EPJ

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EPJ C - Particles and Fields
Particles and Fields
Eur. Phys. J. C 13, 225-240
DOI 10.1007/s100520000323

Measurements of inclusive semileptonic branching fractions
of b hadrons in $\boldmath\mathrm{Z}^0$ decays

The OPAL Collaboration

G.Abbiendi 2 - et al.

2Dipartimento di Fisica dell' Università di Bologna and INFN, 40126 Bologna, Italy

Received: 11 June 1999 / Published online: 3 February 2000 - © Springer-Verlag 2000

Abstract
A measurement of inclusive semileptonic branching fractions of b hadrons produced in Z0 decays is presented. An enriched Z $^0 \to \mathrm{b \bar b}$ sample is obtained with a lifetime flavour-tagging technique. The leptonic events are then selected from this sample, and classified according to their origin, which is determined by comparing the distribution of several kinematic variables using artificial neural network techniques. Using 3.6 million multihadronic events collected with the OPAL detector at energies near the Z0 resonance, the values

\begin{eqnarray*}\mathrm{BR}(\mathrm{b}\rightarrow \ell{\rm X}) &=& (10.84\pm 0.... ...tat.)}\pm 0.22{\rm ~(syst.)}^{~+0.33}_{~-0.29}{\rm ~(model)})\,. \end{eqnarray*}


are measured, where b denotes all weakly decaying b hadrons and $\ell$represents either e or $\mu$. The second error includes all experimental systematic uncertainties whereas the last error is due to uncertainties in modelling of the lepton momentum spectrum in semileptonic decays and b quark fragmentation. The average fraction of the beam energy carried by the weakly decaying b hadron, $\langle x_E \rangle$, is measured to be

\begin{eqnarray*}\langle x_E \rangle = 0.709 \pm 0.003 {\rm ~(stat.)}\pm 0.003 {\rm ~(syst.)} \pm 0.013 {\rm ~(model)} \end{eqnarray*}


where the modelling error is dominated by the choice of b fragmentation model. The agreement between data and various semileptonic decay models and fragmentation functions is also investigated.

Copyright Società Italiana di Fisica, Springer-Verlag 2000

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