Observation of Exclusive Two-Body $\mathit{B}$ 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 $3.3\times {10}^6$ $B\overline{B}$ pairs collected with the CLEO-II detector, we have made the first observation of the decay $B^0\to K^{+}{\pi }^{-},$ the sum of $B^{+}\to {\pi }^{+}{\pi }^0$ and $B^{+}\to K^{+}{\pi }^0$ decays, and see strong evidence for the decay $B^{+}\to K^0{\pi }^{+}$ (an average over charge-conjugate states is always implied). We place upper limits on branching fractions for the remaining decay modes.