Weak Decay of $\Lambda$ in Nuclei : Quarks vs Mesons

Decays of $\Lambda$ in nuclei, nonmesonic mode, are studied by using the $\Lambda N \to NN$ weak transition potential derived from the meson exchange mechanism and the direct quark mechanism. The decay rates are calculated both for the $\Lambda$ in symmetric nuclear matter and light hypernuclei. We consider the exchange of six mesons ($\pi, K, \eta, \rho, \omega, K^\ast$). The form factor in the meson exchange mechanism and short range correlation are carefully studied.