A Concept for A Dark Matter Detector Using Liquid Helium-4
  Direct searches for light dark matter particles (mass $<10$ GeV) are
especially challenging because of the low energies transferred in elastic
scattering to typical heavy nuclear targets. We investigate the possibility of
using liquid Helium-4 as a target material, taking advantage of the favorable
kinematic matching of the Helium nucleus to light dark matter particles. Monte
Carlo simulations are performed to calculate the charge, scintillation, and
triplet helium molecule signals produced by recoil He ions, for a variety of
energies and electric fields. We show that excellent background rejection can
be achieved based on the ratios between different signal channels. We also
present some concepts for a liquid-helium-based dark matter detector. Key to
the proposed approach is the use of a large electric field to extract electrons
from the event site, and the amplification of this charge signal, through
proportional scintillation, liquid electroluminescence, or roton emission. The
sensitivity of the proposed detector to light dark matter particles is
estimated for various electric fields and light collection efficiencies.
