Charmless hadronic B decays involving scalar mesons: Implications on the nature of light scalar mesons

The hadronic charmless B decays into a scalar meson and a pseudoscalar meson are studied within the framework of QCD factorization. Based on the QCD sum rule method, we have derived the leading-twist light-cone distribution amplitudes of scalar mesons and their decay constants. Although the light scalar mesons f0(980) and a0(980) are widely perceived as primarily the four-quark bound states, in practice it is difficult to make quantitative predictions based on the four-quark picture for light scalars. Hence, predictions are made in the 2-quark model for the scalar mesons. The short-distance approach suffices to explain the observed large rates of f0(980)K- and f0(980)K0 that receive major penguin contributions from the b→sss process. When f0(980) is assigned as a four-quark bound state, there exist extra diagrams contributing to B→f0(980)K. Therefore, a priori the f0(980)K rate is not necessarily suppressed for a four-quark state f0(980). The predicted B0→a0±(980)π± and a0+(980)K- rates exceed the current experimental limits, favoring a four-quark nature for a0(980). The penguin-dominated modes a0(980)K and a0(1450)K receive predominant weak annihilation contributions. There exists a twofold experimental ambiguity in extracting the branching ratio of B-→K0*0(1430)π-, which can be resolved by measuring other K0*(1430)π modes in conjunction with the isospin symmetry consideration. Large weak annihilation contributions are needed to explain the K0*(1430)π data. The decay B0→κ+K- provides a nice ground for testing the 4-quark and 2-quark nature of the κ meson. It can proceed through W-exchange and hence is quite suppressed if κ is made of two quarks, while it receives a tree contribution if κ is predominately a four-quark state. Hence, an observation of this channel at the level of > or approx. 10-7 may imply a four-quark assignment for the κ. Mixing-induced CP asymmetries in penguin-dominated modes are studied and their deviations from sin2β are found to be tiny