A new experimental effort to search for particle dark matter, the Chicagoland Observatory for Underground Particle Physics (COUPP) will debut at the end of summer 2004. A prototype bubble chamber sensitive to Weakly Interacting Massive Particles (WIMPs), developed by the Collar group, is to be installed in the MINOS near detector gallery at Fermilab (FNAL). The chamber (Figure 1) will contain two kg of CF₃I, a fire-extinguishing liquid that can be superheated to respond to very low energy nuclear recoils like those expected from WIMPs while being totally insensitive to minimum ionizing particles, the dominant background in this type of searches. In this site the experiment will profit from 300 ft of rock overburden to reduce cosmic ray backgrounds, the convenience of a location nearby University of Chicago and the local expertise of our FNAL collaborators. After a few months of preliminary tests there the chamber will be transported to a final emplacement in the Soudan Underground Laboratory (MN).

Figure 1.
Left: Conceptual design of the 2 kg CF₃I chamber to be used in the preliminary phase of COUPP.
Center: The recompression vessel in this prototype.
Right: Inner quartz vessel and pressure-compensation bellows for the same.

The 2kg Chamber is filled... and working! (summer 2004)

Half-way Filled.	Andrew Sonnenschein & Dante Nakazawa in front of COUPP.	The addition of the buffer liquid.
Side view.	Front View.