2018 Impact factor 4.843
Particles and Fields
Eur. Phys. J. C 13, 47-61
DOI 10.1007/s100520000296

Measurement of Rb and $Br(\mathrm{b} \rightarrow
\ell\nu\mathrm{X})$ at LEP
using double-tag methods

The L3 Collaboration

M.Acciarri26 - et al.

26 INFN-Sezione di Milano, 20133 Milan, Italy

Received: 2 September 1999 / Published online: 3 February 2000 - © Springer-Verlag 2000

Abstract
We present a combined measurement of $R_\mathrm{b} = \Gamma(\mathrm{Z
\rightarrow b\bar{b}}) / \Gamma(\mathrm{Z} \rightarrow \mbox{hadrons})$and the semileptonic branching ratio of b quarks in Z decays, $Br(\mathrm{b} \rightarrow
\ell\nu\mathrm{X})$, using double-tag methods. Two analyses are performed on one million hadronic Z decays collected in 1994 and 1995. The first analysis exploits the capabilities of the silicon microvertex detector. The tagging of b-events is based on the large impact parameter of tracks from weakly decaying b-hadrons with respect to the e+ e- collision point. In the second analysis, a high-pt lepton tag is used to enhance the b-component in the sample and its momentum spectrum is used to constrain the model dependent uncertainties in the semileptonic b-decay. The analyses are combined in order to provide precise determinations of Rb and $Br(\mathrm{b} \rightarrow
\ell\nu\mathrm{X})$:

\begin{displaymath}R_\mathrm{b} = 0.2174 \pm 0.0015\mbox{$\;$(stat.)} \pm 0.0028\mbox{$\;$(sys.)};\end{displaymath}


\begin{displaymath}Br(\mathrm{b} \rightarrow\ell\nu\mathrm{X}) = (10.16 \pm
0.13\mbox{$\;$(stat.)} \pm 0.30\mbox{$\;$(sys.)})\%.\end{displaymath}


Copyright Società Italiana di Fisica, Springer-Verlag 2000