https://doi.org/10.1140/epjc/s10052-021-09564-0
Regular Article - Experimental Physics
Background modeling for dark matter search with 1.7 years of COSINE-100 data
1
Center for Underground Physics, Institute for Basic Science (IBS), 34126, Daejeon, Republic of Korea
2
Department of Physics, University of California, San Diego, 92093, La Jolla, CA, USA
3
Department of Physics and Wright Laboratory, Yale University, 06520, New Haven, CT, USA
4
Physics Institute, University of São Paulo, 05508-090, São Paulo, Brazil
5
Department of Physics and Astronomy, Seoul National University, 08826, Seoul, Republic of Korea
6
Department of Physics, Bandung Institute of Technology, 40132, Bandung, Indonesia
7
Department of Physics and Astronomy, University of Sheffield, S3 7RH, Sheffield, UK
8
Department of Physics, Chung-Ang University, 06973, Seoul, Republic of Korea
9
Department of Science Education, Ewha Womans University, 03760, Seoul, Republic of Korea
10
Center for Exotic Nuclear Studies, Institute for Basic Science (IBS), 34126, Daejeon, Republic of Korea
11
IBS School, University of Science and Technology (UST), 34113, Daejeon, Republic of Korea
12
Department of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin-Madison, 53706, Madison, WI, USA
13
Department of Physics, Kyungpook National University, 41566, Daegu, Republic of Korea
14
Department of Physics and Astronomy, Sejong University, 05006, Seoul, Republic of Korea
15
Korea Research Institute of Standards and Science, 34113, Daejeon, Republic of Korea
16
Department of Accelerator Science, Graduate School, Korea University, 30019, Sejong City, Republic of Korea
17
Department of Physics, Sungkyunkwan University, 16419, Seoul, Republic of Korea
m
ejjeon@ibs.re.kr
aa
yjko@ibs.re.kr
Received:
27
January
2021
Accepted:
19
August
2021
Published online:
21
September
2021
We present a background model for dark matter searches using an array of NaI(Tl) crystals in the COSINE-100 experiment that is located in the Yangyang underground laboratory. The model includes background contributions from both internal and external sources, including cosmogenic radionuclides and surface 
Pb contamination. To build the model in the low energy region, with a threshold of 1 keV, we used a depth profile of Pb contamination in the surface of the NaI(Tl) crystals determined in a comparison between measured and simulated spectra. We also considered the effect of the energy scale errors propagated from the statistical uncertainties and the nonlinear detector response at low energies. The 1.7 years COSINE-100 data taken between October 21, 2016 and July 18, 2018 were used for this analysis. Our Monte Carlo simulation provides a non-Gaussian peak around 50 keV originating from beta decays of bulk Pb in a good agreement with the measured background. This model estimates that the activities of bulk Pb and 
H are dominating the background rate that amounts to an average level of 
counts/day/keV/kg in the energy region of (1–6) keV, using COSINE-100 data with a total exposure of 97.7 kg
years.
© The Author(s) 2021
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Funded by SCOAP3
