Observation of B Decays to Two Kaons

Using 449x10{sup 6} BB pairs collected with the Belle detector at the KEKB asymmetric-energy e{sup +}e{sup -} collider, we observe clear signals for B{sup +}{yields}K{sup 0}K{sup +} and B{sup 0}{yields}K{sup 0}K{sup 0} decays with 5.3{sigma} and 6.0{sigma} significance, respectively. We measure the branching fractions B(B{sup +}{yields}K{sup 0}K{sup +})=(1.22{sub -0.28-0.16}{sup +0.32+0.13})x10{sup -6} and B(B{sup 0}{yields}K{sup 0}K{sup 0})=(0.87{sub -0.20}{sup +0.25}{+-}0.09)x10{sup -6}, and partial-rate asymmetries A{sub CP}(B{sup +}{yields}K{sup 0}K{sup +})=0.13{sub -0.24}{sup +0.23}{+-}0.02 and A{sub CP}(B{sup 0}{yields}K{sup 0}K{sup 0})=-0.58{sub -0.66}{sup +0.73}{+-}0.04. From a simultaneous fit, we also obtain B(B{sup +}{yields}K{sup 0}{pi}{sup +})=(22.8{sub -0.7}{sup +0.8}{+-}1.3)x10{sup -6} and A{sub CP}(B{sup +}{yields}K{sup 0}{pi}{sup +})=0.03{+-}0.03{+-}0.01. The first and second error in the branching fractions and the partial-rate asymmetries are statistical and systematic, respectively. No signal is observed for B{sup 0}{yields}K{sup +}K{sup -} decays, and for this branching fraction, we set an upper limit of 4.1x10{sup -7} at the 90% confidence level.