Experiment PERKEO III and weak magnetism form factor in polarized neutron decay

The decay of free neutrons offers unique insight into the weak interaction at low energies and allows high precision tests of the Standard Model. In the past two years we have measured improved values for the beta-asymmetry A and the neutrino-asymmetry B, and, for the first time, have measured the proton-asymmetry C in neutron decay. The new spectrometer Perkeo III now offers increased statistics by two orders of magnitude compared to its predecessor Perkeo II. With this precision it is now possible to directly measure the underlying structure of the weak interaction of semileptonic decays. In a first run 2007 at the Institute Laue-Langevin we aimed to measure the weak magnetism prediction of electroweak theory, which results in an energy dependent correction on the beta asymmetry A coefficient. Weak magnetism mirrors the fact that in the Standard Model the electric and weak currents are united in one isotriplet. Therefore weak magnetism is a strong pillar of electroweak unification and weak magnetism form factor is directly related to the difference of the magnetic moments of the proton μp and the neutron μn