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

TL;DR

This study searched for neutron decay into an antineutrino and a neutral kaon using extensive Super-Kamiokande data, setting a new lower limit on neutron lifetime and employing a novel spectral fit method.

Contribution

It introduces a new analysis method with spectrum fitting to improve sensitivity in neutron decay searches in Super-Kamiokande data.

Findings

No significant excess observed in the signal region.

Established a lower limit of 7.8×10^32 years on neutron lifetime.

Analyzed 0.401 Mton·years of data, more than previous studies.

Abstract

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 $7.8\times10^{32}$ years on the neutron lifetime at a 90% confidence level.