In late October, the detector for the LUX-ZEPLIN (LZ) dark matter experiment was moved from a clean room on the Earth’s surface to its new home 4,850 feet underground. The LZ experiment, located at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, is designed to search for dark matter interactions and perhaps detect a dark matter particle for the first time.
Astrophysical observations have led to the conclusion that about 80% of the matter in the universe is made up of dark matter. But despite overwhelming indirect evidence for its existence, dark matter has eluded direct detection. Theory predicts that dark matter particles would interact very weakly with normal matter, making them challenging to detect. Dark matter particles are also thought to be heavy: a single particle could weigh about the size of a silver atom. These two properties are combined into a possible dark matter particle called a “weakly interacting massive particle,” or a WIMP. The LZ experiment will provide the most sensitive detector ever built for detecting dark matter.
U-M Physics Professor Wolfgang Lorenzon and graduate student Maris Arthurs are members of the LZ collaboration. Regarding the move, Professor Lorenzon says, “This marks a major milestone in getting the LZ experiment underground and ready for science in about 6 months from now.”
In 2020, LZ will start taking data using a 10-ton tank of liquid xenon called a time projection chamber. When an interaction occurs between a particle and a xenon atom, light-sensitive detectors surrounding the chamber are used to find the location of the interaction within the xenon tank. Some of these interactions are unwanted and are known as “background,” and finding the location of the interaction within the tank is one tool for distinguishing background from interactions that could come from dark matter particles.
Part of U-M’s efforts in the LZ collaboration has been in the reduction of radon atoms present in the xenon tank. Radon is the largest source of background in the experiment, and it is produced constantly via radioactive decay. Professor Lorenzon and his group worked to develop a charcoal trap that will filter out the radon and decrease the background contribution tenfold. This in turn significantly increases the sensitivity of the experiment to dark matter interactions.
Regarding his work with the LZ collaboration, Mr. Arthurs says, “The time projection chamber (TPC) is the innermost component and the heart of the LZ detector. Working alongside my colleagues on the assembly of a section of the TPC was a remarkable experience. Now, that the TPC was successfully moved underground to its final destination, we are one major step closer to our first science data.”