Status of PICO Bubble Chambers in the Search for Dark Matter

The PICO Collaboration uses bubble chamber technology for direct-detection Weakly-Interacting Massive Particle (WIMP) dark matter searches. Filled with superheated C₃F₈, the thermodynamic threshold of PICO detectors can be set such that the detectors are optimised for dark matter detection while being insensitive to electrons and gammas. PICO-40L is currently operating in an active nickel mine 2 km underground at SNOLAB in Sudbury, Ontario, Canada. It is the first large-scale implementation of the “right-side up” bubble chamber design in which the absence of a buffer fluid in contact with the C₃F₈ minimises background rates from particulates entering the chamber. It acts as a proof-of-concept for the next generation PICO-500 detector, a 260-L bubble chamber with a projected ton-year exposure currently under construction at SNOLAB. PICO-500 is expected to continue to push world-leading limits in the search for spin-dependent dark matter. This talk will present the status of PICO-40L and will provide an overview of PICO-500, including recent developments in radon permeation and cleaning procedures as well as its commissioning timeline.