A measurement of the semileptonic branching ratio

Inclusive pi(+/-), K+/- and (p,(p)over-bar) production is investigated using data recorded by the ALEPH detector between 1992 and 1994. The momentum spectra and multiplicities are measured separately in Z --> b(b)over-bar, Z --> c(c)over-bar and Z --> u(u)over-bar, d(d)over-bar; s(s)over-bar decays. The number of protons found in b-hadron decays is used to estimate the fraction of b-baryons in b events to be (10.2 +/- 0.7 +/- 2.7)% assuming BR(b-baryon --> pX) = (58 +/- 6)%. From an additional study of proton-lepton correlations in b events, the branching ratio BR(b-baryon --> pl(v)over-bar-X) = (4.63 +/- 0.72 +/- 0.98)% is obtained. The ratio BR(b-baryon --> pl(nu)over-bar-X)/BR(b-baryon --> pX) is found to be 0.080 +/- 0.012 +/- 0.014