2018 Impact factor 4.843
Particles and Fields

Eur. Phys. J. C 20, 455-478 (2001)
DOI: 10.1007/s100520100690

Measurement of the semileptonic b branching fractions and average b mixing parameter in Z decays

The DELPHI Collaboration P. Abreu and et al.

LIP, IST, FCUL - Av. Elias Garcia, 14-$1^{o}$, 1000 Lisboa Codex, Portugal

(Received: 3 March 2000 / Revised version: 23 April 2001 / Published online: 28 May 2001 -© Springer-Verlag / Società Italiana di Fisica 2001 )

The semileptonic branching fractions for primary and cascade b decays ${\mathrm{BR}}(b\rightarrow \ell^-)$, $\mathrm{BR}(b\rightarrow c\rightarrow \ell^+)$ and $\mathrm{BR}(b\rightarrow\bar{c}\rightarrow \ell^-$ were measured in hadronic Z decays collected by the DELPHI experiment at LEP. The sample was enriched in b decays using the lifetime information and various techniques were used to separate leptons from direct or cascade b decays. By fitting the momentum spectra of di-leptons in opposite jets, the average b mixing parameter $\bar{\chi}$ was also extracted. The following results have been obtained: $
\mathrm{BR}({b\rightarrow \ell^- \ell^-}) = (10.70\pm0.08 (stat)\pm0.21(syst)_{+0.44}^{-0.30}(model))\%
$ $
\mathrm{BR}({b\rightarrow c\rightarrow \ell^+})= (7.98\pm0.22 (stat)\pm0.21(syst)^{+0.14}_{-0.20}(model))\%
$ $
\mathrm{BR}({b\rightarrow \bar{c} \rightarrow \ell^-})= (1.61\pm0.20 (stat)\pm0.17(syst)^{+0.30}_{-0.44}(model))\%
$ $
\bar{\chi} = 0.127\pm0.013 (stat)\pm0.005(syst)\pm0.004(model) $

© Società Italiana di Fisica, Springer-Verlag 2001