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"Augier, C."
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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
ν
β
β
) of
100
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
Mo
-enriched 0.2 kg
Li
2
MoO
4
crystals operated as scintillating bolometers at
∼
20
mK
. The
Li
2
MoO
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
100
Mo
0
ν
β
β
. We present limits on the crystals’ radiopurity:
≤
3
μ
Bq/kg
of
226
Ra
and
≤
2
μ
Bq/kg
of
232
Th
. We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the
100
Mo
0
ν
β
β
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
ν
β
β
experiment.
Journal Article
Searching for beyond the Standard Model physics using the improved description of .sup.100Mo Formula omitted decay spectral shape with CUPID-Mo
The current experiments searching for neutrinoless double- [Formula omitted] ( [Formula omitted]) decay also collect large statistics of Standard Model allowed two-neutrino double- [Formula omitted] ( [Formula omitted]) decay events. These can be used to search for Beyond Standard Model (BSM) physics via [Formula omitted] decay spectral distortions. .sup.100Mo has a natural advantage due to its relatively short half-life, allowing higher [Formula omitted] decay statistics at equal exposures compared to the other isotopes. We demonstrate the potential of the dual read-out bolometric technique exploiting a .sup.100Mo exposure of 1.47 kg [Formula omitted] years, acquired in the CUPID-Mo experiment at the Modane underground laboratory (France). We set limits on [Formula omitted] decays with the emission of one or more Majorons, on [Formula omitted] decay with Lorentz violation, and [Formula omitted] decay with a sterile neutrino emission. In this analysis, we investigate the systematic uncertainty induced by modeling the [Formula omitted] decay spectral shape parameterized through an improved model, an effect never considered before. This work motivates searches for BSM processes in the upcoming CUPID experiment, which will collect the largest amount of [Formula omitted] decay events among the next-generation experiments.
Journal Article
Measurement of the double-Formula omitted decay of Formula omittedNd to the 0Formula omitted excited state of Formula omittedSm in NEMO-3
The NEMO-3 results for the double- [Formula omitted] decay of [Formula omitted]Nd to the 0 [Formula omitted] and 2 [Formula omitted] excited states of [Formula omitted]Sm are reported. The data recorded during 5.25 year with 36.6 g of the isotope [Formula omitted]Nd are used in the analysis. The signal of the [Formula omitted] transition to the 0 [Formula omitted] excited state is detected with a statistical significance exceeding 5 [Formula omitted]. The half-life is measured to be [Formula omitted] year, which is the most precise value that has been measured to date. 90% confidence-level limits are set for the other decay modes. For the [Formula omitted] decay to the 2 [Formula omitted] level the limit is [Formula omitted]. The limits on the [Formula omitted] decay to the 0 [Formula omitted] and 2 [Formula omitted] levels of [Formula omitted]Sm are significantly improved to [Formula omitted] and [Formula omitted].
Journal Article
Fast neutron background characterization of the future Ricochet experiment at the ILL research nuclear reactor
The future
Ricochet
experiment aims at searching for new physics in the electroweak sector by providing a high precision measurement of the Coherent Elastic Neutrino-Nucleus Scattering (CENNS) process down to the sub-100 eV nuclear recoil energy range. The experiment will deploy a kg-scale low-energy-threshold detector array combining Ge and Zn target crystals 8.8 m away from the 58 MW research nuclear reactor core of the Institut Laue Langevin (ILL) in Grenoble, France. Currently, the
Ricochet
Collaboration is characterizing the backgrounds at its future experimental site in order to optimize the experiment’s shielding design. The most threatening background component, which cannot be actively rejected by particle identification, consists of keV-scale neutron-induced nuclear recoils. These initial fast neutrons are generated by the reactor core and surrounding experiments (reactogenics), and by the cosmic rays producing primary neutrons and muon-induced neutrons in the surrounding materials. In this paper, we present the
Ricochet
neutron background characterization using
3
He proportional counters which exhibit a high sensitivity to thermal, epithermal and fast neutrons. We compare these measurements to the
Ricochet
Geant4 simulations to validate our reactogenic and cosmogenic neutron background estimations. Eventually, we present our estimated neutron background for the future
Ricochet
experiment and the resulting CENNS detection significance. Our results show that depending on the effectiveness of the muon veto, we expect a total nuclear recoil background rate between 44 ± 3 and 9 ± 2 events/day/kg in the CENNS region of interest, i.e. between 50 eV and 1 keV. We therefore found that the
Ricochet
experiment should reach a statistical significance of 4.6 to 13.6
σ
for the detection of CENNS after one reactor cycle, when only the limiting neutron background is considered.
Journal Article
The background model of the CUPID-Mo Formula omitted experiment
CUPID-Mo, located in the Laboratoire Souterrain de Modane (France), was a demonstrator for the next generation [Formula omitted] decay experiment, CUPID. It consisted of an array of 20 enriched Li [Formula omitted] [Formula omitted]MoO [Formula omitted] 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 [Formula omitted] decay and other processes with high precision. We also measure the radio-purity of the Li [Formula omitted] [Formula omitted]MoO [Formula omitted] 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 [Formula omitted] (stat) [Formula omitted] (syst) [Formula omitted] counts/ [Formula omitted] the lowest in a bolometric [Formula omitted] decay experiment.
Journal Article
Precise measurement of Formula omitted decay of Formula omittedMo with the CUPID-Mo detection technology
We report the measurement of the two-neutrino double-beta ( [Formula omitted]) decay of [Formula omitted]Mo to the ground state of [Formula omitted]Ru using lithium molybdate ( [Formula omitted]) scintillating bolometers. The detectors were developed for the CUPID-Mo program and operated at the EDELWEISS-III low background facility in the Modane underground laboratory (France). From a total exposure of 42.235 kg [Formula omitted]day, the half-life of [Formula omitted]Mo is determined to be [Formula omitted] years. This is the most accurate determination of the [Formula omitted] half-life of [Formula omitted]Mo to date.
Journal Article
High Impedance TES Bolometers for EDELWEISS
The EDELWEISS collaboration aims for direct detection of light dark matter using germanium cryogenic detectors with low threshold phonon sensor technologies and efficient charge readout designs. We describe here the development of Ge bolometers equipped with high impedance thermistors based on a Nb
x
Si
1−x
TES alloy. High aspect ratio spiral designs allow the TES impedance to match with JFET or HEMT front-end amplifiers. We detail the behavior of the superconducting transition properties of these sensors and the detector optimization in terms of sensitivity to a-thermal phonons. We report preliminary results of a 200 g Ge detector that was calibrated using
71
Ge activation by neutrons at the LSM underground laboratory.
Journal Article
Improved EDELWEISS-III sensitivity for low-mass WIMPs using a profile likelihood approach
We report on a dark matter search for a Weakly Interacting Massive Particle (WIMP) in the mass range
m
χ
∈
[
4
,
30
]
GeV
/
c
2
with the EDELWEISS-III experiment. A 2D profile likelihood analysis is performed on data from eight selected detectors with the lowest energy thresholds leading to a combined fiducial exposure of 496 kg-days. External backgrounds from
γ
- and
β
-radiation, recoils from
206
Pb
and neutrons as well as detector intrinsic backgrounds were modelled from data outside the region of interest and constrained in the analysis. The basic data selection and most of the background models are the same as those used in a previously published analysis based on boosted decision trees (BDT) [
1
]. For the likelihood approach applied in the analysis presented here, a larger signal efficiency and a subtraction of the expected background lead to a higher sensitivity, especially for the lowest WIMP masses probed. No statistically significant signal was found and upper limits on the spin-independent WIMP-nucleon scattering cross section can be set with a hypothesis test based on the profile likelihood test statistics. The 90 % C.L. exclusion limit set for WIMPs with
m
χ
=
4
GeV
/
c
2
is
1.6
×
10
-
39
cm
2
, which is an improvement of a factor of seven with respect to the BDT-based analysis. For WIMP masses above
15
GeV
/
c
2
the exclusion limits found with both analyses are in good agreement.
Journal Article