Dark Matter Search Results from the PICO-60 C_{3}F_{8} Bubble Chamber

Area of Science:

• Particle physics
• Astrophysics
• Nuclear physics

Background:

• Direct detection experiments aim to identify dark matter particles.
• Bubble chambers offer unique capabilities for dark matter detection.
• Previous PICO experiments have provided valuable constraints.

Purpose of the Study:

• To report new results from the PICO-60 dark matter detector.
• To search for WIMP-proton spin-dependent interactions.
• To set new direct-detection limits for WIMPs.

Main Methods:

• Operation of the PICO-60 dark matter detector, a bubble chamber using 52 kg of C3F8.
• Utilizing the SNOLAB underground laboratory for reduced background noise.
• Performing a blind analysis of an efficiency-corrected 1167-kg day exposure at a 3.3-keV thermodynamic threshold.

Main Results:

• Excellent electron recoil and alpha decay rejection demonstrated.
• Single-scatter neutron background rate less than one event per month observed.
• No single-scattering nuclear recoil candidates found in the analyzed exposure.

Conclusions:

• The results set the most stringent direct-detection constraint to date on the WIMP-proton spin-dependent cross section.
• The constraint is 3.4×10^-41 cm^2 for a 30-GeV/c^2 WIMP.
• This represents more than a 1-order of magnitude improvement over previous PICO results.