The LUX-ZEPLIN dark matter experiment has recorded an unexplained particle interaction that could potentially stem from a weakly interacting massive particle, Berkeley Lab reported on Tuesday. The event, identified during an analysis of 220 live days of operational data, stands as the detector's most compelling candidate signal to date.
Researchers presented the measurement at the 2026 TeV Particle Astrophysics conference in Japan, with plans to submit the findings to Physical Review Letters and release the paper on arXiv. The signal reached a statistical significance of 2.6 sigma, representing approximately a 0.5 percent probability that the interaction arose from known background radiation. In particle physics, confirming a formal discovery requires a 5-sigma threshold.
A candidate dark matter particle responsible for the event would require a mass of at least 200 gigaelectronvolts, or more than 200 times the mass of a proton. That mass profile would point to an interaction mechanism between dark matter and normal matter that goes beyond standard minimal models. Rick Gaitskell, an LZ spokesperson and physics professor at Brown University, stated that the collaboration is not claiming a discovery from a single event, but noted that the interaction appeared in an energy region with minimal competing background noise.
The collaboration evaluated data gathered between March 2023 and April 2024 at the Sanford Underground Research Facility in South Dakota. While earlier sweeps focused on simpler particle interactions, the new study evaluated higher energy depositions. Lead author Sam Eriksen, a senior research associate at the University of Bristol, noted that the team spent months investigating detector backgrounds before confirming the validity of the outlier event.
Aaron Manalaysay, a physicist at Berkeley Lab and chair of the experiment's Institutional Board, stated that the interaction is the first outlier across his experimental career to remain valid after exhaustive background screening. The detector continues to collect data at the South Dakota site to determine whether subsequent runs reinforce or diminish the signal.
The experiment operates nearly one mile underground using 10 tonnes of ultrapure liquid xenon to register particle collisions as flashes of light. To minimize false readings from cosmic rays and ambient neutrons, the system relies on overhead rock shielding, an encompassing water tank, outer detector arrays, and specialized data filters. The LZ project is supported by 39 institutions across 250 scientists and engineers, with primary backing from the U.S. Department of Energy's Office of Science alongside international research agencies in the United Kingdom, Portugal, Switzerland, Australia, and South Korea.
