554 research outputs found
Measurement of ortho-Positronium Properties in Liquid Scintillators
Pulse shape discrimination in liquid scintillator detectors is a
well-established technique for the discrimination of heavy particles from light
particles. Nonetheless, it is not efficient in the separation of electrons and
positrons, as they give rise to indistinguishable scintillator responses. This
inefficiency can be overtaken through the exploitation of the formation of
ortho-Positronium (o-Ps), which alters the time profile of light pulses induced
by positrons.
We characterized the o-Ps properties in the most commonly used liquid
scintillators, i.e. PC, PXE, LAB, OIL and PC + PPO. In addition, we studied the
effects of scintillator doping on the o-Ps properties for dopants currently
used in neutrino experiments, Gd and Nd. Further measurements for Li-loaded and
Tl-loaded liquid scintillators are foreseen. We found that the o-Ps properties
are suitable for enhancing the electron-positron discrimination.Comment: 4 pages, 1 figure. Contribution to proceedings of the Low
Radioactivity Techniques 2013 Workshop at LNGS, Assergi (AQ), Italy, April
10-12 201
A new anti-neutrino detection technique based on positronium tagging with plastic scintillators
The main signature for anti-neutrino detection in reactor and geo-neutrino
experiments based on scintillators is provided by the space-time coincidence of
positron and neutron produced in the Inverse Beta Decay reaction. Such a
signature strongly suppresses backgrounds and allows for measurements performed
underground with a relatively high signal-to-background ratio. In an
aboveground environment, however, the twofold coincidence technique is not
sufficient to efficiently reject the high background rate induced by cosmogenic
events. Enhancing the positron-neutron twofold coincidence efficiency has the
potential to pave the way future aboveground detectors for reactor monitoring.
We propose a new detection scheme based on a threefold coincidence, between the
positron ionization, the ortho-positronium (o-Ps) decay, and the neutron
capture, in a sandwich detector with alternated layers of plastic scintillator
and aerogel powder. We present the results of a set of dedicated measurements
on the achievable light yield and on the o-Ps formation and lifetime. The
efficiencies for signal detection and background rejection of a preliminary
detector design are also discussed.Comment: 18 pages, 10 figure
First Report on the Benthic Invertebrate Community Associated With a Bronze Naval Ram From the First Punic War: A Proxy of Marine Biodiversity
Historical traces of organisms on the seafloor, such as shells and tubes, constitute the
ecological memory of ancient benthic assemblages and serve as an important resource
for understanding the assembly of modern communities. Archeological shipwrecks are
particularly interesting submerged substrata for both their archeological and biological
implications. For the first time, we studied the species composition and life-history
traits of dominant organisms in the benthic assemblage on a bronze Carthaginian
naval ram, which sank more than two thousand years ago in the Southern Tyrrhenian
Sea. By comparing the species composition of the ram assemblage with those of
the surrounding habitats, we inferred possible colonization patterns for the ram and
discussed the informative role of the shipwreck as a proxy of marine biodiversity.
The ram assemblage was rich in species, including both sessile (bryozoans, serpulid
polychaetes, and few bivalves) and motile (gastropods) species. Sexual reproduction
with free-spawning fertilization and long-duration larvae characterized most species.
The long submersion time of the ram, together with the reproductive strategies, growth
forms, and motility of the dominant species were key factors shaping the community
of the ram. The ram itself offers an archeological artifact of inestimable value, but
our analysis revealed it to be an effective collector of fauna from the surrounding
seabed. The ram community hosted species from a range of nearby natural habitats
(mostly coralligenous, detritic bottoms, and zoosteracean meadows) and thus served
as a proxy for marine biodiversity on the surrounding seabed. We conclude that the
presence of many species on the ram that commonly occur in adjacent habitats of great
environmental value was informative and highlight the important marine biodiversity in
the area of the Aegadian archipelago
The Waveform Digitiser of the Double Chooz Experiment: Performance and Quantisation Effects on PhotoMultiplier Tube Signals
We present the waveform digitiser used in the Double Chooz experiment. We
describe the hardware and the custom-built firmware specifically developed for
the experiment. The performance of the device is tested with regards to
digitising low light level signals from photomultiplier tubes and measuring
pulse charge. This highlights the role of quantisation effects and leads to
some general recommendations on the design and use of waveform digitisers.Comment: 14 pages, 8 figures, accepted for publication in JINS
Measurement of the solar 8B neutrino rate with a liquid scintillator target and 3 MeV energy threshold in the Borexino detector
We report the measurement of electron neutrino elastic scattering from 8B
solar neutrinos with 3 MeV energy threshold by the Borexino detector in Gran
Sasso (Italy). The rate of solar neutrino-induced electron scattering events
above this energy in Borexino is 0.217 +- 0.038 (stat) +- 0.008 (syst) cpd/100
t, which corresponds to the equivalent unoscillated flux of (2.4 +- 0.4 (stat)
+- 0.1 (syst))x10^6 cm^-2 s^-1, in good agreement with measurements from SNO
and SuperKamiokaNDE. Assuming the 8B neutrino flux predicted by the high
metallicity Standard Solar Model, the average 8B neutrino survival probability
above 3 MeV is measured to be 0.29+-0.10. The survival probabilities for 7Be
and 8B neutrinos as measured by Borexino differ by 1.9 sigma. These results are
consistent with the prediction of the MSW-LMA solution of a transition in the
solar electron neutrino survival probability between the low energy
vacuum-driven and the high-energy matter-enhanced solar neutrino oscillation
regimes.Comment: 10 pages, 8 figures, 6 table
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Search for Solar Axions Produced in Reaction with Borexino Detector
A search for 5.5-MeV solar axions produced in the reaction was performed using the Borexino detector. The Compton
conversion of axions to photons, ; the
axio-electric effect, ; the decay of axions into
two photons, ; and inverse Primakoff conversion on
nuclei, , are considered. Model independent
limits on axion-electron (), axion-photon (), and
isovector axion-nucleon () couplings are obtained: and at 1 MeV (90% c.l.). These limits are
2-4 orders of magnitude stronger than those obtained in previous
laboratory-based experiments using nuclear reactors and accelerators.Comment: 11 pages, 7 figures, submitted to Phys.Rev.
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Measurement of geo-neutrinos from 1353 days of Borexino
We present a measurement of the geo--neutrino signal obtained from 1353 days
of data with the Borexino detector at Laboratori Nazionali del Gran Sasso in
Italy. With a fiducial exposure of (3.69 0.16) proton
year after all selection cuts and background subtraction, we detected
(14.3 4.4) geo-neutrino events assuming a fixed chondritic mass Th/U
ratio of 3.9. This corresponds to a geo-neutrino signal = (38.8
12.0) TNU with just a 6 probability for a null geo-neutrino
measurement. With U and Th left as free parameters in the fit, the relative
signals are = (10.6 12.7) TNU and =
(26.5 19.5) TNU. Borexino data alone are compatible with a mantle
geo--neutrino signal of (15.4 12.3) TNU, while a combined analysis with
the KamLAND data allows to extract a mantle signal of (14.1 8.1) TNU. Our
measurement of a reactor anti--neutrino signal =
84.5 TNU is in agreement with expectations in the presence of
neutrino oscillations.Comment: 9 pages, 6 figure
Low-energy (anti)neutrino physics with Borexino: Neutrinos from the primary proton-proton fusion process in the Sun
The Sun is fueled by a series of nuclear reactions that produce the energy
that makes it shine. The primary reaction is the fusion of two protons into a
deuteron, a positron and a neutrino. These neutrinos constitute the vast
majority of neutrinos reaching Earth, providing us with key information about
what goes on at the core of our star. Several experiments have now confirmed
the observation of neutrino oscillations by detecting neutrinos from secondary
nuclear processes in the Sun; this is the first direct spectral measurement of
the neutrinos from the keystone proton-proton fusion. This observation is a
crucial step towards the completion of the spectroscopy of pp-chain neutrinos,
as well as further validation of the LMA-MSW model of neutrino oscillations.Comment: Proceedings from NOW (Neutrino Oscillation Workshop) 201
Muon and Cosmogenic Neutron Detection in Borexino
Borexino, a liquid scintillator detector at LNGS, is designed for the
detection of neutrinos and antineutrinos from the Sun, supernovae, nuclear
reactors, and the Earth. The feeble nature of these signals requires a strong
suppression of backgrounds below a few MeV. Very low intrinsic radiogenic
contamination of all detector components needs to be accompanied by the
efficient identification of muons and of muon-induced backgrounds. Muons
produce unstable nuclei by spallation processes along their trajectory through
the detector whose decays can mimic the expected signals; for isotopes with
half-lives longer than a few seconds, the dead time induced by a muon-related
veto becomes unacceptably long, unless its application can be restricted to a
sub-volume along the muon track. Consequently, not only the identification of
muons with very high efficiency but also a precise reconstruction of their
tracks is of primary importance for the physics program of the experiment. The
Borexino inner detector is surrounded by an outer water-Cherenkov detector that
plays a fundamental role in accomplishing this task. The detector design
principles and their implementation are described. The strategies adopted to
identify muons are reviewed and their efficiency is evaluated. The overall muon
veto efficiency is found to be 99.992% or better. Ad-hoc track reconstruction
algorithms developed are presented. Their performance is tested against muon
events of known direction such as those from the CNGS neutrino beam, test
tracks available from a dedicated External Muon Tracker and cosmic muons whose
angular distribution reflects the local overburden profile. The achieved
angular resolution is 3-5 deg and the lateral resolution is 35-50 cm, depending
on the impact parameter of the crossing muon. The methods implemented to
efficiently tag cosmogenic neutrons are also presented.Comment: 42 pages. 32 figures on 37 files. Uses JINST.cls. 1 auxiliary file
(defines.tex) with TEX macros. submitted to Journal of Instrumentatio
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New experimental limits on the Pauli forbidden transitions in C nuclei obtained with 485 days Borexino data
The Pauli exclusion principle (PEP) has been tested for nucleons () in
with the Borexino detector.The approach consists of a search for
, , and emitted in a non-Paulian transition of
1- shell nucleons to the filled 1 shell in nuclei. Due to the
extremely low background and the large mass (278 t) of the Borexino detector,
the following most stringent up-to-date experimental bounds on PEP violating
transitions of nucleons have been established:
y, y,
y,
y and y, all at 90% C.L. The corresponding upper
limits on the relative strengths for the searched non-Paulian electromagnetic,
strong and weak transitions have been estimated: , and .Comment: 9 pages, 6 figure
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