Observations of galaxies, superclusters, distant supernovae, and the cosmic microwave background radiation tell us that about 85% of the matter in the universe is not made of known particles. Deciphering the nature of this dark matter would be of fundamental importance to cosmology, astrophysics, and high-energy particle physics. A leading hypothesis is that it is comprised of Weakly Interacting Massive Particles, or WIMPs, that were produced moments after the Big Bang. If WIMPs are the dark matter, then their presence in our galaxy may be detectable via scattering from atomic nuclei in a terrestrial detector.
The Cryogenic Dark Matter Search (CDMS) Collaboration has pioneered the use of low temperature phonon-mediated detectors to detect the rare scattering of WIMPs on nuclei and to distinguish them from backgrounds. This powerful technology is operating deep underground in the Soudan mine in Minnesota. This award provides construction funding for the SuperCDMS Soudan project which will extend the deployed germanium target mass at Soudan from the present 4 kg to 15 kg.
The SuperCDMS experiment will have a broad impact which extends beyond the dark matter search. The technical developments will further advance phonon-mediated detectors, which have already found many applications in cosmology, astronomy and industry. The project will contribute to the training of undergraduate and graduate students, and postdoctoral researchers, using techniques at the leading edge of measurement technologies. In addition, the SuperCDMS collaboration will expand its public outreach program at the Soudan mine.
Weakly Interacting Massive Particles (WIMPs) are one of the main candidates to explain the mysterious dark matter in the universe, through new particle physics at the "TeV scale" or a "dark sector" which could co-exist with the ordinary matter that we know. A number of experiments are attempting to detect the WIMPs from the halo of our galaxy through their scattering in sophisticated detectors located deep underground. Over the last 25 years, the National Science Foundation and the Department of Energy have supported a number of experiments to check this hypothesis. The Cryogenic Dark Matter Search, CDMS, uses sophisticated low temperature detectors currently operating underground in the Soudan (MN) mine, to detect interactions of these putative WIMPs and distinguish them from experimental background. We measure both the quantized crystal vibrations (phonons) and the charged produced (ionization) produced by particle interactions. This is based on a combination of advanced photolithographic techniques, state-of-the-art superconducting and semi-conductor electronics, and low radioactivity techniques. This SuperCDMS Soudan award has supported six NSF university groups in their responsibilities in the construction, testing and deployment of a new generation of low temperature detectors in the Soudan underground facility. This NSF support was coordinated with a DOE award that supported this project at Fermilab and the collaborating DOE universities. The installed payload represents a total of 9 kg of Germanium, which, because of the much higher background rejection efficiency of the new detectors, is equivalent to a factor 5 improvement over the 4kg previously deployed in CDMS II. Routine data are being taken since March 2012 and have lead already to two publications, one on the impressive rejection power of the detectors and another improving on our world leading limits for very low mass WIMP. The results of a third analysis on low mass WIMP should be published in January 2014 and a fourth analysis focus on high mass WIMP is scheduled for public release in the Spring 2014. Analysis is expected to continue for another two years. In the course of this project we have made significant progress in the development of our low temperature technology, both in terms of phonon sensing and of the geometry of our ionization collection, which provides exceptional surface background rejection. These new techniques will undoubtedly have broad applications not only in the second generation of dark matter experiments but also in other fields such as neutrinoless double beta decay and detection of coherent neutrino scattering. Although this project did not them support directly, this award has provided the infrastructure needed for the PhD for some seven graduate students and the research of three postdocs. Ten undergraduate students were also directly involved. An active outreach program at Soudan and in the participating universities accompanied this project.
