G. Pessina

CUORE: a cryogenic underground observatory for rare events

CUORE is a proposed tightly packed array of 1000 TeO2 bolometers, each being a cube 5cm on a side with a mass of 760g. The array consists of 25 vertical towers, arranged in a square of 5 towers×5 towers, each containing 10 layers of four crystals. The design of the detector is optimized for ultralow-background searches: for neutrinoless double-beta decay of 130Te (33.8% abundance), cold dark matter, solar axions, and rare nuclear decays. A preliminary experiment involving 20 crystals 3×3×6cm3 of 340g has been completed, and a single CUORE tower is being constructed as a smaller-scale experiment called CUORICINO. The expected performance and sensitivity, based on Monte Carlo simulations and extrapolations of present results, are reported.

A next-generation neutrinoless double beta decay experiment based on ZnMoO4 scintillating bolometers

Article history: The search for neutrinoless double β decay probes lepton number conservation with high sensitivity and investigates the neutrino nature and mass scale. Experiments presently in preparation will cover the quasi-degeneracy region of the neutrino mass pattern. Probing the inverted hierarchy region requires improved sensitivities and next-generation experiments, based either on large expansions of the present searches or on new ideas. We examine here a novel technology relying on ZnMoO4 scintillating bolometers, which can provide an experiment with background close to zero in the ton × year exposure scale. The promising performance of a pilot detector is presented, both in terms of energy resolution and background control. A preliminary study of the sensitivities of future experiments shows that the inverted hierarchy region is within the reach of the technique here proposed. A realistic phased approach program towards a next-generation search is presented and briefly discussed.

Performance of ZnMoO4 crystal as cryogenic scintillating bolometer to search for double beta decay of molybdenum

Zinc molybdate (ZnMoO4) single crystals were grown for the first time by the Czochralski method and their luminescence was measured under X-ray excitation in the temperature range 85–400 K. Properties of ZnMoO4 crystal as cryogenic low temperature scintillator were checked for the first time. Radioactive contamination of the ZnMoO4 crystal was estimated as ≤ 0.3 mBq/kg (228Th) and 8 mBq/kg (226Ra). Thanks to the simultaneous measurement of the scintillation light and the phonon signal, the α particles can be discriminated from the γ/β interactions, making this compound extremely promising for the search of neutrinoless Double Beta Decay of 100Mo. We also report on the ability to discriminate the α-induced background without the light measurement, thanks to a different shape of the thermal signal that characterizes γ/β and α particle interactions.

A scintillating bolometer for experiments on double beta decay

Abstract The scintillation yields of CaF 2 crystals with different doping concentration of Europium have been measured at low temperatures and their bolometric behavior has been investigated. After these studies we have constructed the first “scintillating bolometer” where the heat and scintillation pulses produced by charged particles are simultaneously recorded. With this method a strong suppression of the background from α -particles in the energy region of interest for searches on double beta decay of 48 Ca can be achieved.

Measurements of internal radioactive contamination in samples of Roman lead to be used in experiments on rare events

Improved results of a series of measurements carried out on two diAerent types of Roman lead to be used in shields for experiments on rare events are reported. The chemical impurities in both samples have been determined by neutron activation. Underground measurements based on c-spectroscopy on large masses of the two types of lead, show the absence in both samples of radioactive contamination from 214 Bi and 232 Th, in secular equilibrium, with upper limits of a few tenths of a mBq kg ˇ1 . The contamination from 40 K is less than a few mBq kg ˇ1 . Much care has been addressed to the contamination due to 210 Pb which breaks secular equilibrium and which contributes to most of the background in experiments searching low energy events like direct interactions of Weakly Interacting Massive Particles (WIMPS). We have applied to this problem the technique of cryogenic detection and found for the two samples upper limits for contamination of 210 Pb of 4 and 7 mBq kg ˇ1 , the lowest ever determined for any type of lead. ” 1998 Published by Else

A calorimetric search on double beta decay of 130Te

We report on the final results of a series of experiments on double beta decay of 130 Te carried out with an array of twenty cryogenic detectors. The set-up is made with crystals of TeO2 with a total mass of 6.8 kg, the largest operating one for a cryogenic experiment. Four crystals are made with isotopically enriched materials: two in 128 Te and two others in 130 Te. The remaining ones are made with natural tellurium, which contains 31.7% and 33.8% 128 Te and 130 Te, respectively. The array was run under a heavy shield in the Gran Sasso Underground Laboratory at a depth of about 3500 m.w.e. By recording the pulses of each detector in anticoincidence with the others a lower limit of 2.1 × 10 23 years has been obtained at the 90% C.L. on the lifetime for neutrinoless double beta decay of 130 Te. In terms of effective neutrino mass this leads to the most restrictive limit in direct experiments, after those obtained with Ge diodes. Limits on other lepton violating decays of 130 Te and on the neutrinoless double beta decay of 128 Te to the ground state of 128 Xe are also reported and discussed. An indication is presented for the two neutrino double beta decay of 130 Te. Some consequences of the present results in the interpretation of geochemical experiments are discussed.  2003 Elsevier Science B.V. All rights reserved.

Physics potential and prospects for the CUORICINO and CUORE experiments

Abstract The Cryogenic Underground Observatory for Rare Events (CUORE) experiment projects to construct and operate an array of 1000 cryogenic thermal detectors of TeO 2 , of a mass of 760 g each, to investigate rare events physics, in particular, double beta decay and non-baryonic particle dark matter. A first step towards CUORE is CUORICINO, an array of 62 bolometers, currently being installed in the Gran Sasso Laboratory. In this paper we report the physics potential of both stages of the experiment regarding neutrinoless double beta decay of 130 Te, WIMP searches and solar axions.The CUORE experiment projects to construct and operate an array of 1000 cryogenic thermal detectors of TeO2, of a mass of 760 g each, to investigate rare events physics, in particular, double beta decay and non baryonic particle dark matter. A first step towards CUORE is CUORICINO, an array of 62 bolometers, currently being installed in the Gran Sasso Laboratory. In this paper we report the physics potential of both stages of the experiment regarding neutrinoless double beta decay of 130Te, WIMP searches and solar axions.

New experimental results on double beta decay of 130Te

New results are presented of a search for double beta decay of Te isotopes carried out, using the bolometric technique, with an array of 20 natural tellurite crystals with a total cryogenic mass of ; 6.8 kilograms. The array has been run at a temperature around 10 mK in the Gran Sasso Underground Laboratory. No evidence has been found for neutrinoless double beta decay of 128 Te and 130 Te and upper limits of 8.6 = 10 22 and 1.44 = 10 23 years, respectively, have been achieved at the 90% confidence level. From the latter we obtain limits on the lepton non-conserving parameters which are the most restrictive ones in direct experiments after those on 76 Ge according to theoretical calculations. Results on two neutrino and majoron mediated decays are also presented and discussed with respect to those obtained for the same nuclei in geochemical experiments. q 2000 Elsevier Science B.V. All rights reserved.

Characterization of ZnSe scintillating bolometers for Double Beta Decay

Abstract ZnSe scintillating bolometers are good candidates for future Double Beta Decay searches, because of the 82Se high Q-value and thanks to the possibility of alpha background rejection on the basis of the scintillation signal. In this paper we report the characteristics and the anomalies observed in an extensive study of these devices. Among them, an unexpected high emission from alpha particles, accompanied with an unusual pattern of the light vs. heat scatter plot. The perspectives for the application of this kind of detectors to search for the Neutrinoless Double Beta Decay of 82Se are presented.

A new search for neutrinoless ββ decay with a thermal detector

Abstract A 334 g TeO2 crystal has been operated at a temperature of around 10 mK for more than one year in a low intrinsic radioactivity dilution refrigerator installed in the Gran Sasso Underground Laboratory. From the spectrum collected in 9234 h of effective running time we improve our limit on neutrinoless double beta decay of 130Te by an order of magnitude with respect to our previous experiment. It is the most stringent on this nucleus and excludes a large contribution of the neutrinoless mode to the rate of double beta decay found in geochemical experiments. Upper limits on the effective neutrino mass and on the contributions of right banded currents are given.