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The decays of B mesons to a pair of charmless pseudoscalar (P ) mesons are analyzed within a framework of flavor SU(3). Symmetry breaking is taken into account in tree (T ) amplitudes through ratios of decay constants; exact SU(3) is assumed elsewhere. Acceptable fits to B → ππ and B → Kπ branching ratios and CP asymmetries are obtained with tree, color-suppressed (C), penguin (P ), and electroweak penguin (P EW ) amplitudes. Crucial additional terms for describing processes involving η and η ′ include a large flavor-singlet penguin amplitude (S) as proposed earlier and a penguin amplitude P tu associated with intermediate t and u quarks. For the B + → π + η ′ mode a term S tu associated with intermediate t and u quarks also may be needed. Values of the weak phase γ are obtained consistent with an earlier analysis of B → V P decays, where V denotes a vector meson, and with other analyses of CKM parameters.

We study the effects of an extra U(1) gauge boson with flavor changing couplings with fermion mass eigenstates on certain B meson decays that are sensitive to such new physics contributions. In particular, we examine to what extent the current data on B d → φK and B d → η K decays may be explained in such models, concentrating on the example in which the flavor changing couplings are left-chiral. We find that within reasonable ranges of parameters, the Z contribution can readily account for the anomaly in S φK S but is not sufficient to explain large branching ratio of B d → η K with the same parameter value. S φK S and S η K S are seen to be the dominant observables that constrain the extra weak phase in the model. 