MEASUREMENT OF THE PARTIAL WIDTH OF THE Z0 INTO B(B)OVER-BAR FINAL-STATES USING THEIR SEMILEPTONIC DECAYS

The spectra of prompt electrons and muons from the semi-leptonic decays of heavy hadrons produced in Z0 decays have been used to measure the coupling of the Z0 to b quarks weighted by the B hadrons mean semi-leptonic branching fraction, giving a value: BR(sl)b*GAMMA(bbBAR)/GAMMA(H)=0.0221+/-0.0015. The data has also been used to measure the value of the fragmentation parameter, defined in the context of the LUND PS Model, version 7.2, giving: epsilon(b)=(8(+5/-3)+/-2) 10(-3). The corresponding value of the mean fraction of the beam energy taken by a B hadron in the fragmentation of a b quark is: X(E)bBAR=0.69(+0.02/-0.03)+/-0.01. If the values of GAMMA(bbBAR) and GAMMA(H) are taken from the Standard Model, the following value is obtained for the mean semi-leptonic braching fraction of B hadrons: BR(sl)b=(10.1+/-0.7)%. Taking the value of GAMMA(bbBAR)/GAMMA(H) from an independent analysis of DELPHI data based on the use of the boosted sphericity product, a value: BR(sl)b=(10.1+/-1.3)% is obtained.