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

  • Experimental Physics
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Abstract.

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

$C_A/C_F = 2.261 \pm 0.014_{\mathrm{stat.}} \pm 0.036_{\mathrm{exp.}} \pm 0.066_{\mathrm{theo.}}$

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 \(r = N_{gg}(s)/N_{q\bar q}(s)\) of the gluon and quark multiplicities and \(r^{(1)} = N_{gg}'(s)/N_{q\bar q}'(s)\) 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).

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Received: 28 June 2005, Revised: 31 August 2005, Published online: 6 October 2005

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The DELPHI Collaboration. Charged particle multiplicity in three-jet events and two-gluon systems. Eur. Phys. J. C 44, 311–331 (2005). https://doi.org/10.1140/epjc/s2005-02390-x

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