The CUPID-Mo experiment to search for 0
ν
β
β
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
ν
β
β
decay experiment. CUPID-Mo was comprised of 20 enriched
Li
2
100
MoO
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 (
100
Mo exposure of 1.47
kg
×
year
) used to search for lepton number violation via 0
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
Mo 0
ν
β
β
decay half-life of
T
1
/
2
0
ν
>
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
m
β
β
<
(
0.28
-
0.49
)
eV, dependent upon the nuclear matrix element utilized.
Abstract
The 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.
CUPID is a next-generation tonne-scale bolometric neutrinoless double beta decay experiment that will probe the Majorana nature of neutrinos and discover lepton number violation in case of ...observation of this singular process. CUPID will be built on experience, expertise and lessons learned in CUORE and will be installed in the current CUORE infra-structure in the Gran Sasso underground laboratory. The CUPID detector technology, successfully tested in the CUPID-Mo experiment, is based on scintillating bolometers of Li
2
MoO
4
enriched in the isotope of interest
100
Mo. In order to achieve its ambitious science goals, the CUPID collaboration aims to reduce the backgrounds in the region of interest by a factor 100 with respect to CUORE. This performance will be achieved by introducing the high efficient
α
/
β
discrimination demonstrated by the CUPID-0 and CUPID-Mo experiments, and using a high transition energy double beta decay nucleus such as
100
Mo to minimize the impact of the gamma background. CUPID will consist of about 1500 hybrid heat-light detectors for a total isotope mass of 250 kg. The CUPID scientific reach is supported by a detailed and safe background model based on CUORE, CUPID-Mo and CUPID-0 results. The required performances have already been demonstrated and will be presented.
CUORE Upgrade with Particle IDentification (CUPID) is a foreseen ton-scale array of Li
2
MoO
4
(LMO) cryogenic calorimeters with double readout of heat and light signals. Its scientific goal is to ...fully explore the inverted hierarchy of neutrino masses in the search for neutrinoless double beta decay of
100
Mo. Pile-up of standard double beta decay of the candidate isotope is a relevant background. We generate pile-up heat events via injection of Joule heater pulses with a programmable waveform generator in a small array of LMO crystals operated underground in the Laboratori Nazionali del Gran Sasso, Italy. This allows to label pile-up pulses and control both time difference and underlying amplitudes of individual heat pulses in the data. We present the performance of supervised learning classifiers on data and the attained pile-up rejection efficiency.
The EDELWEISS-II collaboration has completed a direct search for WIMP dark matter using cryogenic Ge detectors (400g each) and 384kg×days of effective exposure. A cross-section of 4.4×10-8pb is ...excluded at 90% C. L. for a WIMP mass of 85GeV. The next phase, EDELWEISS-III, aims to probe spin-independent WIMP-nucleon cross-sections down to a few ×10-9pb. We present here the study of gamma and neutron background coming from radioactive decays in the set-up and shielding materials. We have carried out Monte Carlo simulations for the completed EDELWEISS-II setup with GEANT4 and normalised the expected background rates to the measured radioactivity levels (or their upper limits) of all materials and components. The expected gamma-ray event rate in EDELWEISS-II at 20–200keV agrees with the observed rate of 82 events/kg/day within the uncertainties in the measured concentrations. The calculated neutron rate from radioactivity of 1.0–3.1 events (90% C. L.) at 20–200keV in the EDELWEISS-II data together with the expected upper limit on the misidentified gamma-ray events (⩽0.9), surface betas (⩽0.3), and muon-induced neutrons (⩽0.7), do not contradict five observed events in nuclear recoil band. We have then extended the simulation framework to the EDELWEISS-III configuration with 800g crystals, better material purity and additional neutron shielding inside the cryostat. The gamma-ray and neutron backgrounds in 24kg fiducial mass of EDELWEISS-III have been calculated as 14–44 events/kg/day and 0.7–1.4 events per year, respectively. The results of the background studies performed in the present work have helped to select better purity components and improve shielding in EDELWEISS-III to further reduce the expected rate of background events in the next phase of the experiment.
Abstract The CUPID Collaboration is designing a tonne-scale, background-free detector to search for double beta decay with sufficient sensitivity to fully explore the parameter space corresponding to ...the inverted neutrino mass hierarchy scenario. One of the CUPID demonstrators, CUPID-Mo, has proved the potential of enriched Li $$_{2}$$ 2 $$^{100}$$ 100 MoO $$_4$$ 4 crystals as suitable detectors for neutrinoless double beta decay search. In this work, we characterised cubic crystals that, compared to the cylindrical crystals used by CUPID-Mo, are more appealing for the construction of tightly packed arrays. We measured an average energy resolution of ( $$6.7\pm 0.6$$ 6.7 ± 0.6 ) keV FWHM in the region of interest, approaching the CUPID target of 5 keV FWHM. We assessed the identification of $$\alpha $$ α particles with and without a reflecting foil that enhances the scintillation light collection efficiency, proving that the baseline design of CUPID already ensures a complete suppression of this $$\alpha $$ α -induced background contribution. We also used the collected data to validate a Monte Carlo simulation modelling the light collection efficiency, which will enable further optimisations of the detector.
Abstract
The CUPID Collaboration is designing a tonne-scale, background-free detector to search for double beta decay with sufficient sensitivity to fully explore the parameter space corresponding to ...the inverted neutrino mass hierarchy scenario. One of the CUPID demonstrators, CUPID-Mo, has proved the potential of enriched Li
$$_{2}$$
2
$$^{100}$$
100
MoO
$$_4$$
4
crystals as suitable detectors for neutrinoless double beta decay search. In this work, we characterised cubic crystals that, compared to the cylindrical crystals used by CUPID-Mo, are more appealing for the construction of tightly packed arrays. We measured an average energy resolution of (
$$6.7\pm 0.6$$
6.7
±
0.6
) keV FWHM in the region of interest, approaching the CUPID target of 5 keV FWHM. We assessed the identification of
$$\alpha $$
α
particles with and without a reflecting foil that enhances the scintillation light collection efficiency, proving that the baseline design of CUPID already ensures a complete suppression of this
$$\alpha $$
α
-induced background contribution. We also used the collected data to validate a Monte Carlo simulation modelling the light collection efficiency, which will enable further optimisations of the detector.
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