Gluon radiation in electron-positron annihilation at center-of-mass energies from 50 to 60.8 GeV

One of the key characteristics of QCD is the existence of gluons. Experimentally, these are realized as jets of hadrons. It is expected that jets initiated by gluons are different from those initiated by quarks. Gluon jets are expected to be wider than quark jets and the momenta of particles in gluon jets are expected to be lower than those in quark jets.

Three-jet events produced in $e\sp{+}e\sp{-}$ annihilations are used to provide comparisons between quark and gluon jets. Differences between quark-induced and gluon-induced jets are observed. Quark jets tend to have a more tightly collimated structure than gluon jets, which is reflected in the concentration of a larger fraction of the jet's energy near the jet axis, the higher rapidity relative to the jet direction of the most energetic particle in a jet, and the narrower distribution of the energy weighted angular correlation. Studies with a QCD-motivated event generator that uses the same fragmentation procedure for quarks and gluons indicate that the observed differences are not introduced by the effects of detector acceptance or by our analysis procedures, but are reflections of basic differences in the fragmentation processes of the partons.