Evidence for b baryons in Z decays

Abstract In 160 000 hadronic Z decays recorded with the ALEPHdetector at LEP, the yields of Λ l − and Λ l + combinations have been measured. The observed excess of Λ l − over Λ l + of 53±13 is interpreted as evidence for b baryonsand their semileptonic decay. Assuming that three body decay processes such as Λ b →Λ c + l − v dominate the semileptonic decayof b baryons, this ex cess corresponds to a product branching ratio BR ( b →Λ b )· BR (Λ b →Λ c + l − v )· BR (Λ c + →ΛX) = (0.95±0.22 ( stat. )±0.21( syst. ))% , where Λ b and Λ c + denote the bottom and charm baryonsrespectively.