A new design of a cryogenic germanium detector for dark matter search is presented, taking advantage of the coplanar grid technique of event localisation for improved background discrimination. ...Experiments performed with prototype devices in the EDELWEISS II setup at the Modane underground facility demonstrate the remarkably high efficiency of these devices for the rejection of low-energy β, approaching 105. This opens the road to investigate the range beyond 10−8 pb in the WIMP–nucleon collision cross-sections, as proposed in the EURECA project of a one-ton cryogenic detector mass.
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.
A dedicated analysis of the muon-induced background in the EDELWEISS dark matter search has been performed on a data set acquired in 2009 and 2010. The total muon flux underground in the Laboratoire ...Souterrain de Modane (LSM) was measured to be Φμ=(5.4±0.2-0.9+0.5)muons/m2/d. The modular design of the μ-veto system allows the reconstruction of the muon trajectory and hence the determination of the angular dependent muon flux in LSM. The results are in good agreement with both MC simulations and earlier measurements. Synchronization of the μ-veto system with the phonon and ionization signals of the Ge detector array allowed identification of muon-induced events. Rates for all muon-induced events Γμ=(0.172±0.012)evts/(kgd) and of WIMP-like events Γμ–n=0.008-0.004+0.005evts/(kgd) were extracted. After vetoing, the remaining rate of accepted muon-induced neutrons in the EDELWEISS-II dark matter search was determined to be Γirredμ–n<6·10-4evts/(kgd) at 90% C.L. Based on these results, the muon-induced background expectation for an anticipated exposure of 3000kgd for EDELWEISS-III is N3000kgdμ–n<0.6 events.
We report the measurement of the two-neutrino double-beta (
2
ν
β
β
) decay of
100
Mo to the ground state of
100
Ru using lithium molybdate (
Li
2
100
MoO
4
) 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
×
day, the half-life of
100
Mo is determined to be
T
1
/
2
2
ν
=
7
.
12
-
0.14
+
0.18
(
stat
.
)
±
0.10
(
syst
.
)
×
10
18
years. This is the most accurate determination of the
2
ν
β
β
half-life of
100
Mo to date.
Abstract We report the measurement of the two-neutrino double-beta ($$2\nu \beta \beta $$ 2νββ ) decay of $$^{100}$$ 100 Mo to the ground state of $$^{100}$$ 100 Ru using lithium molybdate ($$\hbox ...{Li}_2^{\;\;100}\hbox {MoO}_4$$ Li2100MoO4 ) 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$$\times $$ × day, the half-life of $$^{100}$$ 100 Mo is determined to be $$T_{1/2}^{2\nu }=7.12^{+0.18}_{-0.14}\,\mathrm {(stat.)}\pm 0.10\,\mathrm {(syst.)}\times 10^{18}$$ T1/22ν=7.12-0.14+0.18(stat.)±0.10(syst.)×1018 years. This is the most accurate determination of the $$2\nu \beta \beta $$ 2νββ half-life of $$^{100}$$ 100 Mo to date.
Abstract
We report the measurement of the two-neutrino double-beta (
$$2\nu \beta \beta $$
2
ν
β
β
) decay of
$$^{100}$$
100
Mo to the ground state of
$$^{100}$$
100
Ru using lithium molybdate (
...$$\hbox {Li}_2^{\;\;100}\hbox {MoO}_4$$
Li
2
100
MoO
4
) 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
$$\times $$
×
day, the half-life of
$$^{100}$$
100
Mo is determined to be
$$T_{1/2}^{2\nu }=7.12^{+0.18}_{-0.14}\,\mathrm {(stat.)}\pm 0.10\,\mathrm {(syst.)}\times 10^{18}$$
T
1
/
2
2
ν
=
7
.
12
-
0.14
+
0.18
(
stat
.
)
±
0.10
(
syst
.
)
×
10
18
years. This is the most accurate determination of the
$$2\nu \beta \beta $$
2
ν
β
β
half-life of
$$^{100}$$
100
Mo to date.
We report the measurement of the two-neutrino double-beta ($2\nu \beta \beta $) decay of $^{100}$Mo to the ground state of $^{100}$Ru using lithium molybdate ($\hbox {Li}_2^{\;\;100}\hbox {MoO}_4$) ...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$\times $day, the half-life of $^{100}$Mo is determined to be $T_{1/2}^{2\nu }=7.12^{+0.18}_{-0.14}\,\mathrm {(stat.)}\pm 0.10\,\mathrm {(syst.)}\times 10^{18}$ years. This is the most accurate determination of the $2\nu \beta \beta $ half-life of $^{100}$Mo to date.
In the present work, we describe the results obtained with a large (≈133cm3) TeO2 bolometer, with a view to a search for neutrinoless double-β decay (0νββ) of Te130. We demonstrate an efficient ...α-particle discrimination (99.9%) with a high acceptance of the 0νββ signal (about 96%), expected at ≈2.5 MeV. This unprecedented result was possible thanks to the superior performance (10-eV rms baseline noise) of a Neganov-Luke-assisted germanium bolometer used to detect a tiny (70-eV) light signal from the TeO2 detector, dominated by γ(β)-induced Cherenkov radiation but exhibiting also a clear scintillation component. The obtained results represent a major breakthrough toward the TeO2-based version of the CUORE Upgrade with Particle IDentification (CUPID), a ton-scale cryogenic 0νββ experiment proposed as a followup to the Cryogenic Underground Observatory for Rare Events (CUORE) project with particle identification. The CUORE experiment recently began a search for neutrinoless double-β decay of Te130 with an array of 988 125-cm3TeO2 bolometers. The lack of α discrimination in CUORE makes α decays at the detector surface the dominant background component, at the level of ≈0.01 counts/(keV kg y) in the region of interest. We show here, for the first time with a CUORE-size bolometer and using the same technology as CUORE for the readout of both heat and light signals, that surface α background can be fully rejected.
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