Simultaneous Measurement of Ionization and Scintillation from Nuclear   Recoils in Liquid Xenon as Target for a Dark Matter Experiment
  We report the first measurements of the absolute ionization yield of nuclear recoils in liquid xenon, as a function of energy and electric-field. Independent experiments were carried out with two dual-phase time projection chamber prototypes, developed for the XENON Dark Matter project. We find that the charge yield increases with decreasing recoil energy, and exhibits only a weak field dependence. These results are a first demonstration of the capability of dual phase xenon detectors to discriminate between electron and nuclear recoils, a key requirement for a sensitive dark matter search at recoil energies down to 20 keV. 
E. Aprile, C.E. Dahl, L. DeViveiros, R. Gaitskell, K.L. Giboni, J.   Kwong, P. Majewski, K. Ni, T. Shutt, M. Yamashita