95 research outputs found
Demonstration and Comparison of Operation of Photomultiplier Tubes at Liquid Argon Temperature
Liquified noble gases are widely used as a target in direct Dark Matter
searches. Signals from scintillation in the liquid, following energy deposition
from the recoil 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
Efficiency 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
Galactic axions search with a superconducting resonant cavity
To account for the dark matter content in our Universe, post-inflationary
scenarios predict for the QCD axion a mass in the range
(10-10^3)\,\mu\mbox{eV}. Searches with haloscope experiments in this mass
range require the monitoring of resonant cavity modes with frequency above
5\,GHz, where several experimental limitations occur due to linear amplifiers,
small volumes, and low quality factors of Cu resonant cavities. In this paper
we deal with the last issue, presenting the result of a search for galactic
axions using a haloscope based on a 36\,\mbox{cm}^3 NbTi superconducting
cavity. The cavity worked at T=4\,\mbox{K} in a 2\,T magnetic field and
exhibited a quality factor for the TM010 mode at 9\,GHz.
With such values of the axion signal is significantly increased with
respect to copper cavity haloscopes. Operating this setup we set the limit
g_{a\gamma\gamma}<1.03\times10^{-12}\,\mbox{GeV}^{-1} on the axion photon
coupling for a mass of about 37\,eV. A comprehensive study of the NbTi
cavity at different magnetic fields, temperatures, and frequencies is also
presented
Measurement of the specific activity of Ar-39 in natural argon
We report on the measurement of the specific activity of Ar-39 in natural
argon. The measurement was performed with a 2.3-liter two-phase (liquid and
gas) argon drift chamber. The detector was developed by the WARP Collaboration
as a prototype detector for WIMP Dark Matter searches with argon as a target.
The detector was operated for more than two years at Laboratori Nazionali del
Gran Sasso, Italy, at a depth of 3,400 m w.e. The specific activity measured
for Ar-39 is 1.01 +/- 0.02(stat) +/- 0.08(syst) Bq per kg of natural Ar.Comment: 11 pages, 6 figures, to be submitted to Nucl. Instrum. Methods
Discovery of underground argon with low level of radioactive 39Ar and possible applications to WIMP dark matter detectors
We report on the first measurement of 39Ar in argon from underground natural
gas reservoirs. The gas stored in the US National Helium Reserve was found to
contain a low level of 39Ar. The ratio of 39Ar to stable argon was found to be
<=4x10-17 (84% C.L.), less than 5% the value in atmospheric argon
(39Ar/Ar=8x10-16). The total quantity of argon currently stored in the National
Helium Reserve is estimated at 1000 tons. 39Ar represents one of the most
important backgrounds in argon detectors for WIMP dark matter searches. The
findings reported demonstrate the possibility of constructing large multi-ton
argon detectors with low radioactivity suitable for WIMP dark matter searches.Comment: 6 pages, 2 figures, 2 table
First results from a Dark Matter search with liquid Argon at 87 K in the Gran Sasso Underground Laboratory
A new method of searching for dark matter in the form of weakly interacting
massive particles (WIMP) has been developed with the direct detection of the
low energy nuclear recoils observed in a massive target (ultimately many tons)
of ultra pure Liquid Argon at 87 K. A high selectivity for Argon recoils is
achieved by the simultaneous observation of both the VUV scintillation
luminescence and of the electron signal surviving columnar recombination,
extracted through the liquid-gas boundary by an electric field. First physics
results from this method are reported, based on a small 2.3 litre test chamber
filled with natural Argon and an accumulated fiducial exposure of about 100 kg
x day, supporting the future validity of this method with isotopically purified
40Ar and for a much larger unit presently under construction with
correspondingly increased sensitivities.Comment: 26 pages, 8 figures, submitted to astroparticle physic
Oxygen contamination in liquid Argon: combined effects on ionization electron charge and scintillation light
A 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. Purpose of the test with the 0.7 lt
detector is to detect the reduction of the long-lived component lifetime of the
Argon scintillation light emission at increasing O2 concentration. Data from
the WArP prototype are used for determining the behavior of both the ionization
electron lifetime and the scintillation long-lived component lifetime during
the O2-purification process activated in closed loop during the acquisition
run. The electron lifetime measurements allow to infer the O2 content of the
Argon and correlate it with the long-lived scintillation lifetime data. The
effect of Oxygen contamination on the scintillation light has been thus
measured over a wide range of O2 concentration, spanning from about 10^-3 ppm
up to about 10 ppm. The rate constant of the light quenching process induced by
Oxygen in LAr has been found to be k'(O2)=0.54+-0.03 micros^-1 ppm^-1
Effects of Nitrogen contamination in liquid Argon
A 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. 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 about 10^-1 ppm up to about 10^3 ppm, has been explored.
Measurements have been done with electrons in the energy range of minimum
ionizing particles (gamma-conversion from radioactive sources). Source spectra
at different Nitrogen contaminations are analyzed, showing sensitive reduction
of the scintillation yield at increasing concentrations. The rate constant of
the light quenching process induced by Nitrogen in liquid Ar has been found to
be k(N2)=0.11 micros^-1 ppm^-1. Direct PMT signals acquisition at high time
resolution by fast Waveform recording 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
the warp dark matter search
WArP is a graded programme to search for Wimp dark matter with liquid argon. The WArP 100l detector is being assembled and should start data taking in the next few months. We expect to increase the sensitivity of about a factor 100 with respect to the 2.3 liters protoype, which has been operational since 2005, allowing for an intense R&D programme that has given us insight to crucial LAr properties. The current status of the experiment and the main results obtained with the prototype are reviewed
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