DECAMP, D (reprint author), CNRS,INST NATL PHYS NUCL & PHYS PARTICULES,PHYS PARTICULES LAB,F-74019 ANNECY LE VIEUX,FRANCE.
In 160 000 hadronic Z decays recorded with the ALEPH detector at LEP, the yields of LAMBDA-l- and LAMBDA-l+ combinations have been measured. The observed excess of LAMBDA-l- over LAMBDA-l+ of 53 +/- 13 is interpreted as evidence for b baryons and their semileptonic decay. Assuming that three body decay processes such as LAMBDA(b) --> LAMBDA(c)+ l- vBAR dominate the semileptonic decay of b baryons, this excess corresponds to a product branching ratio BR(b --> LAMBDA(b)).BR(LAMBDA(b) --> LAMBDA(c)+ l- vBAR).BR(LAMBDA(c)+ --> LAMBDA-X) = (0.95 +/- 0.22 (stat.) +/- 0.21 (syst.))%, where LAMBDA(b) and LAMBDA(c)+ denote the bottom and charm baryons respectively.