An international team of scientists says it has detected an intriguing signal that could point to the existence of dark matter, offering a clue that may bring researchers closer to solving one of physics' biggest mysteries.
The signal was picked up by the LUX-ZEPLIN experiment, known as LZ, a detector containing 7 metric tons of active liquid xenon housed nearly 1.5 kilometers underground in a former gold mine at the Sanford Underground Research Facility in South Dakota. The detector recorded an unusual particle interaction in June 2023 that produced a flash of light and cautious excitement among researchers.
The LZ Collaboration is an international group of 250 scientists and engineers from 39 institutions. After months of analysis, the team estimates there is only a 0.5% chance that a known source of interference caused the event, making it the most convincing hint of dark matter the instrument has ever recorded.
Dark matter makes up about 85% of all matter in the universe and is roughly five times more abundant than the ordinary matter that forms stars, planets and everything else scientists can observe. It is invisible because it neither absorbs nor reflects light, but its gravitational effects are needed to explain the structure of the universe. For nearly half a century, since American astronomers Vera Rubin and W. Kent Ford provided some of the strongest evidence of its existence, scientists have tried to identify the substance using increasingly sophisticated detectors.
Even so, claiming a discovery requires a much higher degree of confidence, according to Alvine Kamaha, an assistant professor of physics at the University of California, Los Angeles, and a member of the LZ Collaboration who helped build the detector. She said in an email that a single event on its own is not enough, and that researchers need to see whether additional events emerge as more data is collected and whether the statistical significance of the observation grows.
Sam Eriksen, a senior research associate in physics at the University of Bristol and a member of the LZ Collaboration, presented the findings on September 1 at the TeV Particle Astrophysics 2026 conference in Japan, and the team has submitted a study for publication in the journal Physical Review Letters.
Researchers are now working on additional analyses that could raise the statistical significance of the event. The threshold for declaring a discovery in particle physics is known as five-sigma, representing roughly a 1-in-3.5-million chance that a result is a statistical fluke rather than a genuine signal. The current analysis stands at 2.6-sigma, or about a 1-in-200 chance of coincidence.
A definitive detection of dark matter would be a major breakthrough, Kamaha said. She noted that scientists know dark matter plays a key role in the formation of galaxies and the large-scale structure of the universe but still do not know what it actually is, adding that a confirmed detection would open up an entirely new area of particle physics.
Planting fake dark matter signals
Dark matter could take several forms, including primordial black holes or a particle yet to be discovered. Detectors such as LZ search for a hypothetical class of particles called weakly interacting massive particles, or WIMPs.
If WIMPs exist, they would pass through ordinary matter without interacting with it, meaning large numbers could move through the human body every second undetected. On rare occasions, though, one might strike an atomic nucleus and produce a tiny recoil, the exact kind of event LZ was built to detect.
The detector uses highly purified liquid xenon because its atoms have heavy nuclei that make them especially sensitive targets for WIMPs, producing collision signals the instrument can measure easily. LZ sits deep underground and is wrapped in protective layers shielding it from cosmic rays and other radiation that could mimic a dark matter signal, though that background noise can only be reduced, not eliminated.
Rick Gaitskell, a physics professor at Brown University in Providence, Rhode Island, and spokesperson for the LZ experiment, said researchers will always face the possibility that events in the detector stem from more conventional mechanisms. Potential dark matter collisions are believed to be extremely rare, he said, adding that scientists understand dark matter interacts so weakly with conventional matter that even a detector the scale of LZ may need to search for months or years to find a single interaction.
The LZ Collaboration identified the 2023 event through an analysis of 220 days of data collected between March 2023 and April 2024. Gaitskell said researchers are now working with a newer dataset spanning 700 days, in the hope it contains more collisions that could help determine whether the 2023 event was a genuine dark matter interaction. For this broader analysis, the team is also introducing techniques to avoid unconscious bias, including inserting "synthetic events" into the data that resemble genuine dark matter interactions to the analysis team and are only removed once the analysis is complete.
Tension between excitement and doubt
Kimberly Palladino, a physics professor at the University of Oxford in England and a member of the LZ Collaboration, said in an email that a possible detection brings a lot of tension between excitement that the experiment is working as intended and worry that the team could be making mistakes or being misled by something rare, new or coincidental happening inside the detector. She compared it to having a teenage crush on someone, where you tell yourself to act naturally but tend to read too much into every small gesture.
Palladino cautioned, however, that history is full of experiments that recorded one or two unexplained events that were never fully understood. She said that if the new LZ data contains further potential dark matter collisions, similar experiments designed to detect dark matter, such as XENONnT in Italy and PandaX-4T in China, could provide an independent test of the results.
A confirmed detection of dark matter would bring scientists significantly closer to understanding the composition of the universe and how it has evolved since the Big Bang. Palladino added that many more scientists would need to study dark matter to understand its properties across a range of different experiments, and then use that information to run astrophysical simulations of the universe, noting there are many theories about what dark matter could be and that there may be several types of it.
Much still to learn
The potential detection is intriguing but needs confirmation, according to Tim M.P. Tait, a professor in the department of physics and astronomy at the University of California, Irvine, who is not part of the LZ Collaboration. He said in an email that only time will tell whether the team sees more events as the detector accumulates more data, or whether this proves to be a temporary statistical anomaly. Tait noted the LZ event occurred at a much higher energy than most models predict for WIMPs, meaning dark matter could prove stranger and more interesting than initially imagined.
Tracy Slatyer, a physics professor at the Massachusetts Institute of Technology who is not involved with the LZ Collaboration, agreed that more data analysis is needed to determine whether the event represents dark matter. She said in an email that if it is dark matter, the fact that the event occurred at a fairly high energy without accompanying events at lower energies is very interesting.
The energy measured in the event indicates how much the xenon nucleus recoiled due to the possible interaction with dark matter. Slatyer explained that a high-energy dark matter particle would already reveal a great deal about the nature of dark matter and how it interacts with ordinary particles, with other experiments able to help pin down its properties more precisely. She said there is still much to do and learn, but that if this does turn out to be a dark matter signal, it could unlock a large amount of information about new physics and offer a new way to measure the behavior of dark matter both near Earth and potentially across the cosmos.
