Aberration features in directional dark matter detection

TL;DR

This paper explores how Earth's orbital motion causes detectable annual variations in the direction and count of dark matter particle interactions in directional detectors, offering a new method to study dark matter distribution.

Contribution

It introduces the concept of Galactic Hemisphere Annual Modulations (GHAM) as a detectable signature of Earth's motion affecting dark matter detection.

Findings

Annual variation of recoil directions is potentially detectable with moderate exposures.

GHAM amplitudes can surpass non-directional annual modulation signals.

Directional detection can provide insights into the local dark matter velocity distribution.

Abstract

The motion of the Earth around the Sun causes an annual change in the magnitude and direction of the arrival velocity of dark matter particles on Earth, in a way analogous to aberration of stellar light. In directional detectors, aberration of weakly interacting massive particles (WIMPs) modulates the pattern of nuclear recoil directions in a way that depends on the orbital velocity of the Earth and the local galactic distribution of WIMP velocities. Knowing the former, WIMP aberration can give information on the latter, besides being a curious way of confirming the revolution of the Earth and the extraterrestrial provenance of WIMPs. While observing the full aberration pattern requires extremely large exposures, we claim that the annual variation of the mean recoil direction or of the event counts over specific solid angles may be detectable with moderately large exposures. For example, integrated counts over Galactic hemispheres separated by planes perpendicular to Earth's orbit would modulate annually, resulting in Galactic Hemisphere Annual Modulations (GHAM) with amplitudes larger than the usual non-directional annual modulation.