World's largest dark matter experiment captures potential WIMP signal

- International research team detects candidate signal for WIMP, a leading dark matter particle

- WIMP estimated to be more than 200 times heavier than a proton

The LUX-ZEPLIN main detector sits in an above-ground laboratory before being installed at an underground research facility. [Source: Matthew Kapust/Sanford Underground Research Facility]

Scientists may have found a compelling clue to the identity of dark matter — the mysterious substance that makes up roughly 85 percent of all matter in the universe yet has never been directly observed.

The LUX-ZEPLIN (LZ) international research collaboration, which includes a team from the Institute for Basic Science (IBS) Underground Physics Group led by Director Kim Young-duk, announced Tuesday that it had detected a particle interaction that could be a signal from a WIMP, the leading dark matter candidate particle.

The signal was captured at the world's largest dark matter search experiment, located roughly 1.5 kilometers underground at the Sanford Underground Research Facility (SURF) in South Dakota. If confirmed as a genuine WIMP trace, it could mark the first direct detection of dark matter.

WIMP — short for weakly interacting massive particle — is one of the foremost candidates for dark matter. WIMPs are thought to be far heavier than electrons or protons, yet they interact almost not at all with light or ordinary matter, making them extraordinarily difficult to detect.

The research team used the LZ detector, which contains about 10 metric tons of ultra-pure liquid xenon, to track the faint flashes of light and electrical signals produced when particles collide.

Analyzing 220 days of data collected from March 2023 to April 2024, the team identified a single anomalous particle interaction in the region where a dark matter signal would be expected to appear.

Over several months, researchers carefully examined known sources of background noise — including natural radiation, neutrons and detector interference — but were unable to account for the signal through any of them.

If the signal does originate from dark matter, the researchers estimate the WIMP's mass would be at least 200 GeV/c², making it more than 200 times heavier than a proton.

A large detector component fitted with hundreds of golden photomultiplier tubes. [Source: Matthew Kapust/Sanford Underground Research Laboratory]

The signal carries a statistical significance of 2.6 sigma, meaning there is roughly a 0.5 percent probability that such an event could arise by chance from known background sources alone.

However, it is too early to declare a discovery of dark matter. Particle physicists require a threshold of 5 sigma before recognizing a new particle as confirmed. The possibility that the signal reflects a rare but unknown phenomenon or a statistical fluctuation cannot be ruled out, and further observation and verification are needed.

The LZ team plans to continue its WIMP search at SURF to determine whether the signal genuinely originated from dark matter.

Rick Gaitskell, a professor at Brown University and the LZ collaboration's principal investigator, said the team was paying close attention because the signal appeared in a region where a dark matter signature would be expected and where contributions from other sources are very low.

IBS Underground Physics Group Director Kim said the IBS was the only Asian institution involved in the research and would also participate in the next-generation experiment, XLZD. "Korea will be able to play a more leading role in liquid xenon detector experiments," he said.

The findings were presented Tuesday at the 2026 International Symposium on TeV Particle Astrophysics (TeVPA 2026) held in Japan. The paper was posted the same day to the preprint server arXiv and submitted to the international journal Physical Review Letters.

nbgkoo@heraldcorp.com