Limitations in measuring the angle by using SU(3) relations for B-meson decay-amplitudes

Abstract Flavour SU (3) symmetry of strong interactions and certain dynamical assumptions have been used in a series of recent publications to extract weak CKM phases from B -decays into {ππ, πK, K K } final states. We point out that irrespectively of SU (3)-breaking effects the presence of QCD-penguin contributions with internal u - and c -quarks precludes a clean determination of the angle β in the unitarity triangle by using the branching ratios only. This difficulty can be overcome by measuring in addition the ratio x d / x s of B d 0 − B d 0 to B s 0 − B s 0 mixings. The measurement of the angle γ is unaffected by these new contributions. Some specific uncertainties related to SU (3)-breaking effects and electroweak penguin contributions are briefly discussed.