The determination of the absolute scale of the neutrino masses is one of the most challenging questions in particle physics. Different approaches are followed to achieve a sensitivity on neutrino masses in the sub-eV range. Among them, experiments exploring the beta decay and electron capture processes of suitable nuclides can provide necessary information on the electron neutrino mass value. The Electron Capture 163Holmium experiment ECHo aims to investigate the electron neutrino mass in the sub-eV range by means of the analysis of the calorimetrically measured energy spectrum following the electron capture process of 163 Ho . A high precision and high statistics spectrum will be measured by means of low temperature magnetic calorimeter arrays.
Solving a long-standing atomic mass difference puzzle paves way to the neutrino mass
To solve this puzzle, a German-Russian-Swiss-French team of physicists, chemists, and engineers combined their expertise and unique instrumentation. While natural dysprosium contains sufficient amounts of 163Dy, samples of 163Ho, which does not occur in nature, first had to be prepared from natural erbium enriched in 162Er by intense neutron irradiation in the high-flux research reactor at the Institut Laue Langevin in Grenoble, France. Sample purification and processing was done at Paul Scherrer Institute Villigen, Switzerland and Johannes Gutenberg University Mainz, Germany. The atomic mass difference of 163Ho and 163Dy was directly measured using the SHIPTRAP Penning-trap mass spectrometer at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Based on the equivalence of mass and energy according to Einstein’s famous equation E = mc2, the mass difference translates into the energy available for the decay.
Direct measurement of the mass difference of 163Ho and 163Dy solves Q-value puzzle for the neutrino mass determination
S. Eliseev et al.
Physical Review Letters 115, 062501 (2015)