PICO-2L is the first effort of the PICO (COUPP and PICASSO) collaboration. It is a prototype for a ton scale detector, and at the same time, a device capable of setting world-best limits on spin-dependent dark matter and also test recent claims of evidence for light WIMPs (Weakly Interacting Massive Particles). The detector is a bubble chamber, where the formation of bubbles is started by a single nuclear recoil due to elastic scattering, neutron interactions or alpha decays.
The bubble chambers consist of a synthetic fused silica jar filled with 2.9kg of C3F8 as the target material and ultra pure water as a buffer. The system is enclosed in a stainless steel pressure vessel filled with a hydraulic fluid, mineral oil, and connected to a pressure control unit. The detector has been deployed in the same location of COUPP4, re-using existing infrastructure, including the polypropylene tank water shield, recirculating chiller heater and much of the data acquisition electronics.
PICO-2L is operational and taking data, with a threshold as low as 3 keV. Its physics potential is remarkable, and complimentary to the ongoing COUPP60 experiment filled with 37 kg of CF3I.