Measurement of the Beta-Asymmetry in the Decay of Free Polarized Neutrons with the Spectrometer Perkeo III

The charged current in Weak Interaction, mediated by the W-boson, is maximally parity violating in the Standard Model of particle physics. Studies of neutron decay are very suitable to get access to this property of the Standard Model due to the absence of a nuclear structure, compared with nuclear beta decay. High precision experiments in this field are intended to test the Standard Model and the extensions. In this thesis the first asymmetry measurement with the new neutron decay spectrometer Perkeo III is described. During a nine-month beamtime at the Institute Laue Langevin the beta-asymmetry A in the decay of free polarized neutrons was measured. For the first time, a pulsed neutron beam was used. This significantly improved the experimental systematics. The data analysis confirmed the clean systematics, resulting in new values and improved uncertainties on the beta-asymmetry A and the ratio of axialvector to vector coupling lambda. Compared to the current world average given by the Particle Data Group (PDG), the uncertainty of this measurement is smaller by a factor of 5