Shedding light on the "dark side" of B<inf>d</inf>⁰-B<inf>d</inf>⁰̄ mixing through B<inf>d</inf> → π⁺π^-, K → πvv̄ and B <inf>d,s</inf> → μ⁺μ^-

In a wide class of new-physics models, which can be motivated through generic arguments and within supersymmetry, we obtain large contributions to Bd0-Bd0̄ mixing, but not to ΔB = 1 processes. If we assume such a scenario, the solutions φ d ∼ 47° V 133° for the Bd0-B d0̄ mixing phase implied by ACPmix(Bd → J/ψKs) cannot be converted directly into a constraint in the ρ̄-η̄ plane. However, we may complement φd with |Vub/Vcb| and the recently measured CP asymmetries in Bd → π +π- to determine the unitarity triangle, with its angles α, β and γ. To this end, we have also to control penguin effects, which we do by means of the CP-averaged Bd → π∓K± branching ratio. Interestingly, the present data show a perfectly consistent picture not only for the "standard" solution of φd ∼ 47°, but also for φd ∼ 133°. In the latter case, the preferred region for the apex of the unitarity triangle is in the second quadrant, allowing us to accommodate conveniently γ > 90°, which is also favoured by other non-leptonic B decays such as B → πK. Moreover, also the prediction for BR(K+ → π+vv̄) can be brought to better agreement with experiment. Further strategies to explore this scenario with the help of Bd,s → μ+μ- decays are discussed as well. © SISSA/ISAS 2003.