The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-β (0νββ) decay of ^{76}Ge, whose discovery would have far-reaching implications in ...cosmology and particle physics. By operating bare germanium diodes, enriched in ^{76}Ge, in an active liquid argon shield, GERDA achieved an unprecedently low background index of 5.2×10^{-4} counts/(keV kg yr) in the signal region and met the design goal to collect an exposure of 100 kg yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg yr of total exposure. A limit on the half-life of 0νββ decay in ^{76}Ge is set at T_{1/2}>1.8×10^{26} yr at 90% C.L., which coincides with the sensitivity assuming no signal.
Modeling of GERDA Phase II data Agostini, M.; Bakalyarov, A. M.; Balata, M. ...
The journal of high energy physics,
03/2020, Volume:
2020, Issue:
3
Journal Article
Peer reviewed
Open access
A
bstract
The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta (0
νββ
) decay of
76
Ge. The technological ...challenge of Gerda is to operate in a “background-free” regime in the region of interest (ROI) after analysis cuts for the full 100 kg
·
yr target exposure of the experiment. A careful modeling and decomposition of the full-range energy spectrum is essential to predict the shape and composition of events in the ROI around
Q
ββ
for the 0
νββ
search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos (2
νββ
) and in order to identify the location of residual impurities. The latter will permit future experiments to build strategies in order to further lower the background and achieve even better sensitivities. In this article the background decomposition prior to analysis cuts is presented for Gerda Phase II. The background model fit yields a flat spectrum in the ROI with a background index (BI) of
16.04
−
0.85
+
0.78
·
10
−
3
cts/(keV
·
kg
·
yr) for the enriched BEGe data set and
14.68
−
0.52
+
0.47
·
10
−
3
cts/(keV
·
kg
·
yr) for the enriched coaxial data set. These values are similar to the one of Phase I despite a much larger number of detectors and hence radioactive hardware components.
Pulse shape analysis in Gerda Phase II Agostini, M.; Araujo, G.; Bakalyarov, A. M. ...
The European physical journal. C, Particles and fields,
04/2022, Volume:
82, Issue:
4
Journal Article
Peer reviewed
Open access
The GERmanium Detector Array (
Gerda
) collaboration searched for neutrinoless double-
β
decay in
76
Ge using isotopically enriched high purity germanium detectors at the Laboratori Nazionali del ...Gran Sasso of INFN. After Phase I (2011–2013), the experiment benefited from several upgrades, including an additional active veto based on LAr instrumentation and a significant increase of mass by point-contact germanium detectors that improved the half-life sensitivity of Phase II (2015–2019) by an order of magnitude. At the core of the background mitigation strategy, the analysis of the time profile of individual pulses provides a powerful topological discrimination of signal-like and background-like events. Data from regular
228
Th calibrations and physics data were both considered in the evaluation of the pulse shape discrimination performance. In this work, we describe the various methods applied to the data collected in
Gerda
Phase II corresponding to an exposure of 103.7 kg year. These methods suppress the background by a factor of about 5 in the region of interest around
Q
β
β
=
2039
keV, while preserving
(
81
±
3
)
% of the signal. In addition, an exhaustive list of parameters is provided which were used in the final data analysis.
In this work, semi-empirical Leverett J-Function relationships relating capillary pressure and water saturation are experimentally derived for commercial and experimental polymer electrolyte fuel ...cell materials developed for automotive applications. Relationships were derived for Mitsubishi Rayon Corp. (MRC) 11105 and General Motors (GM) experimental high tortuosity diffusion media (DM), the micro-porous layer (MPL), and the catalyst layer (CL). The standard Leverett J-Function under-predicted drainage curves for the DM at high saturation levels and significantly under-predicted the capillary pressure requirements for the MPL and CL across the entire saturation range. Composite structures were tested to understand interfacial effects for DMMPL and MPLCL Each additional layer was found to superimpose its effects on capillary pressure onto the previous layers. The MPL formulation tested increased in porosity from a 136 nm peak average to a 153 nm peak average with increased surface porosity of the substrate. Additionally, small voids and pockets that accumulate liquid water were found to exist in the MPLCL interface. The results of this work are useful for computational modelers seeking to enhance the resolution of their macroscopic multi-phase flow models which underestimate capillary pressure using the standard Leverett J-Function.
Calibration of the Gerda experiment Agostini, M.; Araujo, G.; Bakalyarov, A. M. ...
European physical journal. C, Particles and fields,
08/2021, Volume:
81, Issue:
8
Journal Article
Peer reviewed
Open access
The GERmanium Detector Array (
Gerda
) collaboration searched for neutrinoless double-
β
decay in
76
Ge with an array of about 40 high-purity isotopically-enriched germanium detectors. The ...experimental signature of the decay is a monoenergetic signal at
Q
β
β
=
2039.061
(
7
)
keV in the measured summed energy spectrum of the two emitted electrons. Both the energy reconstruction and resolution of the germanium detectors are crucial to separate a potential signal from various backgrounds, such as neutrino-accompanied double-
β
decays allowed by the Standard Model. The energy resolution and stability were determined and monitored as a function of time using data from regular
228
Th calibrations. In this work, we describe the calibration process and associated data analysis of the full
Gerda
dataset, tailored to preserve the excellent resolution of the individual germanium detectors when combining data over several years.
Lime additions to arsenic-containing wastes have been proven to be beneficial in reducing the mobility of dissolved arsenic, presumably through the formation of low-solubility calcium arsenates. ...However, the role of calcium arsenate formation in reducing the concentrations of dissolved arsenic has not been well established. Therefore, slurries with varying Ca/As ratios were equilibrated, and the compounds that formed at elevated pH values were established. In contrast to the literature, Ca3(AsO4)2 was not observed, rather Ca4(OH)2(AsO4)2·4H2O, Ca5(AsO4)3OH (arsenate apatite), and Ca3(AsO4)2·32/3H2O had formed. The equilibrium concentrations of arsenic were found to be the lowest at high pH. Minimum arsenic concentrations in equilibrium with Ca4(OH)2(AsO4)2·4H2O and Ca5(AsO4)3OH were 0.01 and 0.5 mg/L, respectively. Because arsenate apatite is stable to near-neutral pH values, the extent of its solid solubility with Ca5(PO4)3OH was determined. This was done to assess the effects of phosphate ion on the possible release of arsenate ion. Although equilibrium arsenate ion concentrations increased with decreasing pH, solid solution formation did not occur under ambient conditions. Rather, the arsenate apatite formed at the expense of Ca5(PO4)3OH.
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, Volume:
83, Issue:
9
Journal Article
Peer reviewed
Open access
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.
Neutrinoless double-
β
decay of
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
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-
β
decay of
76
Ge (
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
·
year, the background index after analysis cuts is measured to be
4
.
9
-
3.4
+
7.3
×
10
-
4
counts
/
(
keV
·
kg
·
year
)
around
Q
β
β
. This work confirms the feasibility of IC detectors for the next-generation experiment
Legend
.
The stabilities of calcium arsenate compounds were established by analysis of suspensions made with varying molar Ca/As ratios. Solution chemistry analyses determined the concentrations of calcium ...and arsenic and pH. The phases that were shown to form in order of descending pH were Ca
4(OH)
2(AsO
4)
2·4H
2O, Ca
5(AsO
4)
3OH (arsenate–apatite), Ca
3(AsO
4)
2·3
2
3
H
2O, Ca
3(AsO
4)
2·4
1
4
H
2O, Ca
5H
2(AsO
4)
4·9H
2O — ferrarisite, Ca
5H
2(AsO
4)
4·9H
2O — guerinite and CaHAsO
4·H
2O. The analytical concentrations of calcium and arsenic and pH were used in estimating solubility products. The estimated values were then refined through the comparison of the analytical data with calculated
K
sp values using the computer program PhreeqC. From the refined solubility products, the free energies of formation of the calcium arsenate hydrates were calculated as follows: Ca
4(OH)
2(AsO
4)
2·4H
2O (−4941 kJ/mol), Ca
5(AsO
4)
3OH (−5087 kJ/mol), Ca
3(AsO
4)
2·3
2
3
H
2O (−3945 kJ/mol), Ca
3(AsO
4)
2·4
1
4
H
2O (−4085 kJ/mol), Ca
5H
2(AsO
4)
4·9H
2O — ferrarisite (−7808 kJ/mol), Ca
5H
2(AsO
4)
4·9H
2O — guerinite (−7803 kJ/mol), and CaHAsO
4·H
2O (−1533 kJ/mol). Unlike other solubility studies on arsenate immobilization, this study was the first to consider the complete array of calcium arsenate hydrates that can form and to use the associated ions, CaAsO
4
−, CaHAsO
4
0 and CaH
2AsO
4
+ in determining their solubility products.
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