Search for n-nbar oscillation in Super-Kamiokande

TL;DR

This study searched for neutron-antineutron oscillations in Super-Kamiokande data, setting new lower limits on neutron lifetime and oscillation time, thus testing predictions of certain baryon number violation models.

Contribution

The paper provides the first comprehensive search for $n-ar{n}$ oscillation in large-scale water Cherenkov detector data, establishing new experimental lower bounds.

Findings

No evidence of $n-ar{n}$ oscillation was observed.

Lower limit on neutron lifetime in ${}^{16}$O was $1.9 imes 10^{32}$ years.

Lower limit on free neutron oscillation time was $2.7 imes 10^8$ seconds.

Abstract

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 $2.7 \times 10^8$~s using a theoretical value of the nuclear suppression factor of $0.517 \times 10^{23}$~s$^{-1}$ and its uncertainty.