LNGS Research Articles

First Search for Bosonic Superweakly Interacting Massive Particles with Masses up to 1 MeV/c^{2} 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 ^{76}Ge 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 60 keV/c^{2} to 1 MeV/c^{2}. Noevidence 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 axionlike particles and dark photons to electrons of g_{ae}<3×10^{-12} and α^{'}/α<6.5×10^{-24} at 90% credible interval, respectively, were obtained.

Search for a remnant violation of the Pauli exclusion principle in a Roman lead target

In this paper we report on the results of two analyses of the data taken with a dedicated VIP-Lead experiment at the Gran Sasso National Laboratory of the INFN. We use measurements taken in an environment that is especially well screened from cosmic rays, with a metal target made of “Roman lead” which is characterised by a low level of intrinsic radioactivity. The analyses lead to an improvement, on the upper bounds of the Pauli Exclusion Principle violation for electrons, which is more than one (four) orders of magnitude, when the electron-atom interactions are described in terms of scatterings (or close encounters) respectively.

Search for α decay of naturally occurring Hf-nuclides using a Cs2HfCl6 scintillator

Residual radioactive contaminants of a caesium hafnium chloride (Cs2HfCl6) crystal scintillator have been measured in a low background setup at the Gran Sasso National Laboratory of the INFN, Italy. The total alpha activity of the detector is at the level of 7.8(3) mBq/kg. The results of direct studies of the α decay of naturally occurring Hf isotopes that have been performed using the “source=detector” approach are presented. In 2848 h of data taking, the α decay of 174Hf was observed with T=1/2(7.0±1.2)×1016 y.

The key role of the Silicon Drift Detectors in testing the Pauli Exclusion Principle for electrons: the VIP-2 experiment

The VIP experiment performed an accurate investigation of the Pauli Exclusion Principle for electrons. The apparatus was installed in the Gran Sasso Laboratories of the National Institute of Nuclear Physic in Italy, an underground environment with an extremely low cosmic background. The aim of the experiment was to test the Pauli Exclusion Principle for electrons in a copper target circulated by a Direct Current (DC) current, searching for X-rays emission due to an atomic transition forbidden by Pauli exclusion principle, from the L shell to the K shell of copper when the K shell is already occupied by two electrons. VIP set an upper limit on the Pauli exclusion principle violation probability 1/2β 2 <4.7 χ 10–29. The goal of the upgraded VIP-2 experiment, presently in data taking at Gran Sasso Laboratories, is to improve this limit by two orders of magnitude. The VIP-2 experimental apparatus, in which the Silicon Drift Detectors have the key role of X-ray detectors, and preliminary results are presented.

Setup commissioning for an improved measurement of the D(p,$$\gamma $$)$$^3$$He cross section at Big Bang Nucleosynthesis energies

Among the reactions involved in the production and destruction of deuterium during Big Bang Nucleosynthesis, the deuterium-burning D(p,gamma)3He reaction has the largest uncertainty and limits the precision of theoretical estimates of primordial deuterium abundance. Here we report the results of a careful commissioning of the experimental setup used to measure the cross-section of the D(p,gamma)3He reaction at the Laboratory for Underground Nuclear Astrophysics of the Gran Sasso Laboratory (Italy). The commissioning was aimed at minimising all sources of systematic uncertainty in the measured cross sections. The overall systematic error achieved (< 3 %) will enable improved predictions of BBN deuterium abundance.

Fluid-dynamics and transport of 210Po in the scintillator Borexino detector: A numerical analysis

Moving beyond the important contributions to neutrino physics obtained by the Borexino experiment during the last years, research activities are ongoing at INFN Gran Sasso National Laboratories to further improve the detector sensitivity in order to perform an accurate measurement of the subdominant CNO solar neutrino rate. To this purpose, the improvement of the detector fluid-dynamic stability is the key to further reduce the 210Po background, that is continuously being transported inside the measurement fiducial volume by convective currents. In this framework, numerical simulations of the detector fluid-dynamics may help to better comprehend the 210Po behaviour, and also to suggest effective countermeasures, able to minimize the natural convection inside the detector.In the present work, two-dimensional numerical simulations have been performed to improve the current understanding of Borexino thermal and fluid-dynamics. Adopted models have been optimized for different regions and periods of interest, focusing on the most critical aspects that were identified as influencing the polonium background concentrations. In particular, a Borexino-specific benchmark was constructed in order to validate the model temperature predictions. The derived inner vessel surface temperatures are successively used as boundary conditions for a more refined convective model of the inner most part of the detector. Based on the calculated convective currents, the transport behaviour of background 210Po inside the detector active volume was investigated by means of a convection–diffusion model, showing a reasonable good agreement between calculations and experimental data.

Long term operation with the DarkSide-50 detector

DarkSide is a staged experimental project based on radiopure argon aiming at direct dark matter detection. The DarkSide-50 (DS-50) detector is currently operating underground at the Gran Sasso National Laboratory. DS-50 detector is a dual-phase, 50 kg, liquid argon time-projection-chamber readout by 38 cryogenic PMTs (Hamamatsu R11065), surrounded by an active liquid scintillator veto and contained in a water Cherenkov detector acting as a muon veto. DS-50 has been operating continuously since 2013, first with atmospheric argon and subsequently filled in 2015 with argon from an underground source, allowing a reduction of the 39Ar isotope by more than a factor 1000. Features of the DS-50 detector are described, long term operations and stability are reported and its performances in scintillation light detection discussed. Results on dark matter searches obtained with DarkSide-50 detector are briefly reported.

Analysis strategies for the updated geoneutrino measurement with Borexino

Borexino is a 280-ton liquid scintillator detector located at the Laboratori Nazionali del Gran Sasso (LNGS), Italy and is one of the two detectors that has measured geoneutrinos so far. The unprecedented radio-purity of the scintillator, the shielding with highly purified water, and the placement of the detector at a 3800 m w.e. depth have resulted in very low background levels and have made Borexino an excellent apparatus for geoneutrino measurements. The analysis techniques of the latest geoneutrino results with Borexino were presented using the data obtained from December 2007 to April 2019, corresponding to an exposure of (1.12 ± 0.05) × 1032 protons × yr. Enhanced analysis techniques, such as an increased fiducial volume, improved veto for cosmogenic backgrounds, extended energy and coincidence time windows, as well as a more efficient α/β particle discrimination have been adopted in this measurement. The updated statistics and these elaborate resulted in a geoneutrino signal of with total precision.

Directional Dark Matter Searches with the CYGNO Project

The goal of the CYGNO project is to deploy at Laboratori Nazionali del Gran Sasso (LNGS) an high resolution Time Projection Chamber (TPC) with Gas Electron Multipliers (GEMs) amplification and optical 3D readout of an Helium/Fluorine based gas mixture for directional Dark Matter (DM) searches at low 1-10 GeV WIMP masses. The determination of the incoming direction of WIMP particles can in fact offer not only additional handles for discrimination of the annoying backgrounds, but especially an unique key for a positive, unambiguous identification of a DM signal.

Updated geoneutrino measurement with Borexino

Borexino is a 280-ton liquid scintillator detector located at the Laboratori Nazionali del Gran Sasso (LNGS), Italy and is one of the two detectors that has measured geoneutrinos so far. The unprecedented radio-purity of the scintillator, the shielding with highly purified water, and the placement of the detector at a 3800 m w.e. depth have resulted in very low background levels and has made Borexino an excellent apparatus for geoneutrino measurements. The new update of the Borexino geoneutrino measurement, using the data obtained from December 2007 to April 2019, has been presented. Enhanced analysis techniques, adopted in this measurement, have been also presented (poster presentation #39 by S. Kumaran). The updated statistics and the new elaborate analysis have led to more than a factor two increase in exposure ((1.12 ± 0.05) × 1032 protons × yr) when compared to the latest Borexino result from 2015. The resulting geoneutrino signal of TNU has total precision. The geological interpretations of this measurement have been discussed. In particular, the 99% C.L. observation of the mantle signal by exploiting the relatively well-known lithospheric contribution, the estimation of the radiogenic heat, as well as the comparison of these results to the predictions based on different geological models. The upper limits on the power of a hypothetical georeactor that might be present at different locations inside the Earth have been set.

Nuclear astrophysics at Gran Sasso : the study of BBN and post-main sequence fusion reactions at LUNA

The first nuclei were formed a few minutes after the Big Bang, through the process called Big Bang nucleosynthesis, that left our universe containing about 75% hydrogen, 24% helium by mass, with small traces of other elements such as lithium and the hydrogen isotope deuterium. Heavier nuclei are produced during the different characteristic phases of the star evolution. At astrophysical energies the cross section of nuclear processes is usually extremely small and the cosmogenic background prevents their measurement at stellar energies on Earth surface. Deep underground in the Gran Sasso laboratory, several crucial reactions involved in hydrogen burning has been measured directly at astrophysical energies by the LUNA (Laboratory for Underground Nuclear Astrophysics) Collaboration with both the LUNA-50kV and the LUNA-400kV accelerators. This intense work will continue with the installation of a new LUNA-MV machine able to provide hydrogen, helium and carbon high current beams: the new facility will allow to explore the helium and carbon burning processes, by studying the key reactions shaping the evolution of massive stars towards their final fate. The present contribution is aimed to summarise the most recent results achieved by LUNA Collaboration and to highlight the rich experimental program connected to the new facility.

Study on the contributions to the CUORE energy spectra

CUORE is a cryogenic experiment searching for the neutrinoless double beta decay of 130Te, and it is located at the underground Gran Sasso National Laboratories in the centre of Italy. With its 988 TeO2 crystals, operating at a base temperature of ~10 mK, CUORE is the first ton-scale and ultra-low background bolometric experiment ever realized for this purpose. There are many phenomena that contribute to the CUORE energy spectra, such as 2vββ decay, cosmic rays and materials and environmental radioactivity: disentangle these contributions is of fundamental importance for a correct interpretation of the results. In this poster, some relevant aspect of the CUORE background study is presented.

HIGH PURE SUBSTANCES FOR ASTROPHYSICAL RESEARCH

The features of the application of high-purity substances for studying rare nuclear events in astrophysics, in particular double beta decay, are considered. It was noted that for such studies, the special underground laboratories are needed to eliminate the cosmic radiation background, and the use of high-purity materials for possibility to record rare nuclear events. The content of neutral impurity elements should not exceed 0.1 ppm, and the level of radionuclide contamination should be less than units mBq/kg. At the NSC KIPT, the technologies have been developed for the production of high-purity refractory (W, Mo, Re, Ru, Os) and low-melting metals (Zn, Cd, Te, archPb), including isotopically-enriched 106Cd, 116Cd, satisfying these requirements. Using these metals both as individual elements and as part of low-background scintillation single crystals, it was possible to obtain a number of new fundamental results in the field of astrophysics, together with the Institute for Nuclear Research of the National Academy of Sciences of Ukraine and the Gran Sasso Laboratory of the National Institute of Physics (Italy)

Comprehensive geoneutrino analysis with Borexino

This paper presents a comprehensive geoneutrino measurement using the Borexino detector, located at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The analysis is the result of 3262.74 days of data between December 2007 and April 2019. The paper describes improved analysis techniques and optimized data selection, which includes enlarged fiducial volume and sophisticated cosmogenic veto. The reported exposure of (1.29±0.05)×1032 protons ×year represents an increase by a factor of two over a previous Borexino analysis reported in 2015. By observing 52.6−8.6+9.4(stat)−2.1+2.7(sys) geoneutrinos (68% interval) from U238 and Th232, a geoneutrino signal of 47.0−7.7+8.4(stat)−1.9+2.4(sys) TNU with −17.2+18.3% total precision was obtained. This result assumes the same Th/U mass ratio as found in chondritic CI meteorites but compatible results were found when contributions from U238 and Th232 were both fit as free parameters. Antineutrino background from reactors is fit unconstrained and found compatible with the expectations. The null-hypothesis of observing a geoneutrino signal from the mantle is excluded at a 99.0% C.L. when exploiting detailed knowledge of the local crust near the experimental site. Measured mantle signal of 21.2−9.0+9.5(stat)−0.9+1.1(sys) TNU corresponds to the production of a radiogenic heat of 24.6−10.4+11.1 TW (68% interval) from U238 and Th232 in the mantle. Assuming 18% contribution of K40 in the mantle and 8.1−1.4+1.9 TW of total radiogenic heat of the lithosphere, the Borexino estimate of the total radiogenic heat of the Earth is 38.2−12.7+13.6 TW, which corresponds to the convective Urey ratio of 0.78−0.28+0.41. These values are compatible with different geological predictions, however there is a ∼2.4σ tension with those Earth models which predict the lowest concentration of heat-producing elements in the mantle. In addition, by constraining the number of expected reactor antineutrino events, the existence of a hypothetical georeactor at the center of the Earth having power greater than 2.4 TW is excluded at 95% C.L. Particular attention is given to the description of all analysis details which should be of interest for the next generation of geoneutrino measurements using liquid scintillator detectors.50 MoreReceived 5 September 2019Corrected 25 February 2020DOI:https://doi.org/10.1103/PhysRevD.101.012009Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNeutrino interactionsTechniquesNeutrino detectorsScintillatorsParticles & Fields

Dark matter search with the SABRE experiment

The SABRE (Sodium Iodide with Active Background REjection) experiment will search for an annually modulating signal from dark matter using an array of ultra-pure NaI(Tl) detectors surrounded by an active scintillator veto to further reduce the background. The first phase of the experiment is the SABRE Proof of Principle (PoP), a single 5 kg crystal detector operated in a liquid scintillator filled vessel at Laboratori Nazionali del Gran Sasso (LNGS). The SABRE-PoP installation is underway with the goal of running in 2018 and performing the first in situ measurement of the crystal background, testing the veto efficiency, and validating the SABRE concept. The second phase of SABRE will be twin arrays of NaI(Tl) detectors operating at LNGS and at the Stawell Underground Physics Laboratory (SUPL) in Australia. By locating detectors in both hemispheres, SABRE will minimize seasonal systematic effects. This paper presents the status report of the SABRE activities as well as the results from the most recent Monte Carlo simulation and the expected sensitivity.

Analytical response function for the Borexino solar neutrino analysis

Borexino experiment is located at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, and its primary goal is detecting solar neutrinos, in particular those below 2 MeV, with unprecedentedly high sensitivity. Its technical distinctive feature is the ultra-low radioactive background of the inner scintillating core, which is the basis of the outstanding achievements obtained by the experiment (fluxes of 7Be, pep, pp, and limit on CNO). A spectral fit in the whole energy range from 200 keV up to 2 MeV has been performed for the first time, allowing to obtain simultaneously fluxes of all the solar neutrino components. To make such a fit possible, one requires the exact shapes of neutrino signals and backgrounds, as seen in the detector. Therefore, the transformation of the spectra from the original energy scale to the scale of the desired energy estimator, such as the number of hit PMTs or photoelectrons, is one of the key steps of the analysis. This conversion accounts for the energy scale non-linearity and the detector’s energy response, and can be performed using two approaches: the Monte Carlo simulation and the use of analytical models. The details and advantages of the analytical approach are presented in this contribution.

Search for sterile neutrinos with SOX: Monte Carlo studies of the experiment sensitivity and systematic effects

Some neutrino experiments reveal anomalous results which can make room for new physics beyond the three-flavor neutrino oscillation model. These hints suggest the existence of sterile neutrinos with mass m <eV. SOX will be a short-baseline disappearance experiment aiming to test this hypotesis, performed with the liquid scintillator detector Borexino at Gran Sasso National Laboratory in Italy [1]. Due to the good energy and position resolution, a light sterile neutrino can create an oscillatory pattern in the signal. The SOX sensitivity, the related analysis and systematics will be briefly discussed.

Study of the 22Ne(α , γ)26Mg reaction at LUNA

The 22Ne( α , γ)26Mg reaction competes with the 22Ne(α, n)25Mg reac-tion which is the main source of neutrons for the s-process in low-mass Asymptotic Giant Branch (AGB) and massive stars. The 22Ne( α , γ)26Mg reaction rateis affected by a high uncertainty mainly due to the poorly constrained 395 keVresonance which has been studied only indirectly leading to a wide range of pos-sible values for its resonance strength (10-14 - 10-9 eV). The present study represents the direct measurement of the 395 keV resonance of the 22Ne( α , γ)26Mgreaction at LUNA (Laboratory for Underground Nuclear Astrophysics), located at Gran Sasso National Laboratory. Here, the experimental campaigns, setupand some very preliminary results are presented.

Supernova neutrino detection in XENONnT neutron and muon Vetoes

The current phase of the XENON Dark Matter Project, named XENONnT, will be operative in 2020 in the underground Laboratori Nazionali del Gran Sasso (LNGS). It is a multi-ton detector for direct search of Dark Matter, consisting of a double phase liquid-gas xenon Time Projection Chamber (TPC) which contains 5.9 tons of liquid xenon target mass, inserted in a cryostat surrounded by a tank containing 700 tons of water doped with Gd sulphate. Its aim, as that of its precursor XENON1T, is to detect elastic scattering of Weakly Interacting Massive Particles (WIMPs) off xenon nuclei. The presence of two Veto sub-systems, the muon Veto instrumented with 84 photomultiplier tubes (PMTs) and the neutron Veto with other 120 PMTs, allows to reduce the background for WIMPs search through muon and neutron tagging, while the presence of Gd sulphate increases the neutron capture cross section. Thanks to the large xenon target used and the presence of the two Vetoes, XENONnT will be able also to detect all flavours of Supernova neutrinos. Here the results from Monte Carlo simulations of XENONnT detection efficiency are presented for Supernova neutrinos through their inverse beta decay interactions in water of the two Veto sub-systems.

Measurement of Seasonal Variations of Horizontal Muons with Underground LVD Setup

The Large-Volume scintillation Detector commonly known as LVD and located at the Gran Sasso Laboratory at an average depth of 3650 m w.e. measures muons of intensity $$3.31\times 10^{-4}$$ m$${}^{-2}$$ s$${}^{-1}$$. The results obtained from an analysis of the properties of seasonal variations of the horizontal and vertical muon fluxes are presented in this article. Horizontal muons detected in LVD mostly correspond to rock depths of about 5 km w.e. and zenith angles $$\theta$$ of about $$75^{\circ}$$, while vertical muons ($$\theta\approx 13^{\circ}$$) correspond to depths of about 4.6 km w.e.