Mitigation of Radon Daughter Plate-out in the LUX-ZEPLIN Experiment

Growing theoretical and empirical evidence for the existence of dark matter has driven a search in the field of physics for its elusive elementary particle. A wide variety of experiments have spawned in order to discover the leading candidate, the WIMP. The primary goal of the LUX-ZEPLIN (LZ) experiment is to detect an interaction between a WIMP and a xenon nucleus, allowing physicists to begin understanding this exotic type of matter. An important background arises from charged radon daughters that attach to PTFE during construction and upon decay generate (α,n) reactions and recoiling ²⁰⁶Pb atoms in the detector. PTFE is of particular interest because it is used for the walls of the inner detector and its radon daughter plate-out rate can be orders of magnitude larger than the plate-out rate onto other materials. To mitigate radon contamination and meet LZ cleanliness goals, filtration systems have been constructed to provide low-radon air to locations where materials are exposed during detector assembly. Results on the measured PTFE radon daughter plate-out rate and the effectiveness of the radon reduction air filtration systems will be discussed.