LZ Dark Matter Detector Sees One Event Backgrounds Struggle to Explain
LUX-ZEPLIN saw one event where WIMP dark matter would appear, at 2.6 sigma. Intriguing, but well short of the 5 sigma needed to claim a discovery.
The LUX-ZEPLIN (LZ) experiment has recorded a single event in the region where dark matter particles would be expected to show up and known backgrounds are very low. The U.S. Department of Energy’s Office of Science described the result on September 1, 2026. It was presented at the 2026 TeV Particle Astrophysics conference in Japan, and the paper is being submitted to Physical Review Letters, so it has not yet been peer reviewed.
LZ holds 10 tonnes of ultrapure liquid xenon nearly one mile underground at the Sanford Underground Research Facility in South Dakota, shielded from cosmic rays. The new analysis covers 220 live days of data taken between March 2023 and April 2024, and looks for WIMPs (weakly interacting massive particles) that would deposit more energy in the xenon. LZ’s first search in 2023, using 60 live days, found nothing above background.
The significance is 2.6 sigma, meaning there is about a 0.5% chance that known backgrounds alone would produce such an event. Physicists require 5 sigma, roughly a one-in-3.5-million fluke, before claiming a discovery. If the event were caused by dark matter, the particle would likely have a mass of at least 200 GeV/c2, more than 200 times the mass of a proton.
Dark matter makes up about 85% of the mass in the universe but has never been directly detected. That is why even one tentative event will be scrutinized, and why it may well turn out to be an unmodeled background. More in our dark matter guide.
What to watch next: more LZ exposure will show whether similar events pile up or the hint fades.
Primary source
This summary is based on U.S. Department of Energy Office of Science. Read the original for full details, data and caveats.
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