Direct Detection of Dark Matter Bound to the Earth

TL;DR

This paper investigates a previously overlooked population of Earth-bound dark matter particles, analyzing their properties and how they could be detected through nuclear recoil signals in direct detection experiments.

Contribution

It introduces the concept of Earth-bound dark matter, calculates its flux and recoil spectra, and discusses detection strategies with various detector configurations.

Findings

Earth-bound dark matter causes a rise in low-energy nuclear recoil signals.

Detection requires ultra-low threshold energies around 1 eV.

The recoil spectrum shape is independent of scattering cross-section normalization.

Abstract

We study the properties and direct detection prospects of an as of yet neglected population of dark matter (DM) particles moving in orbits gravitationally bound to the Earth. This DM population is expected to form via scattering by nuclei in the Earth's interior. We compute fluxes and nuclear recoil energy spectra expected at direct detection experiments for the new DM population considering detectors with and without directional sensitivity, and different types of target materials and DM-nucleon interactions. DM particles bound to the Earth manifest as a prominent rise in the low-energy part of the observed nuclear recoil energy spectrum. Ultra-low threshold energies of about 1 eV are needed to resolve this effect. Its shape is independent of the DM-nucleus scattering cross-section normalisation.