Dark Matter Search Results from the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>PICO</mml:mi><mml:mtext>−</mml:mtext><mml:mn>60</mml:mn><mml:msub><mml:mrow><mml:mtext> </mml:mtext><mml:mi mathvariant="normal">C</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>8</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:mrow></mml:math> Bubble Chamber

New results are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 52 kg of C3F8 located in the SNOLAB underground laboratory. As in previous PICO bubble chambers, PICO-60 C3F8 exhibits excellent electron recoil and alpha decay rejection, and the observed multiple-scattering neutron rate indicates a single-scatter neutron background of less than 1 event per month. A blind analysis of an efficiency-corrected 1167-kg-day exposure at a 3.3-keV thermodynamic threshold reveals no single-scattering nuclear recoil candidates, consistent with the predicted background. These results set the most stringent direct-detection constraint to date on the WIMP-proton spin-dependent cross section at 3.4 10 -41 cm 2 for a 30-GeV c -2 WIMP, more than one order of magnitude improvement from previous PICO results.