The LUX-ZEPLIN experiment (LZ) looks for one popular dark matter candidate: WIMPs, or weakly interacting massive particles, which would pass through ordinary material almost unnoticed and only rarely strike an atom.
The detector sits nearly a mile underground at the Sanford Underground Research Facility in South Dakota. It holds ten tonnes of ultrapure liquid xenon, a dense noble liquid chosen because a particle strike can produce a brief flash of light. Rock, a water tank, and outer detectors reduce cosmic rays and other ordinary particles. Remaining false signals, called backgrounds, are mapped with calibrations and software. Lawrence Livermore National Laboratory (LLNL) researchers lead much of that calibration work.
A new look at 220 days of data from March 2023 to April 2024 found one interaction that is hard to match to known backgrounds. Earlier work on the same set hunted only the simplest WIMP collisions. This analysis allowed a wider class of collisions that would leave more energy. LZ researchers said the event sits where dark matter might appear and where backgrounds are low, but added that one event is not a claim of discovery.
What the numbers do and do not mean
If the hit were a WIMP, its mass would likely be at least 200 GeV/c², more than two hundred times the mass of a proton. The result is 2.6 sigma. In this field, sigma is a measure of how unlikely a fluke would be; 2.6 sigma means about a 0.5 percent chance the event is a known background. A discovery claim is usually reserved for 5 sigma. The researchers said the data point could fit some dark-matter models, but unexpected backgrounds have appeared before as detectors improve. They added that months were spent checking other causes, and that a first WIMP signal might involve only a handful of events.
The finding was presented at the 2026 TeV Particle Astrophysics meeting in Japan. A paper, which will be published on arXiv and sent to Physical Review Letters, is available from the LZ website. LZ will keep taking data, which should show whether similar events pile up or fade.
"It is a single data point, but enough to send a shiver down physicists’ spines," notes Nature News (open copy).