Bouchet Award Talk: The making of the biggest and cleanest xenon TPC for dark matter searches

The LUX-ZEPLIN experiment (LZ) uses a dual-phase xenon time projection chamber (TPC) with 7 tonnes of active volume, aided by a veto system to primarily search for dark matter in the form of Weakly Interacting Massive particles (WIMPs). LZ recently published world-leading WIMP search results from its first science run, after concluding one of the most extensive and stringent radio-contaminant control programs for any TPC to date. The program included a wide-ranging contaminant assay program: gamma-ray spectrometry, mass spectrometry, radon emanation, and optical/radiometric techniques for material selections and surface contamination. Moreover, a cleanliness program developed by LZ has ensured the minimization of any additional sources of contaminants other than those intrinsic to the detector materials. In this talk, I will review the construction phase of LZ with an emphasis on the comprehensive assay and cleanliness efforts of the collaboration. These included measurements of over 1000 individual items (raw materials and finalized components) and more than 4000 hours following numerous cleanliness protocols developed to ensure the sensitivity goal of the experiment would be reached.