A high precision calorimeter for hunting the sterile neutrino in the SOX experiment

Abstract A thermal calorimetric apparatus was designed, built and calibrated for measuring the activity of the artificial 144 Ce —144 Pr antineutrino source. This measurement will be performed at the Laboratori Nazionali del Gran Sasso in Italy, just before the source insertion in the tunnel under the Borexino detector and a precision better than 1% is required for a disappearance technique measurement in the SOX (Short distance neutrino Oscillation with BoreXino) project. In this work the apparatus is described and the most important results from the calibration measurements are shown, where the final precision of few per thousand is demonstrated.

Solar neutrino physics with Borexino

We present the most recent solar neutrino results from the Borexino experiment at the Gran Sasso underground laboratory. In particular, refined measurements of all neutrinos produced in the {\it pp} fusion chain have been made. It is the first time that the same detector measures the entire range of solar neutrinos at once. These new data weakly favor a high-metallicity Sun. Prospects for measuring CNO solar neutrinos are also discussed.

The next-generation liquid-scintillator neutrino observatory LENA

We propose the liquid-scintillator detector LENA (Low Energy Neutrino Astronomy) as a next-generation neutrino observatory on the scale of 50 kt. The outstanding successes of the Borexino and KamLAND experiments demonstrate the large potential of liquid-scintillator detectors in low-energy neutrino physics. LENA's physics objectives comprise the observation of astrophysical and terrestrial neutrino sources as well as the investigation of neutrino oscillations. In the GeV energy range, the search for proton decay and long-baseline neutrino oscillation experiments complement the low-energy program. Based on the considerable expertise present in European and international research groups, the …

Journal of High Energy Physics

The Double Chooz experiment presents improved measurements of the neutrino mixing angle $\theta_{13}$ using the data collected in 467.90 live days from a detector positioned at an average distance of 1050 m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the $\bar\nu_{e}$ signal has increased. The value of $\theta_{13}$ is measured to be $\sin^{2}2\theta_{13} = 0.090 ^{+0.032}_{-0.029}$ from a fit to the observed energy spectrum. Deviations from the reactor $\bar\nu_{e}$ prediction observed ab…

Recent Borexino results and perspectives of the SOX measurement

International audience; Borexino is a liquid scintillator detector sited underground in the Laboratori Nazionali del Gran Sasso (Italy). Its physics program, until the end of this year, is focussed on the study of solar neutrinos, in particular from the Beryllium, pp, pep and CNO fusion reactions. Knowing the reaction chains in the sun provides insights towards physics disciplines such as astrophysics (star physics, star formation, etc.), astroparticle and particle physics. Phase II started in 2011 and its aim is to improve the phase I results, in particular the measurements of the neutrino fluxes from the pep and CNO processes. By the end of this year, data taking from the sun will be over…

The measurement of the pp chain solar neutrinos in Borexino

SOX: search for short baseline neutrino oscillations with Borexino

International audience; The Borexino detector has convincingly shown its outstanding performances in the low energy regime through its accomplishments in the observation and study of the solar and geo neutrinos. It is then an ideal tool to perform a state of the art source-based experiment for testing the longstanding hypothesis of a fourth sterile neutrino with ~ eV(2) mass, as suggested by several anomalies accumulated over the past three decades in source, reactor, and accelerator-based experiments. The SOX project aims at successively deploying two intense radioactive sources, made of Cerium (antineutrino) and Chromium (neutrino), respectively, in a dedicated pit located beneath the det…

Short distance neutrino oscillations with Borexino

International audience; The Borexino detector has convincingly shown its outstanding performances in the low energy, sub-MeV regime through its unprecedented accomplishments in the solar and geo-neutrinos detection. These performances make it the ideal tool to accomplish a state-of-the-art experiment able to test unambiguously the long-standing issue of the existence of a sterile neutrino, as suggested by the several anomalous results accumulated over the past two decades, i.e. the outputs of the LSND and Miniboone experiments, the results of the source calibration of the two Gallium solar neutrino experiments, and the recently hinted reactor anomaly. The SOX project will exploit two source…

Precision Muon Reconstruction in Double Chooz

We describe a muon track reconstruction algorithm for the reactor anti-neutrino experiment Double Chooz. The Double Chooz detector consists of two optically isolated volumes of liquid scintillator viewed by PMTs, and an Outer Veto above these made of crossed scintillator strips. Muons are reconstructed by their Outer Veto hit positions along with timing information from the other two detector volumes. All muons are fit under the hypothesis that they are through-going and ultrarelativistic. If the energy depositions suggest that the muon may have stopped, the reconstruction fits also for this hypothesis and chooses between the two via the relative goodness-of-fit. In the ideal case of a thro…

Calibration strategy of the JUNO experiment

We present the calibration strategy for the 20 kton liquid scintillator central detector of the Jiangmen Underground Neutrino Observatory (JUNO). By utilizing a comprehensive multiple-source and multiple-positional calibration program, in combination with a novel dual calorimetry technique exploiting two independent photosensors and readout systems, we demonstrate that the JUNO central detector can achieve a better than 1% energy linearity and a 3% effective energy resolution, required by the neutrino mass ordering determination. [Figure not available: see fulltext.]

Muon capture on light isotopes measured with the Double Chooz detector

Using the Double Chooz detector, designed to measure the neutrino mixing angle $\theta_{13}$, the products of $\mu^-$ capture on $^{12}$C, $^{13}$C, $^{14}$N and $^{16}$O have been measured. Over a period of 489.5 days, $2.3\times10^6$ stopping cosmic $\mu^-$ have been collected, of which $1.8\times10^5$ captured on carbon, nitrogen, or oxygen nuclei in the inner detector scintillator or acrylic vessels. The resulting isotopes were tagged using prompt neutron emission (when applicable), the subsequent beta decays, and, in some cases, $\beta$-delayed neutrons. The most precise measurement of the rate of $^{12}\mathrm C(\mu^-,\nu)^{12}\mathrm B$ to date is reported: $6.57^{+0.11}_{-0.21}\time…

Search for low-energy neutrinos from astrophysical sources with Borexino

We report on searches for neutrinos and antineutrinos from astrophysical sources performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy. Electron antineutrinos ($\bar{\nu}_e$) are detected in an organic liquid scintillator through the inverse $\beta$-decay reaction. In the present work we set model-independent upper limits in the energy range 1.8-16.8 MeV on neutrino fluxes from unknown sources that improve our previous results, on average, by a factor 2.5. Using the same data set, we first obtain experimental constraints on the diffuse supernova $\bar{\nu}_e$ fluxes in the previously unexplored region below 8 MeV. A search for $\bar{\nu}_e$ in the solar ne…

The $^{144}$Ce source for SOX

International audience; The SOX (Short distance neutrino Oscillations with BoreXino) project aims at testing the light sterile neutrino hypothesis. To do so, two artificials sources of antineutrinos and neutrinos respectively will be consecutively deployed at the Laboratori Nazionali del Gran Sasso (LNGS) in close vicinity to Borexino, a large liquid scintillator detector. This document reports on the source production and transportation. The source should exhibit a long lifetime and a high decay energy, a requirement fullfilled by the (144)Ce-(144)Pr pair at secular equilibrium. It will be produced at FSUE “Mayak” PA using spent nuclear fuel. It will then be shielded and packed according t…

Perspectives for CNO neutrino detection in Borexino

International audience; Borexino measured with unprecedented accuracy the fluxes of solar neutrinos emitted at all the steps of the pp fusion chain. Still missing is the measurement of the flux of neutrinos produced in the CNO cycle. A positive measurement of the CNO neutrino flux is of fundamental importance for understanding the evolution of stars and addressing the unresolved controversy on the solar abundances. The measurement of the CNO neutrino flux in Borexino is challenging because of the low intensity of this component (CNO cycle accounts for about 1% of the energy emitted by Sun), the lack of prominent spectral features and the presence of background sources. The main background c…

CeSOX: An experimental test of the sterile neutrino hypothesis with Borexino

International audience; The third phase of the Borexino experiment that’s referred to as SOX is devoted to test the hypothesis of the existence of one (or more) sterile neutrinos at a short baseline (~5–10m). The experimental measurement will be made with artificial sources namely with a 144Ce–144Pr antineutrino source at the first stage (CeSOX) and possibly with a 51Cr neutrino source at the second one. The fixed 144Ce–144Pr sample will be placed beneath the detector in a special pit and the initial activity will be about 100 – 150 kCi. The start of data taking is scheduled for April 2018. The article gives a short description of the preparation for the first stage and shows the expected s…

The Design and Sensitivity of JUNO's scintillator radiopurity pre-detector OSIRIS

The European physical journal / C 81(11), 973 (2021). doi:10.1140/epjc/s10052-021-09544-4

Radioactivity control strategy for the JUNO detector

JUNO is a massive liquid scintillator detector with a primary scientific goal of determining the neutrino mass ordering by studying the oscillated anti-neutrino flux coming from two nuclear power plants at 53 km distance. The expected signal anti-neutrino interaction rate is only 60 counts per day, therefore a careful control of the background sources due to radioactivity is critical. In particular, natural radioactivity present in all materials and in the environment represents a serious issue that could impair the sensitivity of the experiment if appropriate countermeasures were not foreseen. In this paper we discuss the background reduction strategies undertaken by the JUNO collaboration…

Understanding the detector behavior through Montecarlo and calibration studies in view of the SOX measurement

International audience; Borexino is an unsegmented neutrino detector operating at LNGS in central Italy. The experiment has shown its performances through its unprecedented accomplishments in the solar and geoneutrino detection. These performances make it an ideal tool to accomplish a state- of-the-art experiment able to test the existence of sterile neutrinos (SOX experiment). For both the solar and the SOX analysis, a good understanding of the detector response is fundamental. Consequently, calibration campaigns with radioactive sources have been performed over the years. The calibration data are of extreme importance to develop an accurate Monte Carlo code. This code is used in all the n…

Solar neutrino spectroscopy in Borexino

International audience; In more than ten years of operation, Borexino has performed a precision measurement of the solar neutrino spectrum, resolving almost all spectral components originating from the proton-proton fusion chain. The presentation will review the results recently released for the second data taking phase 2012–2016 during which the detector excelled by its unprecedentedly low background levels. New results on the rate of pp, 7Be, pep and 8B neutrinos as well as their implications for solar neutrino oscillations and metallicity are discussed.

JUNO sensitivity to low energy atmospheric neutrino spectra

Atmospheric neutrinos are one of the most relevant natural neutrino sources that can be exploited to infer properties about cosmic rays and neutrino oscillations. The Jiangmen Underground Neutrino Observatory (JUNO) experiment, a 20 kton liquid scintillator detector with excellent energy resolution is currently under construction in China. JUNO will be able to detect several atmospheric neutrinos per day given the large volume. A study on the JUNO detection and reconstruction capabilities of atmospheric $\nu_e$ and $\nu_\mu$ fluxes is presented in this paper. In this study, a sample of atmospheric neutrino Monte Carlo events has been generated, starting from theoretical models, and then pro…

Neutrino Physics with JUNO

The Jiangmen Underground Neutrino Observatory (JUNO), a 20 kton multi-purpose underground liquid scintillator detector, was proposed with the determination of the neutrino mass hierarchy as a primary physics goal. It is also capable of observing neutrinos from terrestrial and extra-terrestrial sources, including supernova burst neutrinos, diffuse supernova neutrino background, geoneutrinos, atmospheric neutrinos, solar neutrinos, as well as exotic searches such as nucleon decays, dark matter, sterile neutrinos, etc. We present the physics motivations and the anticipated performance of the JUNO detector for various proposed measurements. By detecting reactor antineutrinos from two power plan…

A calorimeter for the precise determination of the activity of the 144Ce-144Pr anti-neutrino source in the SOX experiment

We describe the design and the performance of a high precision thermal calorimeter, whose purpose was the measurement of the total activity of the 144Ce-144Pr anti-neutrino source of the SOX (Short distance neutrino Oscillation with BoreXino) experiment. SOX aimed at the search for eV-scale sterile neutrinos by means of the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy and of a very powerful artificial anti-neutrino source located at 8.51 m from the detector center. In order to obtain the required sensitivity, the activity of the source (approximately 150 kCi) had to be known at 1% precision. In this work we report the design of the experimental apparatus and the res…

Solar neutrino detectors as sterile neutrino hunters

International audience; The large size and the very low radioactive background of solar neutrino detectors such as Borexino at the Gran Sasso Laboratory in Italy offer a unique opportunity to probe the existence of neutrino oscillations into new sterile components by means of carefully designed and well calibrated anti-neutrino and neutrino artificial sources. In this paper we briefly summarise the key elements of the SOX experiment, a program for the search of sterile neutrinos (and other short distance effects) by means of a (144)Ce-(144)Pr anti-neutrino source and, possibly in the medium term future, with a (51)Cr neutrino source.

A White Paper on keV sterile neutrino Dark Matter

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrin…

Large underground, liquid based detectors for astro-particle physics in Europe: scientific case and prospects

This document reports on a series of experimental and theoretical studies conducted to assess the astro-particle physics potential of three future large-scale particle detectors proposed in Europe as next generation underground observatories. The proposed apparatus employ three different and, to some extent, complementary detection techniques: GLACIER (liquid Argon TPC), LENA (liquid scintillator) and MEMPHYS (\WC), based on the use of large mass of liquids as active detection media. The results of these studies are presented along with a critical discussion of the performance attainable by the three proposed approaches coupled to existing or planned underground laboratories, in relation to…

Potential for a precision measurement of solar pp neutrinos in the Serappis experiment

The European physical journal / C 82(9), 779 (2022). doi:10.1140/epjc/s10052-022-10725-y