Constraining the CKM angleγ and penguin contributions through combined B→πK branching ratios

Motivated by recent CLEO measurements of B-->pi K modes, we investigate their implications for the CKM angle gamma and a consistent description of these decays within the standard model. Interestingly it turns out that already the measurement of the combined branching ratios B+/--->pi(+/-)K and B-d-->pi(+/-)K(+/-) allows us to derive stringent constraints on gamma which are complementary to the presently allowed range for that angle. This range, arising from the usual fits of the unitarity triangle, is typically symmetric around gamma=90 degrees, while our method can in principle exclude a range of this kind. Consistency within the standard model implies furthermore bounds on the ratio r=\T'\/\(P) over tilde\ of the current-current and penguin operator contributions to B-d-->pi(+/-)K(+/-), and upper limits for the CP-violating asymmetry arising in that decay. Commonly accepted means to estimate r yield values at the edge of compatibility with the present CLEO measurements.