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Backgrounds from long-lived radon decay products are often problematic for low-energy neutrino and rare-event experiments. These isotopes, specifically 210Pb, 210Bi, and 210Po, easily plate out onto surfaces exposed to radon-loaded air. The alpha emitter 210Po is particularly dangerous for detectors searching for weakly-interacting dark matter particles. Neutrons produced via (α, n) reactions in detector materials are, in some cases, a residual background that can limit the sensitivity of the experiment. An effective solution is to reduce the 222Rn activity in the air in contact with detector components during fabrication, assembly, commissioning, and operation. We present the design, construction, calibration procedures and performance of an electrostatic radon detector made to monitor two radon-suppressed clean rooms built for the DARKSIDE-50 experiment. A dedicated data acquisition system immune to harsh operating conditions of the radon monitor is also described. A record detection limit for 222Rn specific activity in air achieved by the device is 0.05mBqm-3 (STP). The radon concentration of different air samples collected from the two DARKSIDE-50 clean rooms measured with the electrostatic detector is presented.

A search for solar axions and axion-like particles produced in the p + d → 3 He + A ( 5.5 MeV ) reaction was performed using the complete dataset of the Borexino detector (3995 days of measurement live-time). The following interaction processes have been considered: axion decay into two photons ( A → 2 γ ) , inverse Primakoff conversion on nuclei ( A + Z → γ + Z ), the Compton conversion of axions to photons ( A + e → e + γ ) and the axio-electric effect ( A + e + Z → e + Z ). Model-independent limits on product of axion–photon ( g A γ ), axion–electron ( g Ae ), and isovector axion–nucleon ( g 3 A N ) couplings are obtained: | g A γ × g 3 A N | ≤ 2.3 × 10 - 11 GeV - 1 and | g Ae × g 3 A N | ≤ 1.9 × 10 - 13 at m A < 1 MeV (90% c.l.). The Borexino results exclude new large regions of g A γ , and g Ae coupling constants and axion masses m A , and leads to constraints on the products | g A γ × m A | and | g Ae × m A | for the KSVZ- and the DFSZ-axion models.

The search for neutrino events in correlation with gravitational wave (GW) events for three observing runs (O1, O2 and O3) from 09/2015 to 03/2020 has been performed using the Borexino data-set of the same period. We have searched for signals of neutrino-electron scattering and inverse beta-decay (IBD) within a time window of ± 1000  s centered at the detection moment of a particular GW event. The search was done with three visible energy thresholds of 0.25, 0.8 and 3.0 MeV. Two types of incoming neutrino spectra were considered: the mono-energetic line and the supernova-like spectrum. GW candidates originated by merging binaries of black holes (BHBH), neutron stars (NSNS) and neutron star and black hole (NSBH) were analyzed separately. Additionally, the subset of most intensive BHBH mergers at closer distances and with larger radiative mass than the rest was considered. In total, follow-ups of 74 out of 93 gravitational waves reported in the GWTC-3 catalog were analyzed and no statistically significant excess over the background was observed. As a result, the strongest upper limits on GW-associated neutrino and antineutrino fluences for all flavors ( ν e , ν μ , ν τ ) at the level 10 9 - 10 15 cm - 2 GW - 1 have been obtained in the 0.5–5 MeV neutrino energy range.

A bstract The very low radioactive background of the Borexino detector, its large size, and the well proved capability to detect both low energy electron neutrinos and antineutrinos make an ideal case for the study of short distance neutrino oscillations with artificial sources at Gran Sasso. This paper describes the possible layouts of 51 Cr ( ν e ) and 144 Ce- 144 Pr source experiments in Borexino and shows the expected sensitivity to eV mass sterile neutrinos for three possible different phases of the experiment. Expected results on neutrino magnetic moment, electroweak mixing angle, and couplings to axial and vector currents are shown too.

Borexino is a large volume, real-time, liquid scintillator detector located at the Gran Sasso National Laboratory in Italy. The principal objective of the detector is to measure mono energetic (862 keV) 7Be neutrinos from the sun present with a count rate of several tens of events per day. Measurement at this level requires an extremely low internal background due to natural radioactivity present in the detector components. In this paper the techniques used by Borexino to purify the scintillator and to build the nylon containment vessels are described. The unprecedented high radiopurity reached by Borexino permitted for the first time the realtime detection of 7Be neutrinos from the sun[1].

Borexino is a 280t liquid scintillator detector at the Laboratori Nazionali del Gran Sasso (LNGS), Italy. Its main goal is the precision spectroscopy of solar neutrinos down to energies of 0.19 MeV and for this task it features an unprecedented radio-purity and a high scintillation light yield. The solar neutrinos are measured by the elastic scattering off electrons which induce isotropically emitted scintillation photons as well as a sub-dominant number of Cherenkov photons that are detected by photomulitplier tubes. Here we present the first detection of sub-MeV solar neutrinos using their associated Cherenkov photons in a high light yield liquid scintillator detector. In Borexino electrons with E>0.16MeV produce Cherenkov photons, where the ratio of Cherenkov photons from the neutrino scattered electrons is estimated to be < 1% for all PMT hits, so a typical event by event direction reconstruction is not possible. Instead this analysis looks at the integrated signal of the PMT hits of all detected events by correlating the position of each hit PMT relative to the reconstructed position of the event and the well known position of the Sun. In this way it is possible to measure an angular distribution that shows the statistical contribution of Cherenkov photons from the solar neutrino recoil electrons. Using the Geant4-based Borexino Monte Carlo to produce the expected angular distribution for solar neutrinos and background we have measured 8643 − 2058 +2252 neutrino events out of 19904 total events for an energy region around the 7 Be edge between 0.53 MeV and 0.74 MeV.

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 3800 m w.e. depth have resulted in very low background levels, making Borexino an excellent apparatus for geoneutrino measurements. This article will summarize the recent geoneutrino analysis and results with Borexino, from the period December 2007 to April 2019. The updated statistics and the optimized analysis techniques such as an increased fiducial volume and sophisticated cosmogenic vetoes, have led to more than a two-fold increase in exposure when compared to the previous measurement in 2015, resulting in a significant improvement in the precision. In addition, Borexino has also been able to reject the null hypothesis of the mantle geoneutrino signal with 99% C.L., for the first time, by exploiting the extensive knowledge of the crust surrounding the detector. This article will also include other geological interpretations of the obtained results such as the calculation of the radiogenic heat and the comparison of the results to various predictions. Additionally, upper limits for a hypothetical georeactor that might be present at different locations inside the Earth will also be discussed.

Borexino is a 280-ton liquid scintillator detector located at the Laboratori Nazionali del Gran Sasso (LNGS), Italy. The main goal of Borexino is to measure solar neutrinos via elastic scattering off electrons in the liquid scintillator. The electrons are then detected by the photo-multiplier tubes via isotropically emitted scintillation photons. However, in the first few nanoseconds after a neutrino interaction, Cherenkov photons (<1% of all detected photons) are also produced in the scintillator for electrons with kinetic energy >0.16 MeV. Borexino has successfully obtained the first directional measurement of sub-MeV solar neutrinos, and the 7 Be solar neutrino interaction rate, through the exploitation of this Cherenkov light signal. This is performed through the so-called Correlated and Integrated Directionality (CID) method, by correlating the first few detected photons to the well-known position of the Sun and integrating the angle for a large number of events. This measurement requires a calibration of the relative time differences between Cherenkov and scintillation photons. In Borexino, we obtain this through gamma calibration sources namely, 40 K and 54 Mn. A group velocity correction estimated through the gamma sources is then used for the solar neutrino analysis. This article will discuss the analysis strategy and methods used for this calibration, and provide motivation for a dedicated Cherenkov calibration in next-generation liquid scintillator detectors.

Borexino, located at the Laboratori Nazionali del Gran Sasso in Italy, is a liquid scintillator detector that measures solar neutrinos via elastic scattering off electrons. The scintillation process of detection makes it impossible to distinguish electrons scattered by neutrinos from the electrons emitted from the decays of radioactive backgrounds. Due to the unprecedented radio-purity achieved by the Borexino detector, the real time spectroscopic detection of solar neutrinos from both the pp chain and CNO fusion cycle of the Sun has been performed. With the newly presented analysis, it is now possible for the first time, to perform the directional detection of the sub-MeV solar neutrinos and extract the 7 Be interaction rate using the few Cherenkov photons emitted at early times, in the direction of scattered electrons with an energy threshold of 0.16 MeV in the liquid scintillator. The angle which correlates the direction of the Sun and the direction of the emitted Cherenkov photons is a key parameter to extract the neutrino signal from data. This article will describe the strategy used in the evaluation of various systematic effects including the geometric conditions of the detector and the data selection cuts that can influence the shape of the directional angle distribution for backgrounds, which is crucial to disentangle the directional sub-MeV solar neutrino signal from the isotropic background in data.

Borexino is a large liquid scintillator experiment located at the underground INFN Laboratori Nazionali del Gran Sasso, in Italy. It was designed and built with the primary goal of real-time detection of low energy solar neutrinos, and in more than ten years of data taking it has measured all the neutrino fluxes produced in the proton-proton chain, i.e. the main fusion process accounting for 99% of the energy production in the Sun. Recently, after improvements and developments in both hardware and software, Borexino has provided the first observation of solar neutrinos emitted from the subdominant Carbon-Nitrogen-Oxygen (CNO) fusion cycle. All the crucial steps of the analysis strategy adopted to disentangle the signal of CNO neutrinos from backgrounds present in the detector will be described in this article.