On Diurnal and Annual Variations of Directional Detection Rates of Dark Matter

TL;DR

This paper analyzes how Earth's rotation and orbit cause daily and yearly variations in the directional detection rates of dark matter WIMPs, comparing standard and dark disc halo models for specific gas detectors.

Contribution

It provides detailed calculations of diurnal and annual modulation of WIMP detection rates considering Earth's geometry and two dark matter halo models, including detector-specific sensitivities.

Findings

Detection rates vary significantly over a day and year due to Earth's motion.

Dark disc halo model shows different modulation patterns compared to the standard halo.

Results inform optimal detection strategies for directional dark matter detectors.

Abstract

Direction sensitive direct detection of Weakly Interacting Massive Particles (WIMPs) as dark matter would provide an unambiguous non-gravitational signature of dark matter (DM). The diurnal variation of DM signal due to earth's rotation around its own axis can be a significant signature for galactic WIMPs. Because of particular orientation of earth's axis of rotation with respect to WIMP wind direction, the apparent direction of WIMP wind as observed at a detector can alter widely over a day. In this work we calculate the directional detection rates with their daily and yearly modulations in earth-bound dark matter experiments considering detailed features of the geometry and dynamics of the earth-sun system along with the solar motion in galactic frame. A separate halo model namely the dark disc model other than the usual standard halo model for dark matter halo is also considered and the results for two models are compared. We demonstrate the results for two types of gas detectors namely DRIFT (target material CS2) and NEWAGE (target material CF4) that use Time Projection Chamber techniques for measuring directionality of the recoil nucleus. The WIMP mass and recoil energy dependence of the daily variation of event rates are computed for specific detector and the sensitive ranges of mass and recoil energies for the considered detector are probed.