The Scale Dependence of the Hadron Multiplicity in Quark and Gluon Jets and a Precise Determination of $C_{A}/C_{F}$

TL;DR

This paper measures the ratio of gluon to quark jet multiplicities at LEP, providing a precise determination of the QCD color factor ratio C_A/C_F through analysis of hadron multiplicities and jet opening angles.

Contribution

It offers a direct measurement of the color factor ratio C_A/C_F from hadron multiplicity data, improving precision and understanding of hadronization differences.

Findings

Measured C_A/C_F = 2.246 ± 0.062 (stat.) ± 0.080 (syst.) ± 0.095 (theo.)

Observed the increase of hadron multiplicity with the transverse momentum-like scale in jets

Explained the smaller-than-expected multiplicity ratio by hadronization differences

Abstract

Data collected at the Z resonance using the DELPHI detector at LEP are used to determine the charged hadron multiplicity in gluon and quark jets as a function of a transverse momentum-like scale. The colour factor ratio, \cacf, is directly observed in the increase of multiplicities with that scale. The smaller than expected multiplicity ratio in gluon to quark jets is understood by differences in the hadronization of the leading quark or gluon. From the dependence of the charged hadron multiplicity on the opening angle in symmetric three-jet events the colour factor ratio is measured to be: C_A/C_F = 2.246 \pm 0.062 (stat.) \pm 0.080 (syst.) \pm 0.095 (theo.)