Novel Weak Decays in Doubly Strange Systems

The strangeness-changing (∆S = 1) weak baryon-baryon interaction is studied through the nonmesonic weak decay of double-Λ hypernuclei. Besides the usual nucleon-induced decay ΛN → NN we discuss novel hyperon-induced decay modes ΛΛ → ΛN and ΛΛ → ΣN . These reactions provide unique access to the exotic ΛΛK and ΛΣK vertices which place new constraints on Chiral Pertubation Theory (χPT) 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 ΛΛHe 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.