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.
Highlights
The intranuclear cascade (INC) model used for simulations of inelastic interactions of particles within the nucleus is assumed to hold at energies ≳30–40 MeV
We have endeavored to give an update to the community on recent developments in the modeling of n A annihilation events in service of future beyond standard model (BSM) n → nsearches
Comparisons and discussions of differences and similarities have been made to data where available, previous Monte Carlo (MC) results, and other publicly available event generators such as GENIE
Summary
Popular (modern and minimal) BSM extensions [5,6,7,8] permitting such a process can dynamically create a proper baryon abundance in the early Universe, even while predicting a reasonable and possibly observable upper limit on the mean transformation time in vacuum, allowing the theory to be well constrained if not eventually entirely eliminated experimentally This prospect seems stronger than ever given new studies from lattice quantum chromodynamics calculations [9] and other interesting, highly general recent works [8,10,11,12]. It becomes crucially important that one should take care to model BSM signals and backgrounds as completely, consistently, and rigorously as necessary by employing limited approximations which attempt to preserve as much physics as possible This is especially true given nontrivial automated triggering schemes planned for future rare event searches. Inconsistencies are known to exist in other work [26], and detailed explanations of past simulations’ internal processes are quite lacking [18,27], but to individually contend these here is not the goal of this article
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