New bound on γ from B±→πK decays

A bound on the angle γ of the unitarity triangle is derived using experimental information on the CP-averaged branching ratios for the rare decays B±→π±K0 and B±→π0K±. The theoretical description is cleaner than the Fleischer–Mannel analysis of the decays B±→π±K0 and B0→π∓K± in that the two decay rates differ only in a single isospin amplitude, which has a simple structure in the SU(3) limit. As a consequence, electroweak penguin contributions and strong rescattering effects can be taken into account in a model-independent way. The resulting bound excludes values of cosγ around ≈0.6 and is thus largely complementary to indirect constraints derived from a global analysis of the unitarity triangle.