ECHO: Electron Capture in Ho-163 experiment
Dr. Loredana Gastaldo (KIP Heidelberg)

The Electron Capture 163Ho experiment, ECHo, is designed to investigate the electron neutrino mass in the sub-eV range by means of the analysis of the calorimetrically measured spectrum following the electron capture in 163Ho. Arrays of low temperature metallic magnetic calorimeters (MMCs) will be used in this experiment. With a first prototype of MMC having the 163Ho source embedded in the absorber, we performed the first high energy resolution measurement of the EC spectrum, which demonstrated the feasibility of such an experiment. In addition to the technological challenges for the measurement of the EC spectrum, the success of the experiment relies on the precise description of the expected spectrum and on the identification and reduction of background.
We present the plan for a medium scale experiment, ECHo-1k, in which about 1000 Bq of high purity 163Ho will be implanted in detector arrays. With one year of measuring time we will be able to achieve a sensitivity on the electron neutrino mass below 10 eV/c2 (90% C.L.), improving the present limit by more than one order of magnitude. This experiment will guide the necessary developments to reach the sub-eV sensitivity.