A Mile-Deep Detector in South Dakota Records Its Strongest Dark Matter Hint Yet

A single unexplained signal in the LUX-ZEPLIN detector could be the best dark-matter candidate physicists have seen, but it falls short of a discovery.

For nearly a century, dark matter — the invisible substance thought to make up roughly 85% of the universe's mass — has eluded every direct detection attempt. That record may have just hit its closest call yet: the LUX-ZEPLIN (LZ) experiment, a 10-ton tank of ultrapure liquid xenon buried nearly a mile underground in South Dakota, has recorded a single particle interaction that researchers struggle to explain with any known background signal.

The finding, presented Tuesday at the TeV Particle Astrophysics conference in Japan, is the most compelling hint of dark matter the experiment has reported to date. If the event really was dark matter, the culprit would likely be a WIMP — a weakly interacting massive particle — with a mass of at least 200 GeV, more than 200 times that of a proton. The analysis looked at 220 live days of data collected between March 2023 and April 2024, probing a broader range of possible WIMP collisions than earlier searches.

But the team is emphatic that this is not a discovery. The signal sits at 2.6-sigma significance, well short of the 5-sigma bar physics requires — roughly a 0.5% chance the event is just known background. 'We are not claiming to have seen dark matter,' said Rick Gaitskell, the LZ spokesperson and a Brown University physicist. 'But we have seen something interesting that we want to share with the scientific community for their input.' A paper has been submitted to Physical Review Letters, and additional data will determine whether the hint grows or fades.

Sources: Brown University, CBS News, UT Austin, ABC News Australia