Distinguishing Dark Matter Signals from Neutron Backgrounds

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The nature of dark matter is one of the great mysteries in physics. Direct signals for dark matter have remained elusive. As future searches push to greater sensitivities and smaller interaction cross sections, backgrounds, especially from neutrons, will necessarily arise. Reducing these backgrounds to a negligible level through greater underground depths and more shielding will become impractical for very large detectors. Thus, as we move toward the time when dark matter searches will be performed at the Deep Underground Science and Engineering Laboratory, it is likely that we may have to depart from the zero-background paradigm, instead searching for signals above a well understood neutron background. This problem calls for a new approach to dark matter searches. The research objective of this award is a search for a dark matter signal above a well understood neutron background, using a liquid Argon (LAr) dark matter detector (MiniCLEAN) underground in SNOLab. The goals of this research are: (i) to develop methods for measuring the neutron background in-situ in LAr dark matter detectors using multiple scattering, inelastic scattering, and neutron capture on 40-Ar; (ii) to develop an active neutron veto surrounding the dark matter detector; and (iii) to apply statistical tools incorporating these neutron background measurements in a dark matter search for signal above background. The MiniCLEAN design is a new direction for dark matter searches. It draws on highly successful, proven approaches of solar neutrino physics to building low-background detectors that scale simply to multi-tonne targets. Successful demonstration of this approach for dark matter by MiniCLEAN will break new ground for future, very large detectors. Success depends critically on background suppression; addressing the difficult neutron component is the focus of this proposal.Broader impacts: Measurements of the neutron flux using these new methods will provide timely input to designing future large dark matter detectors, as well as shielding for other low background experiments, including neutrino-less double beta decay and low-energy solar neutrino experiments.