Observation of exclusive two-body B decays to kaons and pions

We have studied two-body charmless hadronic decays of B mesons into the final states ππ, Kπ, and KK. Using 3.3×10^6 BB pairs collected with the CLEO-II detector, we have made the first observation of the decay B^0 → K^(+)π^(-), the sum of B^(+) → π^(+)π^(0) and B^(+) → K^(+)π^(0) decays, and see strong evidence for the decay B^(+) → K^(0)π^(+) (an average over charge-conjugate states is always implied). We place upper limits on branching fractions for the remaining decay modes.