Dark matter detection with bubble chambers

COUPP (Chicagoland Observatory for Underground Particle Physics) uses stable room-temperature bubble chambers to search for Weakly Interacting Massive Particles (WIMPs) which might compose a significant fraction of the galactic dark matter. The superheated refrigerant used, CF3I, is a fire-extinguishing agent and an optimal target for both spin-dependent and spin-independent WIMP couplings. At the moderate degrees of superheat necessary to detect low-energy nuclear recoils such as those expected from WIMPs, this fluid exhibits a measured intrinsic rejection of minimum-ionizing backgrounds better than 10^10. The metastable superheated state is, however, sensitive to alpha-recoils. This leads to the requirement to reach ultra-trace levels of alpha-emitters within the active volume of the chambers. The eventual goal is to match the radio-purity in alpha-emitters of modern large neutrino detectors