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.
Probing Majorana neutrinos with double-β decay Agostini, M; Bakalyarov, A M; Balata, M ...
Science (American Association for the Advancement of Science),
09/2019, Volume:
365, Issue:
6460
Journal Article
Peer reviewed
Open access
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.
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.
Background coming from the Formula omittedAr decay chain is considered to be one of the most relevant for the Gerda experiment, which searches for the neutrinoless double beta decay of Formula ...omittedGe. The sensitivity strongly relies on the absence of background around the Q-value of the decay. Background coming from Formula omittedK, a progeny of Formula omittedAr, can contribute to that background via electrons from the continuous spectrum with an endpoint at 3.5 MeV. Research and development on the suppression methods targeting this source of background were performed at the low-background test facility LArGe . It was demonstrated that by reducing Formula omittedK ion collection on the surfaces of the broad energy germanium detectors in combination with pulse shape discrimination techniques and an argon scintillation veto, it is possible to suppress Formula omittedK background by three orders of magnitude. This is sufficient for Phase II of the Gerda experiment.
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.
It is necessary to take into account the neutron background in almost all low-background research. In this paper an estimated neutron flux in the underground laboratory DULB-4900 of BNO INR RAS is ...presented. The estimation is based on results of measurements of radionuclide content in surrounding rock (granite).
Results of a search for the masked regularities in the
Po
-active isotope half-life solar-daily variation parameters in the data collected during 2012–2015 years are presented. It is shown, that an ...amplitude of a sinusoidal function approximating half-life solar-daily dependence obtained by averaging data during 90 days for each season of the years could reach
from the average daily value. Similar analysis of the
Po data collected in 2018–2022 years shows that amplitude of the deviation from the average value could reach
. This effect limits an accuracy of the high precision measurements with this or similar short-lived isotopes generating systematic errors if the data were collected during a relatively short time. The new value of the
Po half-life which is
Po
s was obtained on the base of the data collected during 2018–2022 years.
Pulse shape discrimination for Gerda Phase I data Agostini, M.; Allardt, M.; Andreotti, E. ...
The European physical journal. C, Particles and fields,
10/2013, Volume:
73, Issue:
10
Journal Article
Peer reviewed
Open access
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.
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