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

One step into Holmes project. Simulation of the deposition of a metallic Ho film on a target.

This work shows one of the activity of the group in the framework of the HOLMES project for direct neutrino mass search. Starting from Ho oxide and working at high temperature, it is possible to obtain the deposition of a metal Ho film which is necessary for the implantation into cryogenic detectors. A simulation has been developed to evaluate the distribution of the deposition of metallic Holmium onto a target used as a trap and to estimate the efficiency of the process and eventually optimize controllable parameters. Object of this work is the simulation itself, its design, implementations and a discussion of the results

The cryogenic anticoincidence detector for ATHENA X-IFU: Preliminary test of AC-S9 towards the demonstration model

Our team is developing the Cryogenic Anticoincidence Detector (CryoAC) of the ATHENA X-ray Integral Field Unit (X-IFU). It is a 4-pixels TES-based detector, which will be placed less than 1 mm below the main TES array detector. We are now producing the CryoAC Demonstration Model (DM): a single pixel prototype able to probe the detector critical technologies, i.e. The operation at 50 mK thermal bath, the threshold energy at 20 keV and the reproducibility of the thermal conductance between the suspended absorber and the thermal bath. This detector will be integrated and tested in our cryogenic setup at INAF/IAPS, and then delivered to SRON for the integration in the X-IFU Focal Plane Assemby (FPA) DM. In this paper we report the status of the CryoAC DM development, showing the main result obtained with the last developed prototype, namely AC-S9. This is a DM-like sample, which we have preliminary integrated and tested before performing the final etching process to suspend the silicon absorber. The results are promising for the DM, since despite the limitations due to the absence of the final etching (high thermal capacity, high thermal conductance, partial TES surface coverage), we have been able to operate the detector with TB= 50 mK and to detect 6 keV photons, thus having a low energy threshold fully compatible with our requirement (20 keV)

HOLMES: The electron capture decay of 163Ho to measure the electron neutrino mass with sub-eV sensitivity

The European Research Council has recently funded HOLMES, a new experiment to directly measure the neutrino mass. HOLMES will perform a calorimetric measurement of the energy released in the decay of 163Ho. The calorimetric measurement eliminates systematic uncertainties arising from the use of external beta sources, as in experiments with beta spectrometers. This measurement was proposed in 1982 by A. De Rujula and M. Lusignoli, but only recently the detector technological progress allowed to design a sensitive experiment. HOLMES will deploy a large array of low temperature microcalorimeters with implanted 163Ho nuclei. The resulting mass sensitivity will be as low as 0.4 eV. HOLMES will be an important step forward in the direct neutrino mass measurement with a calorimetric approach as an alternative to spectrometry. It will also establish the potential of this approach to extend the sensitivity down to 0.1 eV. We outline here the project with its technical challenges and perspectives.Comment: 11 pages, 9 figure