A measurement of the product branching ratio $f ({\rm b} \to \Lambda_{\rm b}) \cdot{\rm BR} (\Lambda_{\rm b} \to \Lambda {\rm X})$ in ${\rm Z}^0$ decays

Abstract.

The product branching ratio, $f ({\rm b} \to \Lambda_{\rm b}) \cdot{\rm BR} (\Lambda_{\rm b} \to \Lambda{\rm X})$, where $\Lambda_{\rm b}$ denotes any weakly-decaying b–baryon, has been measured using the OPAL detector at LEP. $\Lambda_{\rm b}$'s are selected by the presence of energetic $\Lambda$ particles in bottom events tagged by the presence of displaced secondary vertices. A fit to the momenta of the $\Lambda$ particles separates signal from B meson and fragmentation backgrounds. The measured product branching ratio is \[ f ({\rm b} \to \Lambda_{\rm b}) \cdot{\rm BR} (\Lambda_{\rm b} \to \Lambda{\rm X}) = (2.67) \pm 0.38 ({\rm stat})^{+0.67}_{-0.60} ({\rm sys}))\%\; . \] Combined with a previous OPAL measurement, one obtains \[ f ({\rm b} \to \Lambda_{\bf b}) \cdot{\rm BR} (\Lambda_{\rm b} \to \Lambda{\rm X}) = (3.50) \pm 0.32 ({\rm stat})\pm 0.35 ({\rm sys}))\%\; . \]