A MODEL-INDEPENDENT MEASUREMENT OF QUARK AND GLUON JET PROPERTIES ANDDIFFERENCES

Three jet events are selected from hadronic Z(0) decays with a symmetr y such that the two lower energy jets are produced with the same energ y and in the same jet environment. In some of the events, a displaced secondary vertex is reconstructed in one of the two lower energy jets, which permits the other lower energy jet to be identified as a gluon jet, with an estimated purity of about 93%. Comparing these gluon jets to the inclusive sample of lower energy jets from the symmetric data set yields direct, model independent measurements of quark and gluon j et properties, which have essentially no bias except from the jet defi nition. Results are reported using both the k(perpendicular to) and co ne jet definitions. For the k(perpendicular to) algorithm, we find [n( k perpendicular to)(ch.)]gluon/[n(k perpendicular to)(ch.)]quark = 1.2 5 +/- 002(stat.) +/- 0.03(syst.) for the ratio of the mean charged par ticle multiplicity of gluon to quark jets, while for the cone algorith m, we find [n(cone)(ch.)]gluon/[n(cone)(ch.)]quark = 1.10 +/- 0.02(sta t.) +/- 0.02(syst.)using a cone size of 30 degrees. We also report mea surements of the angular distributions of particle energy and multipli city around the jet directions, and of the fragmentation functions of the jets. Gluon jets are found to be substantially broader and to have a markedly softer fragmentation function than quark jets, in agreemen t with our earlier observations.