Observations indicate that 85% of the matter in the Universe is not made of normal atoms but must be otherwise undetected elementary "dark matter" particles that do not emit or absorb light. Remarkably, particle physics theories proposed for other reasons predict the existence of Weakly Interacting Massive Particles (WIMPs) with just the right properties to be this dark matter. If WIMPs are the dark matter, they may be detectable when they scatter in Earth-based detectors. Direct detection of WIMP dark matter would solve a fundamental mystery in particle physics and cosmology, providing a unique window to learning about the primary matter constituents of the Universe and of physics beyond the Standard Model of particle physics. Over the past three years, the SuperCDMS collaboration has led the field in the search for low-mass dark matter.  The most recent results from CDMSlite reached an energy threshold for electron recoils as low as 56 eV. These results excluded new parameter space for the dark matter-nucleon spin-independent cross section for dark matter masses between 1.6 and 5.5 GeV/c2.  This project will focus on better understanding the response of the signal detectors in a push to make the SuperCDMS yet more sensitive.The SuperCDMS SNOLAB experiment will have a broad impact which extends beyond the search for dark matter. The experiment's phonon-mediated detectors have applications in cosmology, astronomy and industry. This effort will contribute opportunities for training of undergraduate and graduate students and postdoctoral researchers. SuperCDMS will engage in education and outreach at local institutions and will coordinate outreach at SNOLAB and the Sanford Underground Research Facility (SURF) in South Dakota to increase the broader impact with a focus on secondary education. This award will support participating in SNOLAB-hosted teacher workshops, modifying and providing middle school dark matter education modules to U.S. educators, and maintaining SuperCDMS-related outreach materials for SNOLAB in Canada and SURF. Existing alliances will enable out-reach to Sudbury First Nations communities. This effort will also support post-graduate education and outreach to underrepresented groups.In order to maximize the science output of SuperCDMS SNOLAB, detailed understanding of the response of detectors to potential signals and backgrounds is required. Measurements at two underground facilities (NEXUS at Fermilab and CUTE at SNOLAB) will characterize and calibrate pre-production SuperCDMS SNOLAB detectors and the first production SuperCDMS SNOLAB towers, with supporting measurements from small devices at university test facilities. Resulting data will allow energy scale calibration, measurements of background levels, understanding of the detailed phonon and electron physics of the detectors, development of improved background-rejection techniques, validation and tuning of Detector Monte Carlo, and optimization of SuperCDMS SNOLAB operational parameters. These data should also provide a dark matter search with world-leading sensitivity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.