Constraints on the CKM angle γ and strong phases from B → πK decays

As we pointed out recently, the neutral decays B_d -> → π^∓K^± and B_d → π⁰K may provide nontrivial bounds on the CKM angle γ. In this paper, we reconsider this approach in the light of recent CLEO data, which look very interesting. In particular, the results for the corresponding CP-averaged branching ratios are in favour of strong constraints on γ, where the second quadrant is preferred. Such a situation would be in conflict with the standard analysis of the unitarity triangle. Moreover, constraints on a CP-conserving strong phase δ_n are in favour of a negative value of cos δ_n, which would be in conflict with the factorization expectation. In addition, there seems to be an interesting discrepancy with the bounds that are implied by the charged B → πK system: whereas these decays favour a range for γ that is similar to that of the neutral modes, they point towards a positive value of cos δ_c, which would be in conflict with the expectation of equal signs for cos δ_n and cos_c. If future data should confirm this "puzzle", it may be an indication for new-physics contributions to the electroweak penguin sector, or a manifestation of large non-factorizable SU(3)-breaking effects.