Background modeling for dark matter search with 1. 7 years of COSINE-100 data

We present a background model for dark matter searches using an array of (Tl) crystals in the COSINE-100 experiment that is located in the Yangyang laboratory. The model includes background contributions from both and external sources, including cosmogenic radionuclides and surface^210Pb contamination. To build the model in the low energy region, with a of 1 keV, we used a depth profile of ^210Pb contamination in the of the NaI (Tl) crystals determined in a comparison between measured and spectra. We also considered the effect of the energy scale errors from the statistical uncertainties and the nonlinear detector at low energies. The 1. 7 years COSINE-100 data taken between October21, 2016 and July 18, 2018 were used for this analysis. Our Monte Carlo provides a non-Gaussian peak around 50 keV originating from beta of bulk ^210Pb in a good agreement with the measured background. model estimates that the activities of bulk ^210Pb and ^3H are the background rate that amounts to an average level of2. 85\0. 15 counts/day/keV/kg in the energy region of (1-6) keV, using-100 data with a total exposure of 97. 7 kg\years.