Scientific Publications

We report a new search for weakly interacting massive particles (WIMPs) using the combined low background data sets acquired in 2016 and 2017 from the PandaX-II experiment in China. The latest data set contains a new exposure of 77.1 live days, with the background reduced to a level of $0.8×10^{-3} evt/kg/day$, improved by a factor of 2.5 in comparison to the previous run in 2016. No excess events are found above the expected background. With a total exposure of $5.4×10^{4}kg day$, the most stringent upper limit on the spin-independent WIMP-nucleon cross section is set for a WIMP with mass larger than $100 GeV/c^{2}$, with the lowest 90% C.L. exclusion at $8.6×10^{-47}cm^{2}$ at $40 GeV/c^{2}$.

We report on the first dark-matter (DM) search results from PandaX-I, a low threshold dual-phase xenon experiment operating at the China JinPing Underground Laboratory. In the 37-kg liquid xenon target with 17.4 live-days of exposure, no DM particle candidate event was found. This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results. The minimum upper limit, $3.7 × 10^{-44}cm^{2}$, for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of $49GeV/c^{2}$ at 90% confidence level.

New constraints are presented on the spin-dependent weakly-interacting-massive-particle-(WIMP-)nucleon interaction from the PandaX-II experiment, using a data set corresponding to a total exposure of $3.3×10^{4}kg day$. Assuming a standard axial-vector spin-dependent WIMP interaction with ${}^{129}Xe$ and ${}^{131}Xe$ nuclei, the most stringent upper limits on WIMP-neutron cross sections for WIMPs with masses above $10 GeV/c^{2}$ are set in all dark matter direct detection experiments. The minimum upper limit of $4.1×10^{-41}cm^{2}$ at 90% confidence level is obtained for a WIMP mass of $40 GeV/c^{2}$. This represents more than a factor of 2 improvement on the best available limits at this and higher masses. These improved cross-section limits provide more stringent constraints on the effective WIMP-proton and WIMP-neutron couplings.

We discuss an in-situ evaluation of the ${}^{85}Kr$, ${}^{222}Rn$, and ${}^{220}Rn$ background in PandaX-I, a 120-kg liquid xenon dark matter direct detection experiment. Combining with a simulation, their contributions to the low energy electron-recoil background in the dark matter search region are obtained.

We present the results of a search for weakly interacting massive particles (WIMPs) from the commissioning run of the PandaX-II experiment located at the China Jinping Underground Laboratory. A WIMP search data set with an exposure of $306 \times 19.1$ $kg·day$ was taken, while its dominant ${}^{85}Kr$ background was used as the electron recoil calibration. No WIMP candidates are identified, and a $90\%$ upper limit is set on the spin-independent elastic WIMP-nucleon cross section with a lowest excluded cross section of $2.97 \times 10^{−45}$ $cm^2$ at a WIMP mass of $44.7$ $GeV/c^2$.

We report the weakly interacting massive particle (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.

We report the results of a weakly interacting massive particle (WIMP) dark matter search using the full 80.1 live-day exposure of the first stage of the PandaX experiment (PandaX-I) located in the China Jin-Ping Underground Laboratory. The PandaX-I detector has been optimized for detecting low-mass WIMPs, achieving a photon detection efficiency of 9.6%. With a fiducial liquid xenon target mass of 54.0 kg, no significant excess events were found above the expected background. A profile likelihood ratio analysis confirms our earlier finding that the PandaX-I data disfavor all positive low-mass WIMP signals reported in the literature under standard assumptions. A stringent bound on a low-mass WIMP is set at a WIMP mass below $10  GeV/c^{2}$, demonstrating that liquid xenon detectors can be competitive for low-mass WIMP searches.