We report the first dark matter search results from XENON1T, a $\sim$2000-kg-target-mass dual-phase (liquid-gas) xenon time projection chamber in operation at the Laboratori Nazionali del Gran Sasso in Italy and the first ton-scale detector of this kind. The blinded search used 34.2 live days of data acquired between November 2016 and January 2017. Inside the (1042$\pm$12) kg fiducial mass and in the [5, 40] $\mathrm{ keV}_{ \mathrm{ nr}}$ energy range of interest for WIMP dark matter searches, the electronic recoil background was $(1.93 \pm 0.25) \times 10^{ -4}$ events/(kg $\times$ day $\times \mathrm{ keV}_{ \mathrm{ ee}}$), the lowest ever achieved in a dark matter detector. A profile likelihood analysis shows that the data is consistent with the background-only hypothesis. We derive the most stringent exclusion limits on the spin-independent WIMP-nucleon interaction cross section for WIMP masses above 10 GeV/c${ }^2$, with a minimum of 7.7 $\times 10^{ -47}$ cm${ }^2$ for 35-GeV/c${ }^2$ WIMPs at 90% confidence level.
Categories: astro-ph.CO astro-ph.IM hep-ex hep-ph