Gran Sasso Underground Laboratory Research Articles

Light detection and cosmic rejection in the ICARUS LArTPC at Fermilab

The ICARUS-T600 detector is a 760-ton Liquid Argon Time Projection Chamber (LArTPC) currently operating at Fermilab as the Far Detector in the Short Baseline Neutrino (SBN) program. The SBN program is composed of three LArTPCs with a central goal of testing the sterile neutrino hypothesis. After operating for 3-years in the Gran Sasso Underground Laboratory, the ICARUS detector was shipped to CERN where it was outfitted with 360 8” Photomultiplier Tubes (PMTs) for a new optical detection system. The PMT system detects fast scintillation light from charged particles interacting in the Liquid Argon, generating the trigger signal for the full detector and allows 3D reconstruction of events. Now operating at shallow depth, the detector is exposed to a high flux of cosmic rays that can fake neutrino interactions. To mitigate this effect a Cosmic Ray Tagger (CRT) and a 3-meter-thick concrete were installed. Precise timing information from both the PMT and CRT subsystems can help to identify whether an interaction originated from inside or outside of the ICARUS cryostat. This paper reviews a method for cosmogenic background reduction and timing calibration of the CRT and PMT light detection systems in ICARUS.

An adaptive evacuation system for the Gran Sasso underground laboratory

The Gran Sasso National Laboratory (LNGS) is, at present, the largest deep underground laboratory in operation for astroparticle physics and rare event research. The LNGS was created to carry out this research exploiting an overburden of 1,400 m of rock to reduce the flux of muons from cosmic rays. Operating an underground laboratory and its facilities implies a high level of risk. To mitigate risks at the LNGS, a crucial aspect is represented by the evacuation of people from an underground environment during emergencies. The connection between the underground facilities and the outside infrastructure is limited, and the intervention by rescue teams is complicated. This paper reports the study of an adaptive evacuation system to improve the evacuation performance in underground laboratories. The system proposed is composed of a combination of passive, dynamic, and adaptive signage that is able to adapt itself to lead the laboratory occupants to the safe location for evacuation (assembly point). The system collects information from all safety plants, and the data are processed using a customized path-finding algorithm. In the computational algorithm, the underground laboratory is represented as a grid, and the customized path-finding algorithm discovers all available paths to reach the identified evacuation assembly point.

First search for resonant enhanced neutrinoless double electron capture in 152\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{152}$$\\end{document}Gd and other rare decays in natural Gd isotopes

A first search for rare decays of gadolinium isotopes was performed with an ultra-low background high-purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 198 g Gd2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Gd}_2$$\\end{document}O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {O}_3$$\\end{document} powder sample was measured for 63.8 d with a total Gd exposure of 12.6 kg ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes $$\\end{document} d. 152\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{152}$$\\end{document}Gd is the most promising isotope for resonant enhanced neutrinoless double electron capture which could significantly increase the decay rate over other neutrinoless double beta decay processes. The half-life for this decay was constrained to >4.2×1012\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$>4.2\ imes 10^{12}$$\\end{document} year (90% credibility). This limit is still orders of magnitude away from theoretical predictions but it is the first established limit on the transition paving the way for future experiments. In addition, other rare alpha and double beta decay modes were investigated in 152\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{152}$$\\end{document}Gd, 154\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{154}$$\\end{document}Gd, and 160\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{160}$$\\end{document}Gd with half-life limits in the range of 1017-20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{17-20}$$\\end{document} year.

Low-background experiment to search for double beta decay of 106Cd using 106CdWO4 scintillator

An experiment to search for 2ε-, εβ+- and 2β+-decays of 106Cd, using a 215 g cadmium tungstate scintillation crystal enriched at 66 % by 106Cd (106CdWO4) is carried out at the Gran Sasso underground laboratory (Italy). Events in the 106CdWO4 detector are recorded in (anti)coincidences with two large-volume CdWO4 scintillation counters. The design of the detector system, calibration and background measurements, methods, and results of data analysis to determine key detector characteristics are described. The experimental data are compared with Monte Carlo simulation results, and a background model is constructed. The radioactive contamination of the setup components is studied. The sensitivity of the experiment approaches the level of theoretical predictions for the 2νεβ+-decay channel, while for other possible 2β-decay channels it is already on the level of lim T1/2 ∼ 1021-1022 years.

The JUNO experiment Top Tracker

The main task of the Top Tracker detector of the neutrino reactor experiment Jiangmen Underground Neutrino Observatory (JUNO) is to reconstruct and extrapolate atmospheric muon tracks down to the central detector. This muon tracker will help to evaluate the contribution of the cosmogenic background to the signal. The Top Tracker is located above JUNO’s water Cherenkov Detector and Central Detector, covering about 60% of the surface above them. The JUNO Top Tracker is constituted by the decommissioned OPERA experiment Target Tracker modules. The technology used consists in walls of two planes of plastic scintillator strips, one per transverse direction. Wavelength shifting fibres collect the light signal emitted by the scintillator strips and guide it to both ends where it is read by multianode photomultiplier tubes. Compared to the OPERA Target Tracker, the JUNO Top Tracker uses new electronics able to cope with the high rate produced by the high rock radioactivity compared to the one in Gran Sasso underground laboratory. This paper will present the new electronics and mechanical structure developed for the Top Tracker of JUNO along with its expected performance based on the current detector simulation.

Periodic Variations of the Radon Concentration Measured by the Large Volume Detector at the Gran Sasso Underground Laboratory

Periodic Variations of the Radon Concentration Measured by the Large Volume Detector at the Gran Sasso Underground Laboratory

Measurement of fast neutron background in the Gran Sasso underground laboratory using a geyser-concept bubble-chamber

A measurement of the fast neutron background in the Gran Sasso underground laboratory has been performed by the MOSCAB thermodynamic bubble chamber, a neutron detector which identifies fast neutrons passing through the metastable fluid by scattering ions. The result of this measurement confirms the results previously obtained using detectors based on totally different techniques, thus corroborating the previous results in terms of both integral intensity and spectral characteristics, at least in the energy region where the current measurement technique is sensitive.

Underground Tests of Quantum Mechanics by the VIP Collaboration at Gran Sasso

Modern physics lays its foundations on the pillars of Quantum Mechanics (QM), which has been proven successful to describe the microscopic world of atoms and particles, leading to the construction of the Standard Model. Despite the big success, the old open questions at its very heart, such as the measurement problem and the wave function collapse, are still open. Various theories consider scenarios which could encompass a departure from the predictions of the standard QM, such as extra-dimensions or deformations of the Lorentz/Poincaré symmetries. At the Italian National Gran Sasso underground Laboratory LNGS, we search for evidence of new physics proceeding from models beyond standard QM, using radiation detectors. Collapse models addressing the foundations of QM, such as the gravity-related Diósi–Penrose (DP) and Continuous Spontaneous Localization (CSL) models, predict the emission of spontaneous radiation, which allows experimental tests. Using a high-purity Germanium detector, we could exclude the natural parameterless version of the DP model and put strict bounds on the CSL one. In addition, forbidden atomic transitions could prove a possible violation of the Pauli Exclusion Principle (PEP) in open and closed systems. The VIP-2 experiment is currently in operation, aiming at detecting PEP-violating signals in Copper with electrons; the VIP-3 experiment upgrade is foreseen to become operative in the next few years. We discuss the VIP-Lead experiment on closed systems, and the strong bounds it sets on classes of non-commutative quantum gravity theories, such as the θ–Poincaré theory.

Monte Carlo simulation of background components in low level Germanium spectrometry

This proceeding presents the decomposition of the background spectra of the four screening detectors GeMPI 1 - 4 at the Gran Sasso Underground Laboratory (LNGS) using Monte Carlo simulations in the Geant4-based framework MaGe. A detailed understanding of the composition of the background spectra was achieved, allowing for the proposal of two new shield designs for future GeMPI-like detectors and enabling a reduction of the integrated background count rate to 15 counts/d/kg in the interval [40, 2700] keV.

Development of ultralow-background cryogenic calorimeters for the measurement of surface [formula omitted] contamination

Next-generation experiments searching for rare events must satisfy increasingly stringent requirements on the bulk and surface radioactive contamination of their active and structural materials. The measurement of surface contamination is particularly challenging, as no existing technology is capable of separately measuring parts of the 232Th and 238U decay chains that are commonly found to be out of secular equilibrium. We will present the results obtained with a detector prototype consisting of 8 silicon wafers of 150 mm diameter instrumented as bolometers and operated in a low-background dilution refrigerator at the Gran Sasso Underground Laboratory of INFN, Italy. The prototype was characterized by a baseline energy resolution of few keV and a background <100 nBq/cm2 in the full range of α energies, obtained with simple procedures for cleaning of all employed materials and no specific measures to prevent recontamination. Such performance, together with the modularity of the detector design, demonstrate the possibility to realize an alpha detector capable of separately measuring all alpha emitters of the 232Th and 238U chains, possibly reaching a sensitivity of few nBq/cm2.

Deuterium burning measurement at LUNA and its astrophysical and nuclear implications

The deuterium burning reaction D(p,γ)3He at low energies is of primary importance in cosmology because it affects the primordial deuterium abundance, that in turn is very sensitive to fundamental cosmological parameters such as the baryon density and the amount of relativistic species permeating the early Universe. This reaction is also of a particular interest in theoretical nuclear physics because it offers a unique opportunity to test ab initio calculations. In the following a recent study of the D(p,γ)3He reaction in the 30 ≲ Ecm[keV] ≲ 280 energy range will be presented. This measurement has been performed in the underground Gran Sasso Laboratory by the LUNA (Laboratory for Underground Nuclear Astrophysics) collaboration. In addition, the need of having new and precise measurement of the D(d,n)3He and D(d,p)3H reactions will also be discussed.

Direct Detection of Dark Matter with DarkSide-20k

DarkSide run since mid 2015 a 50-kg-active-mass dual phase Liquid Argon Time Projection Chamber (TPC), filled with low radioactivity argon from an underground source and produced world class results for both the low mass (&lt; 20 GeV/c2) and high mass ( &gt; 100 GeV/c2) direct detection search for dark matter. The next stage of the DarkSide program will be a new generation experiment involving a global collaboration from all the current Argon based experiments. DarkSide-20k, is designed as a 20-tonne fiducial mass dual phase Liquid Argon TPC with SiPM based cryogenic photosensors, and is expected to be free of any instrumental background for an exposure of &gt;100 tonne year. Like its predecessor, DarkSide-20k will be housed at the INFN Gran Sasso (LNGS) underground laboratory, and it is expected to attain a WIMP-nucleon cross section exclusion sensitivity of 7.4 × 10−48 cm2 for a WIMP mass of 1 TeV/c2 in a 200 t yr run. DarkSide-20k will be installed inside a membrane cryostat containing more than 700 t of liquid Argon and be surrounded by an active neutron veto based on a Gd-loaded acrylic shell. The talk will give the latest updates of the ongoing R&amp;D and prototype tests validating the initial design. A subsequent objective, towards the end of the next decade, will be the construction of the ultimate detector, ARGO, with a 300 t fiducial mass to push the sensitivity to the neutrino floor region for high mass WIMPs.

Investigation of the N14(p,γ)O15 reaction and its impact on the CNO cycle

The CNO cycle is the main energy source in massive stars during their hydrogen burning phase, and, for our sun, it contributes at the $\ensuremath{\approx}1%$ level. As the $^{14}\mathrm{N}(p,\ensuremath{\gamma})^{15}\mathrm{O}$ reaction is the slowest in the cycle, it determines the CNO energy production rate and thus the CNO contribution to the solar neutrino flux. These CNO neutrinos are produced primarily from the $\ensuremath{\beta}$ decay of $^{15}\mathrm{O}$ and, to a lesser extent, from the decay of $^{13}\mathrm{N}$. Solar CNO neutrinos are challenging to detect, but they can provide independent new information on the metallicity of the solar core. Recently, CNO neutrinos from $^{15}\mathrm{O}$ have been identified for the first time with the Borexino neutrino detector at the INFN Gran Sasso underground laboratory. There are, however, still some considerable uncertainties in the $^{14}\mathrm{N}(p,\ensuremath{\gamma})^{15}\mathrm{O}$ reaction rate under solar temperature conditions. The low energy reaction data presented here, measured at the CASPAR underground accelerator, aim at connecting existing measurements at higher energies and attempts to shed light on the discrepancies between the various data sets, while moving towards a better understanding of the $^{14}\mathrm{N}(p,\ensuremath{\gamma})^{15}\mathrm{O}$ reaction cross section. The present measurements span proton energies between 0.27 and 1.07 MeV, closing a critical gap in the existing data. A multichannel $R$-matrix analysis was performed with the entire new and existing data sets and is used to extrapolate the astrophysical $S$ factors of the ground state and the 6.79 MeV transition to low energies. The extrapolations are found to be in agreement with previous work, but find that the discrepancies between measured data and $R$-matrix fits, both past and present, still exist. We examine the possible reasons for these discrepancies and thereby provide recommendations for future studies.

CUPID: The Next-Generation Neutrinoless Double Beta Decay Experiment

CUPID is a next-generation tonne-scale bolometric neutrinoless double beta decay experiment that will probe the Majorana nature of neutrinos and discover lepton number violation in case of observation of this singular process. CUPID will be built on experience, expertise and lessons learned in CUORE and will be installed in the current CUORE infra-structure in the Gran Sasso underground laboratory. The CUPID detector technology, successfully tested in the CUPID-Mo experiment, is based on scintillating bolometers of Li $$_2$$ MoO $$_4$$ enriched in the isotope of interest $$^{100}$$ Mo. In order to achieve its ambitious science goals, the CUPID collaboration aims to reduce the backgrounds in the region of interest by a factor 100 with respect to CUORE. This performance will be achieved by introducing the high efficient $$\alpha$$ / $$\beta$$ discrimination demonstrated by the CUPID-0 and CUPID-Mo experiments, and using a high transition energy double beta decay nucleus such as $$^{100}$$ Mo to minimize the impact of the gamma background. CUPID will consist of about 1500 hybrid heat-light detectors for a total isotope mass of 250 kg. The CUPID scientific reach is supported by a detailed and safe background model based on CUORE, CUPID-Mo and CUPID-0 results. The required performances have already been demonstrated and will be presented.

The upgraded low-background germanium counting facility Gator for high-sensitivity γ-ray spectrometry

We describe the upgrade and performance of the high-purity germanium counting facility Gator, which is dedicated to low-background γ-ray spectrometry. Gator is operated at the Gran Sasso Underground Laboratory in Italy, at an average depth of 3600 meter water equivalent, and employed for material screening and selection in ultra-low background, rare-event search experiments in astroparticle physics. The detector is equipped with a passive shield made of layers of copper, lead and polyethylene, and the sample cavity is purged with gaseous nitrogen maintained at positive pressure for radon suppression. After upgrading its enclosure, the background rate is (82.0 ± 0.7) counts/(kg·day) in the energy region 100 keV to 2700 keV, a 20% reduction compared to the previously reported rate. We show the stability of various operation parameters as a function of time. We also summarize the sample analysis procedure, and demonstrate Gator's sensitivity by examining one material sample, a candidate photosensor for the DARWIN experiment.

Search for naturally occurring seaborgium with radiopure 116CdWO4 crystal scintillators

A detector containing two radiopure 116CdWO4 crystal scintillators with total mass of 1.2 kg was operated during 35324 h at the Gran Sasso Underground Laboratory (INFN, Italy) with the main aim to investigate double beta decay of 116Cd. As a by-product of the experiment, a new upper limit on atomic abundance of hypothetical naturally occurring long-lived seaborgium (eka-tungsten, Z = 106) in tungsten was set at 5.1 10−15 atom(Sg)/atom(W) with 90% C.L. (assuming the Sg half-life of 109 yr) by the analysis of the alpha decay events. This limit is better than those obtained with a ZnWO4 scintillator and in other types of experiments which used the accelerator mass spectrometry or searched for spontaneous fission of superheavy elements.

Search for a signature of Pauli exclusion principle violation by VIP-2

The VIP-2 experiment performs a high sensitivity test of the Pauli Exclusion Principle for electrons, and is operated in the ultra-low cosmic background environment of the Gran Sasso Underground Laboratories of INFN. The experimental technique consists in testing the symmetry state of an open, continuously supplied, system of fermions; thus representing the only spin-statistics test which strictly fulfills the Messiah-Greenberg superselection rule. In April 2019, VIP-2 started the ongoing data taking campaign in its final layout, with the goal to improve the previous VIP result of at least two orders of magnitude. Before April 2019, VIP-2 collected, in a partial configuration of the external shielding complex, two sets of data in 2018–2019 for a total duration of about 208 days. We present in this work the results of the analyses of the first two data sets collected by VIP-2, which already improve the VIP result by one order of magnitude. The results are also interpreted in the framework of a diffusion random walk model, which provides a significantly enhanced description of the electrons-atoms close encounters process, and hence a boost on the estimated limit on the Pauli Exclusion Principle violation probability.

Search for rare alpha and double beta decays of Yb isotopes to excited levels of daughter nuclei

A search for alpha and double beta decays of ytterbium isotopes was performed with an ultra low-background high purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 194.7 g Yb_2(C_2O_4)_3 powder sample was measured for 11.3 days with a total Yb exposure of 1.25 kgtimes day. Half-life limits for alpha -decay modes of ^{168}mathrm Yb, ^{170}mathrm Yb, ^{171}mathrm Yb, ^{172}mathrm Yb, ^{173}mathrm Yb, ^{174}mathrm Yb and ^{176}mathrm Yb into the first excited states have been obtained between 6times 10^{14} years and 2times 10^{16} years. These are the first experimental constraints of these decay modes. Double electron capture of ^{168}mathrm Yb and double beta decay of ^{176}mathrm Yb into the first excited 2^+ and 0^+ states could be excluded with limits between 1times 10^{14} years to 8times 10^{16} years. This improves the experimental information on some of the decay modes compared to previous constraints.

Directional Dark Matter Search with the NEWSdm experiment

Despite the extensive search for the detection of the dark matter (DM), experiments have yielded null results: they are probing lower and lower cross-section values and touching the so-called neutrino floor. A way to possibly overcome the limitation of the neutrino floor is a directional sensitive approach: one of the most promising techniques for directional detection is nuclear emulsion technology with nanometric resolution. The NEWSdm experiment in the Gran Sasso underground laboratory in Italy is based on a novel nuclear emulsion acting both as the Weakly Interactive Massive Particle (WIMP) target and as the nanometric-accuracy tracking device. This would provide a powerful method of confirming the Galactic origin of the dark matter, thanks to the cutting-edge technology developed to readout sub-nanometric trajectories. Here we discuss the experiment design, its physics potential, the performance achieved in test beam measurements and the near-future plans. After submitting a Letter of Intent, a new facility for emulsion handling was constructed in the Gran Sasso underground laboratory. A Conceptual Design Report was submitted to INFN in Summer 2021.

OPERA tau neutrino charged current interactions

The OPERA experiment was designed to discover the vτ appearance in a vμ beam, due to neutrino oscillations. The detector, located in the underground Gran Sasso Laboratory, consisted of a nuclear photographic emulsion/lead target with a mass of about 1.25 kt, complemented by electronic detectors. It was exposed from 2008 to 2012 to the CNGS beam: an almost pure vμ beam with a baseline of 730 km, collecting a total of 1.8·1020 protons on target. The OPERA Collaboration eventually assessed the discovery of vμ→vτ oscillations with a statistical significance of 6.1 σ by observing ten vτ CC interaction candidates. These events have been published on the Open Data Portal at CERN. This paper provides a detailed description of the vτ data sample to make it usable by the whole community.