CUORE Research Articles

New Results on 0νββ Decay from the CUORE Experiment

New Results on 0νββ Decay from the CUORE Experiment

Optimization of the first CUPID detector module

CUPID will be a next generation experiment searching for the neutrinoless double beta decay, whose discovery would establish the Majorana nature of the neutrino. Based on the experience achieved with the CUORE experiment, presently taking data at LNGS, CUPID aims to reach a background free environment by means of scintillating Li_{2}^{100}MoO_4 crystals coupled to light detectors. Indeed, the simultaneous heat and light detection allows us to reject the dominant background of alpha particles, as proven by the CUPID-0 and CUPID-Mo demonstrators. In this work we present the results of the first test of the CUPID baseline module. In particular, we propose a new optimized detector structure and light sensors design to enhance the engineering and the light collection, respectively. We characterized the heat detectors, achieving an energy resolution of (5.9 ± 0.2) keV FWHM at the Q-value of ^{100}Mo (about 3034 keV). We studied the light collection of the baseline CUPID design with respect to an alternative configuration which features gravity-assisted light detectors’ mounting. In both cases we obtained an improvement in the light collection with respect to past measures and we validated the particle identification capability of the detector, which ensures an alpha particle rejection higher than 99.9%, fully satisfying the requirements for CUPID.

Expected sensitivity to 128Te neutrinoless double beta decay with the CUORE TeO2 cryogenic bolometers

The CUORE experiment is a ton-scale array of hbox {TeO}_2 cryogenic bolometers located at the underground Laboratori Nazionali del Gran Sasso of Istituto Nazionale di Fisica Nucleare (INFN), in Italy. The CUORE detector consists of 988 crystals operated as source and detector at a base temperature of sim 10 mK. Such cryogenic temperature is reached and maintained by means of a custom built cryogen-free dilution cryostat, designed with the aim of minimizing the vibrational noise and the environmental radioactivity. The primary goal of CUORE is the search for neutrinoless double beta decay of ^{130}hbox {Te}, but thanks to its large target mass and ultra-low background it is suitable for the study of other rare processes as well, such as the neutrinoless double beta decay of ^{128}hbox {Te}. This tellurium isotope is an attractive candidate for the search of this process, due to its high natural isotopic abundance of 31.75%. The transition energy at (866.7 ± 0.7) keV lies in a highly populated region of the energy spectrum, dominated by the contribution of the two-neutrino double beta decay of ^{130}hbox {Te}. As the first ton-scale infrastructure operating cryogenic hbox {TeO}_2 bolometers in stable conditions, CUORE is able to achieve a factor >10 higher sensitivity to the neutrinoless double beta decay of this isotope with respect to past direct experiments.

Challenges and opportunities in establishing an Health Examination Survey


 In Italy, the last 30 years witnessed the implementation of cross-sectional surveys providing baseline data on numerous risk factors collected from random samples of the adult general population.
 In order to support those groups who would like to implement an health examination survey (HES), according to the experience of the CUORE Project surveys, the objective of this paper is to describe some information related to the organization of a survey (examination sites and sampling, selection of analytic laboratory, coordination and personnel involved, sample selection, recruitment and appointment scheduling, informative notice and informed consent, participation rate, non-participation bias, quality assurance, survey data, long term storage of the samples, internal quality control, external quality assessment, feedback to participants, error checking, correction and documentation of the data, transfer and storage of the data, statistical analyses and interpretation of results, dissemination of results), usually shortly described in scientific papers but relevant when an HES is planned.

Bolometric Double Beta Decay Experiments: Review and Prospects

This review aims to cover the history and recent developments on cryogenic bolometers for neutrinoless double beta decay (0ν2β) searches. A 0ν2β decay observation would confirm the total lepton charge non-conservation, which is related to a global U(1)LC symmetry. This discovery would also provide essential information on neutrino masses and nature, opening the door to new physics beyond the Standard Model. The bolometric technology shows good prospects for future ton-scale experiments that aim to fully investigate the inverted ordering region of neutrino masses. The big advantage of bolometers is the high energy resolution and the possibility of particle identification, as well as various methods of additional background rejection. The CUORE experiment has proved the feasibility of ton-scale cryogenic experiments, setting the most stringent limit on 130Te 0ν2β decay. Two CUPID demonstrators (CUPID-0 and CUPID-Mo) have set the most stringent limits on 82Se and 100Mo isotopes, respectively, with compatibly low exposures. Several experiments are developing new methods to improve the background in the region of interest with bolometric detectors. CUPID and AMoRE experiments aim to cover the inverted hierarchy region, using scintillating bolometers with hundreds of kg of 100Mo. We review all of these efforts here, with a focus on the different types of radioactive background and the measures put in place to mitigate them.

Search for double-beta decay of mathrm {^{130}Te} to the 0^+ states of mathrm {^{130}Xe} with CUORE

The CUORE experiment is a large bolometric array searching for the lepton number violating neutrino-less double beta decay (0nu beta beta ) in the isotope mathrm {^{130}Te}. In this work we present the latest results on two searches for the double beta decay (DBD) of mathrm {^{130}Te} to the first 0^{+}_2 excited state of mathrm {^{130}Xe}: the 0nu beta beta decay and the Standard Model-allowed two-neutrinos double beta decay (2nu beta beta ). Both searches are based on a 372.5 kgtimes yr TeO_2 exposure. The de-excitation gamma rays emitted by the excited Xe nucleus in the final state yield a unique signature, which can be searched for with low background by studying coincident events in two or more bolometers. The closely packed arrangement of the CUORE crystals constitutes a significant advantage in this regard. The median limit setting sensitivities at 90% Credible Interval (C.I.) of the given searches were estimated as mathrm {S^{0nu }_{1/2} = 5.6 times 10^{24} , mathrm {yr}} for the {0nu beta beta } decay and mathrm {S^{2nu }_{1/2} = 2.1 times 10^{24} , mathrm {yr}} for the {2nu beta beta } decay. No significant evidence for either of the decay modes was observed and a Bayesian lower bound at 90% C.I. on the decay half lives is obtained as: mathrm {(T_{1/2})^{0nu }_{0^+_2} > 5.9 times 10^{24} , mathrm {yr}} for the 0nu beta beta mode and mathrm {(T_{1/2})^{2nu }_{0^+_2} > 1.3 times 10^{24} , mathrm {yr}} for the 2nu beta beta mode. These represent the most stringent limits on the DBD of ^{130}Te to excited states and improve by a factor sim 5 the previous results on this process.

Lowering the Energy Threshold of the CUORE Experiment: Benefits in the Surface Alpha Events Reconstruction

CUORE is a tonne-scale cryogenic experiment located at the Laboratori Nazionali del Gran Sasso that exploits bolometric technique to search for neutrinoless double beta decay of \(^{130}{\hbox {Te}}\). Thanks to its very low background and large mass, CUORE is also a powerful tool to study a broad class of phenomena, such as solar axions and WIMP scattering. The ability to conduct such sensitive searches crucially depends on the energy threshold, which has to be kept as low as possible. In this contribution, we show how the trigger algorithm affects the sensitivity to low-energy phenomena and the interpretation of the energy spectrum. In particular, we focus on the impact that the trigger algorithm has on the identification of the coincidence events among different crystals and, consequently, on the reconstruction of the background.

The CUORE cryostat

The CUORE experiment (Cryogenic Underground Observatory for Rare Events) is a ton-scale detector, operating at a cryogenic temperature around 10 mK, searching for neutrinoless double-beta decay in 130Te and other rare events. The experiment cryogenic infrastructure, its subsystems and the cool-down procedure that allowed CUORE to obtained the first physics results will be presented.

The 0\u03bd2\u03b2-decay CROSS experiment: preliminary results and prospects

Neutrinoless double-beta decay is a key process in particle physics. Its experimental investigation is the only viable method that can establish the Majorana nature of neutrinos, providing at the same time a sensitive inclusive test of lepton number violation. CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) aims at developing and testing a new bolometric technology to be applied to future large-scale experiments searching for neutrinoless double-beta decay of the promising nuclei 100Mo and 130Te. The limiting factor in large-scale bolometric searches for this rare process is the background induced by surface radioactive contamination, as shown by the results of the CUORE experiment. The basic concept of CROSS consists of rejecting this challenging background component by pulse-shape discrimination, assisted by a proper coating of the faces of the crystal containing the isotope of interest and serving as energy absorber of the bolometric detector. In this paper, we demonstrate that ultra-pure superconductive Al films deposited on the crystal surfaces act successfully as pulse-shape modifiers, both with fast and slow phonon sensors. Rejection factors higher than 99.9% of α surface radioactivity have been demonstrated in a series of prototypes based on crystals of Li2MoO4 and TeO2. We have also shown that point-like energy depositions can be identified up to a distance of ∼ 1 mm from the coated surface. The present program envisions an intermediate experiment to be installed underground in the Canfranc laboratory (Spain) in a CROSS-dedicated facility. This experiment, comprising ∼ 3×1025 nuclei of 100Mo, will be a general test of the CROSS technology as well as a worldwide competitive search for neutrinoless double-beta decay, with sensitivity to the effective Majorana mass down to 70 meV in the most favorable conditions.

The CUORE Data Acquisition System

Large mass bolometers, thanks to their good energy resolution and high radiopurity, can be used for rare event searches, such as neutrinoless double beta decay or dark matter direct detection. The bolometric technique has been adopted by the CUORE experiment which is composed by an array of 988 tellurium dioxide bolometers with a total active mass of 741 kg. The experiment started taking data in April 2017 at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, with the scientific goal of searching for neutrinoless double beta decay of 130-Te. Given the increasing number of channels to be acquired, the readout chain became an important aspect of the construction of bolometer arrays. The CUORE data acquisition system here described, called Apollo, was initially developed for CUORE, but its high modularity and flexibility make it possible to use it also in other experiments, regardless of the specific characteristics of the setup such as the number of channels and the bolometer characteristics. Indeed, it has been used not only in CUORE but also in its predecessor CUORE-0, R&D projects and upgrades such as CUPID-0.

The CUORE cryostat: An infrastructure for rare event searches at millikelvin temperatures

The CUORE experiment is the world’s largest bolometric experiment. The detector consists of an array of 988 TeO2 crystals, for a total mass of 742 kg. CUORE is presently taking data at the Laboratori Nazionali del Gran Sasso, Italy, searching for the neutrinoless double beta decay of 130Te. A large custom cryogen-free cryostat allows reaching and maintaining a base temperature of ∼10 mK, required for the optimal operation of the detector. This apparatus has been designed in order to achieve a low noise environment, with minimal contribution to the radioactive background for the experiment. In this paper, we present an overview of the CUORE cryostat, together with a description of all its sub-systems, focusing on the solutions identified to satisfy the stringent requirements. We briefly illustrate the various phases of the cryostat commissioning and highlight the relevant steps and milestones achieved each time. Finally, we describe the successful cooldown of CUORE.

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 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 TeO 2 exposure of 86.3 kg 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 130 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 ν β β decay with a resulting half-life of T 1 / 2 2 ν = [ 7.9 ± 0.1 ( stat . ) ± 0.2 ( syst . ) ] × 10 20 yr which is the most precise measurement of the half-life and compatible with previous results.

First Results from CUORE: A Search for Lepton Number Violation via 0νββ Decay of Te130

The CUORE experiment, a ton-scale cryogenic bolometer array, recently began operation at the Laboratori Nazionali del Gran Sasso in Italy. The array represents a significant advancement in this technology, and in this work we apply it for the first time to a high-sensitivity search for a lepton-number-violating process: ^{130}Te neutrinoless double-beta decay. Examining a total TeO_{2} exposure of 86.3kg yr, characterized by an effective energy resolution of (7.7±0.5) keV FWHM and a background in the region of interest of (0.014±0.002) counts/(keV kg yr), we find no evidence for neutrinoless double-beta decay. Including systematic uncertainties, we place a lower limit on the decay half-life of T_{1/2}^{0ν}(^{130}Te)>1.3×10^{25} yr (90%C.L.); the median statistical sensitivity of this search is 7.0×10^{24} yr. Combining this result with those of two earlier experiments, Cuoricino and CUORE-0, we find T_{1/2}^{0ν}(^{130}Te)>1.5×10^{25} yr (90%C.L.), which is the most stringent limit to date on this decay. Interpreting this result as a limit on the effective Majorana neutrino mass, we find m_{ββ}<(110-520) meV, where the range reflects the nuclear matrix element estimates employed.

A multi-isotope 0nu 2beta bolometric experiment

There are valuable arguments to perform neutrinoless double beta (0nu 2beta ) decay experiments with several nuclei: the uncertainty of nuclear-matrix-element calculations; the possibility to test these calculations by using the ratio of the measured lifetimes; the unpredictability of possible breakthroughs in the detection technique; the difficulty to foresee background in 0nu 2beta decay searches; the limited amount of isotopically enriched materials. We propose therefore approaches to estimate the Majorana neutrino mass by combining experimental data collected with different 0nu 2beta decay candidates. In particular, we apply our methods to a next-generation experiment based on scintillating and Cherenkov-radiation bolometers. Current results indicate that this technology can effectively study up to four different isotopes simultaneously (^{82}Se, ^{100}Mo, ^{116}Cd and ^{130}Te), embedded in detectors which share the same concepts and environment. We show that the combined information on the Majorana neutrino mass extracted from a multi-candidate bolometric experiment is competitive with that achievable with a single isotope, once that the cryogenic experimental volume is fixed. The remarkable conceptual and technical advantages of a multi-isotope investigation are discussed. This approach can be naturally applied to the proposed CUPID project, follow-up of the CUORE experiment that is currently taking data in the Gran Sasso underground laboratory.

CUORE-0 detector: design, construction and operation

The CUORE experiment will search for neutrinoless double-beta decay of 130Te with an array of 988 TeO2 bolometers arranged in 19 towers. CUORE-0, the first tower assembled according to the CUORE procedures, was built and commissioned at Laboratori Nazionali del Gran Sasso, and took data from March 2013 to March 2015. In this paper we describe the design, construction and operation of the CUORE-0 experiment, with an emphasis on the improvements made over a predecessor experiment, Cuoricino. In particular, we demonstrate with CUORE-0 data that the design goals of CUORE are within reach.

Neutrinoless Double Beta Decay with CUORE-0: Physics Results and Detector Performance

The CUORE-0 experiment searches for neutrinoless double beta decay in \(^{130}\)Te. It consists of an array of 52 tellurium dioxide crystals, operated as bolometers at a temperature of 10 mK, with a total mass of about 39 kg of TeO\(_2\). CUORE-0 has been built to test the performance of the upcoming CUORE experiment and represents the largest \(^{130}\)Te bolometric setup currently in operation. This experiment has been running in the Gran Sasso National Laboratory, Italy, since March 2013. We report the results of a search for neutrinoless double beta decay in 9.8 kg years \(^{130}\)Te exposure, which allowed us to set the most stringent limit to date on this half-life. The performance of the detector in terms of background rate and energy resolution are also reported.

Cosmogenic-neutron activation ofTeO2and implications for neutrinoless double-βdecay experiments

Flux-averaged cross sections for cosmogenic-neutron activation of natural tellurium were measured using a neutron beam containing neutrons of kinetic energies up to $\sim$800 MeV, and having an energy spectrum similar to that of cosmic-ray neutrons at sea-level. Analysis of the radioisotopes produced reveals that 110mAg will be a dominant contributor to the cosmogenic-activation background in experiments searching for neutrinoless double-beta decay of 130Te, such as CUORE and SNO+. An estimate of the cosmogenic-activation background in the CUORE experiment has been obtained using the results of this measurement and cross-section measurements of proton activation of tellurium. Additionally, the measured cross sections in this work are also compared with results from semi-empirical cross-section calculations.

The CUORE experiment: status and prospects

CUORE is a bolometric detector composed of 988 TeO2 crystals, with a total mass of about 200 kg of 130Te, currently under construction at Laboratori Nazionali del Gran Sasso in Italy. It will probe the neutrinoless double beta decay (0vDBD) of 130Te, testing the neutrino nature and mass at the level relevant for exploring the inverted neutrino mass hierarchy. On the road towards CUORE, a first tower named CUORE-0, is being assembled and will be operated as an independent experiment in 2012. Detailed information on these detectors and on the expected performance are discussed.

Status report of the final single module detector configuration for the CUORE experiment

The final status of the single module configuration for CUORE experiment will be illustrated. CUORE is a tightly packed array of 988 TeO 2 bolometers and represents one of the best approaches to search for neutrinoless double beta decay ( β β 0 ν ). TeO 2 crystals production is now well established and specific attention was dedicated to test the complete infrastructures. During the last months, dedicated measurements, referred as CCVR (Chinese Crystal Validation Run), were done at the Laboratori Nazionali del Gran Sasso (LNGS). Results obtained in CCVR runs will be presented considering the detector performances achieved and the characteristics that can be attributed to all the final detectors parts.

Monte Carlo evaluation of the external gamma, neutron and muon induced background sources in the CUORE experiment

CUORE is a 1 ton scale cryogenic experiment aiming at the measurement of the Majorana mass of the electron neutrino. The detector is an array of 988 TeO 2 bolometers used for a calorimetric detection of the two electrons emitted in the β β ( 0 ν ) of 130Te. The sensitivity of the experiment to the lowest Majorana mass is determined by the rate of background events that can mimic a β β ( 0 ν ) . In this paper, we investigate the contribution of external sources i.e. environmental gammas, neutrons and cosmic ray muons to the CUORE background and show that the shielding setup designed for CUORE guarantees a reduction of this external background down to a level <10 −2 counts/kg keV yr at the Q-value, as required by the physical goal of the experiment.