DIRECT NEUTRINO MASS MEASUREMENTS

Abstract

The discovery by many different experiments of the flavour oscillation of neutrinos from different sources proved clearly that neutrinos have non-vanishing masses in contrast to their current description within the Standard Model of particle physics. However, the neutrino mass scale, which is – in addition to particle physics – very important for cosmology and astrophysics, cannot be resolved by oscillation experiments. Although there are a few ways to determine the absolute neutrino mass scale, the only model-independent method is the investigation of the electron energy spectrum of a β decay near its endpoint. The tritium β decay experiments at Mainz and Troitsk using tritium have recently been finished and have given upper limits on the neutrino mass scale of about 2 eV/c2. The bolometric experiments using 187 Re have finished the first round of prototype experiments yielding a sensitivity on the neutrino mass of 15 eV/c2. The new Karlsruhe Tritium Neutrino Experiment (KATRIN) will enhance the sensitivity on the neutrino mass by an ultra-precise measurement of the tritium β decay spectrum by another order of magnitude down to 0.2 eV/c2 by using a very strong windowless gaseous molecular tritium source and a huge ultra-high resolution electrostatic spectrometer of MAC-E-Filter type. The recent achievements in test experiments show, that this very challenging experiment is feasible.