Multiplicity distributions of gluon and quark jets and tests of QCD analytic predictions

TL;DR

This paper measures and compares the multiplicity distributions of gluon and quark jets in e+e- collisions, testing QCD predictions with improved theoretical calculations including higher-order corrections and energy conservation.

Contribution

It provides experimental data on gluon and quark jet multiplicities and tests advanced QCD analytic predictions, highlighting the importance of higher-order corrections.

Findings

Gluon jets have higher mean multiplicity than quark jets.

Next-to-next-to-leading order calculations better match the data.

Ratios of cumulant moments agree with QCD predictions.

Abstract

Gluon jets are identified in e+e- hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon jets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent of a jet finding algorithm. The charged particle multiplicity distribution of the gluon jets is presented, and is analyzed for its mean, dispersion, skew, and curtosis values, and for its factorial and cumulant moments. The results are compared to the analogous results found for a sample of light quark (uds) jets, also defined inclusively. We observe differences between the mean, skew and curtosis values of gluon and quark jets, but not between their dispersions. The cumulant moment results are compared to the predictions of QCD analytic calculations. A calculation which includes next-to-next-to-leading order corrections and energy conservation is observed to provide a much improved description of the data compared to a next-to-leading order calculation without energy conservation. There is agreement between the data and calculations for the ratios of the cumulant moments between gluon and quark jets.