Development of 100^{100}Mo-containing scintillating bolometers for a high-sensitivity neutrinoless double-beta decay search

We report recent achievements in the development of scintillating bolometers to search for neutrinoless double-beta decay of $^{100}$Mo. The presented results have been obtained in the framework of the LUMINEU, LUCIFER and EDELWEISS collaborations, and are now part of the R\&D activities towards CUPID (CUORE Update with Particle IDentification), a proposed next-generation double-beta decay experiment based on the CUORE experience. We have developed a technology for the production of large mass ($\sim$1 kg), high optical quality, radiopure zinc and lithium molybdate crystal scintillators (ZnMoO$_4$ and Li$_2$MoO$_4$, respectively) from deeply purified natural and $^{100}$Mo-enriched molybdenum. The procedure is applied for a routine production of enriched crystals. Furthermore, the technology of a single detector module consisting of a large-volume ($\sim 100$~cm$^3$) Zn$^{100}$MoO$_4$ and Li$_2$$^{100}$MoO$_4$ scintillating bolometer has been established, demonstrating performance and radiopurity that are close to satisfy the demands of CUPID. In particular, the FWHM energy resolution of the detectors at 2615 keV --- near the $Q$-value of the double-beta transition of $^{100}$Mo (3034~keV) --- is $\approx$ 4--10~keV. The achieved rejection of $\alpha$-induced dominant background above 2.6~MeV is at the level of more than 99.9\%. The bulk activity of $^{232}$Th ($^{228}$Th) and $^{226}$Ra in the crystals is below 10 $\mu$Bq/kg. Both crystallization and detector technologies favor Li$_2$MoO$_4$, which was selected as a main element for the realization of a CUPID demonstrator (CUPID-0/Mo) with $\sim$7 kg of $^{100}$Mo

Final results on the 0 νββ decay half-life limit of 100 Mo from the CUPID-Mo experiment

The CUPID-Mo experiment to search for 0νββ decay in 100Mo 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 0νββ decay experiment. CUPID-Mo was comprised of 20 enriched Li 2100MoO 4 scintillating calorimeters, each with a mass of ∼ 0.2 kg, operated at ∼ 20 mK. We present here the final analysis with the full exposure of CUPID-Mo (100Mo exposure of 1.47 kg × year) used to search for lepton number violation via 0νββ 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 100Mo 0νββ decay half-life of T1/20ν> 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 〈 mββ〉 <(0.28-0.49) eV, dependent upon the nuclear matrix element utilized

Final results on the 0νββ0νββ decay half-life limit of 100^{100}Mo from the CUPID-Mo experiment

The CUPID-Mo experiment to search for 0$\nu\beta\beta$ decay in $^{100}$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$\nu\beta\beta$ decay experiment. CUPID-Mo was comprised of 20 enriched Li$_2$$^{100}$MoO$_4$ scintillating calorimeters, each with a mass of $\sim$ 0.2 kg, operated at $\sim$20 mK. We present here the final analysis with the full exposure of CUPID-Mo ($^{100}$Mo exposure of 1.47 kg$\times$yr) used to search for lepton number violation via 0$\nu\beta\beta$ 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 $^{100}$Mo 0$\nu\beta\beta$ decay half-life of T^{0\nu}_{1/2} > 1.8 \times 10^{24} year (stat.+syst.) at 90% C.I. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of \left < (0.28--$0.49)$ eV, dependent upon the nuclear matrix element utilized

New measurement of double-β decays of Mo100 to excited states of Ru100 with the CUPID-Mo experiment

The CUPID-Mo experiment, located at the Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of 20Li2Mo100O4 (LMO) calorimeters, each equipped with a Ge light detector for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double-β decays of Mo100 to the first 0+ and 2+ excited states of Ru100 using the full CUPID-Mo exposure (2.71kgyr of LMO). We measure the half-life of 2νββ decay to the 01+ state as T1/22ν→01+=(7.5±0.8(stat.)-0.3+0.4(syst.))×1020yr. The bolometric technique enables measurement of the electron energies as well as the γ rays from nuclear deexcitation and this allows us to set new limits on the two-neutrino decay to the 21+ state of T1/22ν→21+&gt;4.4×1021yr(90% c.i.) and on the neutrinoless modes of T1/20ν→21+&gt;2.1×1023yr(90% c.i.), T1/20ν→01+&gt;1.2×1023yr(90% c.i.). Information on the electrons' spectral shape is obtained, which allows us to make the first comparison of the single and higher state dominance 2νββ decay models for the 01+ excited state of Ru100

The CUPID-Mo experiment for neutrinoless double-beta decay: performance and prospects

CUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay (0 νββ) of 100Mo. In this article, we detail the CUPID-Mo detector concept, assembly and installation in the Modane underground laboratory, providing results from the first datasets. The CUPID-Mo detector consists of an array of 20 100Mo -enriched 0.2 kg Li 2MoO 4 crystals operated as scintillating bolometers at ∼20mK. The Li 2MoO 4 crystals are complemented by 20 thin Ge optical bolometers to reject α events by the simultaneous detection of heat and scintillation light. We observe a good detector uniformity and an excellent energy resolution of 5.3 keV (6.5 keV) FWHM at 2615 keV, in calibration (physics) data. Light collection ensures the rejection of α particles at a level much higher than 99.9% – with equally high acceptance for γ/β events – in the region of interest for 100Mo 0 νββ. We present limits on the crystals’ radiopurity: ≤3μBq/kg of 226Ra and ≤2μBq/kg of 232Th. We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the 100Mo 0 νββ decay in half-a-year’s livetime. The achieved results show that CUPID-Mo is a successful demonstrator of the technology developed by the LUMINEU project and subsequently selected for the CUPID experiment, a proposed follow-up of CUORE, the currently running first tonne-scale bolometric 0 νββ experiment

Precise measurement of 2 ν 2 β decay of 100Mo with Li2MoO4 low temperature detectors: Preliminary results

The half-life of 100Mo relatively to the 2ν2β decay to the ground state of 100Ru was measured as T1/2 = (6.99±0.15) × 1018 yr with the help of enriched in 100Mo lithium molybdate scintillating bolometers in the EDELWEISS-III low background set-up at the Modane underground laboratory. This is the most accurate value of the 2ν2β half-life of 100Mo

The CUPID-Mo experiment for neutrinoless double-beta decay: performance and prospects

International audienceCUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay ($0\nu \beta \beta$) of $^{100}\hbox {Mo}$. In this article, we detail the CUPID-Mo detector concept, assembly and installation in the Modane underground laboratory, providing results from the first datasets. The CUPID-Mo detector consists of an array of 20 $^{100}\hbox {Mo}$-enriched 0.2 kg $\hbox {Li}_2\hbox {MoO}_4$ crystals operated as scintillating bolometers at $\sim 20\hbox { mK}$. The $\hbox {Li}_2\hbox {MoO}_4$ crystals are complemented by 20 thin Ge optical bolometers to reject $\alpha$ events by the simultaneous detection of heat and scintillation light. We observe a good detector uniformity and an excellent energy resolution of 5.3 keV (6.5 keV) FWHM at 2615 keV, in calibration (physics) data. Light collection ensures the rejection of $\alpha$ particles at a level much higher than 99.9% – with equally high acceptance for $\gamma$/$\beta$ events – in the region of interest for $^{100}\hbox {Mo}0\nu \beta \beta$. We present limits on the crystals’ radiopurity: $\le 3~\mu \hbox {Bq/kg}$ of $^{226}\hbox {Ra}$ and $\le 2~\mu \hbox {Bq/kg}$ of $^{232}\hbox {Th}$. We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the $^{100}\hbox {Mo}0\nu \beta \beta$ decay in half-a-year’s livetime. The achieved results show that CUPID-Mo is a successful demonstrator of the technology developed by the LUMINEU project and subsequently selected for the CUPID experiment, a proposed follow-up of CUORE, the currently running first tonne-scale bolometric $0\nu \beta \beta$ experiment

The background model of the CUPID-Mo 0νββ experiment

CUPID-Mo, located in the Laboratoire Souterrain de Modane (France), was a demonstrator for the next generation 0 νββ decay experiment, CUPID. It consisted of an array of 20 enriched Li 2100 MoO 4 bolometers and 20 Ge light detectors and has demonstrated that the technology of scintillating bolometers with particle identification capabilities is mature. Furthermore, CUPID-Mo can inform and validate the background prediction for CUPID. In this paper, we present a detailed model of the CUPID-Mo backgrounds. This model is able to describe well the features of the experimental data and enables studies of the 2 νββ decay and other processes with high precision. We also measure the radio-purity of the Li 2100 MoO 4 crystals which are found to be sufficient for the CUPID goals. Finally, we also obtain a background index in the region of interest of 3.7 -0.8+0.9 (stat) -0.7+1.5 (syst) ×10-3 counts/ Δ EFWHM/ mol iso/ year , the lowest in a bolometric 0 νββ decay experiment