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

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 ×10⁴ 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 /c² , with the lowest 90% C.L. exclusion at 8.6 ×10^-47 cm² at 40 GeV /c² .