Cushman and Liu groups help SuperCDMS to major milestone

School of Physics and Astronomy faculty members Priscilla Cushman and Yan Liu are part of a collaboration that successfully cooled the Super Cryogenic Dark Matter Search (SuperCDMS) experiment to base temperature - the temperature required for the superconducting detectors to become operational.  This temperature is hundreds of times colder than outer space.

“Getting to base temperature is a major milestone in a years-long campaign to build a low-background facility capable of housing our sensitive cryogenic solid state detectors,” said Professor Cushman, who is also the Spokesperson for SuperCDMS. 

“At these extremely low temperatures, our installed detectors can now scan a whole new region of parameter space where the lightest dark matter particles may be lurking.”

Reaching base temperature marks a major transition for SuperCDMS, from construction and installation to commissioning and science operations. For SuperCDMS, that temperature is 0.025 degrees above absolute zero where all atomic and molecular motion ceases.

The experiment is designed to detect dark matter particles—mysterious particles that make up 85 percent of all matter in the Universe, trillions of which pass through your body every minute as the Earth passes through the dark matter cloud which surrounds our galaxy. Dark matter remains strange and illusive, but tremendously important to our understanding of nature, from the most fundamental particles to origins and evolution of the Universe.

Cushman’s research group designed, procured, and assembled the low background shield that protects the detectors from trace radioactivity and neutrons produced by high-energy cosmic rays in the cavern walls. The four-meter tall, four-meter-diameter cylindrical enclosure is made of layers of ultra-pure lead to stop gamma rays and high-density polyethylene to moderate neutrons. 

In addition to major roles in the installation and cooldown of the experiment, University of Minnesota researchers have developed new reconstruction algorithms and analysis techniques designed to rapidly extract dark matter signals from the data that will be flowing in a few months. Assistant Professor Yan Liu, who is the Analysis Working Group Chair for the experiment, led the effort to get the collaboration ready to meet the data challenges posed by SuperCDMS.

“Data coming from SuperCDMS SNOLAB will enable us to explore a significant amount of dark matter parameter space for the very first time,” Liu said. “By developing increasingly sensitive analysis frameworks, we hope to provide clearer insights into these fundamental questions.”

The SuperCDMS experiment is sited at SNOLAB, a research facility located roughly 6,800 feet underground in an active nickel mine near Sudbury, Ontario. At this depth, the experiment is protected from cosmic rays and other background particles that could drown out the faint signals scientists are trying to observe.

With the detectors at operating temperature, the collaboration will move into detector commissioning, a months-long process of turning on, calibrating and optimizing each detector channel. Beyond dark matter, SuperCDMS will allow scientists to study rare isotopes, solar axions and other exotic particles, probing energies no one has explored before and maybe uncovering entirely new kinds of particle interactions.

The SuperCDMS experiment is a joint project of the U.S. Department of Energy Office of Science, the U.S. National Science Foundation, the Canada Foundation for Innovation and the Natural Sciences and Engineering Research Council of Canada.

In addition to Cushman and Liu, the University of Minnesota team includes postdoctoral researchers Shubham Pandey and Himangshu Neog, research scientist Scott Fallows, graduate students, Zachary Williams, Elliott Tanner and Chi Cap, and undergrad Gunther Ahrens and Maxwell Leach — all from the School of Physics and Astronomy.