An international team of scientists say they have detected an intriguing signal that could hint at evidence of dark matter, offering a clue that could bring the mystery of the elusive substance one step closer to a solution. Dark matter makes up about 85% of all matter in the universe and is about five times more abundant than ordinary matter, which makes up stars, planets and everything else scientists can see. Dark matter is invisible because it does not absorb or reflect light, but it interacts with normal matter and its gravitational effects are necessary 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 for the existence of dark matter), scientists have tried to identify the invisible substance, most recently using sophisticated devices designed to detect potential candidates. One such device is the LUX-ZEPLIN experiment, or LZ, a detector containing 7 active metric tons of liquid xenon located in a former gold mine nearly a mile (about 1.5 kilometers) below the Earth’s surface at the Sanford Underground Research Center in South Dakota. The detector recorded an unusual particle interaction in June 2023 that generated a flash of light and cautious excitement. 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 this signal the most compelling hint of dark matter the instrument has ever recorded. However, in scientific terms, claiming a discovery requires a much higher degree of confidence. “One event, by itself, is not enough,” Alvine Kamaha, an assistant professor of physics at the University of California, Los Angeles, said in an email. “We need to see if additional events appear as we collect more data and if the statistical significance of the observation increases,” said Kamaha, a member of the LZ collaboration who helped build the LZ detector. 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 submitted a study for publication in the scientific journal Physical Review Letters. Researchers are already working on more analyzes that could potentially increase the statistical significance of the event. The threshold for claiming a discovery in particle physics is known as 5-sigma, which means roughly a 1 in 3.5 million chance that it is a statistical fluke rather than an actual hint of dark matter. The analysis is currently at 2.6 sigma, or a 1 in 200 chance that this is a fluke. A definitive detection of dark matter would be “a huge advance,” Kamaha said. “We know that dark matter plays a fundamental role in galaxy formation and the large-scale structure of the universe, but we still don’t know what it really is,” he said. “It’s exciting because it would open up a whole new area of particle physics.” There are several candidates for what dark matter could be, including primordial black holes or an undiscovered particle. Detectors like the LZ experiment look for a class of hypothetical particles called weakly interacting massive particles, or WIMPs. If they exist, WIMPs pass through normal matter without interacting with it, and large numbers of them could pass undetected through a human body every second. However, on rare occasions, one of those particles could collide with an atomic nucleus and produce a small recoil—precisely the type of event the LZ experiment is designed for. The detector uses highly purified liquid xenon. The researchers selected this element because its atoms have heavy nuclei that make it a particularly sensitive target for WIMPs. Collisions in xenon produce signals that can be easily measured by the detector. The LZ experiment is located deep underground and is equipped with protective layers to protect it from cosmic rays and other radiation sources, which could produce dark matter-like signals. However, this background noise can only be reduced, not eliminated. “You’re always going to be in a situation where it’s possible that events occurring in your detector are due to more conventional mechanisms,” said Rick Gaitskell, professor of Hazard Physics at Brown University in Providence, Rhode Island, and spokesman for the LZ experiment. Possible dark matter collisions are thought to be extremely rare. “Our understanding is that dark matter interacts so weakly with conventional material,” Gaitskell added, “that even in a detector on the scale of the LZ experiment we need to look for periods of months or years for each interaction.” The LZ collaboration detected the 2023 event through an analysis of 220 days of data, collected between March 2023 and April 2024. Researchers are now working on a more recent data set spanning 700 days, Gaitskell said, hoping it will contain more collisions that can help determine whether the 2023 event was a dark matter interaction. For this broader analysis, the team is also introducing techniques to avoid unconscious bias, for example by inserting “synthetic events” into the data. These look like genuine dark matter interactions to the analysis team and are only removed once the analysis is complete. “A potential detection creates a lot of tension between the excitement of the experiment working the way we imagine, with the worry that we might make mistakes, or just get fooled by something weird and new or a coincidence happening in the detector,” Kimberly Palladino, a physics professor at the University of Oxford in England and a member of the LZ collaboration, said in an email. “It’s a bit like having a crush on someone as a teenager and telling yourself to act calmly, but you have a tendency to overinterpret every little gesture they make.” However, Palladino warned, history is also littered with experiments that have seen one or two inexplicable events that are never fully understood. If the new LZ data contain new potential dark matter collisions, similar experiments also designed to detect dark matter, such as XENONnT in Italy and PandaX-4T in China, could provide independent proof of the results. Finding dark matter would bring scientists closer to understanding what the universe is made of and how it evolved from the Big Bang to today. “But many more scientists will need to study dark matter to understand its properties in a variety of different experiments and then, using that information, run astrophysical simulations of our universe,” Palladino added. “There are many theories about what dark matter may be, and there may be multiple types of dark matter.” There is still much to do and learn The possible detection of dark matter from the LZ experiment is intriguing but needs confirmation, according to Tim MP Tait, a professor in the department of physics and astronomy at the University of California, Irvine, who is not part of the LZ collaboration. “Only time can tell whether you will see more events as the detector accumulates more data, or whether this will turn out to be a temporary statistical fluke,” Tait added in an email. He noted that the LZ event occurred at a much higher energy than most models expect for WIMPs, meaning dark matter could “turn out to be stranger and more wonderful than we had originally imagined.” Tracy Slatyer, a physics professor at the Massachusetts Institute of Technology, agrees that more data analysis is needed to understand whether the LZ event is dark matter. “If this is dark matter,” Slatyer, who is not involved in the LZ collaboration, added in an email, “the fact that the event is quite high energy, without accompanying lower energy events, is very interesting.” The energy measured in the LZ event indicates how much the xenon nucleus recoiled due to potential interaction with dark matter. A high-energy dark matter particle, Slatyer explained, would already reveal quite a bit about the nature of dark matter and how it interacts with ordinary particles. Further experiments could help further clarify its properties. “There would still be a lot to do and learn, but if this is indeed a dark matter signal,” he said, “this could be a key that unlocks a wealth of information about new physics, as well as giving us a new way to measure the behavior of dark matter in the vicinity of Earth and possibly more broadly across the cosmos.” Subscribe to CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific breakthroughs and more.
