A measurement ofD meson production inZ 0 hadronic decays

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 − π +,K − π + K + andD 0 π + followed byD 0→K − π +, respectively. The fractional decay widths $$\Gamma {{(Z^0 \to {D \mathord{\left/ {\vphantom {D {\bar D}}} \right. \kern-\nulldelimiterspace} {\bar D}}X)} \mathord{\left/ {\vphantom {{(Z^0 \to {D \mathord{\left/ {\vphantom {D {\bar D}}} \right. \kern-\nulldelimiterspace} {\bar D}}X)} {\Gamma _h }}} \right. \kern-\nulldelimiterspace} {\Gamma _h }}$$ are determined, and first results are presented for the production ofD mesons from $$c\bar c$$ and $$b\bar b$$ 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 $$\bar B_s $$ orb-baryons is inferred to be 0.268±0.094 (stat)±0.100 (sys) from the measured probability that it fragments into a $$\bar B^0 $$ orB −.