Improved Lower Bounds on Partial Lifetimes for Nucleon Decay Modes

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 $p\to {\ell }^{+}{\ell }^{\prime +}{\ell }^{\prime -}$, $n\to \bar{\nu }{\ell }^{+}{\ell }^{\prime -}$, $p\to {\ell }^{+}\nu \bar{\nu }$, and $n\to \bar{\nu }\bar{\nu }\nu$, where $\ell$ and ${\ell }^{\prime }$ denote $e$ or $\mu$, with both $\ell ={\ell }^{\prime }$ and $\ell \ne {\ell }^{\prime }$ 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.

Comments: 11 pages, 8 figures