Nucleon Decays into Light New Particles in Neutrino Detectors

TL;DR

This paper explores how nucleon decays into light new particles like sterile neutrinos could produce unique signals in neutrino detectors, highlighting the complementarity of different detector types and proposing a simple decay model.

Contribution

It introduces a new perspective on nucleon decay signatures involving light particles and compares detector sensitivities, proposing a simple decay model with observable effects.

Findings

JUNO and DUNE can detect invisible nucleon decay signatures missed by water Cherenkov detectors.

Nucleon decays into sterile neutrinos can produce detectable fluxes in underground detectors.

A simple decay model predicts a large number of observable events in Super-Kamiokande.

Abstract

Proton and neutron decays into light new particles $X$ can drastically change the experimental signatures and benefit from the complementarity of large water-Cherenkov neutrino detectors such as Super/Hyper-Kamiokande and tracking detectors such as JUNO and DUNE. The proton decays $p\to \ell^+ X$ and $p\to \pi^+ X$ with $m_X$ near phase-space closure lead to charged particles below Cherenkov threshold, rendering them practically invisible in Super- and Hyper-Kamiokande but not in JUNO and DUNE, which are therefore uniquely positioned for these baryon-number-violating signatures despite their smaller size. As an additional signature, such nucleon decays in Earth can produce a sizable flux of $X$ particles in underground detectors. We present a simple model in which nucleons decay into sub-GeV sterile neutrinos that subsequently decay through active-sterile neutrino mixing, with a promisingly large number of events in Super-Kamiokande even in the seesaw-motivated parameter space.