Feasibility of liquid-phase xenon proportional scintillation for low-energy physics

Liquid xenon time projection chambers (TPCs) detect both the scintillation photons and ionization electrons created by energy depositions within the liquid xenon (LXe) volume. Dual-phase (liquid-gas) xenon TPCs, which detect ionization electrons through proportional scintillation in a thin gas gap after extracting electrons through the liquid, are now widely used in the field of dark matter direct detection because of their low-energy detection capability and their ability to discriminate between electronic and nuclear recoils. In this paper, we demonstrate that a purely single-phase liquid xenon TPC which produces proportional scintillation directly in the liquid is still capable of discriminating between electronic and nuclear recoils at low energy that is relevant to dark matter direct detection and neutrino-nucleus coherent scattering experiments. Using the single-phase detector, we also investigate the delayed electrons which are a major background in liquid xenon experiments to search for light dark matter. We observed similar behaviors of delayed electrons and concluded that the liquid-gas interface in a dual-phase TPC is unlikely the major source of delayed single-electron background.