Evidence for b-flavoured baryon production in Z0 decays at LEP

We observe evidence for the production of b-flavoured baryons in decays of the Z0 boson with the OPAL detector at LEP. We find 68 Λl−, Λl+ candidates in 458 583 hadronic Z0 decays. We interpret this as a signal of 55 ± 9+0.3−3.1 events from the semi-leptonic decays of b baryons. Assuming weakly decaying b baryons produced in Z0 decays are mostly Λb particles, we measure the product branching ratio (Γbb/Γhad) f (b→Λb) B (Λb→Λl−vX), averaged over the electron and muon channels, to be (6.2±1.0±1.5)×10−4.