Improved Lower Bounds on Partial Lifetimes for Nucleon Decay Modes

TL;DR

This paper derives improved theoretical lower bounds on the partial lifetimes of various nucleon decay modes by relating them to experimentally constrained decay processes, surpassing previous bounds from direct searches.

Contribution

It introduces a method to set stronger lower bounds on nucleon decay lifetimes by connecting decay rates to experimentally measured modes, enhancing constraints on baryon-number violation.

Findings

Lower bounds on proton and neutron decay modes are significantly improved.

The method relates decay rates to experimental bounds on meson emission modes.

New bounds on decay modes involving photons are established.

Abstract

In the framework of a baryon-number-violating effective Lagrangian, we calculate improved lower bounds on partial lifetimes for proton and bound neutron decays, including $p \to \ell^+ \ell'^+ \ell'^-$, $n \to \bar\nu \ell^+ \ell'^-$, $p \to \ell^+ \nu\bar\nu$, and $n \to \bar\nu \bar\nu \nu$, where $\ell$ and $\ell'$ denote $e$ or $\mu$, with both $\ell = \ell'$ and $\ell \ne \ell'$ cases. Our lower bounds are substantially stronger than the corresponding lower bounds from direct experimental searches. We also present lower bounds on $(\tau/B)_{p \to \ell^+\gamma}$, $(\tau/B)_{n \to \bar\nu \gamma}$, $(\tau/B)_{p \to \ell^+ \gamma\gamma}$, and $(\tau/B)_{n \to \bar\nu \gamma\gamma}$. Our method relies on relating the rates for these decay modes to the rates for decay modes of the form $p \to \ell^+ M$ and $n \to \bar\nu M$, where $M$ is a pseudoscalar or vector meson, and then using the experimental lower bounds on the partial lifetimes for these latter decays.