A strong correlation between the LiDAR aerosol backscattering signal and air ion concentration in an enclosed underground room is detected for the first time. Nowadays, air ions monitoring is considered to be the main tool in the search for earthquake precursors, and the revealed correlation opens interesting opportunities of using LiDARs in the search for precursors. LiDARs allow sensing the dynamics of aerosols generated by air ions as condensation nuclei on long tracks along the laser beam, compared to pointwise detection of air ions utilizing appropriate sensors.

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.

In addition to solar-neutrino fluxes, the Borexino detector is able to record antineutrino fluxes by employing reactions of elastic neutrino- and antineutrino-electron scattering. Antineutrino fluxes are produced within the Earth by natural-radioactivity isotopes and at the Earth’s surface by nuclear reactors of nuclear power plants. The most recent data accumulated by the Borexino detector are analyzed upon adding known antineutrino fluxes to the backgrounds and fluxes of solar neutrinos. This analysis made it possible to determine the flux of ^40 K antineutrinos, which turned out to be quite significant in magnitude. At the same time, all fluxes of solar neutrinos are compatible with the low-metallicity model of the Sun.

Measurements and correlation analysis of radon and aeroion concentrations in the underground laboratory were carried out. For pairs of variables “pressure — radon” and “pressure — ions”, a delayed pumping effect was found, similar to that previously observed for neutrons and gamma quanta. A simple phenomenological model explaining the results is presented. In this model, the reason for the delay is the gradual accumulation of radon in the room with a decrease in atmospheric pressure. The balance of the radon accumulation rate, the time of its radioactive decay and the characteristic time of pressure variations leads to an effective delay of 2 days between atmospheric pressure variations and radon concentration. Correlation analysis for the variables “pressure — ions” indicates that ions formed in the pores of the soil are already present in the air carrying radon to the laboratory. These ions make up approximately 21% of the total number of ions in the laboratory.

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 ^76Ge. 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.

We present the measurement of the two-neutrino double-β decay rate of ^{76}Ge performed with the GERDA Phase II experiment. With a subset of the entire GERDA exposure, 11.8 kg yr, the half-life of the process has been determined: T_{1/2}^{2ν}=(2.022±0.018_{stat}±0.038_{syst})×10^{21}  yr. This is the most precise determination of the ^{76}Ge two-neutrino double-β decay half-life and one of the most precise measurements of a double-β decay process. The relevant nuclear matrix element can be extracted: M_{eff}^{2ν}=(0.101±0.001).

We provide the indication of high flux of $^{40}$K geo-antineutrino and geo-neutrino ($^{40}$K-geo-($\bar{\nu} + \nu$)) with Borexino Phase III data. This result was obtained by introducing a new source of single events, namely $^{40}$K-geo-($\bar{\nu} + \nu$) scattering on electrons, in multivariate fit analysis of Borexino Phase III data. Simultaneously we obtained the count rates of events from $^7$Be, $pep$ and CNO solar neutrinos. These count rates are consistent with the prediction of the Low metallicity Sun model SSM B16-AGSS09. MC pseudo-experiments showed that the case of High metallicity Sun and absence of $^{40}$K-geo-($\bar{\nu} + \nu$) can not imitate the result of multivariate fit analysis of Borexino Phase III data with introducing $^{40}$K-geo-($\bar{\nu} + \nu$) events. We also provide arguments for the high abundance of potassium in the Earth.

The results of analysis for the single events energy spectrum obtained in phase III of Borexino detector operation are considered. The experimental spectrum was fitted by a set of standard single events sources with the addition of events from potassium geo-antineutrinos (40K-geo-v) scattering on electrons. The addition of 40K-geo-v events makes it possible to improve the agreement of the experimental and fitted spectra. Experimental results indicate the presence of a significant amount of potassium in the Earth.

The authors consider results from analyzing the energy spectrum of single events obtained in Phase III of the Borexino experiment. The experimental spectrum is fitted by a set of standard sources of single events with the addition of events from potassium geo-antineutrino (40K-geo-ν) scattering on electrons. The adding of 40K-geo-ν events improves the agreement between the experimental and fitted spectra. Experimental results indicate considerable amounts of potassium in the Earth.

The possibility of large geo-antineutrino fluxes from ^40 K decays and the presence of an excess of positive electric charge in the Earth’s crust are predicted by the Hydridic Earth model. The data of the Borexino experiment do not contradict the proportion of potassium equal to several percent of the Earth’s mass and predicted by this model. The detection of an excess of positively charged air ions in underground laboratories can be explained by the presence of an excess of positive electric charge in the Earth’s crust. Further studies are needed to confirm the existence of both of these effects.

Abstract We search for tri-nucleon decays of $$^{76}$$ 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 $$^{73}$$ 73 Cu, $$^{73}$$ 73 Zn, and $$^{73}$$ 73 Ga nuclei, respectively. These nuclei are unstable and eventually proceed by the beta decay of $$^{73}$$ 73 Ga to $$^{73}$$ 73 Ge (stable). We search for the $$^{73}$$ 73 Ga decay exploiting the fact that it dominantly populates the 66.7 keV $$^{73m}$$ 73 m Ga state with half-life of 0.5 s. The nnn-decays of $$^{76}$$ 76 Ge that proceed via $$^{73m}$$ 73 m 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 1.2 $$\times $$ × 10 $$^{26}$$ 26 yr (90% credible interval). This result improves previous limits for tri-nucleon decays by one to three orders of magnitude.

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 1.2 × 10 ^26 yr (90

Low concentrations aerosols quantification is rather challenging for LIDAR instruments due to eye-safety restrictions so high energy pulses cannot be utilized to improve the sensitivity. Highly sensitive but eye-save LIDAR has been developed for the quantification of the water droplet aerosol which was induced by air ions. Few days sensing of aerosols in closed tunnel revealed a strong correlation between air optical transparency (LIDAR measurements) and concentrations of positive/negative ions (ion counter Sapphir 3-M). The correlation coefficient was observed to be almost unity for the air transparency signal and air ions unipolarity coefficient. High sensitivity of the water droplet aerosol quantification makes the developed eye-safe LIDAR a perspective instrument for space resolved measurements of the air ions distribution. Space and time resolved measurements of air ions exhalation can be a new instrument for tectonic activity study including new earthquake forecasting indicators search.

Low background segmented liquid scintillator detector, doped with an indium as a target for solar neutrino registration, can be used for measuring total solar neutrino spectrum including pp neutrinos. A detector consisting of small modules filled with liquid scintillator in the volume of 1–2 L is considered. Silicon matrices are used for light collection. The background of indium beta-activity is suppressed by triple coincidences. The detector of such a type can measure ^7 Be neutrino flux with high accuracy and independently check the measurement performed by the Borexino Collaboration.

Abstract The GERmanium Detector Array (Gerda) collaboration searched for neutrinoless double- $$\beta $$ β decay in $$^{76}$$ 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 $$^{228}$$ 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 $$Q_{\beta \beta }= 2039$$ Q β β = 2039 keV, while preserving $$(81\pm 3)$$ ( 81 ± 3 ) % of the signal. In addition, an exhaustive list of parameters is provided which were used in the final data analysis.

A modification of the LENS (Low Energy Neutrino Spectroscopy) project for spectroscopy of solar neutrinos with energies above about 715 keV on the basis of new technologies and solutions is examined. The respective detector employs $${}^{115}$$ In nuclei as a target for neutrinos. The creation of a detector containing about 200 t of a scintillator loaded with 10 t of indium will make it possible to measure, within five years, the energy spectra of solar neutrinos from $${}^{7}$$ Be, neutrinos from the CNO cycle, and $$pep$$ neutrinos with small systematic errors. The detector was simulated in the form of a set of cells of a liquid scintillator doped with indium (about 10 $${\%}$$ in weight). Necessary technical conditions for detector cells are formulated, and the possible counting rate for events induced by internal and external backgrounds and characterized by an energy release of 600 to 1600 keV is estimated. It is shown that such a detector is implementable, in principle.

This corrects the article DOI: 10.1103/PhysRevLett.125.011801.

We present the results of measurements of the air ion densities of both signs in the unventilated underground laboratory of the Moscow State University. We used the stationary station based on a Sapfir-3M modified air ion counter. We solved the problems of accuracy of relative measurements of air ion densities and stability of measurements in conditions of high humidity of underground cavities. We investigated the spatial distribution of air ion densities and their variability over time. An excess of positively charged air ions was found everywhere in the laboratory. The obtained data indicate the presence of a weak electric field directed downward in the underground laboratory. We observed the dependence of the air ion densities of both signs on the atmospheric pressure. We found the correlation of air ion densities with radon activity in the laboratory air and show that the ionization of air by alpha particles from the decay of radon and its daughter elements is the main source of air ions in closed underground cavities. A variant for explaining the presence of an excess of positive charge in underground cavities is proposed.

A search for Beyond the Standard Model double- β decay modes of 76 Ge has been performed with data collected during the Phase II of the GERmanium Detector Array ( Gerda ) experiment, located at the 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- β decay have been obtained. The isotropic coefficient å of (3) , which embeds Lorentz violation in double- β 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- β decay, including sterile neutrinos.