16 research outputs found
Feasibility of high-voltage systems for a very long drift in liquid argon TPCs
Designs of high-voltage (HV) systems for creating a drift electric field in
liquid argon TPCs are reviewed. In ongoing experiments systems capable of
approx. 100 kV are realised for a drift field of 0.5-1 kV/cm over a length of
up to 1.5 m. Two of them having different approaches are presented: (1) the
ICARUS-T600 detector having a system consisting of an external power supply, HV
feedthroughs and resistive voltage degraders and (2) the ArDM-1t detector
having a cryogenic Greinacher HV multiplier inside the liquid argon volume. For
a giant scale liquid argon TPC, a system providing 2 MV may be required to
attain a drift length of approx. 20 m. Feasibility of such a system is
evaluated by extrapolating the existing designs.Comment: 8 pages, 13 figures, to appear in Proc. of 1st International Workshop
towards the Giant Liquid Argon Charge Imaging Experiment (GLA2010), Tsukuba
(Japan), March 201
First operation and drift field performance of a large area double phase LAr Electron Multiplier Time Projection Chamber with an immersed Greinacher high-voltage multiplier
We have operated a liquid-argon large-electron-multiplier time-projection
chamber (LAr LEM-TPC) with a large active area of 76 40 cm and a
drift length of 60 cm. This setup represents the largest chamber ever achieved
with this novel detector concept. The chamber is equipped with an immersed
built-in cryogenic Greinacher multi-stage high-voltage (HV) multiplier, which,
when subjected to an external AC HV of 1 kV, statically
charges up to a voltage a factor of 30 higher inside the LAr vessel,
creating a uniform drift field of 0.5 kV/cm over the full drift length.
This large LAr LEM-TPC was brought into successful operation in the
double-phase (liquid-vapor) operation mode and tested during a period of
1 month, recording impressive three-dimensional images of very
high-quality from cosmic particles traversing or interacting in the sensitive
volume. The double phase readout and HV systems achieved stable operation in
cryogenic conditions demonstrating their good characteristics, which
particularly suit applications for next-generation giant-scale LAr-TPCs.Comment: 26 pages, 19 figure
ArDM: a ton-scale liquid Argon experiment for direct detection of Dark Matter in the Universe
The ArDM project aims at developing and operating large noble liquid
detectors to search for direct evidence of Weakly Interacting Massive Particle
(WIMP) as Dark Matter in the Universe. The initial goal is to design, assemble
and operate a 1 ton liquid Argon prototype to demonstrate the
feasibility of a ton-scale experiment with the required performance to
efficiently detect and sufficiently discriminate backgrounds for a successful
WIMP detection. Our design addresses the possibility to detect independently
ionization and scintillation signals. In this paper, we describe this goal and
the conceptual design of the detector.Comment: 5 pages, 3 figures, Talk given at IXth international conference on
Topics in Astroparticle and Underground Physics (TAUP05), Zaragoza, (Spain
Nucleon Decay Searches with large Liquid Argon TPC Detectors at Shallow Depths: atmospheric neutrinos and cosmogenic backgrounds
Grand Unification of the strong, weak and electromagnetic interactions into a single unified gauge group is an extremely appealing idea which has been vigorously pursued theoretically and experimentally for many years. The detection of proton or bound-neutron decays would represent its most direct experimental evidence. In this context, we studied the physics potentialities of very large underground Liquid Argon Time Projection Chambers (LAr TPC). We carried out a detailed simulation of signal efficiency and background sources, including atmospheric neutrinos and cosmogenic backgrounds. We point out that a liquid Argon TPC, offering good granularity and energy resolution, low particle detection threshold, and excellent background discrimination, should yield very good signal over background ratios in many possible decay modes, allowing to reach partial lifetime sensitivities in the range of 1034−1035 years with exposures up to 1000 kton×year, often in quasi-background-free conditions optimal for discoveries at the few events level, corresponding to atmospheric neutrino background rejections of the order of 105. Multi-prong decay modes like e.g. p→μ−π+K+ or p→e+π+π− and channels involving kaons like e.g. p→K+ν¯, p→e+K0 and p→μ+K0 are particularly suitable, since liquid Argon imaging (...)This work was in part supported by ETH and the Swiss National Foundation. AB, AJM and SN have been supported by CICYT Grants FPA-2002-01835 and FPA-2005-07605-C02-01. SN acknowledges support from the Ramon y Cajal Programme. We thank P. Sala for help with FLUKA while she was an ETH employee
Searching for energetic cosmic axions in a laboratory experiment: testing the PVLAS anomaly
Astrophysical sources of energetic gamma rays provide the right conditions
for maximal mixing between (pseudo)scalar (axion-like) particles and photons if
their coupling is as strong as suggested by the PVLAS claim. This is
independent of whether or not the axion interaction is standard at all energies
or becomes supressed in the extreme conditions of the stellar interior. The
flux of such particles through the Earth could be observed using a metre long,
Tesla strength superconducting solenoid thus testing the axion interpretation
of the PVLAS anomaly. The rate of events in CAST caused by axions from the Crab
pulsar is also estimated for the PVLAS-favoured parameters.Comment: 5 pages, 3 figur
First results on light readout from the 1-ton ArDM liquid argon detector for dark matter searches
ArDM-1t is the prototype for a next generation WIMP detector measuring both
the scintillation light and the ionization charge from nuclear recoils in a
1-ton liquid argon target. The goal is to reach a minimum recoil energy of
30\,keVr to detect recoiling nuclei. In this paper we describe the experimental
concept and present results on the light detection system, tested for the first
time in ArDM on the surface at CERN. With a preliminary and incomplete set of
PMTs, the light yield at zero electric field is found to be between 0.3-0.5
phe/keVee depending on the position within the detector volume, confirming our
expectations based on smaller detector setups.Comment: 14 pages, 10 figures, v2 accepted for publication in JINS
Determining the WIMP mass from a single direct detection experiment, a more detailed study
The energy spectrum of nuclear recoils in Weakly Interacting Massive Particle
(WIMP) direct detection experiments depends on the underlying WIMP mass. We
study how the accuracy with which the WIMP mass could be determined by a single
direct detection experiment depends on the detector configuration and the WIMP
properties. We investigate the effects of varying the underlying WIMP mass and
cross-section, the detector target nucleus, exposure, energy threshold and
maximum energy, the local circular speed and the background event rate and
spectrum. The number of events observed is directly proportional to both the
exposure and the cross-section, therefore these quantities have the greatest
bearing on the accuracy of the WIMP mass determination. The relative
capabilities of different detectors to determine the WIMP mass depend not only
on the WIMP and target masses, but also on their energy thresholds. We find
that the rapid decrease of the nuclear form factor with increasing momentum
transfer which occurs for heavy nuclei, means that heavy nuclei will not
necessarily be able to measure the mass of heavy WIMPs more accurately.
Uncertainty in the local circular speed and non-negligible background would
both lead to systematic errors in the WIMP mass determination. With a single
detector it will be difficult to disentangle a WIMP signal (and the WIMP mass)
from background if the background spectrum has a similar shape to the WIMP
spectrum (i.e. exponential background, or flat background and a heavy WIMP).Comment: 20 pages, 11 figures, version to appear in JCAP, minor changes to
presentatio
The ArDM experiment
The aim of the ArDM project is the development and operation of a one ton
double-phase liquid argon detector for direct Dark Matter searches. The
detector measures both the scintillation light and the ionization charge from
ionizing radiation using two independent readout systems. This paper briefly
describes the detector concept and presents preliminary results from the ArDM
R&D program, including a 3 l prototype developed to test the charge readout
system.Comment: Proceedings of the Epiphany 2010 Conference, to be published in Acta
Physica Polonica
DM: a ton-scale LAr detector for direct Dark Matter searches
The Argon Dark Matter (ArDM-1t) experiment is a ton-scale liquid argon (LAr) double-phase time projection chamber designed for direct Dark Matter searches. Such a device allows to explore the low energy frontier in LAr with a charge imaging detector. The ionization charge is extracted from the liquid into the gas phase and there amplified by the use of a Large Electron Multiplier in order to reduce the detection threshold. Direct detection of the ionization charge with fine spatial granularity, combined with a measurement of the amplitude and time evolution of the associated primary scintillation light, provide powerful tools for the identification of WIMP interactions against the background due to electrons, photons and possibly neutrons if scattering more than once. A one ton LAr detector is presently installed on surface at CERN to fully test all functionalities and it will be soon moved to an underground location. We will emphasize here the lessons learned from such a device for the design of a large LAr TPC for neutrino oscillation, proton decay and astrophysical neutrinos searches
Development of wavelength shifter coated reflectors for the ArDM argon dark matter detector
To optimise the design of the light readout in the ArDM 1-ton liquid argon
dark matter detector, a range of reflector and WLS coating combinations were
investigated in several small setups, where argon scintillation light was
generated by radioactive sources in gas at normal temperature and pressure and
shifted into the blue region by tetraphenyl butadiene (TPB). Various
thicknesses of TPB were deposited by spraying and vacuum evaporation onto
specular 3M{\small\texttrademark}-foil and diffuse
Tetratex{\small\textregistered} (TTX) substrates. Light yields of each
reflector and TPB coating combination were compared. Reflection coefficients of
TPB coated reflectors were independently measured using a spectroradiometer in
a wavelength range between 200 and 650 nm. WLS coating on the PMT window was
also studied. These measurements were used to define the parameters of the
light reflectors of the ArDM experiment. Fifteen large cm
TTX sheets were coated and assembled in the detector. Measurements in argon gas
are reported providing good evidence of fulfilling the light collection
requirements of the experiment.Comment: 21 pages, 17 figure