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LUX-ZEPLIN (LZ) is a second-generation direct dark matter experiment with spin-independent WIMP-nucleon scattering sensitivity above $${1.4 \times 10^{-48}}\, {\hbox {cm}}^{2}$$ 1.4 × 10 - 48 cm 2 for a WIMP mass of $${40}\, \hbox {GeV}/{\hbox {c}}^{2}$$ 40 GeV / c 2 and a $${1000}\, \hbox {days}$$ 1000 days exposure. LZ achieves this sensitivity through a combination of a large $${5.6}\, \hbox {t}$$ 5.6 t fiducial volume, active inner and outer veto systems, and radio-pure construction using materials with inherently low radioactivity content. The LZ collaboration performed an extensive radioassay campaign over a period of six years to inform material selection for construction and provide an input to the experimental background model against which any possible signal excess may be evaluated. The campaign and its results are described in this paper. We present assays of dust and radon daughters depositing on the surface of components as well as cleanliness controls necessary to maintain background expectations through detector construction and assembly. Finally, examples from the campaign to highlight fixed contaminant radioassays for the LZ photomultiplier tubes, quality control and quality assurance procedures through fabrication, radon emanation measurements of major sub-systems, and bespoke detector systems to assay scintillator are presented.

The nature of dark matter and properties of neutrinos are among the most pressing issues in contemporary particle physics. The dual-phase xenon time-projection chamber is the leading technology to cover the available parameter space for weakly interacting massive particles, while featuring extensive sensitivity to many alternative dark matter candidates. These detectors can also study neutrinos through neutrinoless double-beta decay and through a variety of astrophysical sources. A next-generation xenon-based detector will therefore be a true multi-purpose observatory to significantly advance particle physics, nuclear physics, astrophysics, solar physics, and cosmology. This review article presents the science cases for such a detector.

The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double beta decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to 136 Xe neutrinoless double beta decay, taking advantage of the significant (>600 kg) 136 Xe mass contained within the active volume of LZ without isotopic enrichment. After 1000 livedays, the median exclusion sensitivity to the half-life of 136 Xe is projected to be 1.06×10 26 years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with 136 Xe at 1.06×10 27 years.

The LUX-ZEPLIN dark matter search aims to achieve a sensitivity to the WIMP-nucleon spinindependent cross-section down to (1-2)×10 −12 pb at a WIMP mass of 40 GeV/c 2. This paper describes the simulations framework that, along with radioactivity measurements, was used to support this projection, and also to provide mock data for validating reconstruction and analysis software. Of particular note are the event generators, which allow us to model the background radiation, and the detector response physics used in the production of raw signals, which can be converted into digitized waveforms similar to data from the operational detector. Inclusion of the detector response allows us to process simulated data using the same analysis routines as developed to process the experimental data.