LZ Sees Surprising Result in Search for Dark Matter: South Dakota Mines Researchers Excited About Potential of New Particle Interaction

For the better part of a century, people have been trying to understand dark matter. This invisible substance makes up roughly 85% of the mass in the universe but has never been directly detected. Determining exactly what it is remains one of the biggest questions about our world.

Now, a new analysis from the LUX-ZEPLIN (LZ) experiment has recorded a single particle interaction that researchers have great difficulty explaining with known background signals from normal matter. The result does not yet meet the statistical threshold required to claim a discovery, but is the most compelling hint of dark matter reported by the experiment to date.

“This time of uncertainty as to whether this event is some sort of background or the first hint of dark matter is very exciting,” said Richard Schnee, Ph.D., head of the physics department at South Dakota Mines. Schnee is among the world's leading researchers on radon mitigation for ultra-sensitive physics experiments such as LZ. Schnee led the design and build team for a critical system that removed radon from the LZ cavern. “All of us in the LZ collaboration have been trying to figure out what kind of process other than dark matter could possibly give rise to an interaction like this, high-energy, single-site interaction far from the detector edges, and with signals consistent with a recoiling nucleus.”  

LZ is an international collaboration of 250 scientists and engineers from 39 institutions, including Mines. The detector is managed by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and operates nearly one mile below ground at the Sanford Underground Research Facility (SURF) in South Dakota. The experiment uses 10 tons of ultrapure liquid xenon to search for dark matter and is optimized to look for WIMPs, or weakly interacting massive particles.

The results were presented in a scientific talk at the 2026 TeV Particle Astrophysics conference in Japan. The paper will be released on the online repository arXiv and submitted to the journal “Physical Review Letters.”

“We’re very intrigued to see this event in the data, in the region where we expect dark matter to show up and the competing backgrounds are very low,” said Rick Gaitskell, a professor at Brown University and the spokesperson for LZ. “With only one event, we don’t want to get ahead of ourselves. We are not claiming to have seen dark matter. But we have seen something interesting that we want to share with the scientific community for their input.”

The LZ collaboration studies experimental data in batches. In the new result, researchers analyzed 220 live days of data collected between March 2023 and April 2024. The collaboration had previously searched this dataset for faint signals from the simplest kinds of WIMP interactions. The new analysis searched for a broader range of possible WIMP interactions that could deposit more energy in the detector. LZ is particularly sensitive to such signals while also minimizing false positives.

“This was a detailed study in a region we hadn’t explored within this dataset, and we spent months of additional effort to understand all the possible causes of background events,” said Sam Eriksen, a senior research associate at the University of Bristol in the U.K. and lead author of the study. “We understand our detector and the backgrounds so well that even a single outstanding event, like the one we found, is important. We expect dark matter events to be extremely rare, so only a handful could mark the first detection of WIMP dark matter.”

If the anomalous event was caused by dark matter, the WIMP that generated it would likely have a mass of at least 200 GeV/c² (gigaelectronvolts), or more than 200 times the mass of a proton. It would also suggest a specific type of interaction between WIMPs and ordinary matter beyond the simplest model. The LZ results have not reached “5-sigma” significance, the statistical threshold considered a discovery in physics. The new analysis is 2.6 sigma, meaning there is approximately a 0.5% chance that the event could be explained by known backgrounds.

“WIMP dark matter detection has been a holy grail of particle physics for the past few decades,” said Sagar Sharma Poudel, Ph.D., a Mines postdoctoral researcher. “Experiments have become increasingly sensitive to these rare signals, with LZ leading the field. We have identified an event that we cannot explain with known background sources, making it a particularly intriguing candidate for a possible WIMP signal.”

With additional data, researchers can test whether the finding continues to grow in significance or fades away. LZ has already accumulated the world's largest dark matter dataset and will continue to accrue WIMP search data at SURF, substantially improving their search statistics.

“We have two years of data already collected and yet to be analyzed,” Schnee said. “So, we will hopefully be able to learn whether this is some sort of interaction from normal atoms or an interaction from dark matter, within the coming years.”

LZ searches for dark matter by looking for signature flashes of light from energy deposited in the detector. The collaboration leverages multiple methods to prevent or account for particle interactions caused by normal matter. This includes the mile of rock that shields the detector from cosmic rays from space, a water tank and outer detectors that protect the central detector from background neutrons, and a suite of computational tools that disentangle particle interactions and reject dark matter mimics.

“Outlier events in the data are not unexpected, but they usually stand out as a background of some kind when you look at them deeper,” said Aaron Manalaysay, a physicist at Berkeley Lab and the chair of LZ's Institutional Board. “This is the first example in any experiment I've worked on of an outlier that appears valid in every way. Of course, we're still twisting our brains trying to think if there's a rare background mechanism we could've missed, but it's thrilling to wonder if this could be the first hint of a dark-matter observation.”

Juergen Reichenbacher, Ph.D., associate professor in the Mines physics department, started working with the LZ experiment in 2012. Reichenbacher and his team focused on calibration source characterization and deployment, correcting signal losses and implementing remote control capabilities to operate the LZ detector deep underground.

"Without regularly calibrating the detector, we would basically fly blindly and could not possibly interpret the data that LZ recorded up to now as a potential dark matter particle,” Reichenbacher said.

Reichenbacher's research scientist Gleb Sinev, Ph.D., leads the team responsible for LZ’s remote system control of the detector. "One could reasonably argue that comprehensive remote-control capabilities to operate and monitor the LZ detector underground 24/7 have been mission-critical to record enough quality data in time to be able to come out now with our new exciting dark matter search result, and in the near future, it will be crucial to cross-check our result with even more LZ data,” he said.

Mines has several students, including undergraduates, performing research on LZ or conducting research and development for a next-generation experiment to achieve greater sensitivity after LZ is complete.

“I am very excited to be a part of a collaboration that has such exciting results,” said Victor Hanson, a senior physics and math major. “The reason I became interested in science is because I wanted to be at the forefront of human knowledge and be able to contribute to discoveries. Although the work I did with LZ did not directly contribute to this, the work that I am doing is working towards reducing backgrounds in future dark matter experiments by working on the next generation of radon mitigation systems. I am excited to see further results once more data is analyzed.”

Rayyan Abdullah, a physics doctoral student at Mines, joined the collaboration last year. “I did not expect such an interesting result so soon,” he said. “Even though I did not contribute to this result, I am proud to be part of the LZ collaboration that has made tremendous progress towards the goal of detecting dark matter. This one event might be a big step toward that goal, and I am excited to make contributions to this goal in the future.”

LZ is supported by the U.S. Department of Energy, Office of Science, Office of High Energy and Nuclear Physics, and the National Energy Research Scientific Computing Center, a DOE Office of Science user facility. LZ is also supported by the Science & Technology Facilities Council of the United Kingdom; the Portuguese Foundation for Science and Technology; the Swiss National Science Foundation; the Australian Research Council Centre of Excellence for Dark Matter Particle Physics; and the Institute for Basic Science, Korea. Thirty-nine institutions of higher education and advanced research provided support to LZ. The LZ collaboration acknowledges the assistance of the Sanford Underground Research Facility.

This release was first published by Lawrence Berkeley National Laboratory. The original can be found on their website here.