L. Yang, L.T. Truc, N.J.C. Spooner, M.K. Son, D.F.F.S. Cavalcante, K.A. Shin, C. Rott, S.J. Ra, H. Prihtiadi, R.L.C. Pitta, S.D. Park, K.S. Park, J.C. Park, H.S. Park, H.K. Park, B.J. Park, S.L. Olsen, R.J. Neal, R.H. Maruyama, B.B. Manzato, N.T. Luan, D.S. Leonard, Y.J. Lee, S.M. Lee, S.H. Lee, M.H. Lee, J.Y. Lee, J. Lee, I.S. Lee, H.Y. Lee, H.S. Lee, E.K. Lee, D.H. Lee, Y.J. Ko, Y.H. Kim, Y.D. Kim, W.K. Kim, S.K. Kim, S.H. Kim, K.W. Kim, J. Kim, H.J. Kim, B.H. Kim, M. Kauer, W.G. Kang, H.W. Joo, E.J. Jeon, S.J. Hollick, I.S. Hahn, C. Ha, L.E. França, A.C. Ezeribe, S. Choi, J.J. Choi, J.Y. Cho, N. Carlin, G.H. Yu
COSINE-100 aims to conclusively test the claimed dark matter annual modulation signal detected by DAMA/LIBRA collaboration. DAMA/LIBRA has released updated analysis results by lowering the energy threshold to 0.75 keV through various upgrades. They have consistently claimed to have observed an annual modulation. In COSINE-100, it is crucial to lower the energy threshold for a direct comparison with DAMA/LIBRA, which also enhances the sensitivity of the search for low-mass dark matter, enabling COSINE-100 to explore this area. Therefore, it is essential to have a precise and quantitative understanding of the background spectrum across all energy ranges. This study expands the background modeling from 0.7 to 4000 keV using 2.82 years of COSINE-100 data. The modeling has been improved to describe the background spectrum across all energy ranges accurately. Assessments of the background spectrum are presented, considering the nonproportionality of NaI(Tl) crystals at both low and high energies and the characteristic X-rays produced by the interaction of external backgrounds with materials such as copper. Additionally, constraints on the fit parameters obtained from the alpha spectrum modeling fit are integrated into this model. These improvements are detailed in the paper. © The Author(s) 2025.
Center for Underground Physics, Institute for Basic Science (IBS), Daejeon, 34126, South Korea; Physics Institute, University of São Paulo, São Paulo, 05508-090, Brazil; Department of Physics, Kyungpook National University, Daegu, 41566, South Korea; Department of Physics and Astronomy, Seoul National University, Seoul, 08826, South Korea; Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, United Kingdom; Department of Physics, Chung-Ang University, Seoul, 06973, South Korea; Center for Exotic Nuclear Studies, Institute for Basic Science (IBS), Daejeon, 34126, South Korea; Department of Science Education, Ewha Womans University, Seoul, 03760, South Korea; IBS School, University of Science and Technology (UST), Daejeon, 34113, South Korea; Department of Physics and Wright Laboratory, Yale University, New Haven, 06520, CT, United States; Department of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin-Madison, Madison, 53706, WI, United States; Korea Research Institute of Standards and Science, Daejeon, 34113, South Korea; Department of Accelerator Science, Korea University, Sejong, 30019, South Korea; Department of Physics and IQS, Chungnam National University, Daejeon, 34134, South Korea; Department of Physics, Universitas Negeri Malang, Malang, 65145, Indonesia; Department of Physics and Astronomy, University of Utah, Salt Lake City, 84112, UT, United States; Department of Physics, University of California San Diego, La Jolla, 92093, CA, United States; Department of Physics, Sungkyunkwan University, Suwon, 16419, South Korea
