A measurement of the product branching ratio f(b → Λb) · BR(Λb → ΛX) in Z0 decays

The product branching ratio, f(b→Λb)⋅BR(Λb→ΛX)f(b→Λb)⋅BR(Λb→ΛX) , where ΛbΛb denotes any weakly-decaying b–baryon, has been measured using the OPAL detector at LEP. ΛbΛb 's are selected by the presence of energetic ΛΛ particles in bottom events tagged by the presence of displaced secondary vertices. A fit to the momenta of the ΛΛ particles separates signal from B meson and fragmentation backgrounds. The measured product branching ratio is f(b → Λb) · BR(Λb → ΛX) = (2.67) ± 0.38(stat)+0.67−0.60(sys))%. Combined with a previous OPAL measurement, one obtains f(b → Λb) · BR(Λb → ΛX) = (3.50) ± 0.32(stat) ± 0.35(sys))%.