Absolute Masses of Neutrinos—Experimental Results and Future Possibilities

Abstract

The discovery of neutrino oscillation proved recently that neutrinos have non- vanishing masses in contrast to their description within the Standard Model of particle physics. However, the absolute neutrino mass scale, which is very important for particle physics as well as for cosmology and astrophysics, cannot be revealed by oscillation experiments. Although there are a few ways to determine the 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 187Re have finished the first 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 another order of magnitude down to 0.2 eV/c2 by an ultra-precise measurement of the tritium β decay spectrum using a very strong windowless gaseous molecular tritium source and a huge ultra-high resolution electrostatic spectrometer of MAC-E-Filter type.