Abstract

LUX-ZEPLIN (LZ) is a next-generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with weakly interacting massive particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6-tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above $1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}48}\text{ }\text{ }{\mathrm{cm}}^{2}$ for a $40\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ mass WIMP. Additionally, a $5\ensuremath{\sigma}$ discovery potential is projected, reaching cross sections below the exclusion limits of recent experiments. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of $2.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}43}\text{ }\text{ }{\mathrm{cm}}^{2}$ ($7.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}42}\text{ }\text{ }{\mathrm{cm}}^{2}$) for a $40\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ mass WIMP is expected. With underground installation well underway, LZ is on track for commissioning at SURF in 2020.