Did Scientists Just Catch a Glimpse of a Dark Matter Particle?

On June 16, 2023, nearly a mile below the Earth’s surface, something ghostly went bump in the night. It could have an entirely run-of-the-mill particle crashing into another ordinary particle. But physicists announced September 1 that there is a 99.5 percent chance that the collision was caused by something they’ve never detected before—a mysterious particle of dark matter.

Dark matter is thought to be the invisible glue that binds the cosmos together. Without it, all the ordinary, visible matter we see around us would have no foundations on which to build the universe. But as it cannot be directly detected, scientists don’t know what particle, if any, dark matter is made of.

Instead of seeking the particles themselves, researchers have spent decades hunting for the imprints they may leave on ordinary matter: shadows on a wall, footprints in the sand. The tiny collision took place at the Sanford Underground Research Facility in South Dakota, and it may be the best sign yet that dark matter is indeed made of particles—specifically Weakly Interacting Massive Particles, or WIMPs.

“While we’re excited, we also need to be cautious,” says Daniel Akerib, a particle physicist at Stanford University, and one of the cornucopia of experts involved with the new research.

Other experiments have hinted at the possibility of dark matter particle candidates in the past, but those ultimately fell through. To verify the WIMP signal, researchers will need more data. “This is a tantalizing anomaly, not evidence,” says Chamkaur Ghag, a physicist at University College London and another of the team’s researchers. But if scientists spot more of these odd collisions, a nearly century-long quest to unveil the true nature of dark matter may finally come to an end.

The Shadowy Puzzle of Dark Matter

To us, it seems like ordinary matter rules the universe. But dark matter—first inferred as an unseen mass in the 1930s, then suspected of being an unusual particle in the 1970s—makes up 85 percent of all the universe’s matter. This is based on plentiful observations of the visible universe, and an assessment of the gravitational forces that appear to be shaping its galaxies.

“We know that dark matter exists,” says Daniel Whiteson, a particle physicist at the University of California Irvine. “There are many independent lines of evidence for it.” Stars wouldn’t ignite under the influence of ordinary matter and its gravity alone. Spinning galaxies would be torn apart without its force. Light is bent around hidden halos in space—a process known as gravitational lensing—that only makes sense if copious amounts of dark matter is present.

“Cosmologists have a hard time building a universe—ok, a model of the universe—without dark matter,” says Akerib. “But what is it?”

Dark matter is probably everywhere, but because it doesn’t interact with light, it’s invisible. But it definitely interacts with gravity, which means it probably has mass and exists as a particle.

Various candidates have been put forward as potential culprits. But “WIMPs have always been the front runner because they are the simplest theory,” says Whiteson. Despite being hefty and languorous, these particles are thought to almost always slip through ordinary matter without incident. ‘Almost’ is key: On extremely rare occasions, they may bonk into the atomic nucleus of an ordinary element.

But WIMP-on-regular-particle violence is thought to be so vanishingly rare that only the most sensitive of detectors may be able to spot it. For years, experiments all over the world have been getting bigger, and more technologically sophisticated, all in the hope of catching a dark matter particle clumsily tripping over a regular atom.

“They’ve never seen any hint of it,” says Whiteson.

Perhaps, that is, until now.

(This scientist forced astronomers to rethink dark matter.)

A Quest Below South Dakota

The experiment that picked up the possible WIMP signal is known as LUX-ZEPLIN—or LZ, to its physicist friends. LZ’s heart is a tank filled with liquid xenon. “Xenon is a great target,” says Ann Wang, a particle physicist at the SLAC National Accelerator Laboratory in California, and a member of the LZ research team. For one thing, xenon loves to put on a fireworks show.

If a rogue particle flies into this tank and strikes a xenon atom’s nucleus, the xenon emits a flash of light; at the same time, it fires out electrons that drift to the top of the tank, where light-sensitive detectors await a second flash of light.

If a WIMP crashed into a xenon nucleus, it would generate a pair of flashes, each of a particular energy level that ordinary matter can’t produce. “A major challenge is that there are other things that can reach these caverns and bump into xenon atoms,” Whiteson says. Chief among these interlopers are gamma rays and neutron particles produced by the sun and other cosmic sources.

That’s why the South Dakota facility that houses LZ lies about 4,850 feet down, in an old gold mine: The vast ceiling of rock filters out plenty of radiation from space. (It’s the deepest underground laboratory in the United States.) The experimental tank also has multiple layers of shielding, using both exotic elements and ultra-purified water, that block errant particles. The materials that make up these Russian nesting doll-like tanks are also super-clean, meaning they emit only a smidgen of background noise.

Still, plenty of ordinary matter interactions that can be mistaken for dark matter particles get through. So ever since it began its science runs in December 2021, LZ’s scientists have been extremely judicious in their search.

Between March 2023 and April 2024, physicists interrogated every single curious flash of light. Each proved to be coming from ordinary matter interactions. But on June 16, 2023, something booped a xenon nucleus, and lit up the detector, in a way that ordinary matter couldn’t explain.

“It was only after a huge amount of effort by our analysis team that it became apparent that we could have found something special,” says Samuel Eriksen, a physicist at the University of Bristol in England who was part of the new research team.

(Read about scientists’ efforts to map dark matter.)

Have We Finally Found Dark Matter Particle?

As announced this week at the 2026 TeV Particle Astrophysics conference in Tendo, Japan, and as presented in a pre-print paper yet to be peer-reviewed, the single event could have involved a WIMP—one that would be at least 200 times the mass of a proton.

“The LZ result is very exciting,” says Michael Keim, an astronomer at Yale University, not least because it strongly suggests dark matter is a real particle, and not—as some skeptics have previously suggested—a gap in our understanding of gravity.

Our current understanding of how the universe’s building blocks and fundamental forces are related—a system called the Standard Model—doesn’t include any official dark matter particles. “A confirmed WIMP at this mass would be our first direct laboratory evidence of physics beyond the Standard Model,” says Ghag. This, he adds, is “something particle physicists have been chasing for fifty years.”

Statistically, this one event isn’t a definitive discovery; far from it. The chance that lab’s light show was a routine particle smashup is 1 in 200 is too high for physicists. For this event to be declared a discovery, there must be a 1-in-3.5 million chance that it involved something other than dark matter—a gold standard statistical threshold known as 5-sigma.

Other dark matter candidates, “are all still firmly in the race,” says Ghag. Axions are another theorized particle form of the shadowy substance, as are black holes as small as a single atom that may have popped into existence in the first seconds after the universe formed.

But LZ is still collecting data every day. If it or another comparable experiment detects similar unusual patterns of flashes without ordinary matter explanations, “our confidence that WIMPs are part of the story of dark matter will drastically increase,” says Eriksen.

There’s a chance this event might have come from something more quotidian—a stray neutron, perhaps or a result of some radioactive decay. Still, scientists can’t help but feel hopeful.

“What makes this one different is that we’ve hunted hard for a mundane explanation and, so far, haven’t found one,” says Ghag. “When you spend years understanding every possible way your detector can fool you, and then a single event turns up that resists every explanation you throw at it, that’s when physics gets interesting.”