Unbiased gluon jet multiplicity from e$^+$e$^-$ three-jet events

Abstract

The charged particle multiplicities of two- and three-jet events from the reaction e$^+$e$^-$,\to $Z$^0 \to hadrons$ are measured for Z$^0$ decays to light quark (uds) flavors, using the data sample of the OPAL Collaboration at LEP. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted. The unbiased gluon jet data are compared to corresponding results for quark jets. We determine the ratio $r \equiv \ngluon/\nq$ of multiplicities between gluon and quark jets as a function of energy scale. We also determine the ratio of slopes, $r^{(1)} \equiv ({\mathrm{d}}\ngluon /{\mathrm{d}}y) /({\mathrm{d}}\nq / {\mathrm{d}}y)$, and of curvatures, $r^{(2)} \equiv ({\mathrm{d}}^2\ngluon /{\mathrm{d}}y^2) /({\mathrm{d}}^2\nq / {\mathrm{d}}y^2)$, where $y$ specifies the energy scale. At 30 GeV, we find $r = 1.422\pm0.051$, $r^{(1)} = 1.761\pm0.071$ and $r^{(2)} = 1.98\pm0.13$, where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions.