Particle background characterization and prediction for the NUCLEUS reactor CE ν NS experiment

Area of Science:

• Particle Physics
• Nuclear Physics
• Astrophysics

Background:

• Reactor antineutrino detection relies on measuring Coherent Elastic Neutrino-Nucleus Scattering (CE $\nu$ NS) in the sub-keV energy range.
• Understanding and mitigating particle-induced backgrounds is crucial for isolating the CE $\nu$ NS signal.
• The sub-keV region is poorly characterized, necessitating detailed background predictions.

Purpose of the Study:

• To predict particle-induced backgrounds for the NUCLEUS experiment, focusing on the sub-keV energy range.
• To optimize the NUCLEUS experimental setup for background reduction.
• To estimate residual background rates for detecting reactor antineutrinos via CE $\nu$ NS.

Main Methods:

• Extensive Monte Carlo simulations using the Geant4 package were performed.
• Environmental background radiation measurements at the Chooz nuclear power plant site were incorporated.
• The NUCLEUS experimental setup was designed for high background rejection.

Main Results:

• A total background rejection power exceeding two orders of magnitude is predicted for the NUCLEUS setup.
• Cosmic ray-induced neutrons are identified as the dominant residual background component.
• In the CE $\nu$ NS signal region (10-100 eV), a particle background rate of ~250 d^-1kg^-1keV^-1 is expected in CaWO₄ detectors.

Conclusions:

• The predicted background levels meet the required specifications for detecting reactor antineutrinos through CE $\nu$ NS.
• The signal-to-background ratio is predicted to be greater than or equal to 1 in the region of interest.
• The NUCLEUS experiment is well-positioned to achieve its goals of measuring CE $\nu$ NS and searching for new physics.