Experimental Particle Cosmology: Search for Dark Matter

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A broad range of observations-from galaxies and superclusters to distant supernovae, and the cosmic microwave background radiation, all giving consistent results-tells us that about 85% of the matter in the universe is not made of ordinary particles. Deciphering the nature of this dark matter would be of fundamental importance to cosmology, astrophysics, high-energy particle physics, and our understanding of gravity. A leading hypothesis is that dark matter is comprised of Weakly Interacting Massive Particles, or WIMPs, an elementary particle beyond the Standard Model of particle physics, but predicted in various extensions, such as supersymmetry. If WIMPs are the dark matter, then their local density in our region of the Milky Way potentially makes them detectable via scattering from atomic nuclei in a terrestrial detector.The Cryogenic Dark Matter Search (CDMS) Collaboration, supported jointly by NSF and DOE, has pioneered the use of low temperature phonon-mediated detectors to distinguish the rare scattering of such WIMPs on nuclei from the prominent electron interactions from radioactivity. Using our powerful technology in the Soudan mine, with our high background rejection, CDMS is currently (July 05) the most sensitive WIMP search experiment in the world, by a factor of ten. The two years of funding provided by this award, will mainly support the operation of CDMS II at Soudan in order to extract the best science possible from the five towers of six detectors that we now have installed. Taking over from the CDMS II funding in January 2006, this NSF base funding will allow Berkeley to participate in the extension of CDMS running till June 2007 and in the analysis of the data collected. This should allow us to multiply our raw exposure by roughly a factor twenty and improve our current sensitivity by a factor ten. Berkeley's emphasis will remain the optimization of the detector performance and continuous performance monitoring, improvement of the electronic noise and further development of discrimination methods. The base funding will also support a modest effort of detector characterization in the laboratory, which will believe will become increasingly necessary to demonstrate the discrimination level reached in our analyses.We will also devote approximately 20% of the base funding to R&D for the future stages of CDMS. This second component is essential in maintaining the CDMS leadership worldwide and prepare for extrapolation to larger masses. The Berkeley effort will be divided between the development of the cold hardware for the detectors of the phase A of SuperCDMS (25kg total target mass), the test of phase A detector prototypes produced by Stanford and the study of kinetic inductance phonon sensing for the phase B or C of SuperCDMS (150 kg target mass or more).This proposal will partially support the research of three graduate students. Our education and outreach activity will focus on the improvement of the displays for the science tours at Soudan and on the apprenticeship program for East Bay High-School students. For the latter program, we have entered into collaboration with the SMASH summer academy, which supports academically high school students from underserved backgrounds. Based on last years pilot program involving one of their 9th Grade students in our laboratory, we are planning to have two student apprentices per year over the duration of this award.