Abstract
The Majorana Demonstrator is an ultra low-background experiment searching for neutrinoless double-beta decay in $^{76}$Ge. The heavily shielded array of germanium detectors, placed nearly a mile underground at the Sanford Underground Research Facility in Lead, South Dakota, also allows searches for new exotic physics. We present the first limits for tri-nucleon decay-specific modes and invisible decay modes for Ge isotopes. We find a half-life limit of $4.9 \times 10^{25}$ yr for the decay $^{76}{\rm Ge(ppn)} \to {}^{73}{\rm Zn}\ e^+\pi^+$ and $4.7\times10^{25}$ yr for the decay $^{76}{\rm Ge(ppp)} \to ^{73}{\rm Cu}\ e^+\pi^+\pi^+$. The half-life limit for the invisible tri-proton decay mode of $^{76}$Ge was found to be $7.5\times10^{24}$ yr.
Highlights
We present the first limits for trinucleon decay-specific modes and invisible decay modes for Ge isotopes
The conservation of the number of baryons (B) in any reaction is an empirical symmetry of the Standard Model that is not the result of any fundamental principle
Theories with extra dimensions permit particle disappearance, and nucleon decay can be induced via interactions with dark matter as manifest in asymmetric dark matter theories. =B is one of the Sakharov requirements to explain the matter-antimatter asymmetry of the Universe
Summary
The conservation of the number of baryons (B) in any reaction is an empirical symmetry of the Standard Model that is not the result of any fundamental principle. =B is one of the Sakharov requirements to explain the matter-antimatter asymmetry of the Universe These topics and the possibility of =B are reviewed in Ref. The Standard Model with small neutrino masses has an anomaly-free Z6 symmetry that acts as discrete B [2]. In this model ΔB 1⁄4 1 or 2 processes are forbidden, but ΔB 1⁄4 3 transitions can arise due to a dimension 15 operator. Previous searches in Xe isotopes [3,4] and 127I [5] looked for invisible decay channels assuming no observation of the initial trinucleon decay or disappearance. Typical modes of decay for ΔB 1⁄4 2 are pp → πþπþ pn → π0πþ nn → πþπ−; π0π0: ð2Þ
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