As first suggested by U. Fano in the 1940s, the statistical fluctuation of the number of pairs produced in an ionizing interaction is known to be sub-Poissonian. The dispersion is reduced by the ...so-called “Fano factor,” which empirically encapsulates the correlations in the process of ionization. In modeling the energy response of an ionization measurement device, the effect of the Fano factor is commonly folded into the overall energy resolution. While such an approximate treatment is appropriate when a significant number of ionization pairs are expected to be produced, the Fano factor needs to be accounted for directly at the level of pair creation when only a few are expected. To do so, one needs a discrete probability distribution of the number of pairs created N with independent control of both the expectation μ and Fano factor F. Although no distribution P(N|μ,F) with this convenient form exists, we propose the use of the COM-Poisson distribution together with strategies for utilizing it to effectively fulfill this need. We then use this distribution to assess the impact that the Fano factor may have on the sensitivity of low-mass WIMP search experiments.
New Experiments With Spheres-Gas (NEWS-G) is a direct dark matter detection experiment using Spherical Proportional Counters (SPCs) with light noble gases to search for low-mass Weakly Interacting ...Massive Particles (WIMPs). We report the results from the first physics run taken at the Laboratoire Souterrain de Modane (LSM) with SEDINE, a 60 cm diameter prototype SPC operated with a mixture of Ne + CH4 (0.7%) at 3.1 bars for a total exposure of 9.6 kg · days. New constraints are set on the spin-independent WIMP-nucleon scattering cross-section in the sub-GeV/c2 mass region. We exclude cross-sections above 4.4×10−37cm2 at 90% confidence level (C.L.) for a 0.5 GeV/c2 WIMP. The competitive results obtained with SEDINE are promising for the next phase of the NEWS-G experiment: a 140 cm diameter SPC to be installed at SNOLAB by summer 2018.
The amount of energy released by a nuclear recoil ionizing the atoms of the active volume of detection appears “quenched” compared to an electron of the same kinetic energy. This different behavior ...in ionization between electrons and nuclei is described by the Ionization Quenching Factor (IQF) and it plays a crucial role in direct dark matter searches. For low kinetic energies (below
50
keV
), IQF measurements deviate significantly from common models used for theoretical predictions and simulations. We report measurements of the IQF for proton, an appropriate target for searches of Dark Matter candidates with a mass of approximately
1
GeV
, with kinetic energies in between
2
keV
and
13
keV
in
100
mbar
of methane. We used the Comimac facility in order to produce the motion of nuclei and electrons of controlled kinetic energy in the active volume, and a NEWS-G SPC to measure the deposited energy. The Comimac electrons are used as a reference to calibrate the detector with 7 energy points. A detailed study of systematic effects led to the final results well fitted by
IQF
(
E
K
)
=
E
K
α
/
(
β
+
E
K
α
)
with
α
=
0.70
±
0.08
and
β
=
1.32
±
0.17
. In agreement with some previous works in other gas mixtures, we measured less ionization energy than predicted from SRIM simulations, the difference reaching
33
%
at
2
keV
.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The EDELWEISS-II Collaboration has completed a direct search for WIMP dark matter with an array of ten 400-g cryogenic germanium detectors in operation at the Laboratoire Souterrain de Modane. The ...combined use of thermal phonon sensors and charge collection electrodes with an interleaved geometry enables the efficient rejection of γ-induced radioactivity as well as near-surface interactions. A total effective exposure of 384 kg d has been achieved, mostly coming from fourteen months of continuous operation. Five nuclear recoil candidates are observed above 20 keV, while the estimated background is 3.0 events. The result is interpreted in terms of limits on the cross-section of spin-independent interactions of WIMPs and nucleons. A cross-section of 4.4×10−8 pb is excluded at 90%CL for a WIMP mass of 85 GeV. New constraints are also set on models where the WIMP-nucleon scattering is inelastic.
New Experiments with Spheres-Gas (NEWS-G) is a dark matter direct detection experiment that will operate at SNOLAB (Canada). Similar to other rare-event searches, the materials used in the detector ...construction are subject to stringent radiopurity requirements. The detector features a 140-cm diameter proportional counter comprising two hemispheres made from commercially sourced 99.99% pure copper. Such copper is widely used in rare-event searches because it is readily available, there are no long-lived Cu radioisotopes, and levels of non-Cu radiocontaminants are generally low. However, measurements performed with a dedicated 210Po alpha counting method using an XIA detector confirmed a problematic concentration of 210Pb in bulk of the copper. To shield the proportional counter’s active volume, a low-background electroforming method was adapted to the hemispherical shape to grow a 500-µm thick layer of ultra-radiopure copper to the detector’s inner surface. In this paper the process is described, which was prototyped at Pacific Northwest National Laboratory (PNNL), USA, and then conducted at full scale in the Laboratoire Souterrain de Modane in France. The radiopurity of the electroplated copper was assessed through Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Measurements of samples from the first (second) hemisphere give 68% confidence upper limits of <0.58µBq/kg (<0.24µBq/kg) and <0.26µBq/kg (<0.11µBq/kg) on the 232Th and 238U contamination levels, respectively. These results are comparable to previously reported measurements of electroformed copper produced for other rare-event searches, which were also found to have low concentration of 210Pb consistent with the background goals of the NEWS-G experiment.
A review of the key developments in the Spherical Proportional Counter is presented. The detector technology and operation principles are described along with results, such as the low-energy ...calibration, and more recent advances, including the use of resistive materials and a multi-ball readout system. The Spherical Proportional Counter has been utilised by the NEWS-G experiment, performing a direct search for light DM candidates, and a review of the recent results is provided. Prospects for future applications of the technology are also discussed.
The excellent energy resolution and low threshold of cryogenic detectors have brought them to the forefront of the search for low-mass Weakly Interacting Massive Particles. The next generation of ...large cryogenic detectors for dark matter search promises further improvements in sensitivity, yet it is difficult and in some cases impossible to test and fully characterize these detectors in an unshielded environment. Therefore, the Queen's SuperCDMS team is installing a well shielded Cryogenic Underground detector TEst facility (CUTE) at SNOLAB to support detector testing and characterization for SuperCDMS and future cryogenic rare event search experiments. Significant effort is put into achieving a very low background environment which may open the door for early science results with the first set of SuperCDMS detectors during the time the main experimental apparatus is being installed. We discuss some of the challenges and solutions implemented in the design of this facility as well as the status and schedule for the start of operations underground at SNOLAB.
We present new constraints on the couplings of axions and more generic axion-like particles using data from the EDELWEISS-II experiment. The EDELWEISS experiment, located at the Underground ...Laboratory of Modane, primarily aims at the direct detection of WIMPs using germanium bolometers. It is also sensitive to the low-energy electron recoils that would be induced by solar or dark matter axions. Using a total exposure of up to 448 kg.d, we searched for axion-induced electron recoils down to 2.5 keV within four scenarios involving different hypotheses on the origin and couplings of axions. We set a 95 % CL limit on the coupling to photons g sub()A gamma < 2.15 x 10 super(-9)CeV super(-1) in a mass range not fully covered by axion helioscopes. We also constrain the coupling to electrons, g sub(Ae) < 2.59 x 10 super(-11), similar to the more indirect solar neutrino bound. Finally we place a limit on g sub()Ae x g super(eff) sub() AN < 4.82 x 10 super(-17), where g super(eff) sub() AN is the effective axion-nucleon coupling for super(57)Fe. Combining these results we fully exclude the mass range 0.92 eV < m sub(A) < 80 keV for DFSZ axions and 5.78 eV < m sub(A) < 40 keV for KSVZ axions.
The NEWS-G detector at SNOLAB Balogh, L.; Beaufort, C.; Brossard, A. ...
Journal of instrumentation,
02/2023, Letnik:
18, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
The New Experiments With Spheres-Gas (NEWS-G) collaboration
intends to achieve sub-GeV/c
2
Weakly Interacting
Massive Particles (WIMPs) detection using Spherical Proportional
Counters ...(SPCs). SPCs are gaseous detectors relying on ionisation
with a single ionization electron energy threshold. The latest
generation of SPC for direct dark matter searches has been installed
at SNOLAB in Canada in 2021. This article details the different
processes involved in the fabrication of the NEWS-G experiment. Also
outlined in this paper are the mitigation strategies, measurements
of radioactivity of the different components, and estimations of
induced background event rates that were used to quantify and
address detector backgrounds.
The Cryogenic Underground Test (CUTE) facility will be located 2 km underground in the SNOLAB laboratory, near Sudbury (Ontario, Canada). It is primarily designed to test the performances of ...cryogenic detectors of the Super-Cryogenic Dark Matter Search (SuperCDMS) experiment which will be installed next to CUTE. As a facility, it will also be accessible to scientists developing innovative cryogenic detectors for rare events search like dark matter or double-beta decay. The low temperature required to operate the cryogenic detectors is reached via an advanced dry dilution refrigerator from
CryoConcept
(France). The ‘Ultra Quiet Technique’ (UQT
®
) reduces the vibration transmission by using a proprietary gas-coupled thermal link between the two-stage pulse tube and the cryostat. In order to install the cryostat into a shielding water tank, we have developed a suspension system which decouples the cryostat from the environment with a low stiffness support, making a mechanical low-pass filter with a roll-off below 2 Hz for the vertical attenuation. We report the design choices made for the mechanical architecture to limit the vibration transmission and the material selection to achieve a low radioactive background rate in the detector. The expected background rate is less than 5 counts/day per kg of Ge detector in the 0–1 keV energy range.
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