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.
A discovery that neutrinos are Majorana fermions would have profound implications for particle physics and cosmology. The Majorana character of neutrinos would make possible the neutrinoless double-β ...(0νββ) decay, a matter-creating process without the balancing emission of antimatter. The GERDA Collaboration searches for the 0νββ decay of
Ge by operating bare germanium detectors in an active liquid argon shield. With a total exposure of 82.4 kg⋅year, we observe no signal and derive a lower half-life limit of
> 0.9 × 10
years (90% C.L.). Our
sensitivity, assuming no signal, is 1.1 × 10
years. Combining the latter with those from other 0νββ decay searches yields a sensitivity to the effective Majorana neutrino mass of 0.07 to 0.16 electron volts.
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.
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.
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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