A New Model of Intranuclear Neutron-Antineutron Transformations in ${}^{16}_{8}$O

TL;DR

This paper introduces an advanced simulation model for intranuclear neutron-antineutron transformations in oxygen-16, enhancing physical realism and potentially improving detection efficiency in underground neutrino experiments.

Contribution

The paper presents a new event generator with improved nuclear physics modeling, including a novel radial annihilation distribution and a modern multifragmentation model with photonic de-excitations.

Findings

Enhanced simulation realism for neutron-antineutron transformations.

Potential for increased signal detection efficiency in large detectors.

Applicability to future experiments with different nuclei.

Abstract

There has been much work in recent years pertaining to viability studies for the intranuclear observation of neutron-antineutron transformations. These studies begin firstly with the design and implementation of an event generator for the simulation of this rare process, where one hopes to retain as much of the underlying nuclear physics as possible in the initial state, and then studying how these effects may perturb the final state observable particles for detector efficiency studies following simulated reconstruction. There have been several searches for intranuclear neutron-antineutron transformations, primarily utilizing the ${}^{16}_{8}$O nucleus, and completed within large underground water Cherenkov detectors such as Super-Kamiokande. The latest iteration of a generator is presented here for use in such an experiment. This generator includes several new features, including a new radial (position) annihilation probability distribution and related intranuclear suppression factor for ${}^{16}_{8}$O, as well as a highly general, modern nuclear multifragmentation model with photonic de-excitations. The latter of these may allow for improved identification of the signal using large underground detectors such as Super-Kamiokande and the future Hyper-Kamiokande, potentially increasing the overall signal efficiencies of these rare searches. However, it should be noted that certain fast photonic de-excitations may be washed out by $\pi^0$ decays to photons. These new features implemented in these $\bar{n}$\isotope[15][8]{O} simulations increase the overall physical realism of the model, and are easily portable to other future searches such as to extranuclear $\bar{n}{}^{12}_{6}$C for the ESS NNBAR experiment, as well as intranuclear $\bar{n}{}^{39}_{18}$Ar used in DUNE.