In the last decades the discovery that neutrinos have mass, contrary to what was previously thought, has revolutionized our understanding of neutrinos. Despite the good precision that neutrino experiments have reached in the recent years, many neutrino properties remain still unknown. Among them, the neutrino nature, Dirac vs. Majorana, the existence of CP violation in the leptonic sector, the absolute scale of neutrino masses, and the type of the neutrino mass spectrum. HOLMES is a experiment with the aim to directly measure the neutrino mass. HOLMES will perform a precise calorimetric measurement of the end point of the Electron Capture (EC) decay spectrum of 163Ho in order to extract information on neutrino mass with a sensitivity below 2 eV. Although this measurement was proposed for the first time in 1982, only recently the tremendous technical progresses in low temperature detectors and multiplexing techniques have allowed the design of sensitive experiments.
In its final configuration, HOLMES will deploy 1000 detectors of low temperature microcalorimeters with implanted 163Ho nuclei. The baseline sensors for HOLMES are Mo/Cu TESs (Transition Edge Sensors) on SiNx membrane with gold absorbers. The TES detectors are designed to have an energy resolution of few eV FWHM at the 2.8keV 163Ho end-point and to be fast enough to assure a time resolution of 3μs, in order to contain systematics coming from unresolved pile-up events. Considering the large number of pixels and an event rate of about 300 Hz/pixel, a large multiplexing factor and a large bandwidth are needed. To fulfill this requirement, HOLMES will exploit recent advances on microwave multiplexing (μmux). This technique is based on the use of rf-SQUIDs as input devices with flux ramp modulation.
In this seminar the presenter outlines the project design, the present status of the Holmium production, of the implantation system, of the detector development and the first preliminary results obtained with the developed microwave frequency multiplexing technique.