38 research outputs found
Antineutrino Geophysics with Liquid Scintillator Detectors
Detecting the antineutrinos emitted by the decay of radioactive elements in
the mantle and crust could provide a direct measurement of the total abundance
of uranium and thorium in the Earth. In calculating the antineutrino flux at
specific sites, the local geology of the crust and the background from the
world's nuclear power reactors are important considerations. Employing a global
crustal map, with type and thickness data, and using recent estimates of the
uranium and thorium distribution in the Earth, we calculate the antineutrino
event rate for two new neutrino detectors. We show that spectral features allow
terrestrial antineutrino events to be identified above reactor antineutrino
backgrounds and that the uranium and thorium contributions can be separately
determined.Comment: Published paper differs from original submitted preprint because
reviewers suggested updated continental crust U/Th abundances. Kamioka
geographical location error was in preprint, partially corrected in published
version. This version is the same as the published paper, with Kamioka fully
corrected. Because of recent interest in this topic, this version is being
made available, despite this work being 8 years ol
Final results of Borexino Phase-I on low energy solar neutrino spectroscopy
Borexino has been running since May 2007 at the LNGS with the primary goal of
detecting solar neutrinos. The detector, a large, unsegmented liquid
scintillator calorimeter characterized by unprecedented low levels of intrinsic
radioactivity, is optimized for the study of the lower energy part of the
spectrum. During the Phase-I (2007-2010) Borexino first detected and then
precisely measured the flux of the 7Be solar neutrinos, ruled out any
significant day-night asymmetry of their interaction rate, made the first
direct observation of the pep neutrinos, and set the tightest upper limit on
the flux of CNO neutrinos. In this paper we discuss the signal signature and
provide a comprehensive description of the backgrounds, quantify their event
rates, describe the methods for their identification, selection or subtraction,
and describe data analysis. Key features are an extensive in situ calibration
program using radioactive sources, the detailed modeling of the detector
response, the ability to define an innermost fiducial volume with extremely low
background via software cuts, and the excellent pulse-shape discrimination
capability of the scintillator that allows particle identification. We report a
measurement of the annual modulation of the 7 Be neutrino interaction rate. The
period, the amplitude, and the phase of the observed modulation are consistent
with the solar origin of these events, and the absence of their annual
modulation is rejected with higher than 99% C.L. The physics implications of
phase-I results in the context of the neutrino oscillation physics and solar
models are presented
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Spectroscopy of geo-neutrinos from 2056 days of Borexino data
We report an improved geo-neutrino measurement with Borexino from 2056 days
of data taking. The present exposure is
protonyr. Assuming a chondritic Th/U mass ratio of 3.9, we obtain geo-neutrino events. The null
observation of geo-neutrinos with Borexino alone has a probability of (5.9). A geo-neutrino signal from the mantle is
obtained at 98\% C.L. The radiogenic heat production for U and Th from the
present best-fit result is restricted to the range 23-36 TW, taking into
account the uncertainty on the distribution of heat producing elements inside
the Earth.Comment: 4 pages, 4 figure
Measurement of neutrino flux from the primary proton--proton fusion process in the Sun with Borexino detector
Neutrino produced in a chain of nuclear reactions in the Sun starting from
the fusion of two protons, for the first time has been detected in a real-time
detector in spectrometric mode. The unique properties of the Borexino detector
provided an oppurtunity to disentangle pp-neutrino spectrum from the background
components. A comparison of the total neutrino flux from the Sun with Solar
luminosity in photons provides a test of the stability of the Sun on the
10 years time scale, and sets a strong limit on the power production in
the unknown energy sources in the Sun of no more than 4\% of the total energy
production at 90\% C.L.Comment: 15 pages, 2 tables, 3 figure
Cosmogenic Backgrounds in Borexino at 3800 m water-equivalent depth
The solar neutrino experiment Borexino, which is located in the Gran Sasso
underground laboratories, is in a unique position to study muon-induced
backgrounds in an organic liquid scintillator. In this study, a large sample of
cosmic muons is identified and tracked by a muon veto detector external to the
liquid scintillator, and by the specific light patterns observed when muons
cross the scintillator volume. The yield of muon-induced neutrons is found to
be Yn =(3.10+-0.11)10-4 n/({\mu} (g/cm2)). The distance profile between the
parent muon track and the neutron capture point has the average value {\lambda}
= (81.5 +- 2.7)cm. Additionally the yields of a number of cosmogenic
radioisotopes are measured for 12N, 12B, 8He, 9C, 9Li, 8B, 6He, 8Li, 11Be, 10C
and 11C. All results are compared with Monte Carlo simulation predictions using
the Fluka and Geant4 packages. General agreement between data and simulation is
observed for the cosmogenic production yields with a few exceptions, the most
prominent case being 11C yield for which both codes return about 50% lower
values. The predicted {\mu}-n distance profile and the neutron multiplicity
distribution are found to be overall consistent with data.Comment: 26 pages, 13 figures (in 14 files), 4 tables. 3 extra data files.
accepted by JCA
Large-scale liquid scintillation detectors for solar neutrinos
Large-scale liquid scintillation detectors are capable of providing spectral yields of the low energy solar neutrinos. These detectors require > 100 tons of liquid scintillator with high optical and radiopurity. In this paper requirements for low-energy neutrino detection by liquid scintillation are specified and the procedures to achieve low backgrounds in large-scale liquid scintillation detectors for solar neutrinos are reviewed. The designs, operations and achievements of Borexino, KamLAND and SNO+ in measuring the low-energy solar neutrino fluxes are reviewed
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Experimental evidence of neutrinos produced in the CNO fusion cycle in the Sun
For most of their existence, stars are fuelled by the fusion of hydrogen into helium.
Fusion proceeds via two processes that are well understood theoretically: the proton–
proton (pp) chain and the carbon–nitrogen–oxygen (CNO) cycle1,2
. Neutrinos that are
emitted along such fusion processes in the solar core are the only direct probe of the
deep interior of the Sun. A complete spectroscopic study of neutrinos from the pp
chain, which produces about 99 per cent of the solar energy, has been performed
previously3
; however, there has been no reported experimental evidence of the CNO
cycle. Here we report the direct observation, with a high statistical significance, of
neutrinos produced in the CNO cycle in the Sun. This experimental evidence was
obtained using the highly radiopure, large-volume, liquid-scintillator detector of
Borexino, an experiment located at the underground Laboratori Nazionali del Gran
Sasso in Italy. The main experimental challenge was to identify the excess signal—only
a few counts per day above the background per 100 tonnes of target—that is
attributed to interactions of the CNO neutrinos. Advances in the thermal stabilization
of the detector over the last five years enabled us to develop a method to constrain the
rate of bismuth-210 contaminating the scintillator. In the CNO cycle, the fusion of
hydrogen is catalysed by carbon, nitrogen and oxygen, and so its rate—as well as the
flux of emitted CNO neutrinos—depends directly on the abundance of these elements
in the solar core. This result therefore paves the way towards a direct measurement of
the solar metallicity using CNO neutrinos. Our findings quantify the relative
contribution of CNO fusion in the Sun to be of the order of 1 per cent; however, in
massive stars, this is the dominant process of energy production. This work provides
experimental evidence of the primary mechanism for the stellar conversion of
hydrogen into helium in the Universe
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DarkSide-50: a WIMP search with a two-phase argon TPC
DarkSide-50 is a two phase argon TPC for direct dark matter detection which is installed at the Gran Sasso underground laboratory, Italy. DarkSide-50 has a 50-kg active volume and will make use of underground argon low in Ar-39. The TPC is installed inside an active neutron veto made with boron-loaded high radiopurity liquid scintillator. The neutron veto is installed inside a 1000 m(3) water Cherenkov muon veto. The DarkSide-50 TPC and cryostat are assembled in two radon-free clean rooms to reduce radioactive contaminants. The overall design aims for a background free exposure after selection cuts are applied. The expected sensitivity for WIMP-nucleon cross section is of the order of 10(-45) cm(2) for WIMP masses around 100 GeV/c(2). The commissioning and performance of the detector are described. Details of the low-radioactivity underground argon and other unique features of the projects are reported. (C) 2015 The Authors. Published by Elsevier B.V
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