Dark Matter Search Results from a One Ton-Year Exposure of XENON1T

We report on a search for weakly interacting massive particles (WIMPs) using 278.8 days of data collected with the XENON1T experiment at LNGS. XENON1T utilizes a liquid xenon time projection chamber with a fiducial mass of (1.30±0.01) ton, resulting in a 1.0 ton yr exposure. The energy region of interest, [1.4,10.6] keVₑₑ ([4.9,40.9] keVₙᵣ), exhibits an ultralow electron recoil background rate of [82₋₃⁺⁵(syst)±3(stat)] events/(ton yr keVₑₑ). No significant excess over background is found, and a profile likelihood analysis parametrized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross section for WIMP masses above 6 GeV/c², with a minimum of 4.1×10⁻⁴⁷ cm² at 30 GeV/c² and a 90% confidence level.