We present the first search for a dark matter annual modulation signal in the Southern Hemisphere conducted with NaI(Tl) detectors, performed by the DM-Ice17 experiment. Nuclear recoils from dark ...matter interactions are expected to yield an annually modulated signal independent of location within the Earth’s hemispheres. DM-Ice17, the first step in the DM-Ice experimental program, consists of 17 kg of NaI(Tl) located at the South Pole under 2200 m.w.e. overburden of Antarctic glacial ice. Taken over 3.6 years for a total exposure of 60.8 kg yr, DM-Ice17 data are consistent with no modulation in the energy range of 4–20 keV, providing the strongest limits on weakly interacting massive particle dark matter from a direct detection experiment located in the Southern Hemisphere. The successful deployment and stable long-term operation of DM-Ice17 establishes the South Pole ice as a viable location for future dark matter searches and in particular for a high-sensitivity NaI(Tl) dark matter experiment to directly test the DAMA/LIBRA claim of the observation of dark matter.
We present new constraints on the dark matter-induced annual modulation signal using 1.7 years of COSINE-100 data with a total exposure of 97.7 kg yr. The COSINE-100 experiment, consisting of 106 kg ...of NaI(Tl) target material, is designed to carry out a model-independent test of DAMA/LIBRA's claim of WIMP discovery by searching for the same annual modulation signal using the same NaI(Tl) target. The crystal data show a 2.7 cpd/kg/keV background rate on average in the 2-6 keV energy region of interest. Using a χ-squared minimization method we observe best fit values for modulation amplitude and phase of 0.0092±0.0067 cpd/kg/keV and 127.2±45.9 d, respectively.
We report the measurement of muons and muon-induced phosphorescence in DM-Ice17, a NaI(Tl) direct detection dark matter experiment at the South Pole. Muon interactions in the crystal are identified ...by their observed pulse shape and large energy depositions. The measured muon rate in DM-Ice17 is 2.93+ or -0.04 mu /crystal/day with a modulation amplitude of 12.3+ or -1.7%, consistent with expectation. Following muon interactions, we observe long-lived phosphorescence in the NaI(Tl) crystals with a decay time of 5.5+ or -0.5s. The prompt energy deposited by a muon is correlated to the amount of delayed phosphorescence, the brightest of which consist of tens of millions of photons. These photons are distributed over tens of seconds with a rate and arrival timing that do not mimic a scintillation signal above 2keV sub(ee). While the properties of phosphorescence vary among individual crystals, the annually modulating signal observed by DAMA cannot be accounted for by phosphorescence with the characteristics observed in DM-Ice17.
We present results from a 54.7 live-day shielded run of the DRIFT-IId detector, the world's most sensitive, directional, dark matter detector. Several improvements were made relative to our previous ...work including a lower threshold for detection, a more robust analysis and a tenfold improvement in our gamma rejection factor. After analysis, no events remain in our fiducial region leading to an exclusion curve for spin-dependent WIMP-proton interactions which reaches 0.28pb at 100GeV/c2, a fourfold improvement on our previous work. We also present results from a 45.4 live-day unshielded run of the DRIFT-IId detector during which 14 nuclear recoil-like events were observed. We demonstrate that the observed nuclear recoil rate of 0.31 ± 0.08 events per day is consistent with detection of ambient, fast neutrons emanating from the walls of the Boulby Underground Science Facility.
We present a comprehensive study of the nonproportionality of NaI(Tl) scintillation detectors within the context of dark matter search experiments. Our investigation, which integrates COSINE-100 data ...with supplementary
γ
spectroscopy, measures light yields across diverse energy levels from full-energy
γ
peaks produced by the decays of various isotopes. These
γ
peaks of interest were produced by decays supported by both long and short-lived isotopes. Analyzing peaks from decays supported only by short-lived isotopes presented a unique challenge due to their limited statistics and overlapping energies, which was overcome by long-term data collection and a time-dependent analysis. A key achievement is the direct measurement of the 0.87 keV light yield, resulting from the cascade following electron capture decay of
22
Na
from internal contamination. This measurement, previously accessible only indirectly, deepens our understanding of NaI(Tl) scintillator behavior in the region of interest for dark matter searches. This study holds substantial implications for background modeling and the interpretation of dark matter signals in NaI(Tl) experiments.
COSINE-100 is a dark matter detection experiment that uses NaI(Tl) crystal detectors operating at the Yangyang underground laboratory in Korea since September 2016. Its main goal is to test the ...annual modulation observed by the DAMA/LIBRA experiment with the same target medium. Recently DAMA/LIBRA has released data with an energy threshold lowered to 1 keV, and the persistent annual modulation behavior is still observed at 9.5σ. By lowering the energy threshold for electron recoils to 1 keV, COSINE-100 annual modulation results can be compared to those of DAMA/LIBRA in a model-independent way. Additionally, the event selection methods provide an access to a few to sub-GeV dark matter particles using constant rate studies. In this article, we discuss the COSINE-100 event selection algorithm, its validation, and efficiencies near the threshold.
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