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Modeling of GERDA Phase II data
The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta (0νββ) decay of 76Ge. The technological challenge of Gerda is to operate in a âbackground-freeâ 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 Qββ for the 0νββ search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos (2νββ) 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+0.78â0.85â
10â3 cts/(keV¡kg¡yr) for the enriched BEGe data set and 14.68+0.47â0.52â
10â3 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
Modeling of GERDA Phase II data
The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground
laboratory (LNGS) of INFN is searching for neutrinoless double-beta
() decay of 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 100kgyr 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 for the search, to extract a precise
measurement of the half-life of the double-beta decay mode with neutrinos
() 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 cts/(kgkeVyr) for the enriched BEGe data set and
cts/(kgkeVyr) for the
enriched coaxial data set. These values are similar to the one of Gerda Phase I
despite a much larger number of detectors and hence radioactive hardware
components
Limits on uranium and thorium bulk content in Gerda Phase I detectors
Internal contaminations of U, U and Th in the bulk of high purity germanium detectors are potential backgrounds for experiments searching for neutrinoless double beta decay of Ge. The data from Gerda Phase I have been analyzed for alpha events from the decay chain of these contaminations by looking for full decay chains and for time correlations between successive decays in the same detector. No candidate events for a full chain have been found. Upper limits on the activities in the range of a few nBq/kg for Ra, Ac and Th, the long-lived daughter nuclides of U, U and Th, respectively, have been derived. With these upper limits a background index in the energy region of interest from Ra and Th contamination is estimated which satisfies the prerequisites of a future ton scale germanium double beta decay experiment
Modeling of GERDA Phase II data
The GERmanium Detector Array (Gerda) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta (0νββ) decay of 76Ge. The technological challenge of Gerda is to operate in a âbackground-freeâ 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 Qββ for the 0νββ search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos (2νββ) 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+0.78â0.85â
10â3 cts/(keV¡kg¡yr) for the enriched BEGe data set and 14.68+0.47â0.52â
10â3 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
First Search for Bosonic Superweakly Interacting Massive Particles with Masses up to 1 MeV/c2 with GERDA
We present the first search for bosonic superweakly interacting massive particles (super-WIMPs) as keV-scale dark matter candidates performed with the GERDA experiment. GERDA is a neutrinoless double-β decay experiment which operates high-purity germanium detectors enriched in 76Ge in an ultralow background environment at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN in Italy. Searches were performed for pseudoscalar and vector particles in the mass region from 60ââkeV/c2 to 1ââMeV/c2. No evidence for a dark matter signal was observed, and the most stringent constraints on the couplings of super-WIMPs with masses above 120ââkeV/c2 have been set. As an example, at a mass of 150ââkeV/c2 the most stringent direct limits on the dimensionless couplings of axionlike particles and dark photons to electrons of gae<3Ă10â12 and Îąâ˛/Îą<6.5Ă10â24 at 90% credible interval, respectively, were obtained
Modeling of GERDA Phase II data / Working Paper
The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta (0νββ) decay of 76Ge. 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 100kgâ
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 Qββ for the 0νββ search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos (2νββ) 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+0.78â0.85â
10â3cts/(kgâ
keVâ
yr) for the enriched BEGe data set and 14.68+0.47â0.52â
10â3cts/(kgâ
keVâ
yr) for the enriched coaxial data set. These values are similar to the one of Gerda Phase I despite a much larger number of detectors and hence radioactive hardware components
Improved Limit on Neutrinoless Double-β Decay of Ge76 from GERDA Phase II
The GERDA experiment searches for the lepton-number-violating neutrinoless double-β decay of Ge76 (Ge76âSe76+2e-) operating bare Ge diodes with an enriched Ge76 fraction in liquid argon. The exposure for broad-energy germanium type (BEGe) detectors is increased threefold with respect to our previous data release. The BEGe detectors feature an excellent background suppression from the analysis of the time profile of the detector signals. In the analysis window a background level of 1.0-0.4+0.6Ă10-3ââcounts/(keVâkgâyr) has been achieved; if normalized to the energy resolution this is the lowest ever achieved in any 0νββ experiment. No signal is observed and a new 90% C.L. lower limit for the half-life of 8.0Ă1025ââyr is placed when combining with our previous data. The expected median sensitivity assuming no signal is 5.8Ă1025ââyr
Characterization of 3076Ge enriched Broad Energy Ge detectors for GERDA Phase II
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 76Ge into 76Se + 2eâ. Gerda has been conceived in two phases. Phase II, which started in December 2015, features several novelties including 30 new 76Ge 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 GerdaPhase 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
GERDA results and the future perspectives for the neutrinoless double beta decay search using 76Ge
The GERmanium Detector Array (GERDA) is a low background experiment at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN designed to search for the rare neutrinoless double beta decay (0νββ) of 76Ge. In the first phase (Phase I) of the experiment, high purity germanium diodes were operated in a âbareâ mode and immersed in liquid argon. The overall background level of 10â2cts/(keVâ
kgâ
yr) was a factor of ten better than those of its predecessors. No signal was found and a lower limit was set on the half-life for the 0νββ decay of 76Ge T0ν1/2>2.1Ă1025 yr (90% CL), while the corresponding median sensitivity was 2.4Ă1025 yr (90% CL). A second phase (Phase II) started at the end of 2015 after a major upgrade. Thanks to the increased detector mass and performance of the enriched germanium diodes and due to the introduction of liquid argon instrumentation techniques, it was possible to reduce the background down to 10â3cts/(keVâ
kgâ
yr). After analyzing 23.2 kgâ
yr of these new data no signal was seen. Combining these with the data from Phase I a stronger half-life limit of the 76Ge 0νββ decay was obtained: T0ν1/2>8.0Ă1025 yr (90% CL), reaching a sensitivity of 5.8Ă1025 yr (90% CL). Phase II will continue for the collection of an exposure of 100 kgâ
yr. If no signal is found by then the GERDA sensitivity will have reached 1.4Ă1026 yr for setting a 90% CL. limit. After the end of GERDA Phase II, the flagship experiment for the search of 0νββ decay of 76Ge will be LEGEND. LEGEND experiment is foreseen to deploy up to 1-ton of 76Ge. After ten years of data taking, it will reach a sensitivity beyond 1028 yr, and hence fully cover the inverted hierarchy region