Low-mass Dark Matter Search Using Ionization Signals in LUX

LUX (Large Underground Xenon) is a retired, 250 kg, liquid xenon, direct dark matter detection experiment that has published three, previously world leading limits on the spin-independent cross section for WIMP-nucleon scattering in the 5-1000+ GeV mass range. LUX was successful thanks to a two channel readout of both scintillation (S1) and ionization (S2) that allows for event position reconstruction and, thus, rejection of backgrounds occurring primarily at the edges of the xenon volume. However, because the S2 signal is detected with approximately ⨉10 greater efficiency than the S1 signal, xenon detectors can lower their energy threshold and look for the nuclear recoils of lower mass dark matter particles by letting go of the requirement of an S1. In this type of analysis, additional background events are expected, because the reconstructed z-coordinate is no longer accessible. In addition to this expected increase, we have found an excess of background events emitted by the electrodes. In this talk, a new mitigation strategy for electrode events is outlined and the latest results from LUX’s ionization-only low-mass dark matter analysis are presented.