The charged particle multiplicity distribution of hadronic Z decays was measured on the peak of the Z resonance using the ALEPH detector at LEP. Using a model independent unfolding procedure the distribution was found to have a mean <n>= 20.85 +/- 0.24 and a dispersion D = 6.34 +/- 0.12. Comparison with lower energy data supports the KNO scaling hypothesis in the energy range square-root s = 29-91.25 GeV. At square-root s = 91.25 GeV the shape of the multiplicity distribution is well described by a log-normal distribution, as predicted from a cascading model for multi-particle production. The same model also successfully describes the energy dependence of the mean and width of the multiplicity distribution. A next-to-leading order QCD prediction in the frame-work of the modified leading-log approximation and local parton-hadron duality is found to fit the energy dependence of the mean but not the width of the charged multiplicity distribution, indicating that the width of the multiplicity distribution is a sensitive probe for higher order QCD or non-perturbative effects.

Measurement of the Charged-particle Multiplicity Distribution In Hadronic-Z Decays

BATIGNANI, GIOVANNI;CIOCCI, MARIA AGNESE;FERRANTE, ISIDORO;FIDECARO, FRANCESCO;FORTI, FRANCESCO;GIORGI, MARCELLO;MESSINEO, ALBERTO MARIA;TONELLI, GUIDO EMILIO;G. TRIGGIANI;
1991

Abstract

The charged particle multiplicity distribution of hadronic Z decays was measured on the peak of the Z resonance using the ALEPH detector at LEP. Using a model independent unfolding procedure the distribution was found to have a mean = 20.85 +/- 0.24 and a dispersion D = 6.34 +/- 0.12. Comparison with lower energy data supports the KNO scaling hypothesis in the energy range square-root s = 29-91.25 GeV. At square-root s = 91.25 GeV the shape of the multiplicity distribution is well described by a log-normal distribution, as predicted from a cascading model for multi-particle production. The same model also successfully describes the energy dependence of the mean and width of the multiplicity distribution. A next-to-leading order QCD prediction in the frame-work of the modified leading-log approximation and local parton-hadron duality is found to fit the energy dependence of the mean but not the width of the charged multiplicity distribution, indicating that the width of the multiplicity distribution is a sensitive probe for higher order QCD or non-perturbative effects.
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H.; Heusse, P.; Janot, P.; Kim, D. W.; Lediberder, F.; Lefrancois, J.; Lutz, A. M.; Veillet, J. J.; Videau, I.; Zhang, Z.; Zomer, F.; Abbaneo, D.; Amendolia, S. R.; Bagliesi, G.; Batignani, Giovanni; Bosisio, L.; Bottigli, U.; Bradaschia, C.; Carpinelli, M.; Ciocci, MARIA AGNESE; Dellorso, R.; Ferrante, Isidoro; Fidecaro, Francesco; Foa, L.; Focardi, E.; Forti, Francesco; Gatto, C.; Giassi, A.; Giorgi, Marcello; Ligabue, F.; Mannelli, E. B.; Marrocchesi, P. S.; Messineo, ALBERTO MARIA; Palla, F.; Sanguinetti, G.; Steinberger, J.; Tenchini, R.; Tonelli, GUIDO EMILIO; Triggiani, G.; Vannini, C.; Venturi, A.; Verdini, P. G.; Walsh, J.; Carter, J. M.; Green, M. G.; March, P. V.; Medcalf, T.; Quazi, I. S.; Strong, J. A.; West, L. R.; Wildish, T.; Botterill, D. R.; Clifft, R. W.; Edgecock, T. R.; Edwards, M.; Fisher, S. M.; Jones, T. J.; Norton, P. R.; Salmon, D. P.; Thompson, J. C.; Blochdevaux, B.; Colas, P.; Locci, E.; Loucatos, S.; Monnier, E.; Perez, P.; Perlas, J. 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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/828624
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