Grant: Subatomic Physics Envelope - Project

The DEAP collaboration has been vary active with detector construction completion, cooldown, filling with liquid argon, detector commissioning, data collection and analysis. Operation of the detector will continue through the period covered by this request, and will require significant collaboration effort, enabled by the requested funds. The origin of dark matter in our universe is currently one of the most important questions in particle astrophysics. It is well-established that most of the matter in our universe is dark. A favored hypothesis is that the dark matter consists of WIMPs, weakly interacting massive particles, which could be detected by observing their elastic scattering from nuclei. This proposal builds on research using liquid argon for a sensitive dark matter search. The current best limit on the spin-independent WIMP-nucleon cross-section is approximately 2.2x10^-46 cm^2 for a WIMP mass of 50 GeV, obtained by the LUX collaboration. Scaling the current-generation experiments to larger masses is critical since current theoretical models predict that improvements of sensitivity of several orders of magnitude may be needed before dark matter particles can be detected. Our research targets sensitivity to the WIMP-nucleon cross-section of 10^-46 cm^2 for a 100-GeV WIMP, and with good sensitivity to high-mass WIMPs. Noble liquids as low-energy particle astrophysics detectors have gained much interest since many of these can be cleaned to extremely low levels of radioactivity, and it is recognized that these can be used to build very large target mass detectors. Unique to the DEAP-3600 experiment is the novel technique of providing discrimination based on the time evolution of the scintillation pulse. This leads to a simple detector design that can be scaled to a very large target mass. The detector includes a large spherical acrylic vessel viewed by photomultiplier tubes (PMTs) to allow the recording of the evolution of a scintillation event in the argon. The PMT positions for each event will be used to estimate the initial event vertex, and serve as the primary rejection for external-source background events to allow a fiducial target mass of approximately 1000 kg of argon. The experiment resides in a large shielding tank approximately 8 meters in diameter and 8 meters high. Construction of the detector was completed in 2015, and the collaboration has been commissioning the detector systems and performing detector calibration, in preparation for the science run with liquid argon. This proposal will lead to further training of HQP in Canada. In addition to attracting students and international highly qualified researchers, it is anticipated that several post-doctoral fellows and RAs will be supported by the requested funds, in addition to technical personnel to enable operations at the experimental site.