Neutrinoless Double Beta Decay Experiments With TeO2 Low-Temperature Detectors

Neutrinoless double beta decay (0νββ) is a powerful tool to investigate Lepton Number Violation (LNV), and the only practical way to assess the nature of the neutrinos. It can therefore provide unique information about the Physics Beyond the Standard Model. If observed, 0νββ would unambiguously demonstrate that neutrinos are Majorana particles and would provide a precise measurement of their mass. Among the many experimental techniques used in the search for this rare process, low-temperature detectors represent one of the most promising choices: they show an excellent energy resolution and can scale to very large masses. In this work, we review the most relevant experiments based on TeO2 bolometers that have been developed and taking data at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, since the early 90's. This 30-years-old effort has led to the design and construction of the CUORE detector, currently taking data at LNGS. The use of low-temperature detectors allows to study the 0νββ of 130Te on both ground and excited states, and to explore different decay mechanisms ("standard" light neutrino exchange, Majoron emission, …). At the same time, the investigation of other rare nuclear physics processes is also possible, such as the two-neutrino double beta decay of 130Te as well as the rare decays (120Te and 123Te). Next generation bolometric experiments anticipate top leading sensitivities. The corresponding challenges in the development of ton-scale, low background detectors are highlighted

Results From the Cuore 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 TeO2 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 TeO2 exposure of 86.3kg yr, characterized by an effective energy resolution of 7.7 keV FWHM and a background in the region of interest of 0.014 counts/ (keV kg yr). In this physics run, CUORE placed a lower limit on the decay half- life of neutrinoless double beta decay of 130Te \u3e 1.3.1025 yr (90% C. L.). Moreover, an analysis of the background of the experiment is presented as well as the measurement of the 130Te 2 &nuββ decay with a resulting half- life of T 2v 1/2 = [7.9 ±0.1 (stat.) ±0.2 (syst.)] x 1020 yr which is the most precise measurement of the half- life and compatible with previous results

The commissioning of the CUORE experiment: the mini-tower run

CUORE is a ton-scale experiment approaching the data taking phase in Gran Sasso National Laboratory. Its primary goal is to search for the neutrinoless double-beta decay in 130Te using 988 crystals of tellurim dioxide. The crystals are operated as bolometers at about 10 mK taking advantage of one of the largest dilution cryostat ever built. Concluded in March 2016, the cryostat commissioning consisted in a sequence of cool down runs each one integrating new parts of the apparatus. The last run was performed with the fully configured cryostat and the thermal load at 4 K reached the impressive mass of about 14 tons. During that run the base temperature of 6.3 mK was reached and maintained for more than 70 days. An array of 8 crystals, called mini-tower, was used to check bolometers operation, readout electronics and DAQ. Results will be presented in terms of cooling power, electronic noise, energy resolution and preliminary background measurements

Results from the Cuore 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 TeO2 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 TeO2 exposure of 86.3kg yr, characterized by an effective energy resolution of 7.7 keV FWHM and a background in the region of interest of 0.014 counts/ (keV kg yr). In this physics run, CUORE placed a lower limit on the decay half- life of neutrinoless double beta decay of 130Te > 1.3.1025 yr (90% C. L.). Moreover, an analysis of the background of the experiment is presented as well as the measurement of the 130Te 2vo3p decay with a resulting half- life of T2 2. [7.9 :- 0.1 (stat.) :- 0.2 (syst.)] x 10(20) yr which is the most precise measurement of the half- life and compatible with previous results

Production, characterization, and selection of the heating elements for the response stabilization of the CUORE bolometers

One of the critical issues while operating bolometric detectors over periods of time of 1 year or more consists of keeping their response stable within a 0.1% level, despite the unavoidable temperature fluctuations of the cryogenic set-up. By using an energy pulser, which periodically delivers a fixed amount of energy in the absorber, it is possible to stabilize the response of the bolometers. A stabilization technique using heating devices, made up of heavily doped semiconductor material (well above the metal-to-insulator transition), has been developed in the framework of the CUORE experiment. In this paper we describe in detail the procedure for the realization of the heating elements, based on silicon planar technology. We then report on the multi-step low temperature characterization (77 K, 4.2 K, 1.5 K, 35 mK) of the heaters. Finally, an example of achieved stabilization for a CUORE-like detector is reported. The ∼1500 heaters tested at View the MathML source show less than 0.5% change in resistance between View the MathML source and 3 mV, and less than 1% change in value between 50 mK and 800 mK. In particular, the resistance change between 4.2 K and 1.5 K is less than 0.1%

ASPECT-BET: An sdd-SPECTrometer for BETa decay studies

We present the status of the ASPECT-BET (An sdd-SPECTrometer for BETa decay studies) project which is aimed at developing a new detection strategy to perform high-precision, high-accuracy measurements of the energy spectra of beta decays of interest for the physics community, in particular in the field of nuclear physics, double beta decay and reactor neutrinos. The aim is to exploit a relatively novel spectroscopic technique based on Silicon Drift Detectors. An SDD-spectrometer, equipped with all the ancillary detectors required to reject events with only a partial energy deposition in the main sensitive elements, will provide high-statistics and virtually zero-background data. In order to isolate and study the systematic uncertainties, the statistical error on the measured spectra has to be reduced to a negligible level, balancing source activity, measurement duration and background. Reliable and well understood Montecarlo simulations are a key component of this application, as they provide a model for the response functions of the spectrometer, to be deconvolved from the data in order to correctly reconstruct the original spectral shapes. Thanks to the flexibility of the SDD detector technology, the here presented spectrometer could be coupled to a variety of beta sources, ranging from nuclei deposited on the surface of SDDs to minimise source self-absorpion to short-lived isotopes created and collected at unstable isotope beams like ISOLDE at CERN or the exotic beams at LNS, Catania. The current status of the technology, as well as some preliminary sensitivity studies, are presented and discussed

Double beta decay search with CUPID-0: Results and Perspectives

International audienceCUPID-0 is the first large mass experiment based on cryogenic calorimeters (bolometers) that implements the dual read-out of light and heat for background rejection. The detector, consisting of 24 enriched Zn$^{82}$Se crystals (5.28 kg of $^{82}$Se), is taking data in the underground LNGS (Italy) from March 2017. In this contribution we present the analysis that allowed to set the most stringent limit on the half-life of neutrino-less double beta decay of $^{82}$Se. We prove that the particle identification, enabled by the simultaneous read-out of heat and light, provides an unprecedented background level for cryogenic calorimeters of few 10$^{−3}$ counts/keV/kg/y. Finally, we discuss the impact of these results on next generation projects