Microcalorimeter measurements

The technique of calorimetric beta spectroscopy with Low Temperature Detectors (LTD) has been applied recently to the electron anti-neutrino mass search experiments. The best suited beta isotope for a calorimetric measurement is Re-187, which is characterized by the lowest known end-point energy, about 2.5 keV. The experiments with Re-187 are designed in order to realize the "total energy dispersive beta spectroscopy", that is sensitive to all the energy emissions of the beta decay, except that of the emitted anti-neutrino. This specific feature allows us to avoid the model dependent correction for the atomic and molecular final states, which are conversely applied in the electron impulse beta spectroscopy of Tritium. For the first time, a limit of 26 eV/c(2) (95% CL) to the anti-neutrino mass is obtained from high statistics spectra of Re-187 that are measured with this technique. In addition, the high accuracy of the actual measurements has remarkably increased our knowledge of the beta decay of this isotope. Currently three groups are engaged in different rhenium experiments. I present some historical hints and the main features of these experiments, the current status and the results.