A Fresh Look at B_{s,d} -> pi pi, pi K, K K Decays

Using updated measurements and SU(3)-breaking form factors, we have a detailed look at the B_d -> pi^+ pi^-, B_s -> K^+ K^- and B_d -> pi^\mp K^\pm, B_s -> pi^\pm K^\mp systems. The corresponding decays are related to each other by the U-spin symmetry of strong interactions and offer determinations of the angle gamma of the unitarity triangle. In the former case, we obtain gamma=(68.3^{+4.8}_{-5.7}^{+5.0}_{-3.7}) deg, which is in excellent agreement with the Standard-Model fits of the unitarity triangle. The first errors correspond to experimental input uncertainties, while the latter are an estimate of U-spin-breaking effects. In view of this result, large CP-violating new-physics effects at the amplitude level are excluded. However, the effective B_s -> K^+ K^- lifetime and the mixing-induced CP violation in this channel offer interesting probes for New Physics in B^0_s-\bar B^0_s mixing. In the case of the B_d -> π^\mp K^\pm, B_s -> pi^\pm K^\mp system, using additional information from B^\pm -> π^\pm K, we obtain a bound of gamma \leq (71.8^{+5.4}_{-4.3}) deg, and the range 24 deg \leq gamma \leq 71 deg. We perform also tests of the U-spin symmetry and do not find any indication for large non-factorizable corrections.

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