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This thesis describes the determination of the strong coupling constant $\alpha\sb{s}$ from measurements of multi-jet rates in deep inelastic electron-proton scattering at HERA by the ZEUS collaboration for values of the squared four-momentum transfer $Q\sp2$ between 120 and 3600 GeV$\sp2.$ A total integrated luminosity of 3.2 pb$\sp{-1},$ collected during 1994, was used for the measurement. Jets are identified with the JADE algorithm. The jet rates were fitted to a next-to-leading order $O\ (\alpha\sbsp{s}{2})$ perturbative QCD calculation with $\alpha\sb{s}$ left as a free parameter. Using the fitted value for $\alpha\sb{s}$ the perturbative calculation describes well the measured rates and kinematic properties of multi-jet events. A cut on the angular distribution of parton emission in the $\gamma\sp{\*}$-parton center of mass is introduced to remove forward going jets. The value of $\alpha\sb{s}$ is measured in three $Q\sp2$ regions and finally combined over the full kinematic range. The $\alpha\sb{s}$ value decreases for increasing $Q\sp2,$ consistent with the running of the strong coupling constant, as expected by QCD. The determined value is $\alpha\sb{s}\ (M\sb{Z\sp0})=0.117\pm0.005\ (stat)\ \pm\ \sbsp{0.005}{0.004}(syst\sb{exp})\ \pm\ 0.007\ (syst\sb{theory}).$
This book provides an introduction to Quantum Chromodynamics (QCD), the theory of strong interactions. It covers in full detail both the theoretical foundations and the experimental tests of the theory. Although the experimental chapters focus on recent measurements, the subject is placed into historical perspective by also summarizing the steps which led to the formulation of QCD. Measurements are discussed as they were performed by the LEP experiments at CERN, or at hadron-hadron and lepton-hadron colliders such as the TEVATRON at Fermilab and HERA at DESY. Emphasis is placed on high energy tests of QCD, such as measurements of the strong coupling constant, investigations of the non-abelian structure of the underlying gauge group, determinations of nucleon structure functions, and studies of the non-perturbative hadronization process. This excellent text gives a detailed overview of how QCD developed in the 20th century and where we stand with respect to a quantitative understanding after the turn of the millenium. The text is intended for graduate and postgraduate students as well as researchers, and includes numerous problems and solutions.