Particle Astrophysics with Neutrinos and Weakly Interacting Dark Matter: Borexino and DarkSide

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This award provides base support for the particle astrophysics program at the University of Massachusetts, Amherst to participate in the Borexino solar neutrino experiment and the DarkSide project for the search of weakly interacting particle dark matter (WIMPs) in our galaxy. Solar neutrinos have played a crucial role in the experimental confirmation that neutrinos have mass and oscillate. Since data acquisition started in 2007, Borexino has reached its design goal and measured the flux of mono-energetic 7-Beryllium solar neutrinos with enough precision to test the predictions of current solar models. After a scintillator purification campaign in 2011, Borexino is in a new phase of solar neutrino physics with the goal of measuring the entire solar neutrino spectrum. A precise knowledge of solar neutrinos will allow us to understand how the sun and other stars work, test the MSW-LMA neutrino oscillation paradigm and search for deviations from it. Borexino will possibly resolve an open question on the metallicity of the Sun's core, an important piece of information with which to study the evolution of larger stars in the universe. DarkSide-50, a dual-phase time projection chamber scheduled to come online in late 2012, will prototype design solutions for background free multi-tonne detectors with liquid argon as active target for WIMPs. A null observation would exclude some of the current leading dark matter candidates. A positive detection would begin to give answers to one of the big scientific unknowns of our times. DarkSide-50 will run with 50 kg of argon depleted more than 100-fold in the radioactive 39-Argon isotope. The DarkSide-50 Argon cryostat is surrounded by a compact, liquid scintillator neutron detector and immersed in the Borexino Counting Test Facility (CTF) water tank instrumented and operated as a Cherenkov muon veto. The Borexino and DarkSide collaborations have a significant overlap in personnel and technical and operational resources. Broader Impacts: The Borexino and DarkSide projects provide excellent opportunities for the training of graduate and undergraduate students in applications of software and hardware development, and fundamental physics. The techniques developed for Borexino and Darkside-50 can more broadly benefit technology relevant for medical imaging, nuclear non-proliferation and geology.