $\nu K^0$ the limit is $\frac{\tau }{B}>0.8\mathrm{}\times {10}^{31}$ yr (90% confidence level).