Novel Weak Decays in Doubly Strange Systems

Abstract

The strangeness-changing ($\Delta S=1$) weak baryon-baryon interaction is studied through the nonmesonic weak decay of double-$\Lambda$ hypernuclei. Besides the usual nucleon-induced decay $\Lambda N\to NN$ we discuss novel hyperon-induced decay modes $\Lambda \Lambda \to \Lambda N$ and $\Lambda \Lambda \to \Sigma N$. These reactions provide unique access to the exotic $\Lambda \Lambda$K and $\Lambda \Sigma$K vertices which place new constraints on Chiral Pertubation Theory ($\chi$PT) in the weak SU(3) sector. Within a meson-exchange framework, we use the pseudoscalar $\pi ,\eta ,K$ octet for the long-range part while parametrizing the short-range part through the vector mesons $\rho ,\omega ,K^{\ast }$. Realistic baryon-baryon forces for the $S=0,-1$ and -2 sectors account for the strong interaction in the initial and final states. For ${}_{\Lambda \Lambda }^6$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.

Comments: 19 pages, 2 ps figures, 9 tables