**44**: 311-331

http://dx.doi.org/10.1140/epjc/s2005-02390-x

Experimental Physics

## Charged particle multiplicity in three-jet events and two-gluon systems

The DELPHI Collaboration

The charged particle multiplicity in hadronic three-jet events from *Z* decays is investigated. The topology dependence of the event multiplicity is found to be well described by a modified leading logarithmic prediction. A parameter fit of the prediction to the data yields a measurement of the colour factor ratio *C*
_{
A
}/*C*
_{
F
} with the result

in agreement with the SU(3) expectation of QCD. The quark-related contribution to the event multiplicity is subtracted from the three-jet event multiplicity resulting in a measurement of the multiplicity of two-gluon colour-singlet states over a wide energy range. The ratios of the gluon and quark multiplicities and of their derivatives are compared with perturbative calculations.

While a good agreement between calculations and data is observed for *r*
^{(1)}, larger deviations are found for *r* indicating that non-perturbative effects are more important for *r* than for *r*
^{(1)}.

*© Springer-Verlag, 2005*