The funding and start of construction for the SuperCDMS SNOLAB experiment have been approved by the U.S. Department of Energy. The operations will be started in the early 2020s to search for hypothetical dark matter particles known as weakly interacting massive particles (WIMPs).
The experiment will be at least 50 times more sensitive when compared to its predecessor in investigating the properties of WIMPs that cannot be analyzed by other experiments, thereby offering scientists a robust, innovative tool to get insights into one of the biggest mysteries of modern physics.
The construction project for the international SuperCDMS collaboration of 111 members from 26 institutions has been managed by the DOE’s SLAC National Accelerator Laboratory. The collaboration has been preparing to perform the study with the help of the experiment.
Understanding dark matter is one of the hottest research topics—at SLAC and around the world. We’re excited to lead the project and work with our partners to build this next-generation dark matter experiment.
JoAnne Hewett, Head of SLAC’s Fundamental Physics Directorate & Chief Research Officer
With the help of the DOE approvals, called Critical Decisions 2 and 3, the scientists can now develop the experiment. The DOE Office of Science will contribute 19 million dollars toward the work, apart from the 12 million dollars contributed by the National Science Foundation and 3 million dollars contributed by the Canada Foundation for Innovation.
“Our experiment will be the world’s most sensitive for relatively light WIMPs—in a mass range from a fraction of the proton mass to about 10 proton masses,” stated Richard Partridge, head of the SuperCDMS group at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of SLAC and Stanford University. “This unparalleled sensitivity will create exciting opportunities to explore new territory in dark matter research.”
An Ultracold Search 6800 Feet Underground
Researchers are already aware that visible matter in the universe is attributive of just 15% of all matter. The remaining is a strange substance known as dark matter. The dark matter has a gravitational pull on normal matter, and is hence an important driver for the evolution of the universe, having an impact on the formation of galaxies, such as our Milky Way galaxy. Hence, it is fundamental to our very own survival.
However, researchers have not yet discovered the constituents of dark matter. They propose that it could be made of dark matter particles, of which WIMPs are on top. In case these particles exist, they would hardly interact with their surroundings and would fly untouched right through normal matter. Yet, now and then, they could collide with an atom of the visible researchers, and scientists studying dark matter are on the search for such rare interactions.
As part of the SuperCDMS SNOLAB experiment, germanium and silicon crystals will be used for the search, where tiny vibrations would be triggered by the collisions. Yet, if the atomic jiggles have to be measured, the crystals have to be cooled to less than −459.6 °F—a fraction of a degree over absolute zero temperature. The experiment gets its name—Cryogenic Dark Matter Search, or CDMS—from such ultracold conditions. The prefix “Super” relates to an improved sensitivity than earlier versions of the experiment.
Pairs of electrons and electron deficiencies that travel along the crystals would also be generated by the collisions, thereby triggering secondary atomic vibrations that amplify the signal from the collision of dark matter. With the experiment, the “fingerprints” left by dark matter can be measured with advanced superconducting electronics.
Assembly and operation of the experiment will be performed at the Canadian laboratory SNOLAB—6800 feet underground within a nickel mine at the city of Sudbury—which is the deepest underground laboratory in North America. In that location, it will be protected from high-energy particles, known as cosmic radiation, which can produce undesirable background signals.
“SNOLAB is excited to welcome the SuperCDMS SNOLAB collaboration to the underground lab,” stated Kerry Loken, SNOLAB project manager. “We look forward to a great partnership and to supporting this world-leading science.”
In the last few months, SLAC has successfully tested a detector prototype. “These tests were an important demonstration that we’re able to build the actual detector with high enough energy resolution, as well as detector electronics with low enough noise to accomplish our research goals,” stated KIPAC’s Paul Brink, who oversees the fabrication of the detector at Stanford.
In collaboration with seven other collaborating institutions, SLAC will develop the centerpiece of the experiment, that is, four detector towers, where each tower consists of six crystals with oversized hockey puck shape. It is estimated that the first tower will be sent to SNOLAB by the end of 2018.
“The detector towers are the most technologically challenging part of the experiment, pushing the frontiers of our understanding of low-temperature devices and superconducting readout,” stated Bernard Sadoulet, a collaborator from the University of California, Berkeley.
A Strong Collaboration for Extraordinary Science
Apart from SLAC, two other national labs have taken part in the study. Fermi National Accelerator Laboratory will be contributing toward the experiment in terms of intricate shielding and cryogenics infrastructure. Pacific Northwest National Laboratory will provide its assistance in understanding background signals in the experiment, a major difficulty for the detection of feeble WIMP signals.
Various U.S. and Canadian universities also have significant roles in the experiment, contributing their expertise toward tasks such as from detector fabrication and testing to data analysis and simulation. The major international contribution is from Canada and includes the research infrastructure at SNOLAB.
“We’re fortunate to have a close-knit network of strong collaboration partners, which is crucial for our success,” stated KIPAC’s Blas Cabrera, who directed the project through the CD-2/3 approval milestone. “The same is true for the outstanding support we’re receiving from the funding agencies in the U.S. and Canada.”
According to Dan Bauer from Fermilab, spokesperson of the SuperCDMS collaboration, “Together we’re now ready to build an experiment that will search for dark matter particles that interact with normal matter in an entirely new region.”
SuperCDMS SNOLAB will be the most up-to-date in a sequence of highly sensitive dark matter experiments. The latest version, located at the Soudan Mine in Minnesota, completed operations in 2015.
The project has incorporated lessons learned from previous CDMS experiments to significantly improve the experimental infrastructure and detector designs for the experiment. The combination of design improvements, the deep location and the infrastructure support provided by SNOLAB will allow the experiment to reach its full potential in the search for a low-mass dark matter.
Ken Fouts, Project Manager for SuperCDMS SNOLAB.