Charmless B→VV decays in QCD factorization implications of recent B→φK∗ measurement

In the heavy quark limit, both vector mesons in the charmless B→VV decay should have zero helicity and the corresponding amplitude is proportional to the form factor difference (A1−A2). The first observed charmless B→VV mode, B→φK∗, indicates that the form factors A1(q2) and A2(q2) cannot be very similar at low q2 as shown in some form-factor models. The approach of QCD-improved factorization implies that the nonfactorizable correction to each partial-wave or helicity amplitude is not the same; the effective parameters ai vary for different helicity amplitudes. The leading-twist nonfactorizable corrections to the transversely polarized amplitudes vanish in the chiral limit and hence it is necessary to take into account twist-3 distribution amplitudes of the vector meson in order to have renormalization scale and scheme independent predictions. Branching ratios of B→VV decays are calculated in two different models for form factors, and the predicted decay rates are different by a factor of 1.5∼2. Owing to the absence of (S−P)(S+P) penguin contributions to the W-emission amplitudes, tree-dominated decays tend to have larger branching ratios than the penguin-dominated ones.