B-->J/ψ K* decays in QCD factorization

The hadronic decay B-->J/ψK^* is analyzed within the framework of QCD factorization. The spin amplitudes A₀, A_||, and A_⊥ in the transversity basis and their relative phases are studied using various different form-factor models for the B-K^* transition. The effective parameters a^h₂ for helicity h=0,+,- states receive different nonfactorizable contributions and hence they are helicity-dependent, contrary to naive factorization where a^h₂ are universal and polarization-independent. QCD factorization breaks down even at the twist-2 level for transverse hard spectator interactions. Although a nontrivial strong phase for the A_|| amplitude can be achieved by adjusting the phase of an infrared-divergent contribution, the present QCD factorization calculation cannot say anything definite about the phase φ_||. Unlike B-->J/ψK decays, the longitudinal parameter a⁰₂ for B-->J/ψK^* does not receive twist-3 corrections and is not large enough to account for the observed branching ratio and the fraction of the longitudinal polarization. Possible enhancement mechanisms for a⁰₂ are discussed.