Remarks on the Differing Lifetimes of Charmed Mesons

Differences in the D⁺ and D⁰ lifetimes may arise either from 6 dominance in the effective nonleptonic Hamiltonian, or from the dominance of a particular W⁺-exchange diagram which behaves like a D⁰-K̄⁰* pole. If 6 dominance holds, then the F⁺ will have a relatively short lifetime and a small semileptonic branching ratio, just like the D⁰; but if W⁺ exchange is dominant, the F⁺ will have a long lifetime and large semileptonic branching ratio, like the D⁺.