Charmless 3-body B Decays: Resonant and Nonresonant Contributions

Charmless 3-body decays of $B$ mesons are studied using a simple model based on the framework of the factorization approach. We have identified a large source of the nonresonant signal in the matrix elements of scalar densities, e.g. $<K\bar K|\bar ss|0>$. This explains the dominance of the nonresonant background in $B\to KKK$ decays, the sizable nonresonant fraction of order $(35\sim 40)$ in $K^-\pi^+\pi^-$ and $\bar K^0\pi^+\pi^-$ modes and the smallness of nonresonant rates in $B\to \pi\pi\pi$ decays. We have computed the resonant and nonresonant contributions to charmless 3-body decays and determined the rates for the quasi-two-body decays $B\to VP$ and $B\to SP$. Time-dependent CP asymmetries $\sin2\beta_{\rm eff}$ and $A_{CP}$ in $K^+K^-K_S,K_SK_SK_S,K_S\pi^+\pi^-$ and $K_S\pi^0\pi^0$ modes are estimated.