Search for the Higgs boson and a study of $e^+ e^- \to Z Z$ using the L3 detector at LEP

The first part of this thesis is devoted to the searc h for the Higgs boson predicted by the Standard Mo del (SM). By the introduction of this particle into the theory , the masses of bosons and fermions can be explained. The searc h is performed in channels characterised by quarks and leptons in the nal state. The analysis uses data tak en during the years 1999{2000 with the L3 detector at the Large Electron Positron collider LEP . The observ ed candidates are consisten t with the exp ectation from Standard Mo del bac k- ground processes. Evidence for Higgs boson production is not found. New mass limits were determined superseding previous mass limits established by L3 and other experiments. (not complete)