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

The L3 Collaboration     M.Acciarri - et al.

doi:doi:10.1007/s100520000296

2022 Impact factor 4.4

Particles and Fields

Eur. Phys. J. C 13, 47-61
DOI 10.1007/s100520000296

Measurement of R_b 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-p_t 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 R_b and $Br(\mathrm{b} \rightarrow \ell\nu\mathrm{X})$ :