نبذة مختصرة : A study of the fragmentation properties of charm and bottom quarks intoD mesons is presented. From 263 700Z 0 hadronic decays collected in 1991 with the DELPHI detector at the LEP collider,D 0,D + andD *+ are reconstructed in the modesK − Ï€ +,K − Ï€ + K + andD 0 Ï€ + followed byD 0→K − Ï€ +, respectively. The fractional decay widths Γ(Z0→D/DˉX)/Γh are determined, and first results are presented for the production ofD mesons from ccˉ and bbˉ events separately. The average energy fraction ofD *± in charm quark fragmentation is found to be 〈X E (D *)〉 c =0.487±0.015 (stat)±0.005 (sys.). Assuming that the fraction ofD s and charm-baryons produced at LEP is similar to that around 10 GeV, theZ 0 partial width into charm quark pairs is determined to beΓ c /Γ h =0.187±0.031 (stat)±0.023 (sys). The probability for ab quark to fragment into Bˉs orb-baryons is inferred to be 0.268±0.094 (stat)±0.100 (sys) from the measured probability that it fragments into a Bˉ0 orB −.
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