For nearly a century, scientists have been trying to identify dark matter, the invisible material thought to account for about 85% of all matter in the universe. Its gravitational effects can be seen throughout the cosmos, yet no experiment has directly detected the substance itself. Discovering what dark matter is made of remains one of the most important unresolved problems in modern physics.
A new analysis from the LUX-ZEPLIN (LZ) experiment has now uncovered a particularly intriguing event. Researchers recorded a single particle interaction that has proven difficult to explain using known background signals produced by ordinary matter.
The finding is not statistically strong enough to qualify as a discovery. Even so, researchers say it represents the most compelling potential dark matter signal LZ has reported so far.
A Giant Detector Nearly a Mile Underground
LZ is an international project involving 250 scientists and engineers from 39 institutions. The experiment is managed by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and operates nearly one mile underground at the Sanford Underground Research Facility (SURF) in South Dakota.
At the heart of the detector are 10 tonnes of extremely pure liquid xenon. The instrument was designed primarily to search for WIMPs, or weakly interacting massive particles, one of the leading candidates proposed to explain dark matter.
The new results were presented during a scientific talk at the 2026 TeV Particle Astrophysics conference in Japan. The paper will also be posted to arXiv and submitted to 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.”
Searching a New Part of the Data
The LZ collaboration examines its experimental results in batches. For this latest study, scientists analyzed 220 live days of observations gathered between March 2023 and April 2024.
Researchers had previously searched the same dataset for very faint signatures associated with the simplest forms of WIMP interactions. This time, they expanded the search to include a wider variety of possible WIMP interactions capable of depositing larger amounts of energy inside the detector.
LZ is especially sensitive to events of this kind, while its design also helps scientists reduce the chances of mistaking ordinary particle interactions for dark matter.
“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.”
What the Mysterious Event Could Mean
If dark matter really did produce the unusual signal, the responsible WIMP would probably have a mass of at least 200 GeV/c2 (gigaelectronvolts). That would make it more than 200 times as massive as a proton.
Such a result would also point toward a particular type of interaction between WIMPs and ordinary matter that goes beyond the simplest models typically considered in dark matter searches.
There is an important reason scientists are remaining cautious. Particle physics generally requires a result to reach “5-sigma” statistical significance before it is considered a discovery. The new LZ finding currently sits at 2.6 sigma.
According to the researchers, that corresponds to roughly a 0.5% chance that the unusual event could be produced by known background sources.
More observations will be crucial. As LZ collects additional data, scientists will be able to see whether the statistical significance of the event increases or whether the apparent signal eventually disappears.
LZ has already assembled the world’s largest dataset for dark matter searches and will continue gathering WIMP data at SURF, giving researchers much stronger statistics in the future.
How LZ Separates Dark Matter From Background Noise
The experiment searches for dark matter by watching for characteristic flashes of light created when particles deposit energy inside the detector.
The challenge is that ordinary matter can also produce particle interactions. LZ therefore uses several layers of protection and analysis to identify these background events and prevent them from being mistaken for dark matter.
Its underground location provides one of the first defenses. Nearly a mile of rock above the experiment blocks much of the cosmic ray radiation arriving from space. A surrounding water tank and additional outer detectors help shield the central detector from background neutrons.
Researchers also use sophisticated computational techniques to distinguish different kinds of particle interactions and reject events that imitate the signatures expected from dark matter.
The unusual event has attracted particular attention because, so far, it has not revealed the kinds of problems scientists normally find when they investigate an outlier more closely.
“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.”
For now, one unexplained event is not enough to say that dark matter has finally been detected. But because the signal appeared in a region where dark matter could be expected and has survived extensive scrutiny, researchers believe it deserves close attention as the experiment continues collecting data.
International Support for the Dark Matter Search
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.
Additional support comes from 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 also acknowledges the assistance of the Sanford Underground Research Facility.
