Correlations in the charged-particle multiplicity distribution
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Mangeol, Dominique Jean-Marie Jacques
[S.l. : s.n.]
Number of pages
II, 143 p.
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In this thesis, we perform an analysis on e+e- hadronic Z decays recorded in 1994 and 1995 by the L3 detector of LEP at center-of-mass energy corresponding to the Z mass. The analysis is performed in parallel for all hadronic events and for selected b-quark and light-quark events. The distribution of two variables, the charged-particle multiplicity and the inclusive charged-particle momentum are measured, from which all the analysis is carried out. From the measurement of the charged-particle multiplicity distribution, it is possible to extract information concerning the dynamics of the interaction. Using moments, one can obtain informations on particle correlation. We measure the Hq moments of the charged-particle multiplicity distribution which give the relative amount of genuine q-particle correlation. These Hq moments are known to display oscillations when plotted versus the order q. An explanation for these oscillations has been given by perturbative QCD. In the framework of the Next-to-Next to Leading Logarithm Approximation (NNLLA), one predicts such an oscillatory behavior for the Hq moments calculated from the multiplicity distribution of partons and under the assumption of the local parton-hadron duality (LPHD) for the one of final-state particles. However, further studies performed on Monte Carlo show that this oscillatory behavior can be reproduced without the need for the NNLLA, thus suggesting the need of an explanation different from that provided by perturbative QCD. In the absence of confirmation of pQCD, we search for an alternative explanation using a more phenomenological approach by investigating the possibility that the Hq oscillatory behavior could be due to the fact that the charged-particle multiplicity distribution derives from a superposition of final states of different event topology, such as 2-jet, 3-jet events or light- and b-quark events
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