We believe this collaboration has now solved the major technical questions that have previously prevented construction of such an experiment. Sensitivity should improve proportional to exposure. Remaining electrons will pass through the detector. This arises from radon in the gas and U, Th contamination in vessel wires and components at rates comparable to electrons. Alphas in the wires can cause short track events that would mimic recoil events by losing most energy in the metal before emerging.
Diffusion fixes the minimum track length observable and hence the sensitivity.
An idea from C.J. Martoff is to use negative ion drift in which transport of the charge is carried out by negative ions rather than electrons. This greatly reduces the diffusion. Xe TPC as a directional dark matter detector relies on keeping diffusion of the charge released below this level as the track is drifted through the interaction volume to the readout. In the our first 0.2 m3 detector developed by UCSD this was achieved using a 5T magnetic field applied parallel to the projection axis. Increasing the track length, by operating at lower pressure, can help though this reduces the target mass and is technically difficult.