Measurement of the semileptonic branching ratio of charm hadrons produced in ${\rm Z}^0\to{\rm c\bar c}$ decays

Abstract.

The inclusive charm hadron semileptonic branching fractions ${\rm B}({\rm c}\to{\rm e})$ and ${\rm B}({\rm c}\to\mu)$ in $\mathrm{Z}^0\to\mathrm c\bar{\mathrm c}$ events have been determined using 4.4 million hadronic $\mathrm{Z}^0$ decays collected with the OPAL detector at LEP. A charm-enriched sample is obtained by selecting events with reconstructed $\mathrm{D}^{*\pm}$ mesons. Using leptons found in the hemisphere opposite that of the $\mathrm{D}^{*\pm}$ mesons, the semileptonic branching fractions of charm hadrons are measured to be \[ {\rm B}({\rm c}\to{\rm e})= 0.103 \pm 0.009^{+0.009}_{-0.008} {\rm and} {\rm B}({\rm c}\to\mu) = 0.090 \pm 0.007^{+0.007}_{-0.006}\,, \] where the first errors are in each case statistical and the second systematic. Combining these measurements, an inclusive semileptonic branching fraction of charm hadrons of \[ {\rm B}({\rm c}\to\ell) = 0.095 \pm{0.006}^{+0.007}_{-0.006} \] is obtained.