The ability to detect liquid argon scintillation light from within a densely packed high-purity germanium detector array allowed the
Gerda
experiment to reach an exceptionally low background rate in ...the search for neutrinoless double beta decay of
76
Ge. Proper modeling of the light propagation throughout the experimental setup, from any origin in the liquid argon volume to its eventual detection by the novel light read-out system, provides insight into the rejection capability and is a necessary ingredient to obtain robust background predictions. In this paper, we present a model of the
Gerda
liquid argon veto, as obtained by Monte Carlo simulations and constrained by calibration data, and highlight its application for background decomposition.
Five new HPGe detectors enriched in 76Ge have been characterized in the framework of the on-going upgrade of the Gerda experiment. These new detectors have been designed such as to combine excellent ...spectral and pulse shape discrimination properties, together with an increase of a factor ∼2 in mass with respect to the detectors currently used in Gerda. Excellent spectral performances have been confirmed (energy resolution ∼0.1% for all prototypes), though an unexpected feature in the Pulse Shape Discrimination parameter has been observed, and has to be further investigated.
Abstract
Neutrinoless double-
$$\beta $$
β
decay of
$$^{76}$$
76
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
$$^{76}$$
76
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-
$$\beta $$
β
decay of
$$^{76}$$
76
Ge (
$$Q_{\beta \beta }$$
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
$$\cdot $$
·
year, the background index after analysis cuts is measured to be
$$4.9^{+7.3}_{-3.4}\times 10^{-4} \ \text {counts}/(\text {keV} \cdot \text {kg} \cdot \text {year})$$
4
.
9
-
3.4
+
7.3
×
10
-
4
counts
/
(
keV
·
kg
·
year
)
around
$$Q_{\beta \beta }$$
Q
β
β
. This work confirms the feasibility of IC detectors for the next-generation experiment
Legend
.
The GERmanium Detector Array (
Gerda
) experiment operated enriched high-purity germanium detectors in a liquid argon cryostat, which contains 0.33% of
36
Ar, a candidate isotope for the two-neutrino ...double-electron capture (2
ν
ECEC) and therefore for the neutrinoless double-electron capture (0
ν
ECEC). If detected, this process would give evidence of lepton number violation and the Majorana nature of neutrinos. In the radiative 0
ν
ECEC of
36
Ar, a monochromatic photon is emitted with an energy of 429.88 keV, which may be detected by the
Gerda
germanium detectors. We searched for the
36
Ar 0
ν
ECEC with
Gerda
data, with a total live time of 4.34 year (3.08 year accumulated during
Gerda
Phase II and 1.26 year during
Gerda
Phase I). No signal was found and a 90% CL lower limit on the half-life of this process was established
T
1
/
2
>
1.5
·
10
22
year.
Abstract The GERmanium Detector Array ( Gerda ) experiment operated enriched high-purity germanium detectors in a liquid argon cryostat, which contains 0.33% of $$^{36}$$ 36 Ar, a candidate isotope ...for the two-neutrino double-electron capture (2 $$\nu $$ ν ECEC) and therefore for the neutrinoless double-electron capture (0 $$\nu $$ ν ECEC). If detected, this process would give evidence of lepton number violation and the Majorana nature of neutrinos. In the radiative 0 $$\nu $$ ν ECEC of $$^{36}$$ 36 Ar, a monochromatic photon is emitted with an energy of 429.88 keV, which may be detected by the Gerda germanium detectors. We searched for the $$^{36}$$ 36 Ar 0 $$\nu $$ ν ECEC with Gerda data, with a total live time of 4.34 year (3.08 year accumulated during Gerda Phase II and 1.26 year during Gerda Phase I). No signal was found and a 90% CL lower limit on the half-life of this process was established $$T_{1/2} >1.5\cdot 10^{22} $$ T 1 / 2 > 1.5 · 10 22 year.
Search for tri-nucleon decays of 76Ge in GERDA Agostini, M.; Alexander, A.; Bakalyarov, A. M. ...
The European physical journal. C, Particles and fields,
09/2023, Letnik:
83, Številka:
9
Journal Article
Recenzirano
Odprti dostop
We search for tri-nucleon decays of
76
Ge in the dataset from the GERmanium Detector Array (GERDA) experiment. Decays that populate excited levels of the daughter nucleus above the threshold for ...particle emission lead to disintegration and are not considered. The ppp-, ppn-, and pnn-decays lead to
73
Cu,
73
Zn, and
73
Ga nuclei, respectively. These nuclei are unstable and eventually proceed by the beta decay of
73
Ga to
73
Ge (stable). We search for the
73
Ga decay exploiting the fact that it dominantly populates the 66.7 keV
73
m
Ga state with half-life of 0.5 s. The nnn-decays of
76
Ge that proceed via
73
m
Ge are also included in our analysis. We find no signal candidate and place a limit on the sum of the decay widths of the inclusive tri-nucleon decays that corresponds to a lower lifetime limit of 1.2
×
10
26
yr (90% credible interval). This result improves previous limits for tri-nucleon decays by one to three orders of magnitude.
We search for tri-nucleon decays of
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76
Ge in the dataset from the GERmanium Detector Array (GERDA) experiment. Decays that populate excited levels of the daughter nucleus above the threshold for particle emission lead to disintegration and are not considered. The ppp-, ppn-, and pnn-decays lead to
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73
Cu,
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73
Zn, and
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73
Ga nuclei, respectively. These nuclei are unstable and eventually proceed by the beta decay of
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73
Ga to
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73
Ge (stable). We search for the
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73
Ga decay exploiting the fact that it dominantly populates the 66.7 keV
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73
m
Ga state with half-life of 0.5 s. The nnn-decays of
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76
Ge that proceed via
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73
m
Ge are also included in our analysis. We find no signal candidate and place a limit on the sum of the decay widths of the inclusive tri-nucleon decays that corresponds to a lower lifetime limit of 1.2
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×
10
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26
yr (90% credible interval). This result improves previous limits for tri-nucleon decays by one to three orders of magnitude.
Abstract Neutrinoless double- $$\beta $$ β decay of $$^{76}$$ 76 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 $$^{76}$$ 76 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- $$\beta $$ β decay of $$^{76}$$ 76 Ge ( $$Q_{\beta \beta }$$ 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 $$\cdot $$ · year, the background index after analysis cuts is measured to be $$4.9^{+7.3}_{-3.4}\times 10^{-4} \ \text {counts}/(\text {keV} \cdot \text {kg} \cdot \text {year})$$ 4 . 9 - 3.4 + 7.3 × 10 - 4 counts / ( keV · kg · year ) around $$Q_{\beta \beta }$$ Q β β . This work confirms the feasibility of IC detectors for the next-generation experiment Legend.
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