Measurements of branching fractions for b→Kπ and b→ππ decays

We report measurements of branching fractions for B -> K pi and B ->pi pi decays based on a data sample of 449x10(6) B (B) over bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We also measure the ratios of partial widths for B -> K pi decays, namely R-c equivalent to 2 Gamma(B+-> K+pi(0))/Gamma(B+-> K-0 pi(+))=1.08 +/- 0.06 +/- 0.08 and R-n equivalent to Gamma(B-0 -> K+pi(-))/2 Gamma(B-0 -> K-0 pi(0))=1.08 +/- 0.08 +/- 0.08, where the first and the second errors are statistical and systematic, respectively. These ratios are sensitive to enhanced electroweak penguin contributions from new physics; the new measurements are, however, consistent with standard model expectations.