Development of superconducting microresonators for a neutrino mass experiment

The determination of the neutrino mass is still an open issue in particle physics. The calorimetric measurement of the energy released in a nuclear beta decay allows to measure all the released energy, except the fraction carried away by the neutrino: a finite neutrino mass m causes the energy spectrum to be truncated at Q m, where Q is the transition energy. The electron capture of Ho (Q 2.5 keV) results to be an ideal decay. In order to achieve enough statistics, a large number of detectors (10) is required. Superconducting microwave microresonators are detectors suitable for large-scale multiplexed frequency domain readout, with theoretical energy and time resolution of eV and s. Our aim is to develop arrays of microresonator detectors applicable to the calorimetric measurement of the energy spectra of Ho. Currently, a study aimed to the selection of the best design and material for the detectors is in progress. In this contribution, a comparison between the measurements (critical temperature, gap parameter, quasiparticle recombination time and X-ray energy spectra) made with stoichiometric, sub-stoichiometric TiN and Ti/TiN multilayer films are presented.