Background model for the NaI(Tl) crystals in COSINE-100

Area of Science:

• Experimental particle physics
• Astroparticle physics
• Dark matter detection

Background:

• Understanding background radiation is crucial for sensitive dark matter experiments.
• Internal and external radioactive sources, including cosmogenic nuclides, contribute to detector backgrounds.
• Precise background modeling is essential to distinguish potential dark matter signals from known radioactive processes.

Purpose of the Study:

• To develop accurate background models for the COSINE-100 experiment.
• To identify and quantify the sources of measured backgrounds in NaI(Tl) detectors.
• To improve the sensitivity of dark matter searches by accounting for background contributions.

Main Methods:

• Utilized Geant4 toolkit for Monte Carlo simulations of detector responses.
• Developed crystal-specific background models incorporating internal and external sources.
• Performed material assays to guide and validate simulation parameters.
• Compared simulation results with experimental measurement data.

Main Results:

• Established background models for six NaI(Tl) crystals (70 kg total mass).
• Determined an average background level of 3.5 counts/day/keV/kg in the (2-6) keV energy range.
• Identified lead ($$ Pb) and tritium ($$ H) as the dominant background contributors in the studied energy interval.

Conclusions:

• The developed background models provide a reliable framework for interpreting COSINE-100 data.
• Lead and tritium are significant sources of background noise, necessitating mitigation strategies.
• Accurate background understanding enhances the capability to search for Weakly Interacting Massive Particles (WIMPs).