Abstract
The COSINE-100 dark matter search experiment is an array of NaI(Tl) crystal detectors located in the Yangyang Underground Laboratory (Y2L). To understand measured backgrounds in the NaI(Tl) crystals we have performed Monte Carlo simulations using the Geant4 toolkit and developed background models for each crystal that consider contributions from both internal and external sources, including cosmogenic nuclides. The background models are based on comparisons of measurement data with Monte Carlo simulations that are guided by a campaign of material assays and are used to evaluate backgrounds and identify their sources. The average background level for the six crystals (70 kg total mass) that are studied is 3.5 counts/day/keV/kg in the (2–6) keV energy interval. The dominant contributors in this energy region are found to be ^{210}Pb and ^3H.
Highlights
COSINE-100 is a dark matter search experiment consisting of a 106 kg array of eight ultra-pure NaI(Tl) crystals [1,2].Its primary goal is to test DAMA/LIBRA’s assertion of an observation of annual modulation signal [3,4,5,6]
To determine the sources of the backgrounds, we have performed Monte Carlo simulations using the Geant4 toolkit (V.4.9.6.p02) [17] and built a background model for the eight detectors by iteratively fitting their contributions to the measured energy spectra; two crystals are excluded in this paper due to their low light yields, which result in a background spectrum without characteristic peaks of iso
By using the full shielding structure with N2 gas flowing into the inside of the copper shield to avoid backgrounds from 222Rn in the air at Y2L, we reduced the environmental background by a factor of 10,000 based on the measurements of a high-purity Ge (HPGe) detector, ensuring that those contributions are negligibly small
Summary
COSINE-100 is a dark matter search experiment consisting of a 106 kg array of eight ultra-pure NaI(Tl) crystals [1,2]. COSINE-100 is one of several NaI(Tl)-based dark matter searches in operation (DM-Ice17 [8], ANAIS [9,10]) or under development (DM-Ice [11], KamLAND-PICO [12], SABRE [13], COSINUS [14]). The KIMS-CsI experiment put a limit on interaction rates in CsI crystals [15,16] that precluded the interpretation of the DAMA modulation signal as being due to WIMPs scattering from I or Tl nuclei, considering the different quenching factors of iodine and thallium for NaI(Tl) and CsI(Tl).
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