A model independent measurement of quark and gluon jet properties and differences

The OPAL Collaboration

Research output: Contribution to journalArticlepeer-review

64 Scopus citations


Three jet events are selected from hadronic Z0 decays with a symmetry such that the two lower energy jets are produced with the same energy 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 jet properties, which have essentially no bias except from the jet definition. Results are reported using both the k and cone jet definitions. For the k algorithm, we find {Mathematical expression} for the ratio of the mean charged particle multiplicity of gluon to quark jets, while for the cone algorithm, we find {Mathematical expression} using a cone size of 30°. We also report measurements of the angular distributions of particle energy and multiplicity 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 agreement with our earlier observations.

Original languageEnglish
Pages (from-to)179-201
Number of pages23
JournalZeitschrift fur Physik C-Particles and Fields
Issue number2
StatePublished - 1 Jun 1995
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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