Speaker: Peter Geltenbort, Institute Laue-Langevin, Grenoble
Abstract: Due to their outstanding property to be storable and hence observable for long periods of time (several hundreds of seconds) in suitable material or magnetic traps, ultra-cold neutrons (UCN)with energies around 100 neV are an unique tool to study fundamental properties of the free neutron. Their properties and production are described in detail. Selected experiments with ultra-cold neutrons (UCN) - the measurement of its lifetime and the search for an electric dipole moment - performed at the instrument "Physique Fondamentale 2 (PF2)" of the Institut Laue-Langevinn (ILL) are highlighted. For particles to have electric dipole moments, the forces concerned in their structure must be asymmetric with regard to space-parity (P) and time reversal (T). P violation is a well-known intrinsic feature of the weak interaction which is responsible for the beta-decay of the free neutron. T violation turns out to be necessary to explain the survival of matter at the expense of antimatter after the Big Bang. By searching for an EDM of the free neutron hypothetical new channels of T-violation can be investigated. The experiments at the ILL will be compared to competing EDM projects worldwide. The measurement of the lifetime of the free neutron together with the determination of one of the correlation parameters characterizing neutron decay allows tests of the Standard Model. Furthermore, the neutron lifetime plays an important role in Big-Bang Nucleosynthesis cosmology. Up to 180 s after the big-bang nuclei with more than one nucleon are unstable. The neutron lifetime determines how many neutrons have decayed up to this moment and hence the relative helium abundance in the universe. The different methods to measure the lifetime of the free neutron are reviewed and the latest experiments using storage of UCN at the ILL are described in detail. A brief outlook on future projects worldwide will be given.