Directional sensitivity, WIMP detection, and the galactic halo

Distinguishing the signals due to scattering of WIMP dark matter off of nuc lear targets from those due to background noise is a major challenge. The E arth's motion relative to the galactic halo should produce halo-dependent s easonal 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 predicte d angular signal for a variety of halo models and calculate the number of e vents needed to distinguish a dark matter signal from an isotropic backgrou nd. (C) 1999 Published by Elsevier Science B.V. All rights reserved.