Novel Weak Decays in Doubly Strange Systems

Abstract

The strangeness-changing ($ΔS = 1$) weak baryon-baryon interaction is studied through the nonmesonic weak decay of double-$Λ$ hypernuclei. Besides the usual nucleon-induced decay $ΛN \to N N$ we discuss novel hyperon-induced decay modes $ΛΛ\to ΛN$ and $ΛΛ\to ΣN$. These reactions provide unique access to the exotic $ΛΛ$K and $ΛΣ$K vertices which place new constraints on Chiral Pertubation Theory ($χ$PT) in the weak SU(3) sector. Within a meson-exchange framework, we use the pseudoscalar $π,η,K$ octet for the long-range part while parametrizing the short-range part through the vector mesons $ρ, ω, K^*$. Realistic baryon-baryon forces for the $S=0,-1$ and -2 sectors account for the strong interaction in the initial and final states. For $^6_{ΛΛ}$He the new hyperon-induced decay modes account for up to 4% of the total nonmesonic decay rate. Predictions are made for all possible nonmesonic decay modes.