Search for neutron decay into an antineutrino and a neutral kaon in 0.401 megaton-years exposure of Super-Kamiokande

We searched for bound neutron decay via $n\to \bar{\nu }+K^0$ predicted by the Grand Unified Theories in 0.401 Mton$\cdot$years exposure of all pure water phases in the Super-Kamiokande detector. About 4.4 times more data than in the previous search have been analyzed by a new method including a spectrum fit to kaon invariant mass distributions. No significant data excess has been observed in the signal regions. As a result of this analysis, we set a lower limit of $7.8\times {10}^{32}$ years on the neutron lifetime at a 90% confidence level.