Search for Light Dark Matter from the Atmosphere in PandaX-4T.

Area of Science:

• Particle Physics
• Astroparticle Physics
• Cosmology

Background:

• Dark matter remains a significant mystery in physics.
• Cosmic ray interactions with Earth's atmosphere produce secondary particles, including eta (η) mesons.
• Eta mesons can decay into dark matter particles, which may interact with atomic nuclei.

Purpose of the Study:

• To search for light dark matter produced by eta meson decays.
• To develop and apply a new framework for simulating boosted dark matter.
• To establish constraints on the interaction cross-section between light dark matter and atomic nuclei.

Main Methods:

• Utilized PandaX-4T detector commissioning data with 0.63 tonne·year exposure.
• Developed a general framework for simulating boosted dark matter, including Earth attenuation effects (elastic and quasielastic scattering).
• Performed dedicated simulations accounting for atmospheric production and detector interactions.

Main Results:

• No significant excess of signal events above background was observed.
• Established the first constraints on light dark matter-nucleus interactions mediated by a light scalar particle.
• Set a lower exclusion limit on the interaction cross-section at 5.9×10⁻³⁷ cm² for dark matter mass of 0.1 MeV/c² and mediator mass of 300 MeV/c².
• Achieved an upper limit on the eta (η) to dark matter decay branching ratio of 1.6×10⁻⁷.

Conclusions:

• The search did not yield evidence for light dark matter from eta meson decays.
• The study provides the most stringent constraints to date for this specific light dark matter model.
• The developed simulation framework is publicly accessible and applicable to other boosted dark matter searches.