  The quasiparticle propagation away from the track of a highly ionizing
particle in superfluid helium at low temperatures has previously been shown to
exhibit anisotropy. We discuss the mechanism responsible for this behavior and
show that it occurs for nuclear scattering by dark matter for recoil energies
down to a few keV, and perhaps lower. This makes it possible to extend WIMP
searches with interaction cross sections that reach into the neutrino floor in
a meaningful energy range.
