Development and characterisation of high-resolution metallic magnetic calorimeter arrays for the ECHo neutrino mass experiment

This work is focused on the development of cryogenic metallic magnetic calorimeter detectors with implanted Ho-163 source for the ECHo (Electron Capture in Ho-163)experiment for the determination of the effective electron neutrino mass by studying the Ho-163 electron capture spectrum. The detector prototype fabricated for the first experimental phase, ECHo-1k, has been fully characterised, in terms of thermodynamic properties, detector response, energy resolution and Ho-163 activity per detector pixel. The specific heat per holmium ion in silver has been determined, comparing the response of detector pixels with and without implanted Ho-163. This accurate measurement indicates a lower value of the Ho-163 half-life with respect to the value reported in literature. Two implanted ECHo-1k detector chips have been operated in parallel in a dilution refrigerator which has been equipped with a 64-channel read-out chain. A high-statistics measurement with more than 10^8 Ho-163 electron capture events has been performed and the analysis of the resulting spectrum will allow to reach a sensitivity below 20 eV on the effective electron neutrino mass. Based on the outcomes of the ECHo-1k experimental phase, a novel detector design has been conceived in order to achieve the detector performance required for the succeeding experimental phase, ECHo-100k. The new ECHo-100k detector has been successfully fabricated and fully characterised, showing an improved detector response and an excellent energy resolution that reaches 3 eV FWHM, matching the designed value. The results obtained in this thesis set the starting point of the ECHo-100k experiment.