https://psu.zoom.us/j/7408461462

Over the past half-century overwhelming evidence has mounted indicating the existence of a non-baryonic and enigmatic dark matter that constitutes approximately 85% of the total matter in the universe. Among the potential dark matter detection methods, dual-phase time projection chambers (TPCs) have emerged as the leading detector technology. LUX-ZEPLIN (LZ) is a direct detection dark matter experiment located at the 4850-ft level of the Sanford Underground Research Facility in South Dakota, USA, employing a 7-tonne active volume of liquid xenon in a dual-phase TPC. It’s surrounded by an instrumented xenon “Skin” region and gadolinium-loaded liquid scintillator outer detector, primarily serving as active vetoes for gamma-ray and neutron backgrounds, respectively, and contained within an ultra-pure water tank. The LZ detector began its first science run in December of 2021 and released its first results in the Summer of 2022.

In order to ensure a low background environment, a comprehensive material assay and selection campaign, for detector components, along with a xenon purification campaign were pursued prior to and during construction. These mitigations have allowed LZ to achieve a background rate of 63.0 ± 4.5 × 10⁻⁶ events/keV_ee/kg/day in the low energy region, approximately 60 times lower than that of its predecessor, the LUX experiment. LZ performed comprehensive measurements to constrain backgrounds in situ and construct a well-constrained time dependent background model to use search for novel physics signals within the low energy (≤15 keV_ee) regime.

In this low background region with a strong background model, LZ was able to set world-leading limits for the spin-independent and spin-dependent elastic scattering of nuclear recoils of Weakly Interacting Massive Particles (WIMPs) with masses above 9 GeV/c². Additionally, the well-constrained time dependent background model allowed LZ to achieve strong limits to electron recoil signals: WIMPs undergoing the Migdal effect, neutrino effective magnetic moment, neutrino effective millicharge, solar axions coupling to electrons, axion-like particles, and dark photons.