Dark Matter Results From 54-Ton-Day Exposure of PandaX-II Experiment

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