Studies of hadronic event structure and comparisons with QCD models at the Z 0 resonance

The structure of hadronic events fromZ0 decay is studied by measuring event shape variables, factorial moments, and the energy flowdistribution. The distributions, after correction for detector effects and initialand final state radiation, are compared with the predictions of different QCD Monte Carlo programs with optimized parameter values. These Monte Carlo programs use either the second order matrix element or the parton showerevolution for the perturbative QCDcalculations and use the string, the cluster, or the independent fragmentation model for hadronization. Both parton showerandO(α 2 s matrixelement based models with string fragmentation describe the data well. The predictions of the model based on parton showerand cluster fragmentation are also in good agreement with the data. The model with independent fragmentation gives a poor description of the energy flowdistribution. The predicted energy evolutions for the mean values of thrust, sphericity, aplanarity, and charge multiplicity are compared with the data measured at different center-of-mass energies. The parton showerbased models with string or cluster fragmentation are found to describe the energy dependences well while the model based on theO(α 2 s calculation fails to reproduce the energy dependences of these mean values.