Progress and simulations for intranuclear neutron-antineutron transformations in Ar 18 40

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 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 $\\mathcal{B}\\ensuremath{-}\\mathcal{L}$ violating processes such as neutron-antineutron transformations ($n\\ensuremath{\\rightarrow}\\overline{n}$), 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 $_{18}^{40}\\mathrm{Ar}$, which plays the role of both detector and target within the DUNE\u0027s 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, such as the first calculations of the $_{18}^{40}\\mathrm{Ar}$ intranuclear radial annihilation probability distribution and the inclusion of a realistic $\\overline{n}A$ potential, are discussed. A Monte Carlo simulation comparison to another publicly available $n\\ensuremath{\\rightarrow}\\overline{n}$ generator within GENIE is shown in some detail. The first calculation of $_{18}^{40}\\mathrm{Ar}$\u0027s $n\\ensuremath{\\rightarrow}\\overline{n}$-intranuclear suppression factor, an important quantity for future searches at the DUNE, is also completed, finding ${T}_{R}^{\\mathrm{Ar}}\\ensuremath{\\sim}5.6\\ifmmode\\times\\else\\texttimes\\fi{}{10}^{22}\\text{ }\\text{ }{\\mathrm{s}}^{\\ensuremath{-}1}$.