New strategies to extract beta and gamma from B-d -> pi(+)pi(-) and B-s ->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 t he CP-violating observables of these modes is presented within the framewor k of the Standard Model, allowing the determination of the angles beta and gamma of the unitarity triangle. This strategy is affected neither by pengu in contributions nor by any final-state-interaction effects, and its theore tical 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 exam ple with the help of B-d --> J/psi K-S, gamma can be extracted with a reduc ed U-spin flavour symmetry input. A variant of this strategy to determine g amma, 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 assumpt ion, is also briefly discussed. (C) 1999 Published by Elsevier Science B.V. All rights reserved.