Search for rare hadronic B decays

A search for rare decays of B hadrons has been performed using approximately two million hadronic Z 0 decays collected by the OPAL experiment between 1990 and 1993. The exclusive decay channels B d 0 → π + π − , B d 0 → K + π − , B s 0 → π + K − and B s 0 → K + K − have been studied. Such decays include contributions from flavour changing neutral current processes such as hadronic penguin decays. No significant excess of events has been observed in the π + π − , π + K − and K + K − invariant mass distributions. Consequently, upper limits on the B d 0 branching ratios, Br(B d 0 → π + π − ) −5 and Br(B d 0 →K + π − ) −5 , and on the B s 0 branching ratios, Br(B s 0 → π + K − ) −4 and Br(B s 0 →K + K − ) −4 , have been set at the 90% confidence level. These limits assume that the ratio of the partial decay widths of the Z 0 , λ (Z 0 → bb)/λ(Z 0 → hadrons), is 0.217 and that the fractions of B d 0 and B s 0 mesons produced during fragmentation are 39.5% and 12% respectively. The B s 0 branching ratio limits are the first such limits obtained.