The status of the HOLMES experiment

This work summarizes the current status of HOLMES, a calorimetric experiment for the direct neutrino mass measurement. The state-of-the-art in this field is represented by the KATRIN spectrometer that is under data-taking aiming at a sensitivity of 0.2 eV. HOLMES will prove the feasibility of the calorimetric approach, that is an alternative method to the spectrometric one. HOLMES detectors are Transition Edge Sensors in which a source of 163Ho will be ion-implanted. These microcalorimeters allow a multiplexed readout and ensure high energy and time resolutions. 163Ho is an interesting candidate for the direct neutrino mass determination. In fact, the low Q-value (∼2.83 keV) of its electron capture decay increases the fraction of useful events in the region close to the end-point. HOLMES will assess mν by analyzing the spectrum deformation due to a non-zero mν. This contribution describes the detector working principles, their fabrication for HOLMES and their characterization. At the same time, a focus on the ion-implantation is given together with the latest results from its tests. HOLMES is now close to the first low-dose measurement. By implanting a small 163Ho activity per detector it will be possible to fine-tune the entire experimental procedure and also to analyze a preliminary spectrum in order to assess an initial upper limit on mν of about ∼ 10 eV.