Thermal description of hadron production in e+e- collisions

This thesis gives a comprehensive analysis of hadron production in $e^{+}e^{-}$ collisions at different center of mass energies in the framework of the Statistical Model of the hadron resonance gas. The model used for the analysis is formulated in the canonical ensemble with exact conservation of five quantum numbers. The corresponding canonical partition function in quantum statistics is derived and the canonical factor as the striking feature of the canonical framework will be investigated in detail. The parameters of the underlying model were determined using a fit to the average multiplicities of the latest measurements at $\sqrt{s}$=10, 29-35, 91 and 130-200 GeV. The measurements are compared to the pure thermal production like in heavy ion collisions as well as to the production in a second scenario accounting for hard collisions and the resulting enhancement of heavy quark. The results demonstrate that, within the accuracy of the experiments, none of the data sets is satisfactorily described with this approach, calling into question the notion that particle production in $e^{+}e^{-}$ collisions is thermal in origin. Nevertheless it is observed that the charm and bottom particle yields produced in hard collisions can be explained by large canonical enhancements of such particles in heavy jets, almost independent of the model parameters.