Scientists Detect a Signal That Could Be the First Direct Evidence of Dark Matter

An international experiment has recorded a single particle interaction that researchers cannot attribute to any known background source. The event may be the strongest indication yet of dark matter, but the scientists involved are warning against calling it a discovery.

The signal came from the LUX-ZEPLIN detector, nearly two kilometers underground in South Dakota. The instrument uses 10 tonnes of ultrapure liquid xenon to capture flashes of light produced by possible particle interactions. The study was led by Sam Eriksen of the University of Bristol.

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What we observed in this analysis could be the first step toward understanding dark matter as a particle. After an enormous scientific effort, this is incredibly exciting.

“What we observed in this analysis could be the first step toward understanding dark matter as a particle. After an enormous scientific effort, this is incredibly exciting,” Eriksen said in a statement from the university.

Dark matter is thought to account for about 85 percent of the universe’s mass, but researchers have never detected it directly. The LZ event could have been caused by a WIMP, or weakly interacting massive particle, one of the leading theoretical candidates for dark matter. If that interpretation is correct, the particle would have a mass of at least 200 GeV/c², more than 200 times the mass of a proton, and would point to a more complex interaction than the simplest model.

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We are very intrigued to see this event in the data, in the region where we expect dark matter to appear and where competing backgrounds are very low.

The result had a statistical significance of 2.6 sigma, corresponding to an approximately 0.5 percent probability that known processes could explain the event. Physics discoveries generally require 5 sigma. Rick Gaitskell of Brown University, a spokesperson for the LZ collaboration, said the team was intrigued because the event appeared in the region where dark matter was expected and competing backgrounds were low. “With one event, we do not want to get ahead of ourselves. We are not claiming to have seen dark matter. But we did see something interesting that we want to share with the scientific community,” he said.

The analysis covered 220 days of data collected between March 2023 and April 2024. Unlike earlier searches focused on simpler WIMP interactions, the study examined a broader range of possible interactions that could deposit more energy in the detector. A Bristol group has worked on this type of LZ search for eight years.

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With one event, we do not want to get ahead of ourselves. We are not claiming to have seen dark matter. But we did see something interesting that we want to share with the scientific community.