Loredana Gastaldo: Electron Capture in Ho-163 experiment (ECHo) and discussion of the recent results

Direct determination of the electron neutrino and anti-neutrino mass can be obtained by the analysis of electron capture and beta spectra respectively. In the last years, experiments analyzing the ³H beta spectrum reached a limit on the electron antineutrino mass of 2 eV. The upper limit on the electron neutrino mass m(𝜈_𝑒) is still two orders of magnitudes higher, at 225 eV. The Electron Capture in ¹⁶³Ho experiment, ECHo, is designed to investigate m(𝜈_𝑒) in the sub-eV region and reach the same sensitivity as foreseen for electron antineutrino mass in new ³H-based experiments. 

In ECHo, high sensitivity on a finite m(𝜈_𝑒)  will be reached by the analysis of the endpoint region in high statistics and high resolution calorimetrically measured ¹⁶³Ho spectra. To perform this experiment, high purity ¹⁶³Ho source will be enclosed in a large number of low temperature metallic magnetic micro-calorimeters which are readout using the microwave multiplexing technique. This approach allows for a very good energy resolution, below Δ𝐸_FWHM < 5 eV and for a fast time resolution well below 1 𝜇s.

Thanks to the modular approach, the ECHo experiment is designed to be stepwise up-graded. The first on-going phase, ECHo-1k, is characterized by a ¹⁶³Ho activity of about 1 kBq enclosed in about 100 pixels. The statistics of 10¹⁰ events in the ¹⁶³Ho spectrum will allow for improving the limit on m(𝜈_𝑒) by more than one order of magnitude.

In this talk, the present status of the ECHo-1k experiment will be discussed as well as the plans for the next phases.