$\Delta B=2$ neutron decay into antiproton mode $n\to \bar pe^+\nu(\bar\nu)$

TL;DR

This paper explores a rare neutron decay mode violating baryon number by two units, estimates its lifetime bounds from existing experiments, and discusses potential signatures and astrophysical implications.

Contribution

It introduces and analyzes the neutron decay mode $n o ar p e^+ u(ar u)$ within effective field theory, providing lifetime bounds and experimental signatures.

Findings

Lower bound on decay lifetime: >5.7×10^{39} years

Kinematically allowed but rarely discussed

Potential signatures for future experiments

Abstract

We discuss the unique baryon number violation by two units neutron decay mode $n\to \bar p e^+\chi$, with $\chi$ being the standard model (SM) neutrino $\nu$ or antineutrino $\bar\nu$ or any beyond SM light fermion, in the framework of effective field theory. This mode is kinematically allowed but rarely discussed theoretically or searched for experimentally. We estimate the lower bound on its partial lifetime from that of the dinucleon decay $np\to e^+\chi$ per oxygen nucleus $^{16}$O set by the Super-Kamiokande experiment, with a conservative bound $\Gamma^{-1}_{n\to\bar pe^+\chi}>5.7\times 10^{39}~\rm yrs$. We also discuss its characteristic signature for the future experimental search and astrophysical implications.