New strategies to extract β and γ from Bd → π+π- and Bs → K+K-

The decays B-d --> pi(+)pi(-) and B-s --> K+K- are related to each other by interchanging all down and strange quarks, i.e. through the U-spin flavour symmetry of strong interactions. A completely general parametrization of the CP-violating observables of these modes is presented within the framework of the Standard Model, allowing the determination of the angles beta and gamma of the unitarity triangle. This strategy is affected neither by penguin contributions nor by any final-state-interaction effects, and its theoretical accuracy is only limited by U-spin-breaking collections. If the B-d(0)-<(B-d(0))over bar> mixing phase 2 beta is determined separately, for example with the help of B-d --> J/psi K-S, gamma can be extracted with a reduced U-spin flavour symmetry input. A variant of this strategy to determine gamma, which uses B-d --> pi(-/+)K(+/-) instead of B-s --> K+K- and relies - in addition to the SU(3) flavour symmetry - on a certain dynamical assumption, is also briefly discussed. (C) 1999 Published by Elsevier Science B.V. All rights reserved.