The total energy available for the decay of 163Ho to 163Dy is a fundamental parameter to reach the sub-eV sensitivity to the electron neutrino mass by the analysis of the high energy part of the 163Ho EC spectrum. The recommended value is QEC = 2.555(16)keV as can be found in M. Wang, G. Audi et al., Chinese Phys. C 36, 1603, (2012), but other measurements give values that range from about 2.3 keV from the measurement of the x-ray spectrum to about 2.8 keV obtained by two calorimetric measurements performed using low temperature detectors.
The aim of the ECHo collaboration is to reach a precision on the QEC of 1 eV or better. After preliminary measurements at the double-Penning trap mass spectrometers SHIPTRAP and TRIGA-TRAP, the final high accuracy measurement will be accomplished by the novel Penning-trap mass spectrometer PENTATRAP. The uniqueness and complexity of this Penning-trap mass spectrometer is associated with the unprecedented relative accuracy of a few parts in 1012 with which the QEC must be measured.
