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.