Dark matter is the invisible stuff that accounts for roughly 85% of the mass in the universe, and for decades, physicists have been trying to figure out what it’s made of. Now an experimental facility located nearly a mile below ground in South Dakota has recorded a single interaction between subatomic particles that doesn’t match what’s expected from normal matter.
Has a dark-matter particle been detected at last? It’s too early to say, but the anomaly is attracting attention from dark-matter detectives.
The detection was made at the Sanford Underground Research Facility, or SURF, a converted gold mine that now houses the world’s most sensitive detector for dark matter. Since 2021, the LUX-ZEPLIN Dark Matter Experiment has been recording flashes of light in a shielded tank that’s filled with 10 tons of ultra-pure liquid xenon. Those flashes occur when weakly interacting massive particles, or WIMPs, collide with xenon atoms.
The results are analyzed by an international team of 250 scientists and engineers from 39 institutions. The U.S. Department of Energy’s Lawrence Berkeley National Laboratory manages the experiment.
Researchers recently reviewed 220 days’ worth of data collected by the detector between March 2023 and April 2024. An earlier analysis searched for faint signals from the simplest kinds of WIMP interactions, but the follow-up review widened the search parameters to look for more energetic interactions. One event exhibited a spectrum of nuclear recoil energy that was difficult to explain in the context of known background signals involving normal matter.
“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,” Rick Gaitskell, a professor at Brown University and the spokesperson for LUX-ZEPLIN, said in a news release. “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.”
A report on the research was presented this week in a scientific talk at the 2026 TeV Particle Astrophysics conference in Japan. The report will be submitted to Physical Review Letters for publication.
The research team’s analysis determined that the particle behind the anomalous event would have more than 200 times the mass of a proton — if it was truly a piece of dark matter. But it’s too early to make that assumption. The significance level for the detection was 2.6 sigma, which is well below the 5-sigma standard for claiming a discovery. For now, the statistics suggest there’s a roughly 0.5% chance that the event could be explained by known background interactions.
Daniel Akerib, a physicist at SLAC National Accelerator Laboratory and a member of the LUX-ZEPLIN science team, said it will take more than one anomalous event to solve the decades-old mysteries surrounding dark matter.
“You would want to see the result confirmed, learn its coupling to matter by seeing it in another isotope — possibly liquid argon,” he said via email. “You would also want to produce it (and its cousins) in the laboratory. Seeing something go ‘bump’ is quite different from being able to determine its cosmological abundance.”
The dark-matter mystery dates back to the 1930s, when Swiss astronomer Fritz Zwicky noted that the total mass of the galaxies in the Coma Cluster had to be hundreds of times greater than what could be accounted for by visible starlight. In the 1970s, American astronomer Vera Rubin found that the “missing mass” problem extended to a wide range of galaxies. Astrophysicists eventually came to the conclusion that the missing mass consisted of invisible matter. But what was it, exactly?
WIMPs are currently the prime suspects in the dark-matter mystery. For a time, physicists also proposed that dark objects made of ordinary matter — such as rogue planets, burned-out stars, brown dwarfs and primordial black holes — might make up the missing mass. Astronomical surveys eventually determined that there weren’t enough of those massive compact halo objects, or MACHOs, to explain the abundance of dark matter. Other suspects in the cosmic lineup include strongly interacting massive particles, or SIMPs, and a theoretical class of light subatomic particles known as axions.
LUX-ZEPLIN isn’t the only experiment looking for signs of dark matter. The XENON Dark Matter Project at Italy’s Gran Sasso National Laboratory and the China Jinping Underground Laboratory are also in on the hunt.
Today, scientists say only about 5% of the universe’s mass-energy content consists of ordinary matter, with 27% consisting of dark matter. The other 68% appears to consist of dark energy, the force that’s thought to drive the accelerating expansion of the universe. NASA’s Nancy Grace Roman Space Telescope, which was launched earlier this week, is expected to shed additional light on the nature of dark energy as well as dark matter.
This report was published on Universe Today with the headline “Scientists Intrigued by a Surprising Result in the Search for Dark Matter.” Licensed for republication under Creative Commons Attribution 4.0 International License.
