Electron Capture in Ho-163 - Large Experiment

The discovery of the neutrino mass scale is a milestone for shaping the extension of the Standard Model of Particle Physics. Experiments looking at the endpoint region of low energy beta decay and electron capture spectra benefit from a clear signature of massive neutrinos which only depends on energy and momentum conservation. Along with the well-established use of tritium, as in the KATRIN experiment where the present best limit of 0.45 eV at 95% CL was reached, two collaborations, ECHo and HOLMES have pioneered the use of Ho-163. In both experiments, low temperature microcalorimeters enclosing the Ho-163 source are used. Both collaborations have demonstrated the suitability of Ho-163 for a large experiment. The project ECHo-LE (ECHo-Large Experiment) will be built on the hardware and on solid results obtained with the ECHo experiment and will feature large arrays of metallic magnetic calorimeters where each detector encloses Ho-163 for an activity of 10 Bq. A new cryogenic multiplexer which ensures a homogeneous performance will be used for the readout. On-line data reduction and will be developed to allow for a limited saving space. Following the data analysis developed for the ECHo experiment, new fitting procedures will be tested to reduce the effects of systematic uncertainties. The experiment, consisting of 20000 detectors with gaussian detector response having full width at half maximum of less than 5 eV, will be built in the first two years of the project. After installation, the experiment will run for at least two years. The goal is to acquire more than 10 billion Ho-163 events. The analysis of the data will allow for significantly improving the knowledge of the Ho-163 spectral shape parameters and clearly search for an effect of a finite neutrino mass. ECHo-LE will be the first Ho-163 based experiment able to reach sub-eV/c2 sensitivity on the effective electron neutrino mass and set the basis for the ultimate Ho-163 based experiment.