Search for rare hadronic B decays

A search for rare decays of B hadrons has been performed using approximately two million hadronic Z0 decays collected by the OPAL experiment between 1990 and 1993. The exclusive decay channels Bd0 → π+ π−, Bd0 → K+π−, Bs0 → π+K− and Bs0 → 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 Bd0 branching ratios, Br(Bd0→π+π−) < 4.7 × 10−5 and Br(Bd0→K+π−) < 8.1 × 10−5, and on the Bs0 branching ratios, Br(Bs0→π+K−) < 2.6 × 10−4 and Br(Bs0→K+K−) < 1.4 × 10−4, have been set at the 90% confidence level. These limits assume that the ratio of the partial decay widths of the Z0, λ (Z0 → bb̄)/λ(Z0 → hadrons), is 0.217 and that the fractions of Bd0 and Bs0 mesons produced during fragmentation are 39.5% and 12% respectively. The Bs0 branching ratio limits are the first such limits obtained.