Observation of Exclusive Two-Body<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">B</mml:mi></mml:math>Decays to Kaons and Pions

We have studied two-body charmless hadronic decays of B mesons into the final states \ensuremath{\pi}\ensuremath{\pi}, K\ensuremath{\pi}, and KK. Using $3.3\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ pairs collected with the CLEO-II detector, we have made the first observation of the decay ${B}^{0}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}},$ the sum of ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0}$ and ${B}^{+}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\pi}}^{0}$ decays, and see strong evidence for the decay ${B}^{+}\ensuremath{\rightarrow}{K}^{0}{\ensuremath{\pi}}^{+}$ (an average over charge-conjugate states is always implied). We place upper limits on branching fractions for the remaining decay modes.