Researchers at Pacific Northwest National Laboratory, after eight years of designing and building, have begun commissioning and cooling the MiniCLEAN detector, a small experiment with the big goal of detecting dark matter. CLEAN stands for Cryogenic Low-Energy Astrophysics with Nobles. Scientists will use the detector to search for weakly interacting massive particles, or WIMPs, as they interact with atoms in the detector.
To make this possible, the detector will be filled with over 500 kilograms of very cold, dense, ultra pure materials—argon at first, and later neon. If a WIMP passes through and collides with an atom’s nucleus, it will produce a pulse of light with a unique signature. Scientists can collect and analyze this light to determine whether what they saw was a dark matter particle or some other background event.
Though dark matter is much more abundant than the visible matter that makes up planets, stars and everything we can see, no one has ever identified it. Dark matter particles are chargeless, don’t absorb or emit light, and interact very weakly with matter, making them incredibly difficult to detect.
The use of both argon and neon allows MiniCLEAN to double-check any possible signals. Argon is more sensitive than neon, so a true dark matter signal would disappear when liquid argon is replaced with liquid neon. Only an intrinsic background signal from the detector would persist. Scientists would like to eventually scale this experiment up to a larger version called CLEAN.
MiniCLEAN is located in SNOLAB, a research facility 6,800 feet below the surface in Sudbury, Ontario, Canada. A thick layer of natural rock shields the clean laboratory where air quality, humidity and temperature are highly regulated. These conditions allow scientists to carry out extremely sensitive searches for elusive particles such as dark matter and neutrinos.
“What gives me the energy to persist on this project is that the CLEAN approach is unique, and there isn’t another approach to dark matter that is like it,” says Pacific Northwest National Laboratory scientist Andrew Hime, MiniCLEAN spokesman and principal investigator. “It’s been eight years since we starting pushing hard on this program, and finally getting real data from the detector will be a breath of fresh air.”