We report a measurement of the ionization efficiency of silicon nuclei recoiling with sub-keV kinetic energy in the bulk silicon of a charge-coupled device (CCD). Nuclear recoils are produced by ...low-energy neutrons (<24 keV) from a Sb124−Be9 photoneutron source, and their ionization signal is measured down to 60 eV electron equivalent. This energy range, previously unexplored, is relevant for the detection of low-mass dark matter particles. The measured efficiency is found to deviate from the extrapolation to low energies of the Lindhard model. This measurement also demonstrates the sensitivity to nuclear recoils of CCDs employed by DAMIC, a dark matter direct detection experiment located in the SNOLAB underground laboratory.
We present constraints on the existence of weakly interacting massive particles (WIMPs) from an 11 kg d target exposure of the DAMIC experiment at the SNOLAB underground laboratory. The observed ...energy spectrum and spatial distribution of ionization events with electron-equivalent energies >200 eV_{ee} in the DAMIC CCDs are consistent with backgrounds from natural radioactivity. An excess of ionization events is observed above the analysis threshold of 50 eV_{ee}. While the origin of this low-energy excess requires further investigation, our data exclude spin-independent WIMP-nucleon scattering cross sections σ_{χ-n} as low as 3×10^{-41} cm^{2} for WIMPs with masses m_{χ} from 7 to 10 GeV c^{-2}. These results are the strongest constraints from a silicon target on the existence of WIMPs with m_{χ}<9 GeV c^{-2} and are directly relevant to any dark matter interpretation of the excess of nuclear-recoil events observed by the CDMS silicon experiment in 2013.
Cosmogenic activation of silicon Saldanha, R.; Thomas, R.; Tsang, R. H. M. ...
Physical review. D,
11/2020, Letnik:
102, Številka:
10
Journal Article
Recenzirano
Odprti dostop
The production of 3H, 7Be, and 22Na by interactions of cosmic-ray particles with silicon can produce radioactive backgrounds in detectors used to search for rare events. Through controlled ...irradiation of silicon CCDs and wafers with a neutron beam that mimics the cosmic-ray neutron spectrum, followed by direct counting, we determined that the production rate from cosmic-ray neutrons at sea level is ( 112 ± 24 ) atoms / ( kg day ) for 3H, ( 8.1 ± 1.9 ) atoms / ( kg day ) for 7Be, and ( 43.0 ± 7.2 ) atoms / ( kg day ) for 22Na. Complementing these results with the current best estimates of activation cross sections for cosmic-ray particles other than neutrons, we obtain a total sea-level cosmic-ray production rate of ( 124 ± 25 ) atoms / ( kg day ) for 3H, ( 9.4 ± 2.0 ) atoms / ( kg day ) for 7Be, and ( 49.6 ± 7.4 ) atoms / ( kg day ) for 22Na. These measurements will help constrain background estimates and determine the maximum time that silicon-based detectors can remain unshielded during detector fabrication before cosmogenic backgrounds impact the sensitivity of next-generation rare-event searches.
We report constraints on sub-GeV dark matter particles interacting with electrons from the first underground operation of DAMIC-M detectors. The search is performed with an integrated exposure of ...85.23 g days, and exploits the subelectron charge resolution and low level of dark current of DAMIC-M charge-coupled devices (CCDs). Dark-matter-induced ionization signals above the detector dark current are searched for in CCD pixels with charge up to 7e^{-}. With this dataset we place limits on dark matter particles of mass between 0.53 and 1000 MeV/c^{2}, excluding unexplored regions of parameter space in the mass ranges 1.6,1000 MeV/c^{2} and 1.5,15.1 MeV/c^{2} for ultralight and heavy mediator interactions, respectively.
Here, we employ an 88Y/Be photoneutron source to derive the quenching factor for neutron-induced nuclear recoils in germanium, probing recoil energies from a few hundred eVnr to 8.5 keVnr. A ...comprehensive Monte Carlo simulation of our setup is compared to experimental data employing a Lindhard model with a free electronic energy loss k and an adiabatic correction for sub-keVnr nuclear recoils. The best fit k = 0.179 ± 0.001 obtained using a Monte Carlo Markov chain (MCMC) ensemble sampler is in good agreement with previous measurements, confirming the adequacy of the Lindhard model to describe the stopping of few-keV ions in germanium crystals at a temperature of ~77 K. This value of k corresponds to a quenching factor of 13.7% to 25.3% for nuclear recoil energies between 0.3 and 8.5 keVnr, respectively.
We present results of a dark matter search performed with a 0.6 kg d exposure of the DAMIC experiment at the SNOLAB underground laboratory. We measure the energy spectrum of ionization events in the ...bulk silicon of charge-coupled devices down to a signal of 60 eV electron equivalent. The data are consistent with radiogenic backgrounds, and constraints on the spin-independent WIMP-nucleon elastic-scattering cross section are accordingly placed. A region of parameter space relevant to the potential signal from the CDMS-II Si experiment is excluded using the same target for the first time. This result obtained with a limited exposure demonstrates the potential to explore the low-mass WIMP region (<10 GeV c−2) with the upcoming DAMIC100, a 100 g detector currently being installed in SNOLAB.
We report direct-detection constraints on light dark matter particles interacting with electrons. The results are based on a method that exploits the extremely low levels of leakage current of the ...DAMIC detector at SNOLAB of 2–6×10−22 A cm−2. We evaluate the charge distribution of pixels that collect <10e− for contributions beyond the leakage current that may be attributed to dark matter interactions. Constraints are placed on so-far unexplored parameter space for dark matter masses between 0.6 and 100 MeV c−2. We also present new constraints on hidden-photon dark matter with masses in the range 1.2–30 eV c−2.
An important source of background in direct searches for low-mass dark matter particles are the energy deposits by small-angle scattering of environmental γ rays. We report detailed measurements of ...low-energy spectra from Compton scattering of γ rays in the bulk silicon of a charge-coupled device (CCD). Electron recoils produced by γ rays from Co57 and Am241 radioactive sources are measured between 60 eV and 4 keV. The observed spectra agree qualitatively with theoretical predictions, and characteristic spectral features associated with the atomic structure of the silicon target are accurately measured for the first time. A theoretically motivated parametrization of the data that describes the Compton spectrum at low energies for any incident γ-ray flux is derived. The result is directly applicable to background estimations for low-mass dark matter direct-detection experiments based on silicon detectors, in particular for the DAMIC experiment down to its current energy threshold.
The Selena Neutrino Experiment Chavarria, A.E.
Journal of physics. Conference series,
12/2021, Letnik:
2156, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
Imaging sensors made from an ionization target layer of amorphous selenium (aSe) coupled to a silicon complementary metal-oxide-semiconductor (CMOS) active pixel array for charge readout are ...a promising technology for neutrino physics. The high spatial resolution in a solid-state target provides unparalleled rejection of backgrounds from natural radioactivity in the search for neutrinoless
ββ
decay and for solar neutrino spectroscopy with
82
Se. We present results on the ionization response of aSe measured from the photoabsorption of 122 keV
γ
rays in a single-pixel device. We report on the progress in the fabrication and testing of the first prototype imaging sensors based on the
Topmetal II
−
pixelated CMOS charge readout chip. We explore the scientific reach of a large neutrino detector with the proposed technology based on our experimental understanding of the sensor performance.
We construct the first comprehensive radioactive background model for a dark matter search with charge-coupled devices (CCDs). We leverage the well-characterized depth and energy resolution of the ...DAMIC at SNOLAB detector and a detailed geant4-based particle-transport simulation to model both bulk and surface backgrounds from natural radioactivity down to 50 eVee . We fit to the energy and depth distributions of the observed ionization events to differentiate and constrain possible background sources, for example, bulk H 3 from silicon cosmogenic activation and surface Pb210 from radon plate-out. We observe the bulk background rate of the DAMIC at SNOLAB CCDs to be as low as 3.1±0.6 countskg-1day-1 keVee-1 , making it the most sensitive silicon dark matter detector. Finally, we discuss the properties of a statistically significant excess of events over the background model with energies below 200 eVee .
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