Neutrinoless double-
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β
decay of
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Ge is searched for with germanium detectors where source and detector of the decay are identical. For the success of future experiments it is important to increase the mass of the detectors. We report here on the characterization and testing of five prototype detectors manufactured in inverted coaxial (IC) geometry from material enriched to 88% in
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Ge. IC detectors combine the large mass of the traditional semi-coaxial Ge detectors with the superior resolution and pulse shape discrimination power of point contact detectors which exhibited so far much lower mass. Their performance has been found to be satisfactory both when operated in vacuum cryostat and bare in liquid argon within the
Gerda
setup. The measured resolutions at the
Q
-value for double-
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decay of
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Ge (
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Q
β
β
= 2039 keV) are about 2.1 keV full width at half maximum in vacuum cryostat. After 18 months of operation within the ultra-low background environment of the GERmanium Detector Array (
Gerda
) experiment and an accumulated exposure of 8.5 kg
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·
year, the background index after analysis cuts is measured to be
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\begin{document}$$4.9^{+7.3}_{-3.4}\times 10^{-4} \ \text {counts}/(\text {keV} \cdot \text {kg} \cdot \text {year})$$\end{document}
4
.
9
-
3.4
+
7.3
×
10
-
4
counts
/
(
keV
·
kg
·
year
)
around
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Q
β
β
. This work confirms the feasibility of IC detectors for the next-generation experiment
Legend
.
Abstract The DARWIN observatory is a proposed next-generation experiment to search for particle dark matter and for the neutrinoless double beta decay of $$^{136}$$ 136 Xe. Out of its 50 t total ...natural xenon inventory, 40 t will be the active target of a time projection chamber which thus contains about 3.6 t of $$^{136}$$ 136 Xe. Here, we show that its projected half-life sensitivity is $$2.4\times {10}^{27}\,{\hbox {year}}$$ 2.4 × 10 27 year , using a fiducial volume of 5 t of natural xenon and 10 year of operation with a background rate of less than 0.2 events/(t $$\cdot $$ · year) in the energy region of interest. This sensitivity is based on a detailed Monte Carlo simulation study of the background and event topologies in the large, homogeneous target. DARWIN will be comparable in its science reach to dedicated double beta decay experiments using xenon enriched in $$^{136}$$ 136 Xe.
Abstract The DARWIN observatory is a proposed next-generation experiment to search for particle dark matter and for the neutrinoless double beta decay of $$^{136}$$ 136 Xe. Out of its 50 t total ...natural xenon inventory, 40 t will be the active target of a time projection chamber which thus contains about 3.6 t of $$^{136}$$ 136 Xe. Here, we show that its projected half-life sensitivity is $$2.4\times {10}^{27}\,{\hbox {year}}$$ 2.4×1027year , using a fiducial volume of 5 t of natural xenon and 10 year of operation with a background rate of less than 0.2 events/(t $$\cdot $$ · year) in the energy region of interest. This sensitivity is based on a detailed Monte Carlo simulation study of the background and event topologies in the large, homogeneous target. DARWIN will be comparable in its science reach to dedicated double beta decay experiments using xenon enriched in $$^{136}$$ 136 Xe.
The double-beta decay of 82Se to the 01+ excited state of 82Kr has been studied with the NEMO-3 detector using 0.93 kg of enriched 82Se measured for 4.75 y, corresponding to an exposure of 4.42 kg⋅y. ...A dedicated analysis to reconstruct the γ-rays has been performed to search for events in the 2e2γ channel. No evidence of a 2νββ decay to the 01+ state has been observed and a limit of T1/22ν(Se82,0gs+→01+)>1.3×1021y at 90% CL has been set. Concerning the 0νββ decay to the 01+ state, a limit for this decay has been obtained with T1/20ν(Se82,0gs+→01+)>2.3×1022y at 90% CL, independently from the 2νββ decay process. These results are obtained for the first time with a tracko-calo detector, reconstructing every particle in the final state.
The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of
100
Mo to the ground state of
100
Ru,
T
1
/
2
=
6.81
±
0.01
stat
-
0.40
+
...0.38
syst
×
10
18
year. The two-electron energy sum, single electron energy spectra and distribution of the angle between the electrons are presented with an unprecedented statistics of
5
×
10
5
events and a signal-to-background ratio of
∼
80. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limits on Majoron emitting neutrinoless double beta decay modes with spectral indices of
n
=
2
,
3
,
7
, as well as constraints on Lorentz invariance violation and on the bosonic neutrino contribution to the two-neutrino double beta decay mode are obtained.
Here, using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay (2νββ) half-life of 82Se as T2ν1/2=9.39±0.17( stat )±0.58( syst )×1019 y under the single-state ...dominance hypothesis for this nuclear transition.
Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay ( Formula omitted) half-life of Formula omittedSe as Formula omitted y under the single-state dominance ...hypothesis for this nuclear transition. The corresponding nuclear matrix element is Formula omitted. In addition, a search for neutrinoless double beta decay ( Formula omitted) using 0.93 kg of Formula omittedSe observed for a total of 5.25 y has been conducted and no evidence for a signal has been found. The resulting half-life limit of Formula omitted for the light neutrino exchange mechanism leads to a constraint on the effective Majorana neutrino mass of Formula omitted, where the range reflects Formula omitted nuclear matrix element values from different calculations. Furthermore, constraints on lepton number violating parameters for other Formula omitted mechanisms, such as right-handed currents, majoron emission and R-parity violating supersymmetry modes have been set.
Abstract Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay ($$2\nu \beta \beta $$ 2νββ ) half-life of $$^{82}$$ 82 Se as $$T_{\smash {1/2}}^{2\nu } \!=\! ...\left 9.39 \pm 0.17\left( \text{ stat }\right) \pm 0.58\left( \text{ syst }\right) \right \times 10^{19}$$ T1/22ν=9.39±0.17stat±0.58syst×1019 y under the single-state dominance hypothesis for this nuclear transition. The corresponding nuclear matrix element is $$\left| M^{2\nu }\right| = 0.0498 \pm 0.0016$$ M2ν=0.0498±0.0016 . In addition, a search for neutrinoless double beta decay ($$0\nu \beta \beta $$ 0νββ ) using 0.93 kg of $$^{82}$$ 82 Se observed for a total of 5.25 y has been conducted and no evidence for a signal has been found. The resulting half-life limit of $$T_{1/2}^{0\nu } > 2.5 \times 10^{23} \,\text{ y } \,(90\%\,\text{ C.L. })$$ T1/20ν>2.5×1023y(90%C.L.) for the light neutrino exchange mechanism leads to a constraint on the effective Majorana neutrino mass of $$\langle m_{\nu } \rangle < \left( 1.2{-}3.0\right) \,\text{ eV }$$ ⟨mν⟩<1.2-3.0eV , where the range reflects $$0\nu \beta \beta $$ 0νββ nuclear matrix element values from different calculations. Furthermore, constraints on lepton number violating parameters for other $$0\nu \beta \beta $$ 0νββ mechanisms, such as right-handed currents, majoron emission and R-parity violating supersymmetry modes have been set.
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