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We report the WIMP dark matter search results using the first physics-run data of the PandaX-II 500 kg liquid xenon dual-phase time-projection chamber, operating at the China JinPing underground Laboratory. No dark matter candidate is identified above background. In combination with the data set during the commissioning run, with a total exposure of 3.3×10 4 kg-day, the most stringent limit to the spin-independent interaction between the ordinary and WIMP dark matter is set for a range of dark matter mass between 5 and 1000 GeV/c 2 . The best upper limit on the scattering cross section is found 2.5 × 10 −46 cm 2 for the WIMP mass 40 GeV/c 2 at 90% confidence level.Weakly interacting massive particles, WIMPs in short, are a class of hypothetical particles that came into existence shortly after the Big Bang. The WIMPs could naturally explain the astronomical and cosmological evidences of dark matter in the Universe. The weak interactions between WIMPs and ordinary matter could lead to the recoils of atomic nuclei that produce detectable signals in deep-underground direct detection experiments. Over the past decade, the dual-phase xenon time-projection chambers (TPC) emerged as a powerful technology for WIMP searches both in scaling up the target mass, as well as in improving background rejection [1][2][3]. LUX, a dark matter search experiment with a 250 kg liquid xenon target, has recently reported the best limit of 6×10 −46 cm 2 on the WIMP-nucleon scattering cross section [4] The PandaX-II experiment, a half-ton scale dual-phase xenon experiment at the China JinPing underground Laboratory (CJPL), has recently reported the dark matter search results from its commissioning run (Run 8,19.1 live days) with a 5845 kg-day exposure [5]. The data were contaminated with significant 85 Kr background. After a krypton distillation campaign in early 2016, PandaX-II commenced physics data taking in March 2016. In this paper, we report the combined WIMP search results using the data from the first physics run from March 9 to June 30, 2016 (Run 9, 79.6 live days) and Run 8, with a total of 3.3×10 4 kg-day exposure, the largest reported WIMP data set among dual-phase xenon detectors in the world to date.The PandaX-II detector has been described in detail in Ref. [5]. The liquid xenon target consists of a cylindrical TPC with dodecagonal cross section (opposite-side distance 646 mm), confined by the polytetrafluoroethylene (PTFE) reflective wall, and a vertical drift distance of 600 mm defined by the cathode mesh and gate grid located at the bottom and top. For each physical event, the prompt scintillation photons (S1) and the delayed electroluminescence photons (S2) from the ionized electrons are collected by two arrays of 55 Hamamatsu R11410-arXiv:1607.07400v3 [hep-ex] Hamamatsu R8520-406 1-inch PMTs serving as an active veto. The γ background, which produces electron recoil (ER) events, can be distinguished from the dark matter nuclear recoil (NR) using the S2-to-S1 ratio. During the data taking period in Run 9, a few diffe...

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 × 10 −48 cm 2 for a 40 GeV=c 2 mass WIMP. Additionally, a 5σ 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 × 10 −43 cm 2 (7.1 × 10 −42 cm 2) for a 40 GeV=c 2 mass WIMP is expected. With underground installation well underway, LZ is on track for commissioning at SURF in 2020.

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