Energy dependence of the differences between the quark and gluon jet fragmentation

Three jet eventsarising from decays of the Z boson, collected by the DELPHI detector, were used to measure differences in quarkand gluonfragmentation. Gluonjets were anti-tagged by identifying b quarkjets. Unbiased quarkjets came from events with two jets plus one photon. Quarkand gluonjet properties in different energy ranges were compared for the first time within the same detector. Quarkand gluonjets of nearly the same energy in symmetric three jet eventtopologies were also compared. Using three independent methods, the averagevalue of the ratio of the mean charged multiplicities of gluonand quarkjets is = 1.241 ± 0.015 (stat.) ± 0.025 (syst.). Gluonjets are broader and produce fragments with a softer energy spectrum than quarkjets of equivalent energy. The string effect has been observed in fully symmetric three jet events. The measured ratio R_{gamma} of the charged particle flow in the qoverline{q} inter-jet region of the qar{q}g and qar{q}gamma samples agrees with the perturbative QCDexpectation. The dependence of the mean charged multiplicity on the hadronic center-of-mass energy was analysed in photon plus n-jetevents. The value for alpha_s(M_Z) determined from these data using a QCD prediction with corrections at leading and next-to-leading order is αs(MZ)= 0.116 ± 0.003 (stat.) ± 0.009 (syst.).