Upgrade for Phase II of the Gerda experiment Agostini, M.; Bakalyarov, A. M.; Balata, M. ...
The European physical journal. C, Particles and fields,
05/2018, Volume:
78, Issue:
5
Journal Article
Peer reviewed
Open access
The
Gerda
collaboration is performing a sensitive search for neutrinoless double beta decay of
76
Ge
at the INFN Laboratori Nazionali del Gran Sasso, Italy. The upgrade of the
Gerda
experiment from ...Phase I to Phase II has been concluded in December 2015. The first Phase II data release shows that the goal to suppress the background by one order of magnitude compared to Phase I has been achieved.
Gerda
is thus the first experiment that will remain “background-free” up to its design exposure (
100 kg
year
). It will reach thereby a half-life sensitivity of more than
10
26
year within 3 years of data collection. This paper describes in detail the modifications and improvements of the experimental setup for Phase II and discusses the performance of individual detector components.
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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.
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•We examine changes in stem and crown characteristics along an anthropogenic disturbance gradient.•Crown size becomes less important for radial growth of Fagus sylvatica in undisturbed tree ...communities.•Inter-specific competition enhances crown efficiency of beech in unmanaged stands.•Considering the continuity of ecological processes might refine our understanding of tree-tree interactions.•Minimizing anthropogenic disturbances is recommended to favour higher structural complexity and stand productivity.
Crown size is considered one of the most important traits that affect radial tree growth, but it remains unclear how (anthropogenic) disturbance intensity affects crown size-radial growth relationships. This knowledge, however, is crucial for a better comprehension and prediction of community dynamics, and thus to support management decisions. We analyzed changes in stem and crown characteristics of dominant canopy European beech (Fagus sylvatica) trees along an anthropogenic disturbance gradient based on the duration of non-forestry use. We further investigated the dependency of basal area increment on crown surface area and linked this relationship to growth efficiency. Crown efficiency (basal area growth per unit crown surface area) was used as an indicator for the effectiveness of tree growth. Further stand attributes included stand density and tree species composition. Changes in crown efficiency with tree and stand attributes were assessed using generalized additive models (GAMs). Tree morphology sensitively responded to disturbance intensity. However, the indicative value of crown surface area for basal area increment decreased with increasing duration of non-forestry use and stand density. We found that the interplay between disturbance intensity and species composition modulates crown efficiency of dominant beech trees. Inter-specific competition enhanced crown efficiency in unmanaged stands, whereas managed stands showed an opposite trend. Consequently, crown efficiency significantly increased with decreasing disturbance intensity and intra-specific competition. Thus the widely accepted close correlation between crown size and radial increment needs reconsideration for trees growing under (near-) natural conditions. We hypothesize that carbon allocation in densely stocked stands can be adapted to an efficient trunk-crown relation, which in turn weakens crown size-radial growth relationships as known from managed stands. The importance of continuity in tree-tree interactions therefore imposes significant constraints on the generality of crown traits as radial growth determinants in beech forests. Our findings indicate that a higher structural complexity and stand productivity might be achieved in managed stands by a wider variety of crown size classes and tree species assemblages. Hence, stand dynamics can benefit from lowering anthropogenic disturbances and favouring self-regulation, which would be a further step towards near-natural forest management.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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.
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The dead-layer uniformity of the top surface of two high purity germanium detectors has been studied using a novel automated scanning set-up that allows a fine-grained topography of a detector's top ...and lateral surfaces. Comparisons between measurements and Monte Carlo simulations allowed implementation of a dead-layer variation into the detector model, which reproduces the measurements results. The effect of the non-uniform dead-layer on activity determinations based on low-energy γ-rays (i.e. below ~100keV) has been determined to be of the order of 10% or more.
•We performed a top dead-layer topography of two HPGe detectors.•We identified a non-uniform dead-layer thickness along the surface of one of them.•We built a Monte Carlo model able to reproduce the measurements results.•We estimated an effect on the activity calculation for low energy γ-ray emitters of ~50%.
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6.
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.
Abstract
The GERmanium Detector Array (
Gerda
) is a low background experiment located at the Laboratori Nazionali del Gran Sasso in Italy, which searches for neutrinoless double-beta decay of
...$$^{76}$$
76
Ge into
$$^{76}$$
76
Se+2e
$$^-$$
-
.
Gerda
has been conceived in two phases. Phase II, which started in December 2015, features several novelties including 30 new
76
Ge enriched detectors. These were manufactured according to the Broad Energy Germanium (BEGe) detector design that has a better background discrimination capability and energy resolution compared to formerly widely-used types. Prior to their installation, the new BEGe detectors were mounted in vacuum cryostats and characterized in detail in the
Hades
underground laboratory in Belgium. This paper describes the properties and the overall performance of these detectors during operation in vacuum. The characterization campaign provided not only direct input for
Gerda
Phase II data collection and analyses, but also allowed to study detector phenomena, detector correlations as well as to test the accuracy of pulse shape simulation codes.
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Calibration of the Gerda experiment Agostini, M.; Araujo, G.; Bakalyarov, A. M. ...
The 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.
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Abstract
A search for Beyond the Standard Model double-
β
decay modes of
76
Ge has been
performed with data collected during the Phase II of the GERmanium Detector Array
(
Gerda
) experiment,
...located at the Laboratori
Nazionali del Gran Sasso of INFN (Italy). Improved
limits on the decays involving Majorons have been obtained, compared to previous experiments with
76
Ge, with half-life values on the order of 10
23
yr. For the first time with
76
Ge, limits on Lorentz invariance violation effects in double-
β
decay have been
obtained. The isotropic coefficient å
of
(3)
, which embeds Lorentz
violation in double-
β
decay, has been constrained at the order of 10
-6
GeV. We also
set the first experimental limits on the search for light exotic fermions in double-
β
decay,
including sterile neutrinos.
Pulse shape discrimination is an important handle to improve sensitivity in low background experiments. A dedicated setup was built to investigate the response of high-purity germanium detectors to ...single Compton scattered events. Using properly collimated γ-ray sources, it is possible to select events with known interaction location. The aim is to correlate the position dependent signal shape with geometrical and electrical properties of the detector. We report on design and performance of the setup with a first look on data.
•Automatized setup for the signal characterization of a HPGe detector depending on interaction location and bias voltage.•Compton coincidence measurements with a Broad Energy Germanium (BEGe) detector.•Single site event selection with known interaction location and high purity.
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