Multiplicities of pizero, eta, Kzero and of charged particles in quark and gluon jets

TL;DR

This study compares the multiplicities of various particles in quark and gluon jets, confirming some QCD predictions and challenging others, using OPAL data from LEP to analyze particle ratios and multiplicity slopes.

Contribution

It provides the first detailed comparison of particle multiplicities across different mesons in quark and gluon jets, testing QCD predictions with high-precision data.

Findings

Gluon to quark jet particle multiplicity ratio is independent of particle species.

No significant eta meson enhancement in gluon jets beyond charged particles.

Measured multiplicity slope ratio C is slightly higher than theoretical predictions.

Abstract

We compared the multiplicities of pizero, eta, Kzero and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale Qjet which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of Qjet for pizero, eta and Kzero was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast to some theoretical predictions and previous observations, we observed no evidence for an enhancement of eta meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a next-to-next-to-next-to leading order calculation. Our result, C=2.27+-0.20(stat+syst),is about one standard deviation higher than the perturbative prediction.