[en] In this thesis the first results of measurements on the rare decay of the neutral pion π⁰→e⁺e^- are described. These measurements were performed in a collaboration at the European Organisation for Nuclear Research (CERN) in Geneva, using the OMICRON spectrometer. A negative pion beam of T=190 MeV produced neutral pions via the charge exchange reaction π^-p→π⁰n in a liquid hydrogen target placed inside this spectrometer. The tracks of the incoming pions and any decay leptons emerging from the target were localized using multiwire proportional and drift chamber detectors. In the analysis, the momentum of a particle was then obtained from the curvature of its track and the values of the magnetic field along that track. The magnetic field was accurately measured throughout the volume of the spectrometer. (Auth.)