Search for n-nbar oscillation in Super-Kamiokande

A search for neutron-antineutron ($n-\bar{n}$) oscillation was undertaken in Super-Kamiokande using the 1489 live-day or $2.45\times {10}^{34}$ neutron-year exposure data. This process violates both baryon and baryon minus lepton numbers by an absolute value of two units and is predicted by a large class of hypothetical models where the seesaw mechanism is incorporated to explain the observed tiny neutrino masses and the matter-antimatter asymmetry in the Universe. No evidence for $n-\bar{n}$ oscillation was found, the lower limit of the lifetime for neutrons bound in ${}^{16}$O, in an analysis that included all of the significant sources of experimental uncertainties, was determined to be $1.9\times {10}^{32}$~years at the 90% confidence level. The corresponding lower limit for the oscillation time of free neutrons was calculated to be $2.7 \times 10^8$susingatheoreticalvalueofthenuclearsuppressionfactorof$0.517 \times 10^{23}$s$^{-1}$ and its uncertainty.