First Direct Search for Inelastic Boosted Dark Matter with COSINE-100.

Area of Science:

• Particle Physics
• Cosmology
• Astroparticle Physics

Background:

• Dark matter constitutes a significant portion of the universe's mass, yet its nature remains elusive.
• Inelastic boosted dark matter (IBDM) is a theoretical dark matter candidate that interacts via inelastic scattering with electrons.
• IBDM interactions are predicted to produce a distinct signature of an electron-positron pair alongside the scattered electron.

Purpose of the Study:

• To conduct the first experimental search for inelastic boosted dark matter (IBDM) using a terrestrial detector.
• To establish limits on IBDM interaction cross-sections and explore the parameter space of related dark matter models, such as dark photons.

Main Methods:

• Utilized the COSINE-100 detector, collecting 59.5 days of data.
• Searched for a specific signature: an electron-positron pair in coincidence with an initially scattered electron, indicative of an IBDM interaction.
• Compared observed event rates against predicted background contributions.

Main Results:

• No significant excess of events beyond the expected background was observed.
• Experimental limits were placed on IBDM interactions under various theoretical assumptions.
• A region of the dark photon parameter space, previously unconstrained by experiments, was explored.

Conclusions:

• The first experimental constraints on inelastic boosted dark matter interactions were established.
• The study demonstrates the capability of terrestrial detectors in searching for novel dark matter candidates.
• Future searches with increased sensitivity can further probe IBDM and related dark sector models.