195 research outputs found
Suitability of high-pressure xenon as scintillator for gamma ray spectroscopy
In this paper we report the experimental study of high-pressure xenon used as
a scintillator, in the context of developing a gamma ray detector. We measure a
light yield near 2 photoelectrons per keV for xenon at 40 bar. Together with
the light yield, we also measured an energy resolution of ~9% (FWHM) at 662
keV, dominated by the statistical fluctuations in the number of photoelectrons.Comment: 15 pages, 11 figure
Silicon photomultiplier readout of a scintillating noble gas detector for homeland security
Detectors based on scintillation by high pressure 4He are a viable technology for instruments against the illicit trafficking of nuclear material. A design based on the use of solid state photodetectors is presented in this paper and the preliminary qualification discussed
First operation and performance of a 200 lt double phase LAr LEM-TPC with a 40x76 cm^2 readout
In this paper we describe the design, construction, and operation of a first
large area double-phase liquid argon Large Electron Multiplier Time Projection
Chamber (LAr LEM-TPC). The detector has a maximum drift length of 60 cm and the
readout consists of a cm LEM and 2D projective anode to
multiply and collect drifting charges. Scintillation light is detected by means
of cryogenic PMTs positioned below the cathode. To record both charge and light
signals, we have developed a compact acquisition system, which is scalable up
to ton-scale detectors with thousands of charge readout channels. The
acquisition system, as well as the design and the performance of custom-made
charge sensitive preamplifiers, are described. The complete experimental setup
has been operated for a first time during a period of four weeks at CERN in the
cryostat of the ArDM experiment, which was equipped with liquid and gas argon
purification systems. The detector, exposed to cosmic rays, recorded events
with a single-channel signal-to-noise ratio in excess of 30 for minimum
ionising particles. Cosmic muon tracks and their -rays were used to
assess the performance of the detector, and to estimate the liquid argon purity
and the gain at different amplification fields.Comment: 23 pages, 21 figure
Positronium Portal into Hidden Sector: A new Experiment to Search for Mirror Dark Matter
The understanding of the origin of dark matter has great importance for
cosmology and particle physics. Several interesting extensions of the standard
model dealing with solution of this problem motivate the concept of hidden
sectors consisting of SU(3)xSU(2)_LxU(1)_Y singlet fields. Among these models,
the mirror matter model is certainly one of the most interesting. The model
explains the origin of parity violation in weak interactions, it could also
explain the baryon asymmetry of the Universe and provide a natural ground for
the explanation of dark matter. The mirror matter could have a portal to our
world through photon-mirror photon mixing (epsilon). This mixing would lead to
orthopositronium (o-Ps) to mirror orthopositronium oscillations, the
experimental signature of which is the apparently invisible decay of o-Ps. In
this paper, we describe an experiment to search for the decay o-Ps -> invisible
in vacuum by using a pulsed slow positron beam and a massive 4pi BGO crystal
calorimeter. The developed high efficiency positron tagging system, the low
calorimeter energy threshold and high hermiticity allow the expected
sensitivity in mixing strength to be epsilon about 10^-9, which is more than
one order of magnitude below the current Big Bang Nucleosynthesis limit and in
a region of parameter space of great theoretical and phenomenological interest.
The vacuum experiment with such sensitivity is particularly timely in light of
the recent DAMA/LIBRA observations of the annual modulation signal consistent
with a mirror type dark matter interpretation.Comment: 40 pages, 29 Figures 2 Tables v2: Ref. added, Fig. 29 and some text
added to explain idea for backscattering e+ background suppression, corrected
typos v3: minor corrections: Eq 2.1 corrected (6 lines-> 5 lines), Eq.2.17:
two extra "-" signs remove
A First Comparison of the responses of a He4-based fast-neutron detector and a NE-213 liquid-scintillator reference detector
A first comparison has been made between the pulse-shape discrimination
characteristics of a novel He-based pressurized scintillation detector
and a NE-213 liquid-scintillator reference detector using an Am/Be mixed-field
neutron and gamma-ray source and a high-resolution scintillation-pulse
digitizer. In particular, the capabilities of the two fast neutron detectors to
discriminate between neutrons and gamma-rays were investigated. The NE-213
liquid-scintillator reference cell produced a wide range of scintillation-light
yields in response to the gamma-ray field of the source. In stark contrast, due
to the size and pressure of the He gas volume, the He-based
detector registered a maximum scintillation-light yield of 750~keV to
the same gamma-ray field. Pulse-shape discrimination for particles with
scintillation-light yields of more than 750~keV was excellent in the
case of the He-based detector. Above 750~keV its signal was
unambiguously neutron, enabling particle identification based entirely upon the
amount of scintillation light produced.Comment: 23 pages, 7 figures, Nuclear Instruments and Methods in Physics
Research Section A review addresse
An Improved Limit on Invisible Decays of Positronium
The results of a new search for positronium decays into invisible final
states are reported. Convincing detection of this decay mode would be a strong
evid ence for new physics beyond the Standard Model (SM): for example the
existence of extra--dimensions, of milli-charged particles, of new light gauge
bosons or of mirror particles. Mirror matter could be a relevant dark matter
candidate.
In this paper the setup and the results of a new experiment are presented. In
a collected sample of about orthopositronium decay
s, no evidence for invisible decays in an energy window [0,80] keV was found
and an upper limit on the branching ratio of orthopositronium \invdecay could
be set: \binvdecay<4.2\times 10^{-7} (90% C.L.)
Our results provide a limit on the photon mirror-photon mixing strength
(90% C.L.) and rule out particles lighter
than the electron mass with a fraction of the
electron charge. Furthermore, upper limits on the branching ratios for the
decay of parapositronium (90%
C.L.) and the direct annihilation (90% C.L.) could be set.Comment: 17 pages, 7 figures, added references, fixed limit on millicharged
particles and changed two plots accordingl
Positron annihilation in latex templated macroporous silica films: pore size and ortho-positronium escape
International audienceDepth profling of positron annihilation characteristics has been used to investigate the pore size distribution in macroporous PMMA latex templated SiO2 films deposited on glass or Si and prepared with 11-70% porosity. The correlation between the annihilation characteristics shows that o-Ps escape (re-emission) into vacuum occurs in all films with a porosity threshold that is pore size dependent. For 60 ± 2% porosity, the o-Ps reemission yield decreases from ~ 0:25 to ~ 0:11 as the pore size increases from 32 to 75 nm. The o-Ps reemission yield is shown to vary linearly with the specific surface area per mass unit and the slope is independent of pore size, 9:1±0:4 g cm-1. For 32 nm pores, the o-Ps annihilation lifetimes in the films, 17(2)ns and 106(5) ns, show that o-Ps annihilates from micropores with small effective size (1:4 ± 4 nm) and from macropores with large effective size (~ 32 nm). Above the porosity threshold, the o-Ps-escape model predicts the annihilation lifetime in the films to be 19±2 ns. Our results imply that o-Ps effciently detects the microporosity present in the silica walls. At low porosity, its capture into the micropores competes with its capture into the macropores. At higher porosity (when the distance between micropores and macropores become small), this capture into the micropores assists the capture into the macropores
ArDM: first results from underground commissioning
The Argon Dark Matter experiment is a ton-scale double phase argon Time
Projection Chamber designed for direct Dark Matter searches. It combines the
detection of scintillation light together with the ionisation charge in order
to discriminate the background (electron recoils) from the WIMP signals
(nuclear recoils). After a successful operation on surface at CERN, the
detector was recently installed in the underground Laboratorio Subterr\'aneo de
Canfranc, and the commissioning phase is ongoing. We describe the status of the
installation and present first results from data collected underground with the
detector filled with gas argon at room temperature.Comment: 6 pages, 3 figures, Light Detection In Noble Elements (LIDINE 2013
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
Status of the ArDM Experiment: First results from gaseous argon operation in deep underground environment
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. After
successful operation on surface at CERN, the detector has been deployed
underground and is presently commissioned at the Canfranc Underground
Laboratory (LSC). In this paper, we describe the status of the installation and
present first results on data collected in gas phase.Comment: 21 pages, 20 figure
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