Directional sensitivity, WIMP detection, and the galactic halo

Distinguishing the signals due to scattering of WIMP dark matter off of nuclear targets from those due to background noise is a major challenge. The Earthʹs motion relative to the galactic halo should produce halo-dependent seasonal modulation in the event rate, but it also should produce an angular signal that is both far stronger and less ambiguous. Distinct patterns in the recoil spectrum can reflect the details of the galactic halo. We derive a new formalism to calculate angular event rates, and present the predicted angular signal for a variety of halo models and calculate the number of events needed to distinguish a dark matter signal from an isotropic background.