New constraints and discovery potential of sub-GeV dark matter with
  xenon detectors
  Existing xenon dark matter (DM) direct detection experiments can probe the
DM-nucleon interaction of DM with a sub-GeV mass through a search for photon
emission from the recoiling xenon atom. We show that LUX's constraints on
sub-GeV DM, which utilise the scintillation (S1) and ionisation (S2) signals,
are approximately three orders of magnitude more stringent than previous xenon
constraints in this mass range, derived from the XENON10 and XENON100 S2-only
searches. The new LUX constraints provide the most stringent direct detection
constraints for DM particles with a mass below 0.5 GeV. In addition, the photon
emission signal in LUX and its successor LZ maintain the discrimination between
background and signal events so that an unambiguous discovery of sub-GeV DM is
possible. We show that LZ has the potential to reconstruct the DM mass with 20%
accuracy for particles lighter than 0.5 GeV.
