Determining the Electron Neutrino Mass with Ho-163

Direct determination of the electron neutrino m(ν_e) and anti-neutrino mass m(ν_e) 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 m(ν_e) of 2 eV. The upper limit on m(ν_e)is still two orders of magnitudes higher, at 225 eV. Two large collaborations, ECHo and HOLMES, aim to reach sub-eV sensitivity on m(ν_e) by analyzing the endpoint region of high statistics and high resolution calorimetrically measured ¹⁶³Ho electron capture spectra. To perform such experiments, high purity ¹⁶³Ho sources will be enclosed in a large number of low temperature micro-calorimeters which are readout using multiplexing techniques. In this talk, the experimental challenges to determine the electron neutrino mass using ¹⁶³Ho will be discussed as well as the strategies developed by the two collaborations to overcome them. Theoretical description of the ¹⁶³Ho spectrum will be examined along with methods to validate the proposed models. In conclusion, recent results obtained by the two collaborations will be presented