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Measurement of Branching Fractions for B->ππ, Kπand KK Decays

We report measurements of the branching fractions for $B^0\toπ^+π^-$, $K^+π^-$, $K^+K^-$ and $K^0π^0$, and $B^+\toπ^+π^0$, $K^+π^0$, $K^0π^+$ and $K^+\bar{K}{}^0$. The results are based on 10.4 fb$^{-1}$ of data collected on the $Υ$(4S) resonance at the KEKB $e^+e^-$ storage ring with the Belle detector, equipped with a high momentum particle identification system for clear separation of charged $π$ and $K$ mesons. We find ${\cal B}(B^0\toπ^+π^-) =(0.56^{+0.23}_{-0.20}\pm 0.04)\times 10^{-5}$, ${\cal B}(B^0\to K^+π^-) =(1.93^{+0.34 +0.15}_{-0.32 -0.06})\times 10^{-5}$, ${\cal B}(B^+\to K^+π^0) =(1.63^{+0.35 +0.16}_{-0.33 -0.18})\times 10^{-5}$, ${\cal B}(B^+\to K^0π^+) =(1.37^{+0.57 +0.19}_{-0.48 -0.18})\times 10^{-5}$, and ${\cal B}(B^0\to K^0π^0) =(1.60^{+0.72 +0.25}_{-0.59 -0.27})\times 10^{-5}$, where the first and second errors are statistical and systematic. We also set upper limits of ${\cal B}(B^+\toπ^+π^0)<1.34\times 10^{-5}$, ${\cal B}(B^0\to K^+K^-)<0.27\times 10^{-5}$, and ${\cal B}(B^+\to K^+\bar{K}{}^0)<0.50\times 10^{-5}$ at the 90% confidence level.