UNTOLD - Upgraded Neutron Transmutation dOped germanium Light Detector

Abstract:

The experiments searching for neutrinoless double beta decay (0nbb) have reached the sensitivity to explore the beginning of the so-called inverted Hierarchy (IH) region of neutrino masses. To fully cover this region, the next generation experiments propose to upgrade their current technologies, increasing their source mass and reducing their background. The CUPID interest group aims to upgrade the CUORE technology enabling particle identification to reject the main background contribution coming from radioactive a contaminants. This can be done by exploiting the double read-out of light and heat in a scintillating cryogenic calorimeter. One of the leading candidates for this application are Li2 MoO4 scintillating crystals 95% enriched in the double beta decay emitter ¹⁰⁰Mo. The advantages of this crystal in terms of energy resolution and intrinsic radio-purity come at the cost of a potentially detrimental background source: the 2nbb decay of ¹⁰⁰Mo. The fast (compared to other 2nbb emitters) half-life of this decay mode ((7.1±0.4)*10¹⁸ y), combined with the slow response (tens of ms) of cryogenic calorimeters, would result in pile-up events in the energy region of interest for 0nbb, undermining the experimental sensitivity. In this project we propose to improve the performances of the cryogenic light detector based on the Ge NTD technology in order to exploit them also for the rejection of the pile-up induced background by:

- improving the phonon coupling between NTD Ge thermistor and the Ge wafer exploiting new bonding techniques in order to speed up and increase the NTD Ge thermal response,

- improving the characteristics of the electronic readout in order to increase the detector time resolution

- changing the coupling between the cryogenic experimental setup and the detectors to remove the vibrational noise induced on them improving their energy resolution