Neutrinoless double beta decay (0νββ) is a direct probe of physics beyond the standard model. Its discovery would demonstrate that the lepton number is not a symmetry of nature and would provide us with unique information on the nature and mass of the neutrinos. Among the experimental techniques employed in the investigation of this rare process, thermal detectors fulfill the requirements for a powerful search, showing an excellent energy resolution and the possibility of scaling to very large masses. In this work, we review the long chain of bolometric experiments based on TeO₂ crystals that were and continue to be carried out at the Laboratori Nazionali del Gran Sasso (Italy), searching for 0νββ of ¹³⁰Te. We illustrate the progress and improvements achieved in almost thirty years of measurements and compare the various performance and results. We describe the several steps that led to the CUORE detector, the latest of this series and presently in data taking, and we highlight the challenges that a next bolometric experiment will face in order to further improve the sensitivity, especially concerning the background abatement. Finally, we emphasize the advantages of ¹³⁰Te in the search for 0νββ with a further future experiment.

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for neutrinoless double beta decay that has been able to reach the 1-ton scale. The detector consists of an array of 988 ${\mathrm{TeO}}_2$ crystals arranged in a cylindrical compact structure of 19 towers, each of them made of 52 crystals. The construction of the experiment was completed in August 2016 and the data taking started in spring 2017 after a period of commissioning and tests. In this work we present the neutrinoless double beta decay results of CUORE from examining a total ${\mathrm{TeO}}_2$ exposure of $86.3\mathrm{kg}\mathrm{yr}$ , characterized by an effective energy resolution of 7.7 keV FWHM and a background in the region of interest of $0.014$ $\mathrm{counts}/\left(\mathrm{keV}\mathrm{kg}\mathrm{yr}\right)$ . In this physics run, CUORE placed a lower limit on the decay half-life of neutrinoless double beta decay of ${}^{130}\mathrm{Te}>1.3·{10}^{25}$ yr (90% C.L.). Moreover, an analysis of the background of the experiment is presented as well as the measurement of the ${}^{130}$ Te 2 $\nu \beta \beta$ decay with a resulting half-life of $T_{1/2}^{2\nu }=[7.9\pm 0.1(\mathrm{stat}.)\pm 0.2(\mathrm{syst}.)]\times {10}^{20}$ yr which is the most precise measurement of the half-life and compatible with previous results.

The ASPECT-BET project, or An sdd-SPECTrometer for BETa decay studies, aims to develop a novel technique for the precise measurement of forbidden beta spectra in the 10 keV–1 MeV range. This technique employs a Silicon Drift Detector (SDD) as the main spectrometer with the option of a veto system to reject events exhibiting only partial energy deposition in the SDD. A precise understanding of the spectrometer’s response to electrons is crucial for accurately reconstructing the theoretical shape of the beta spectrum. To compute this response, GEANT4 simulations optimized for low-energy electron interactions are used and validated with a custom-made electron gun. In this article we present the performance of these simulations in reconstructing the electron spectra measured with SDDs of a ¹⁰⁹Cd monochromatic source, both in vacuum and in air. The allowed beta spectrum of a ¹⁴C source was also measured and analyzed, proving that this system is suitable for the application in ASPECT-BET.