Nonmonotonous variation of the optical properties of iron nanoparticles with a temperature increase during heating behind reflected shock waves is discovered. Iron nanoparticles, within 12 nm in ...size, were formed at 0.5–1% Fe(CO)
5
pyrolysis in argon behind the incident shock waves. Using a laser extinction method, a variation of the volume fraction of the condensed phase was registered at the main wavelength of 633 nm and, in several experiments, at the additional wavelengths of 405, 520, and 850 nm. At the second heating of the produced nanoparticles behind the reflected shock waves within the temperature range 800–1500 K, the function of the complex refractive index,
E
(
m
), decreased at all the wavelengths. Within the temperature range of 1500–2250 K, it increased with the temperature increase behind the reflected shock wave almost up to the values that we observed behind the incident shock wave. At the temperatures above 2250 K, due to the essential evaporation of the iron nanoparticle material, the optical properties were not measured. The iron nanoparticle
E
(
m
) variations within the temperature range 800–2250 K are possibly related to their structure variations.
Modeling of GERDA Phase II data Agostini, M.; Bakalyarov, A. M.; Balata, M. ...
The journal of high energy physics,
03/2020, Letnik:
2020, Številka:
3
Journal Article
Recenzirano
Odprti dostop
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.
Pulse shape analysis in Gerda Phase II Agostini, M.; Araujo, G.; Bakalyarov, A. M. ...
The European physical journal. C, Particles and fields,
04/2022, Letnik:
82, Številka:
4
Journal Article
Recenzirano
Odprti dostop
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.
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.
Pulse shape discrimination for Gerda Phase I data Agostini, M.; Allardt, M.; Andreotti, E. ...
The European physical journal. C, Particles and fields,
10/2013, Letnik:
73, Številka:
10
Journal Article
Recenzirano
Odprti dostop
The
Gerda
experiment located at the Laboratori Nazionali del Gran Sasso of INFN searches for neutrinoless double beta (0
νββ
) decay of
76
Ge using germanium diodes as source and detector. In Phase I ...of the experiment eight semi-coaxial and five BEGe type detectors have been deployed. The latter type is used in this field of research for the first time. All detectors are made from material with enriched
76
Ge fraction. The experimental sensitivity can be improved by analyzing the pulse shape of the detector signals with the aim to reject background events. This paper documents the algorithms developed before the data of Phase I were unblinded. The double escape peak (DEP) and Compton edge events of 2.615 MeV
γ
rays from
208
Tl decays as well as two-neutrino double beta (2
νββ
) decays of
76
Ge are used as proxies for 0
νββ
decay.
For BEGe detectors the chosen selection is based on a single pulse shape parameter. It accepts 0.92±0.02 of signal-like events while about 80 % of the background events at
Q
ββ
=2039 keV are rejected.
For semi-coaxial detectors three analyses are developed. The one based on an artificial neural network is used for the search of 0
νββ
decay. It retains 90 % of DEP events and rejects about half of the events around
Q
ββ
. The 2
νββ
events have an efficiency of 0.85±0.02 and the one for 0
νββ
decays is estimated to be
. A second analysis uses a likelihood approach trained on Compton edge events. The third approach uses two pulse shape parameters. The latter two methods confirm the classification of the neural network since about 90 % of the data events rejected by the neural network are also removed by both of them. In general, the selection efficiency extracted from DEP events agrees well with those determined from Compton edge events or from 2
νββ
decays.
Calibration of the Gerda experiment Agostini, M.; Araujo, G.; Bakalyarov, A. M. ...
The European physical journal. C, Particles and fields,
08/2021, Letnik:
81, Številka:
8
Journal Article
Recenzirano
Odprti dostop
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.
The background in the 0νββ experiment Gerda Agostini, M.; Allardt, M.; Andreotti, E. ...
The European physical journal. C, Particles and fields,
04/2014, Letnik:
74, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The GERmanium Detector Array (
Gerda
) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double beta (
0
ν
β
β
) decay of
76
Ge. The signature of the ...signal is a monoenergetic peak at 2039 keV, the
Q
β
β
value of the decay. To avoid bias in the signal search, the present analysis does not consider all those events, that fall in a 40 keV wide region centered around
Q
β
β
. The main parameters needed for the
0
ν
β
β
analysis are described. A background model was developed to describe the observed energy spectrum. The model contains several contributions, that are expected on the basis of material screening or that are established by the observation of characteristic structures in the energy spectrum. The model predicts a flat energy spectrum for the blinding window around
Q
β
β
with a background index ranging from 17.6 to 23.8
×
10
-
3
cts/(keV kg yr). A part of the data not considered before has been used to test if the predictions of the background model are consistent. The observed number of events in this energy region is consistent with the background model. The background at
Q
β
β
is dominated by close sources, mainly due to
42
K,
214
Bi,
228
Th,
60
Co and
α
emitting isotopes from the
226
Ra decay chain. The individual fractions depend on the assumed locations of the contaminants. It is shown, that after removal of the known
γ
peaks, the energy spectrum can be fitted in an energy range of 200 keV around
Q
β
β
with a constant background. This gives a background index consistent with the full model and uncertainties of the same size.
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
.
PDF
