Lowering the low-energy threshold of xenon detectors
  We show that the energy threshold for nuclear recoils in the XENON10 dark
matter search data can be lowered to ~1 keV, by using only the ionization
signal. In other words, we make no requirement that a valid event contain a
primary scintillation signal. We therefore relinquish incident particle type
discrimination, which is based on the ratio of ionization to scintillation in
liquid xenon. This method compromises the detector's ability to precisely
determine the z coordinate of a particle interaction. However, we show for the
first time that it is possible to discriminate bulk events from surface events
based solely on the ionization signal.
