# Progress and Simulations for Intranuclear Neutron--Antineutron Transformations in ${}^{40}_{18} Ar$

## TL;DR

This paper presents a novel intranuclear simulation of neutron-antineutron transformations in argon nuclei, crucial for rare decay searches in upcoming large-scale neutrino experiments, with new theoretical calculations and simulation comparisons.

## Contribution

It introduces a self-consistent intranuclear simulation for neutron-antineutron transformations in argon, including the first calculation of the suppression factor and comparisons with existing models.

## Key findings

- New simulation model for intranuclear $n
ightarrow\bar{n}$ processes in argon.
- First calculation of argon's $ar{n}$-intranuclear suppression factor.
- Comparison with existing Monte Carlo generator models.

## Abstract

With the imminent construction of the Deep Underground Neutrino Experiment (DUNE) and Hyper-Kamiokande, nucleon decay searches as a means to constrain beyond Standard Model (BSM) extensions are once again at the forefront of fundamental physics. Abundant neutrons within these large experimental volumes, along with future high-intensity neutron beams such as the European Spallation Source, offer a powerful, high-precision portal onto this physics through searches for $\mathcal{B}$ and $\mathcal{B}-\mathcal{L}$ violating processes such as neutron--antineutron transformations ($n\rightarrow\bar{n}$), a key prediction of compelling theories of baryogenesis. With this in mind, this paper discusses a novel and self-consistent intranuclear simulation of this process within ${}^{40}_{18} Ar$, which plays the role of both detector and target within DUNE's gigantic liquid argon time projection chambers. An accurate and independent simulation of the resulting intranuclear annihilation respecting important physical correlations and cascade dynamics for this large nucleus is necessary to understand the viability of such rare searches when contrasted against background sources such as atmospheric neutrinos. Recent theoretical improvements to our model, including the first calculation of ${}^{40}_{18} Ar$'s $\bar{n}$-intranuclear suppression factor, and Monte Carlo simulation comparisons to another publicly available $n\rightarrow\bar{n}$ generator within GENIE, are also discussed.