MARE-1 in Milan: Status and Perspectives

Abstract

The international project MARE (Microcalorimeter Array for a Rhenium Experiment) aims at the direct and calorimetric measurement of the electron neutrino mass with sub-eV sensitivity. Although the baseline of the MARE project consists in a large array of rhenium based thermal detectors, a different option for the isotope is also being considered. The different option is Ho-163. The potential of using Re-187 for a calorimetric neutrino mass experiment has been already demonstrated. On the contrary, no calorimetric spectrum of Ho-163 has been so far measured with the precision required to set a useful limit on the neutrino mass.\ud \ud The first phase of the project (MARE-1) is a collection of activities with the aim of sorting out both the best isotope and the most suited detector technology to be used for the final experiment. One of the MARE-1 activities is carried out in Milan by the group of Milano-Bicocca in collaboration with NASA/GSFC and Wisconsin groups. The Milan MARE-1 arrays are based on semiconductor thermistors, provided by the NASA/GSFC group, with dielectric silver perrhenate absorbers, AgReO4. The experiment, which is presently being assembled, is designed to host up to 8 arrays. With 288 detectors, a sensitivity of 3 eV at 90% CL on the neutrino mass can be reached within 3 years.\ud \ud This contribution gives an outlook for the MARE activities for the active isotope selection. In this contribution the status and the perspectives of the MARE-1 in Milan are also reported

Current Direct Neutrino Mass Experiments

“…Besides the selection of the most sensitive detector technology, this phase will also be used to investigate the use of the EC decay of 163 Ho as an alternative to the study of rhenium β-decay to determine the neutrino mass [175] (see also section 5.3). The consideration of 163 Ho was triggered by persisting difficulties with superconducting metallic rhenium absorbers coupled to the sensors [176]. Thermalization of the energy deposited in β-decays seems to be hindered by the excitation of long lived states in the rhenium absorber.…”

“…For readout of the thermistors a cold buffer stage using JFETs at 120 K is installed as close as possible to the sensors, followed by a main amplifier stage at room temperature. With this system it is possible to achieve an energy and time resolutions of 25 eV and 250 µs, respectively [176]. After a first test run with 10 AgReO 4 crystals on one array and two Sn absorbers on a second array to investigate the environmental background near the rhenium endpoint, a 187 Re β-decay measurement with 72 channels should start and provide a sensitivity of 4.5 eV at 90% CL within three years running time [176].…”

“…With this system it is possible to achieve an energy and time resolutions of 25 eV and 250 µs, respectively [176]. After a first test run with 10 AgReO 4 crystals on one array and two Sn absorbers on a second array to investigate the environmental background near the rhenium endpoint, a 187 Re β-decay measurement with 72 channels should start and provide a sensitivity of 4.5 eV at 90% CL within three years running time [176]. With all 8 arrays instrumented a sensitivity of 3.3 eV at 90% CL would be reached with 7 • 10 9 rhenium decays.…”

Neutrino masses

“…MARE is not only aimed at β‐decay but also at investigating the electron capture of , triggered by the persisting difficulties with superconducting metallic rhenium absorbers coupled to the sensors . The isotope could be implanted into well‐suited cryo‐bolometers.…”

Developments of Microresonators Detectors for Neutrino Physics in Milan

“…One type of experiments which can tackle directly these issue without model dependences are direct kinematic studies of a low energy nuclear decay involving the production of a neutrino, where the shape of the decay energy spectrum near its endpoint provides the neutrino mass. The beta decay of 187 Re and the electron capture decay of 163 Ho are being considered for MARE experiment [5]. Our main target is the development of athermal detectors for an electron-capture decay endpoint measurement of the neutrino mass using Holmium as the source material.…”