Measurement of the fraction of hadronic Z decays into charm quark pairs

The full statistics of hadronic Z decays collected with the ALEPH detector are analysed to measure, by three methods, the ratio, Rc , of the partial decay width of the Z into cc¯ quarks to the total hadronic width. One method uses the inclusive p and p⊥ spectra of electrons. The other two use a double-tagging technique to measure Rc independently of the charm-tagging efficiency. In one, the tagging procedure uses the reconstruction of high momentum charmed mesons ( D∗+ , D+ and D0) to detect the charm quarks. In the other, a charm quark is tagged from the D∗ 's reconstructed in the D∗+→π+D0 decay channel and the other from the slow pion from the D∗−→π−D¯0 decay. The combination of these measurements leads to Rc=Γ(Z→cc¯)/Γ(Z→hadrons))=0.1681±0.0054(stat)±0.0062(syst)