We present the first Ge-based constraints on sub-MeV /c2 dark matter (DM) particles interacting with electrons using a 33.4 g Ge cryogenic detector with a 0.53 electron-hole pair (rms) resolution, ...operated underground at the Laboratoire Souterrain de Modane. Competitive constraints are set on the DM-electron scattering cross section, as well as on the kinetic mixing parameter of dark photons down to 1 eV / c2. In particular, the most stringent limits are set for dark photon DM in the 6 to 9 eV / c2 range. These results demonstrate the high relevance of Ge cryogenic detectors for the search of DM-induced eV-scale electron signals.
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.
Cryogenic germanium detectors used in dark matter searches operate at ranges of low temperature
<
100
mK
and electric field
∼
1
V
/
cm
such that charge trapping in the bulk of the detector plays a ...significant role in the net charge collected following a particle interaction. It is shown that in EDELWEISS FID800 detectors, these trapped charges induce residual charge signals that perturb the measurement of the total charge, significantly degrading the energy resolution at high energy. It is also shown that, by reading out the signal on all the electrodes, it is possible to clearly identify these effects and correct the total charge measurement accordingly, resulting in a
∼
30 % improvement of the resolution at high energy. This effect is demonstrated with data. A simple analytical model based on Shockley-Ramo’s theorem is presented, whereby this effect is due to the position dependence of signals induced by trapped charges.
The physics potential of EDELWEISS detectors for the search of low-mass weakly interacting massive particles (WIMPs) is studied. Using a data-driven background model, projected exclusion limits are ...computed using frequentist and multivariate analysis approaches, namely, profile likelihood and boosted decision tree. Both current and achievable experimental performances are considered. The optimal strategy for detector optimization depends critically on whether the emphasis is put on WIMP masses below or above ∼5 GeV/c2. The projected sensitivity for the next phase of the EDELWEISS-III experiment at the Modane Underground Laboratory (LSM) for low-mass WIMP search is presented. By 2018 an upper limit on the spin-independent WIMP-nucleon cross section of σSI=7×10−42 cm2 is expected for a WIMP mass in the range 2–5 GeV/c2. The requirements for a future hundred-kilogram-scale experiment designed to reach the bounds imposed by the coherent scattering of solar neutrinos are also described. By improving the ionization resolution down to 50 eVee, we show that such an experiment installed in an even lower background environment (e.g., at SNOLAB) together with an exposure of 1000 kg·yr, should allow us to observe about 80 B8 neutrino events after discrimination.
We report on a dark matter search for a Weakly Interacting Massive Particle (WIMP) in the mass range
m
χ
∈
4
,
30
GeV
/
c
2
with the EDELWEISS-III experiment. A 2D profile likelihood analysis is ...performed on data from eight selected detectors with the lowest energy thresholds leading to a combined fiducial exposure of 496 kg-days. External backgrounds from
γ
- and
β
-radiation, recoils from
206
Pb
and neutrons as well as detector intrinsic backgrounds were modelled from data outside the region of interest and constrained in the analysis. The basic data selection and most of the background models are the same as those used in a previously published analysis based on boosted decision trees (BDT)
1
. For the likelihood approach applied in the analysis presented here, a larger signal efficiency and a subtraction of the expected background lead to a higher sensitivity, especially for the lowest WIMP masses probed. No statistically significant signal was found and upper limits on the spin-independent WIMP-nucleon scattering cross section can be set with a hypothesis test based on the profile likelihood test statistics. The 90 % C.L. exclusion limit set for WIMPs with
m
χ
=
4
GeV
/
c
2
is
1.6
×
10
-
39
cm
2
, which is an improvement of a factor of seven with respect to the BDT-based analysis. For WIMP masses above
15
GeV
/
c
2
the exclusion limits found with both analyses are in good agreement.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present the results of measurements demonstrating the efficiency of the EDELWEISS-III array of cryogenic germanium detectors for direct dark matter searches. The experimental setup and the FID ...(Fully Inter-Digitized) detector array is described, as well as the efficiency of the double measurement of heat and ionization signals in background rejection. For the whole set of 24 FID detectors used for coincidence studies, the baseline resolutions for the fiducial ionization energy are mainly below 0.7 keVee (FHWM) whereas the baseline resolutions for heat energies are mainly below 1.5 keVee (FWHM). The response to nuclear recoils as well as the very good discrimination capability of the FID design has been measured with an AmBe source. The surface β- and α-decay rejection power of Rsurf<4×10−5 per α at 90% C.L. has been determined with a 210Pb source, the rejection of bulk γ-ray events has been demonstrated using γ-calibrations with 133Ba sources leading to a value of Rγ−mis−fid<2.5×10−6 at 90% C.L.. The current levels of natural radioactivity measured in the detector array are shown as the rate of single γ background. The fiducial volume fraction of the FID detectors has been measured to a weighted average value of (74.6±0.4)% using the cosmogenic activation of the 65Zn and 68,71Ge isotopes. The stability and uniformity of the detector response is also discussed. The achieved resolutions, thresholds and background levels of the upgraded EDELWEISS-III detectors in their setup are thus well suited to the direct search of WIMP dark matter over a large mass range.
High Impedance TES Bolometers for EDELWEISS Marnieros, S.; Armengaud, E.; Arnaud, Q. ...
Journal of low temperature physics,
06/2023, Letnik:
211, Številka:
5-6
Journal Article
Recenzirano
Odprti dostop
The EDELWEISS collaboration aims for direct detection of light dark matter using germanium cryogenic detectors with low threshold phonon sensor technologies and efficient charge readout designs. We ...describe here the development of Ge bolometers equipped with high impedance thermistors based on a Nb
x
Si
1−x
TES alloy. High aspect ratio spiral designs allow the TES impedance to match with JFET or HEMT front-end amplifiers. We detail the behavior of the superconducting transition properties of these sensors and the detector optimization in terms of sensitivity to a-thermal phonons. We report preliminary results of a 200 g Ge detector that was calibrated using
71
Ge activation by neutrons at the LSM underground laboratory.
Spherical proportional counters (SPCs) are a novel gaseous detector technology employed by the NEWS-G low-mass dark matter search experiment for their high sensitivity to single electrons from ...ionization. In this paper, we report on the first characterization of the single electron response of SPCs with unprecedented precision, using a UV-laser calibration system. The experimental approach and analysis methodology are presented along with various direct applications for the upcoming next phase of the experiment at SNOLAB. These include the continuous monitoring of the detector response and electron drift properties during dark matter search runs, as well as the experimental measurement of the trigger threshold efficiency. We measure a mean ionization energy of W=27.6±0.2 eV in Ne+CH4 (2%) for 2.8 keV x-rays, and demonstrate the feasibility of performing similar precision measurements at sub-keV energies for future gas mixtures to be used for dark matter searches at SNOLAB.
Performing restaging transurethral bladder resection (reTURB) for high-risk non-muscle invasive bladder cancer (NMIBC) reduces the risk of recurrence and tumour understaging. Management of residual ...high-grade papillary Ta or T1 after reTURB has changed this last 10years in international recommendations. This study aimed to compare the recurrence free survival according to the different management procedures performed.
Patients who underwent reTURB for initial high-risk NMIBC between 2011 and 2020 were included. Patients with residual high-grade papillary Ta or T1 tumour after reTURB were divided into two groups: BCG instillations upfront versus BCG following a third-look resection (3TURB). Patient and tumour characteristics, BCG instillations, recurrence-free survival were retrospectively analysed.
A total of 162 high-risk patients were included. Sixty-one (37.7%) had residual high-grade papillary Ta or T1 at reTURB: 35 (21.6%) had BCG instillations upfront, 18 (11.2%) had a 3TURB and 8 (5%) had other management. The mean follow-up was 34.2weeks±20.2. Recurrence-free survival was significantly better in patients who underwent BCG instillations upfront (P<0.0043). Recurrence after BCG therapy following reTURB was significantly lower in patients with no residual NMIBC at 6 (92.5% vs. 72.4%, P<0.004) and 12months (85% vs. 67.3%, P<0.03).
The efficacy of intravesical BCG is compromised in case of residual tumour following TURB. The role of a 3TURB following a positive reTURB is not yet determined. This study has confirmed that residual tumor following reTURB is a negative predictive factor but could not demonstrate the value of a 3TURB compared to upfront BCG.
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