1,721,258 research outputs found
Oxygen contamination in liquid Argon: combined effects on ionization electron charge and scintillation light
No full textA dedicated test of the effects of Oxygen contamination in liquid Argon has been
performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArP R&D program.
Two detectors have been used: the WArP 2.3 lt prototype and a small (0.7 lt) dedicated detector,
coupled with a system for the injection of controlled amounts of gaseous Oxygen.
O2 contamination in LAr leads to depletion of both the free electron charge (via attachment
process) and the scintillation light (via quenching and absorption mechanisms) available for ionization
signal detection. Purpose of the test with the 0.7 lt detector was to detect the reduction of
the long-lived component lifetime of the Argon scintillation light emission and of the overall light
yield at increasing O2 concentration. Data from theWArP prototype were used for determining the behavior of both the ionization electron lifetime and the scintillation long-lived component lifetime
at decreasing O2 concentration by the purification process activated in closed loop during the acquisition
run. The electron lifetime measurements allowed to infer the O2 content of the Argon and
correlate it with the long-lived scintillation lifetime data.
The effects of Oxygen contamination on the scintillation light have been thus extensively measured
over a wide range of O2 concentration, spanning from 103 ppm up to 10 ppm
Effects of Nitrogen and Oxygen contaminations in liquid Argon
No full textTwo dedicated and distinct tests of the effects of Nitrogen and Oxygen contaminations in liquid Argon (LAr) have been performed within the WArP R&D program. Purpose of the tests is to detect the reduction of the LAr scintillation light emission as a function of the amount of the contaminant injected in the Argon volume. The rate constant of the light quenching process induced by Nitrogen in LAr has been found to be kðN2 Þ 1⁄4 0:11 ms1 ppm1 (part per million), while the rate constant for Oxygen has been found to be k0 ðO2 Þ 1⁄4 0:54 0:03 ms1 ppm1 . Direct PMT signals acquisition allowed to extract with high precision the main characteristics of the scintillation light emission in pure and contaminated LAr. In particular, the decreasing behavior in lifetime and relative amplitude of the slow component is found to be appreciable from O (1 ppm) of Nitrogen concentrations and from O (0.1 ppm) of Oxygen concentrations
First Measurement of Neutrino and Antineutrino Coherent Charged Pion Production on Argon
No full textWe report on the first cross section measurements for charged current coherent pion production by neutrinos and antineutrinos on argon. These measurements are performed using the ArgoNeuT detector exposed to the NuMI beam at Fermilab. The cross sections are measured to be 2.6+1.2−1.0(stat)+0.3−0.4(syst)×10−38 cm2/Ar for neutrinos at a mean energy of 9.6 GeV and 5.5+2.6−2.1(stat)+0.6−0.7(syst)×10−39 cm2/Ar for antineutrinos at a mean energy of 3.6 GeV
Effects of Nitrogen contamination in liquid Argon
No full textA dedicated test of the effects of Nitrogen contamination in liquid Argon has been
performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArP R&D program.
A detector has been designed and assembled for this specific task and connected to a system
for the injection of controlled amounts of gaseous Nitrogen into the liquid Argon. The purpose of
the test is to detect the reduction of the Ar scintillation light emission as a function of the amount
of the Nitrogen contaminant injected in the Argon volume. A wide concentration range, spanning
from 101 ppm up to 103 ppm, has been explored.
Measurements have been done with electrons in the energy range of minimum ionizing particles
(g-conversion from radioactive sources). Source spectra at different Nitrogen contaminations
are analyzed, showing sensitive reduction of the scintillation yield at increasing concentrations.
Direct PMT signal acquisition exploiting high time resolution by fast waveform recording
allowed high precision extraction of the main characteristics of the scintillation light emission in
contaminated LAr. In particular, the decreasing behavior in lifetime and relative amplitude of the slow component is found to be appreciable starting from O(1 ppm) of Nitrogen concentrations.
The rate constant of the quenching process induced by Nitrogen in liquid Ar has been found to
be kQ(N2) = 0.11 0.01 ms1ppm1, consistent with a previous measurement of this quantity but
with significant improvement in precision. On the other hand, no evidence for absorption by N2
impurities has been found up to the higher concentrations here explored
Detection of back-to-back proton pairs in charged-current neutrino interactions with the ArgoNeuT detector in the NuMI low energy beam
No full textShort range nucleon-nucleon correlations in nuclei (NN SRC) carry important information on nuclear
structure and dynamics. NN SRC have been extensively probed through two-nucleon knockout reactions in
both pion and electron scattering experiments. We report here on the detection of two-nucleon knockout
events from neutrino interactions and discuss their topological features as possibly involving NN SRC
content in the target argon nuclei. The ArgoNeuT detector in the Main Injector neutrino beam at Fermilab
has recorded a sample of 30 fully reconstructed charged-current events where the leading muon is
accompanied by a pair of protons at the interaction vertex, 19 of which have both protons above the Fermi
momentum of the Ar nucleus. Out of these 19 events, four are found with the two protons in a strictly
back-to-back high momenta configuration directly observed in the final state and can be associated to
nucleon resonance pionless mechanisms involving a pre-existing short range correlated np pair in the
nucleus. Another fraction (four events) of the remaining 15 events has a reconstructed back-to-back
configuration of an np pair in the initial state, a signature compatible with one-body quasielastic interaction
on a neutron in a short range correlation (SRC) pair. The detection of these two subsamples of the collected
(μ− + 2p) events suggests that mechanisms directly involving nucleon-nucleon SRC pairs in the nucleus
are active and can be efficiently explored in neutrino-argon interactions with the Liquid Argon Time
Projection chamber technology
The WArP Experiment
No full textCryogenic noble liquid detectors are presently considered one of the best options for WIMP Dark Matter searches, especially when extensions to multi ton scale sensitive masses are foreseen. The WArP experiment is the first one that exploits the unique characteristics of liquid Argon to make a highly sensitive search for WIMP Dark Matter candidates. In 2008, a double phase detector has been assembled in the Gran Sasso National Laboratory with 140 kg sensitive mass and a discovery potential in the range of 5 x 10(-45) cm(2) in the spin-independent WIMP-nucleon cross-section. In addition to standard neutrons and gamma-rays passive shields, WArP implements an 8 ton liquid Argon active shield with 4 pi coverage. The detector was commissioned and put into operation during the first half of 2009 for a first technical run. Detector design, construction and assembly are described, together with the very first results of this technical run
Demonstration and Comparison of Photomultiplier Tubes at Liquid Argon Temperature
No full textLiquified noble gases are widely used as a target in direct Dark Matter searches.
Signals from scintillation in the liquid, following energy deposition from the re-coil nuclei scattered by Dark Matter particles (e.g. WIMPs), should be recorded down to very low energies by photosensors suitably designed to operate at cryogenic
temperatures. Liquid Argon based detectors for Dark Matter searches currently implement photo multiplier tubes for signal read-out. In the last few years PMTs with photocathodes operating down to liquid Argon temperatures (87 K) have been
specially developed with increasing Quantum Eciency characteristics. The most recent of these, Hamamatsu Photonics Mod. R11065 with peak QE up to about 35%, has been extensively tested within the R&D program of the WArP Collaboration.
During these testes the Hamamatsu PMTs showed superb performance and allowed obtaining a light yield around 7 phel/keVee in a Liquid Argon detector with a photocathodic coverage in the 12% range, sufficient for detection of events down to few
keVee of energy deposition. This shows that this new type of PMT is suited for
experimental applications, in particular for new direct Dark Matter searches with
LAr-based experiments
Neutron to Gamma Pulse Shape Discrimination in Liquid Argon Detectors with High Quantum Efficiency Photomultiplier Tubes
No full textA high Light Yield Liquid Argon chamber has been radiated with an Am/Be source for signal-to-background separation level characterization in a Dark Matter Liquid Argon based detector. Apart from the standard nuclear recoil and electron events, from neutron elastic interactions and gamma conversions respectively, an intermediate population has been observed which is attributed to inelastic neutron scatters on Argon nuclei producing Argon recoil and simultaneous gammas from nuclear de-excitation. Taking account of these events results in a better determination of the recoil-like to electron-like separation based on the shape of the scintillation pulse. The results of this recent study as well as from a previous study with a chamber with a lower Light Yield are presented
Measurements of inclusive muon neutrino and antineutrino charged current differential cross sections on argon in the NuMI antineutrino beam
No full textThe ArgoNeuT collaboration presents measurements of inclusive muon neutrino and antineutrino
charged current dierential cross sections on argon in the Fermilab NuMI beam operating in the
low energy antineutrino mode. The results are reported in terms of outgoing muon angle and
momentum at a mean neutrino energy of 9.6 GeV (neutrinos) and 3.6 GeV (antineutrinos), in the
range 0 < < 36 and 0 < p < 25 GeV/c, for both neutrinos and antineutrinos
The WArP Experiment
No full textCryogenic noble liquid detectors are presently considered one of the best options for
WIMP Dark Matter searches, especially when extensions to multi ton scale sensitive masses
are foreseen. The WArP experiment is the first one that exploits the unique characteristics of
liquid Argon to make a highly sensitive search for WIMP Dark Matter candidates. In 2008, a
double phase detector has been assembled in the Gran Sasso National Laboratory with 140 kg
sensitive mass and a discovery potential in the range of 5 x 10-45 cm2 in the spin-independent
WIMP-nucleon cross-section. In addition to standard neutrons and gamma-rays passive
shields, WArP implements an 8 ton liquid Argon active shield with 4! coverage. The detector
was commissioned and put into operation during the first half of 2009 for a first technical run.
This first run lasted about three months and then it was stopped for some detector repairs and
modifications in the summer of 2009. A second run was started at the beginning of 2010.
Detector design, construction and assembly are described, together with the results of the
technical run and the very first results of the 2010 run
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