COUPP-500 kg: Design of a large-Mass Bubble Chamber for Dark Matter Detection

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This proposal will fund the COUPP (The Chicago-land Observatory for Underground Particle Physics) collaboration through the University of Chicago. The proposal is to employs moderately superheated liquids in the form of room-temperature bubble chambers, to search for dark matter particle candidates. A small engineering prototype containing 2 Kg of CF3I, has been successfully deployed and operated at a shallow depth resulting in an improved limits on spin-dependent WIMP-nucleus couplings. The collaboration has over the past year, introduced measures against radon percolation into the active volume, this together with longer exposures have improved the estimated reach of the technique by approximately two orders of magnitude. COUP WIMP search advantage over other detection technique is its sensitivity to spin dependence couplings. In parallel to these studies the collaboration has completed two larger chambers, one containing 15 kg of target mass, and the second 60 kg. After a short commissioning period in the NUMI gallery at FNAL the second chamber will be deployed during 2009 at the 6000 meter water equivalent depth at SNOlab. The next step funded by this proposal is for the collaboration to initiate a conceptual design of a 500 kg module. The design is to be based on a modest extrapolation of the system already developed and tested in the 60 kg chamber. The ultimate target mass is only limited by the commercial availability of large synthetic silica vessels. This is not considered to be an impediment, since for other reasons of convenience, safety and cost, a possible extension into the multi-ton experiment at DUSEL can very well take form as a small array of such modules. An initial 500-kg module shielded by a modest thickness vertical water tank would be a perfectly adequate as part of the initial set of DUSEL experiments. The relatively low cost of this approach to dark matter detection leaves an option of larger masses as a realistic possibility. The boarder impact of this proposal will include new opportunities for undergraduate participation in research in addition to graduate student and postdoc education. On the technical front, the application of the COUPP technique to cargo screening for fissile materials could have an significant impact. The whole field of dark matter search itself, the broad impact of a truly low-background detector technique would be very large.