• Energy Research

We present the first search for the Majoron-emitting modes of the neutrinoless double $β$ decay ($0νββχ_0$) using scintillating cryogenic calorimeters. We analysed the CUPID-0 Phase I data using a Bayesian approach to reconstruct the background sources activities, and evaluate the potential contribution of the $^{82}$Se $0νββχ_0$. We considered several possible theoretical models which predict the existence of a Majoron-like boson coupling to the neutrino. The energy spectra arising from the emission of such bosons in the neutrinoless double $β$ decay have spectral indices $n=$ 1, 2, 3 or 7. We found no evidence of any of these decay modes, setting a lower limit (90% of credibility interval) on the half-life of 1.2 $\times$ 10$^{23}$ yr in the case of $n=$ 1, 3.8 $\times$ 10$^{22}$ yr for $n=$ 2, 1.4 $\times$ 10$^{22}$ yr for $n=$ 3 and 2.2 $\times$ 10$^{21}$ yr for $n=$ 7. These are the best limits on the $0νββχ_0$ half-life of the $^{82}$Se, and demonstrate the potentiality of the CUPID-0 technology in this field.

The CUORE (Cryogenic Underground Observatory for Rare Events) experiment will be composed by one thousand TeO2 absorbers of 5×5×5 cm3 to be operated in the Gran Sasso Underground Laboratory. CUORICINO, a reduced version of CUORE, as been already approved and funded and will be in operation since the beginning of next year. A description of the CUORE setup, of the mechanical structure and of the single detector performances is shown. The physics goals of CUORE are illustrated.

AbstractThe CUPID-Mo experiment to search for 0$$\nu \beta \beta $$ ν β β decay in $$^{100}$$ 100 Mo has been recently completed after about 1.5 years of operation at Laboratoire Souterrain de Modane (France). It served as a demonstrator for CUPID, a next generation 0$$\nu \beta \beta $$ ν β β decay experiment. CUPID-Mo was comprised of 20 enriched $$\hbox {Li}_{{2}}$$ Li 2 $$^{100}$$ 100 $$\hbox {MoO}_4$$ MoO 4 scintillating calorimeters, each with a mass of $$\sim 0.2$$ ∼ 0.2  kg, operated at $$\sim 20$$ ∼ 20  mK. We present here the final analysis with the full exposure of CUPID-Mo ($$^{100}$$ 100 Mo exposure of 1.47 $$\hbox {kg} \times \hbox {year}$$ kg × year ) used to search for lepton number violation via 0$$\nu \beta \beta $$ ν β β decay. We report on various analysis improvements since the previous result on a subset of data, reprocessing all data with these new techniques. We observe zero events in the region of interest and set a new limit on the $$^{100}$$ 100 Mo 0$$\nu \beta \beta $$ ν β β decay half-life of $$T_{1/2}^{0\nu }$$ T 1 / 2 0 ν $$> {1.8}\times 10^{24}$$ > 1.8 × 10 24  year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of $$\left<m_{\beta \beta }\right>$$ m β β $$<~{(0.28{-}0.49)} $$ < ( 0.28 - 0.49 )  eV, dependent upon the nuclear matrix element utilized.

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.