arXiv subjects

G. Lutter

Publications and source records attributed to G. Lutter.

At least 19 recordsLinked to original sources

arXiv2025

Search for the in-situ production of $^{77}$Ge in the GERDA neutrinoless double-beta decay experiment

The beta decay of $^{77}$Ge and $^{77\mathrm{m}}$Ge, both produced by neutron capture on $^{76}$Ge, is a potential background for Germanium based neutrinoless double-beta decay search experiments such as GERDA or the LEGEND experiment. In this work we present a search for $^{77}$Ge decays in the full GERDA Phase II data set. A delayed coincidence method was employed to identify the decay of $^{77}$Ge via the isomeric state of $^{77}$As (9/2$^+$, 475 keV, ${T_{1/2} = 114}\,\mu $s, $^{77\mathrm{m}}$As). New digital signal processing methods were employed to select and analyze pile-up signals. No signal was observed, and an upper limit on the production rate of was set at $<0.216$ nuc/(kg$\cdot$yr) (90% CL). This corresponds to a total production rate of $^{77}$Ge and $^{77\mathrm{m}}$Ge of $<0.38$ nuc/(kg$\cdot$ yr) (90% CL), assuming equal production rates. A previous Monte Carlo study predicted a value for in-situ $^{77}$Ge and $^{77\mathrm{m}}$Ge production of (0.21$\pm$0.07) nuc/(kg$\cdot$yr), a prediction that is now further corroborated by our experimental limit. Moreover, tagging the isomeric state of $^{77\mathrm{m}}$As can be utilised to further suppress the $^{77}$Ge background. Considering the similar experimental configurations of LEGEND-1000 and GERDA, the cosmogenic background in LEGEND-1000 at LNGS is estimated to remain at a sub-dominant level.

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arXiv2024

Searches for new physics below twice the electron mass with GERDA

A search for full energy depositions from bosonic keV-scale dark matter candidates of masses between 65 keV and 1021 keV has been performed with data collected during Phase II of the GERmanium Detector Array (GERDA) experiment. Our analysis includes direct dark matter absorption as well as dark Compton scattering. With a total exposure of 105.5 kg yr, no evidence for a signal above the background has been observed. The resulting exclusion limits deduced with either Bayesian or Frequentist statistics are the most stringent direct constraints in the major part of the 140-1021 keV mass range. As an example, at a mass of 150 keV the dimensionless coupling of dark photons and axion-like particles to electrons has been constrained to $\alpha$'/$\alpha$ < 8.7x10$^{-24}$ and g$_{ae}$ < 3.3x10$^{-12}$ at 90% credible interval (CI), respectively. Additionally, a search for peak-like signals from beyond the Standard Model decays of nucleons and electrons is performed. We find for the inclusive decay of a single neutron in $^{76}$Ge a lower lifetime limit of $\tau_n$ > 1.5x10$^{24}$ yr and for a proton $\tau_p$ > 1.3x10$^{24}$ yr at 90% CI. For the electron decay e$^-\rightarrow\nu_e\gamma$ a lower limit of $\tau_e$ > 5.4x10$^{25}$ yr at 90% CI has been determined.

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arXiv2023

An improved limit on the neutrinoless double-electron capture of $^{36}$Ar with GERDA

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$\nu$ECEC) and therefore for the neutrinoless double-electron capture (0$\nu$ECEC). If detected, this process would give evidence of lepton number violation and the Majorana nature of neutrinos. In the radiative 0$\nu$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$\nu$ECEC with GERDA data, with a total live time of 4.34 yr (3.08 yr accumulated during GERDA Phase II and 1.26 yr during GERDA Phase I). No signal was found and a 90% C.L. lower limit on the half-life of this process was established T$_{1/2}$ > 1.5x10$^{22}$ yr

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arXiv2023

Final Results of GERDA on the Two-Neutrino Double-$\beta$ Decay Half-Life of $^{76}$Ge

We present the measurement of the two-neutrino double-$\beta$ decay rate of $^{76}$Ge performed with the GERDA Phase II experiment. With a subset of the entire GERDA exposure, 11.8 kg$\cdot$yr, the half-life of the process has been determined: $T^{2\nu}_{1/2} = (2.022 \pm 0.018_{stat} \pm 0.038_{sys})\times10^{21}$ yr. This is the most precise determination of the $^{76}$Ge two-neutrino double-$\beta$ decay half-life and one of the most precise measurements of a double-$\beta$ decay process. The relevant nuclear matrix element can be extracted: $M^{2\nu}_{\text{eff}} = (0.101\pm0.001).$

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arXiv2023

Search for tri-nucleon decays of $^{76}$Ge in GERDA

We search for tri-nucleon decays of $^{76}$Ge in the dataset from the GERmanium Detector Array (GERDA) experiment. Decays that populate excited levels of the daughter nucleus above the threshold for particle emission lead to disintegration and are not considered. The ppp-, ppn-, and pnn-decays lead to $^{73}$Cu, $^{73}$Zn, and $^{73}$Ga nuclei, respectively. These nuclei are unstable and eventually proceed by the beta decay of $^{73}$Ga to $^{73}$Ge (stable). We search for the $^{73}$Ga decay exploiting the fact that it dominantly populates the 66.7 keV $^{73m}$Ga state with half-life of 0.5 s. The nnn-decays of $^{76}$Ge that proceed via $^{73m}$Ge are also included in our analysis. We find no signal candidate and place a limit on the sum of the decay widths of the inclusive tri-nucleon decays that corresponds to a lower lifetime limit of 1.2x10$^{26}$ yr (90% credible interval). This result improves previous limits for tri-nucleon decays by one to three orders of magnitude.

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arXiv2022

Liquid argon light collection and veto modeling in GERDA Phase II

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.

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arXiv2022

Search for exotic physics in double-$\beta$ decays with GERDA Phase II

A search for Beyond the Standard Model double-$\beta$ decay modes of $^{76}$Ge has been performed with data collected during the Phase II of the GERmanium Detector Array (GERDA) experiment, located at 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-$\beta$ decay have been obtained. The isotropic coefficient $\mathring{a}_\text{of}^{(3)}$, which embeds Lorentz violation in double-$\beta$ 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-$\beta$ decay, including sterile neutrinos.

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arXiv2022

Measurement of double-$\beta$ decay of $^{150}$Nd to the 0$^+_1$ excited state of $^{150}$Sm in NEMO-3

The NEMO-3 results for the double-$\beta$ decay of $^{150}$Nd to the 0$^+_1$ and 2$^+_1$ excited states of $^{150}$Sm are reported. The data recorded during 5.25 yr with 36.6 g of the isotope $^{150}$Nd are used in the analysis. For the first time, the signal of the $2\nu\beta\beta$ transition to the 0$^+_1$ excited state is detected with a statistical significance exceeding 5$\sigma$. The half-life is measured to be $T_{1/2}^{2\nu\beta\beta}(0^+_1) = \left[ 1.11 ^{+0.19}_{-0.14} \,\left(\mbox{stat}\right) ^{+0.17}_{-0.15}\, \left(\mbox{syst}\right) \right] \times10^{20}\,\mbox{yr}$. The limits are set on the $2\nu\beta\beta$ decay to the 2$^+_1$ level and on the $0\nu\beta\beta$ decay to the 0$^+_1$ and 2$^+_1$ levels of $^{150}$Sm.

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arXiv2022

Pulse shape analysis in GERDA Phase II

The GERmanium Detector Array (GERDA) collaboration searched for neutrinoless double-$\beta$ 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$\cdot$yr. These methods suppress the background by a factor of about 5 in the region of interest around Q$_{\beta\beta}$ = 2039 keV, while preserving (81$\pm$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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arXiv2022

New limits on double-beta decay of $^{190}$Pt and $^{198}$Pt

A search for double-beta decay of $^{190}$Pt and $^{198}$Pt with emission of $\gamma$-ray quanta was realized at the HADES underground laboratory with a 148 g platinum sample measured by two ultralow-background HPGe detectors over 8946 h. The isotopic composition of the platinum sample has been measured with high precision using inductively coupled plasma mass spectrometry. New lower limits for the half-lives of $^{190}$Pt relative to different channels and modes of the decays were set on the level of $\lim T_{1/2}\sim 10^{14}-10^{16}$ yr. A possible exact resonant $0\nu KN$ transition to the 1,2 1326.9 keV level of $^{190}$Os is limited for the first time as $T_{1/2} \geq 2.5 \times10^{16}$ yr. A new lower limit on the double-beta decay of $^{198}$Pt to the first excited level of $^{198}$Hg was set as $T_{1/2} \geq 3.2\times10^{19}$ yr, one order of magnitude higher than the limit obtained in the previous experiment.

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arXiv2021

Constraints on partial half-lives of Ce-136 and Ce-138 double electron captures

The gamma-ray emissions from a radiopure cerium-bromide crystal with a mass of 4381 g were measured for a total of 497.4 d by means of high-resolution gamma-ray spectrometry in the HADES underground laboratory at a depth of 500 m.w.e. A search for 0/2nee and 0/2neb+ double beta decay transitions of Ce-136 and Ce-138 was performed using Bayesian analysis techniques. No signals were observed for a total of 35 investigated decay modes. 90% credibility limits were set in the order of 1e18-1e19 a. Existing constraints from a cerium oxide powder measurement were tested with a different cerium compound and half-life limits could be improved for most of the decay modes. The most likely accessible decay mode of the Ce-136 2nee transition into the 0+1 state of Ba-136 results in a new best 90% credibility limit of 5.0e18 a.

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arXiv2021

Characterization of inverted coaxial $^{76}$Ge detectors in GERDA for future double-$\beta$ decay experiments

Neutrinoless double-$\beta$ decay of $^{76}$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 $^{76}$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-$\beta$ decay of $^{76}$Ge (Q$_{\beta\beta}$ = 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$\cdot$yr, the background index after analysis cuts is measured to be $4.9^{+7.3}_{-3.4}\times 10^{-4}$ counts /(keV$\cdot$kg$\cdot$yr) around Q$_{\beta\beta}$. This work confirms the feasibility of IC detectors for the next-generation experiment LEGEND.

physics.ins-det↗

arXiv2021

Calibration of the GERDA experiment

The GERmanium Detector Array (GERDA) collaboration searched for neutrinoless double-$\beta$ 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$_{\beta\beta}$ = 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-$\beta$ 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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arXiv2020

Search for Periodic Modulations of the Rate of Double-Beta Decay of $^{100}$Mo in the NEMO-3 Detector

Double-beta decays of $^{100}$Mo from the 6.0195-year exposure of a 6.914 kg high-purity sample were recorded by the NEMO-3 experiment that searched for neutrinoless double-beta decays. These ultra-rare transitions to $^{100}$Ru have a half-life of approximately $7\times10^{18}$ years, and have been used to conduct the first ever search for periodic variations of this decay mode. The Lomb-Scargle periodogram technique, and its error-weighted extension, were employed to look for periodic modulations of the half-life. Monte Carlo modeling was used to study the modulation sensitivity of the data over a broad range of amplitudes and frequencies. Data show no evidence of modulations with amplitude greater than 2.5% in the frequency range of $0.33225\,{\rm y^{-1}}$ to $365.25\,{\rm y^{-1}}$.

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arXiv2020

Final Results of GERDA on the Search for Neutrinoless Double-$\beta$ Decay

The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-$\beta$ ($0\nu\beta\beta$) 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 $5.2\times10^{-4}$ counts/(keV$\cdot$kg$\cdot$yr) in the signal region and met the design goal to collect an exposure of 100 kg$\cdot$yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg$\cdot$yr of total exposure. A limit on the half-life of $0\nu\beta\beta$ decay in $^{76}$Ge is set at $T_{1/2}>1.8\times10^{26}$ yr at 90% C.L., which coincides with the sensitivity assuming no signal.

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arXiv2020

Decay scheme of 50V

Investigation of the $^{50}$V electron-capture to the $2^+$ 1553.8 keV level of $^{50}$Ti and search for $\beta^-$ decay of $^{50}$V to the $2^+$ 783.3 keV level of $^{50}$Cr (both those decays are fourfold forbidden with $\Delta J^{\Delta \pi}=4^+$) have been performed using a vanadium sample of natural isotopic abundance with mass of 955 g. The measurements were conducted with the help of an ultra low-background HPGe-detector system located 225 m underground in the laboratory HADES (Belgium). The measured value of the half-life of $^{50}$V for electron capture was $T^{\mathrm{EC}}_{1/2}=(2.77^{+0.20}_{-0.19})\times 10^{17}$ yr. The $\beta^-$-decay branch was not detected and the corresponding lower bound of the half-life was $T^{\beta}_{1/2}\geq 8.9\times 10^{18}$ yr at the 90\% confidence level.

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arXiv2020

The first search for bosonic super-WIMPs with masses up to 1 MeV/c$^2$ with GERDA

We present the first search for bosonic super-WIMPs as keV-scale dark matter candidates performed with the GERDA experiment. GERDA is a neutrinoless double-beta decay experiment which operates high-purity germanium detectors enriched in $^{76}$Ge in an ultra-low 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 60 keV/c$^2$ to 1 MeV/c$^2$. No evidence for a dark matter signal was observed, and the most stringent constraints on the couplings of super-WIMPs with masses above 120 keV/c$^2$ have been set. As an example, at a mass of 150 keV/c$^2$ the most stringent direct limits on the dimensionless couplings of axion-like particles and dark photons to electrons of $g_{ae} < 3 \cdot 10^{-12}$ and ${\alpha'}/{\alpha} < 6.5 \cdot 10^{-24}$ at 90% credible interval, respectively, were obtained.

hep-ex↗

arXiv2020

Search for the double-beta decay of 82Se to the excited states of 82Kr with NEMO-3

The double-beta decay of 82Se to the 0+1 excited state of 82Kr has been studied with the NEMO-3 detector using 0.93 kg of enriched 82Se measured for 4.75 y, corresponding to an exposure of 4.42 kg y. A dedicated analysis to reconstruct the gamma-rays has been performed to search for events in the 2e2g channel. No evidence of a 2nbb decay to the 0+1 state has been observed and a limit of T2n 1/2(82Se; 0+gs -> 0+1) > 1.3 1021 y at 90% CL has been set. Concerning the 0nbb decay to the 0+1 state, a limit for this decay has been obtained with T0n 1/2(82Se; 0+g s -> 0+1) > 2.3 1022 y at 90% CL, independently from the 2nbb decay process. These results are obtained for the first time with a tracko-calo detector, reconstructing every particle in the final state.

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