HOLMES: The electron capture decay of 163Ho to measure the electron neutrino mass with sub-eV sensitivity: TES detector and array production

The HOLMES experiment aims to directly measure the neutrino mass with a final resulting mass sensitivity as low as 0.4 eV exploiting the energy released in the Electron Capture (EC) decay of the radioactive isotope 163Ho with the calorimetric technique. An array of low temperature microcalorimeters will be used. Specifically, the microcalorimeters two step microfabrication process carried on by NIST and INFN-Genoa laboratories will be presented in this proceeding. Moreover the problem of the effective heat capacity of the microcalorimeters absorber will be discussed. Effectively, the relatively high concentration of Ho could cause an excess heat capacity in the metallic absorber, due to hyperfine level splitting of the implanted ion.