EPJ

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EPJ C - Particles and Fields
Particles and Fields


Eur. Phys. J. C 24, 177-191 (2002)
DOI: 10.1007/s100520200950

Measurement of the forward-backward asymmetry in $\mathrm{Z} \to \mathrm{b} \bar{\mathrm{b}}$ and $\mathrm{Z} \to \mathrm{c} \bar{\mathrm{c}}$ decays with leptons

The ALEPH Collaboration

(Received: 7 January 2002 / Published online: 26 April 2002 - © Springer-Verlag / Società Italiana di Fisica 2002 )

Abstract
The sample of hadronic Z decays collected by the ALEPH detector at LEP in the years 1991-1995 is analysed in order to measure the forward-backward asymmetry in $\mathrm{Z} \to \mathrm{b} \bar{\mathrm{b}}$ and $\mathrm{Z} \to \mathrm{c} \bar{\mathrm{c}}$ events and the ${\mathrm{B}}^0{\mathrm{-}}\bar {\mathrm{B}}^0$ average mixing parameter $\bar \chi$. Quark charges are tagged by the charges of electrons and muons produced in b and c semileptonic decays. Multivariate analyses are used to separate the event flavours and ${\mathrm{b}} \to \ell$/ ${\mathrm{b}} \to {\mathrm{c}} \to \ell$ processes. The b and c quark asymmetries are measured simultaneously; the average mixing parameter and the pole asymmetries are determined to be

\begin{displaymath}\bar \chi = 0.1196 \pm 0.0049 \; {\mathrm{(stat.)}} \;{}^{\di... ...53 \; {\mathrm{(stat.)}} \; \pm 0.0037 \; {\mathrm{(syst.)}}. \end{displaymath}

These asymmetries, combined with the ALEPH measurements of the b asymmetry using inclusive b hadron decays and of the c asymmetry using reconstructed D mesons, correspond to a value of the effective electroweak mixing angle of ${\mathrm{sin}}^2\theta^{\mathrm{eff}}_{\mathrm{W}} = 0.23188 \pm 0.00046$.



© Società Italiana di Fisica, Springer-Verlag 2002

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