The US Department of Energy has approved funding and construction for the SuperCDMS SNOLAB experiment, which in the early 2020s will rely on hypothetical dark matter particles called weakly interacting massive particles or WIMPs.
The experiment will be at least 50 times more sensitive than its predecessor, exploring WIMP properties that can not be explored by other experiments, and providing researchers with a powerful new tool to understand one of the greatest mysteries of modern physics [1
"Understanding dark matter is one of the hottest research topics at SLAC and around the world," said JoAnne Hewett, director of the SLAC Physical Main Directorate te and the research director of the lab. "We look forward to leading the project and working with our partners to develop this next-generation dark matter experiment."
With the DOE approvals, the so-called Critical Decisions 2 and 3, the researchers can now create the experiment. The DOE Office of Science will provide $ 19 million and join forces with the National Science Foundation ($ 12 million) and the Canada Foundation for Innovation ($ 3 million).
"Our experiment will be most sensitive to relatively light WIMPs – in a mass range from a fraction of the proton mass to about 10 proton masses," said Richard Partridge, director of the SuperCDMS Group at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of SLAC and Stanford University. "This unprecedented sensitivity will create exciting opportunities to explore new areas of dark matter exploration."
Scientists know that visible matter in the universe accounts for only 15 percent of all matter. The rest is a mysterious substance called dark matter. Because of its attraction to regular matter, dark matter is a key factor in the evolution of the universe and influences the formation of galaxies like our Milky Way galaxy. It is therefore fundamental to our own existence.
But scientists still have to figure out what dark matter is made of. They believe that it could consist of dark matter particles, and WIMPs are top contenders. If these particles exist, they would barely interact with their environment and remain untouched by normal matter. However, they could occasionally collide with one atom of our visible world, and dark matter researchers seek these rare interactions.
In the SuperCDMS SNOLAB experiment, the search is carried out with the help of silicon and germanium crystals. The collisions would trigger tiny vibrations. However, to measure the atomic shakes, the crystals must be cooled to less than minus 459.6 degrees Fahrenheit – a fraction of a degree above absolute zero. These ultracold conditions give the experiment its name: Cryogenic Dark Matter Search or CDMS. The prefix "Super" indicates increased sensitivity compared to previous versions of the experiment.
The collisions would also create pairs of electrons and electron deficiencies that move through the crystals and trigger additional atomic vibrations that amplify the dark matter collision signal. The experiment will be able to measure these "fingerprints" of dark matter with sophisticated superconducting electronics.
The experiment is being assembled and operated at the Canadian SNOLAB laboratory – 6,800 feet underground at a nickel mine near the town of Sudbury. It is the deepest underground laboratory in North America. There it is protected from high-energy particles, cosmic rays, which can produce unwanted background signals.
"SNOLAB is pleased to welcome the SuperCDMS SNOLAB collaboration to the underground laboratory," said Kerry Loken, project manager of SNOLAB. "We look forward to a great partnership and support for this world-leading science."
In recent months SLAC has successfully tested a detector prototype. "These tests were an important demonstration that we are able to build the actual detector with high enough energy resolution and detector electronics with enough noise to meet our research goals," said Paul Brink of KIPAC, who has completed the detector fabrication at Stanford  Together with seven other cooperating institutions, SLAC will provide the center of the experiment with four detector towers, each containing six crystals in the form of oversized hockey pucks. The first tower could be sent to SNOLAB by the end of 2018.
"The detector towers are the most technologically sophisticated part of the experiment, pushing the boundaries of our understanding of cryogenic devices and superconducting readings," said Bernard Sadoulet, a staff member at the University of California, Berkeley
In addition to SLAC, there are two other national laboratories involved in the project. The Fermi National Accelerator Laboratory is working on the complex screening and cryogenic infrastructure of the experiment. The Pacific Northwest National Laboratory helps understand background signals in the experiment, a major challenge for detecting weak WIMP signals.
A number of US and Canadian universities also play key roles in experimentation and work on tasks ranging from detector fabrication and verification to data analysis and simulation. The largest international contribution comes from Canada and includes the research infrastructure at SNOLAB.