Particle physics.

The various groups of the Physik-Institut in the elds of particle physics are using for their experiments external accelerators at the large international research institutions PSI (Villigen), CERN (Genf), DESY (Hamburg) and Brookhaven. Further activities in the eld of particle physics which are connected to questions of astropar-ticlephysics and cosmology do not require accelerators or they are carried out at a nuclear reactor. Most of these experiments are motivated in a broader sense by the fact that the present, highly successful standard model of particle physics cannot be understood as the ultimate truth for several, often cited reasons: There are too many free parameters, the origin of the masses it not known, the nature of the neutrinos is not known, no symmetry is known which leads to the conservation of the lepton number separately for the three generations, the strong force is not yet uniied with the electroweak force, the quantization of the gravitational force is unsolved, the question of the existence of other forces is still open. A test of the standard model can be done by either a search for new particles or states of matter at medium and high energies or complementarily by a search with high precision at low energies for forbidden lepton number violating processes, or a search for the magnetic moment of the neutrino at a reactor power station. Mainly on the basis of this motivation Part I of the annual report presents the following experiments:-Search for-number violating decays and reactions at PSI-Meson spectroscopy at LEAR with the Crystal Barrel-Particle physics at DESY/HERA and Brookhaven-Search for neutrino masses, mixing and magnetic moment-Remeasurement of the gravitational constant Especially the following result should be mentioned: The H1-Experiment at HERA has observed at the highest momentum transfers accessible so far a number of events exceeding the standard model expectation. If improved during the coming year these data would be a hint at \new physics" beyond the standard model. At lower momentum transfer the standard model is connrmed.