Study of the fragmentation of b quarks into B mesons at the Z peak

The fragmentation of b quarks into B mesons is studied with four million hadronic Z decays collected by the ALEPH experiment during the years 1991-1995. A semi-exclusive reconstruction of B → lvD(*) decays is performed, by combining lepton candidates with fully reconstructed D(*) mesons while the neutrino energy is estimated from the missing energy of the event. The mean value of xB wd, the energy of the weakly-decaying B meson normalised to the beam energy, is found to be (xB wd) = 0.716 ± 0.006 (stat) ± 0.006 (syst), using a model-independent method; the corresponding value for the energy of the leading B meson is (xB L) 0.736 ± 0.006 (stat) ± 0.006 (syst). The reconstructed spectra are compared with different fragmentation models. © 2001 Elsevier Science B.V.