An experiment for the direct calorimetric measurement of the neutrino mass

The oscillation experiments have clearly shown that neutrino are massive particle. Nowadays the experiments based on kinematic analysis of electrons emitted in nuclear beta-decay are the most sensitive for a direct electron-neutrino mass determination. The method consists in searching for a tiny deformation caused by a non-zero neutrino mass to the spectrum of the charged particles emitted near the end point. A possible approach is the calorimetric one. In a calorimetric measurement the source is embedded in the detector and all the energy is measured, except for the one taken away by the neutrino. A drawback of this approach is that the full spectrum is acquired, while only the decays very close to the end-point are useful for measuring the neutrino mass. Therefore, the source activity has to be limited to avoid pile-up which would deform the shape of beta spectrum. As a consequence the statistics near the end-point is limited as well. This limitation may be then partially balanced by using isotopes with an end-point energy as low as possible. In this scenario an international collaboration has grown around the project of Microcalorimeter Arrays for a Rhenium Experiment (MARE) for a direct calorimetric measurement of the neutrino mass with sub-electronvolt 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 two competing isotopes are 187Re and 163Ho. While the first beta decays, the latter decays via electron capture, and both have a Q value around 2.5 keV. The MARE project has a staged approach. 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. The goal of the last phase (MARE-2) is to achieve a sub-eV sensitivity on the neutrino mass. It will deploy several arrays of thermal microcalorimeter
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Ferri
Ferri, E