Dark matter astrometry at underground detectors with multiscatter events

Abstract

We show that current and imminent underground detectors are capable of precision astrometry of dark matter. First, we show that Galactic dark matter velocity distributions can be obtained from reconstructed tracks of dark matter scattering on multiple nuclei during transit; using the liquid scintillator neutrino detector SNO+ as an example, we find that the dark matter velocity vector can be reconstructed event by event with such a small uncertainty that the precision of dark matter astrometry will be limited mainly by statistics. We then determine the number of dark matter events required to determine the dispersion speed, escape speed, and velocity anisotropies of the local dark matter halo and also find that with as few as O(10) events dark matter signals may be discriminated from potential backgrounds arising as power-law distributions. Finally, we discuss the prospects of dark matter astrometry at other liquid scintillator detectors, dark matter experiments, and the recently proposed MATHUSLA detector.