- An unexplained signal observed at the world’s most sensitive dark matter experiment, could have ‘profound consequences’ for our understanding of the universe
- While the findings from the LUX-ZEPLIN (LZ) experiment - an international collaboration located nearly a mile underground in South Dakota - do not yet meet the statistical threshold for a discovery, they represent the experiment’s most compelling evidence to date
- Scientists across the globe, including the University of Sheffield’s LZ team, are now calling on the scientific community for their help with interpreting these potentially groundbreaking findings
An unexplained signal detected by the world’s most sensitive dark matter experiment could mark a major breakthrough in the hunt for the elusive substance, according to analysis involving scientists from the University of Sheffield. The latest results from the LUX-ZEPLIN (LZ) experiment offer tantalising new clues about the mysterious substance that makes up 85 per cent of the matter in the Universe.
Located nearly a mile underground at the Sanford Underground Research Facility in South Dakota, the LZ detector has observed an interaction that could be interpreted as a signal from Weakly Interacting Massive Particles (WIMPs) - one of the leading dark matter candidates.
These findings, uncovered by a major international collaboration including scientists from the University of Sheffield, represent the experiment’s most compelling evidence to date.
For the better part of a century, scientists have been trying to understand dark matter, but the invisible substance has never been directly detected. Determining its exact nature remains one of the greatest unanswered questions in physics.
The new analysis from the LZ experiment has recorded an unexplained particle interaction that researchers cannot easily explain with known background signals from normal matter. While the result does not yet meet the statistical threshold required to claim a definitive discovery, confirmation through future data could transform our understanding of the universe.
Professor Dan Tovey, leader of the LZ team at the University of Sheffield, said: "This new result from LZ is very intriguing. With just one event it is not possible to conclude that we are actually seeing first signs of new physics, but if this were the case then the consequences for our understanding of the universe would be profound.
“A huge amount of work has been undertaken to check that the event is not due to more mundane processes, and so far it has passed every test. The only way to be sure, however, is to look at more data and that is exactly what we are now focused on."
The experiment uses 10 tonnes of liquid xenon to search for dark matter and is optimised to look specifically for WIMPs.
LZ searches for dark matter by looking for signature flashes of light from energy deposited in the detector. The collaboration leverages multiple methods to prevent or account for particle interactions caused by normal matter. This includes the mile of rock that shields the detector from cosmic rays from space, a water tank and outer detectors that protect the central detector from background neutrons, and a suite of computational tools that disentangle particle interactions and reject dark matter mimics.
The results were presented in a scientific talk at the 2026 TeV Particle Astrophysics conference in Japan. The paper will be released on the online repository arXiv and submitted to the journal Physical Review Letters.
“We’re very intrigued to see this event in the data, in the region where we expect dark matter to show up and the competing backgrounds are very low,” said Rick Gaitskell, a professor at Brown University and the spokesperson for LZ.
“With only one event, we don’t want to get ahead of ourselves. We are not claiming to have seen dark matter. But we have seen something interesting that we want to share with the scientific community for their input.”
The LZ collaboration studies experimental data in batches. In the new result, researchers analysed 220 live days of data collected between March 2023 and April 2024. The collaboration had previously searched this dataset for faint signals from the simplest kinds of WIMP interactions. The new analysis searched for a broader range of possible WIMP interactions that could deposit more energy in the detector. LZ is particularly sensitive to such signals while also minimizing false positives.
“This was a detailed study in a region we hadn’t explored within this dataset, and we spent months of additional effort to understand all the possible causes of background events,” said Sam Eriksen, a senior research associate at the University of Bristol in the U.K. and lead author of the study.
“We understand our detector and the backgrounds so well that even a single outstanding event, like the one we found, is important. We expect dark matter events to be extremely rare, so only a handful could mark the first detection of WIMP dark matter.”
If the anomalous event was caused by dark matter, the WIMP that generated it would likely have a mass of at least 200 GeV/c2 (gigaelectronvolts), or more than 200 times the mass of a proton. It would also suggest a specific type of interaction between WIMPs and ordinary matter beyond the simplest model. The LZ results have not reached “5-sigma” significance, the statistical threshold considered a discovery in physics. The new analysis is 2.6 sigma, meaning there is approximately a 0.5% chance that the event could be explained by known backgrounds.
With additional data, researchers can test whether the finding continues to grow in significance or fades away. LZ has already accumulated the world's largest dark matter dataset and will continue to accrue WIMP search data at LZ’s Sanford Underground Research Facility, substantially improving their search statistics.
Aaron Manalaysay, a physicist at Berkeley Lab and the chair of LZ's Institutional Board, said: “Outlier events in the data are not unexpected, but they usually stand out as a background of some kind when you look at them deeper.
“This is the first example in any experiment I've worked on of an outlier that appears valid in every way. Of course, we're still twisting our brains trying to think if there's a rare background mechanism we could've missed, but it's thrilling to wonder if this could be the first hint of a dark-matter observation.”
The University of Sheffield was a founding member of the LZ Collaboration, under the leadership of Emeritus Professor Vitaly Kudryavtsev. The Sheffield team has been deeply involved in many aspects of the design, construction and operation of the LZ detector, with a particular focus on modelling and understanding background processes, including those relevant to this result.
LZ is an international collaboration of 250 scientists and engineers from 39 institutions. The detector is managed by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and operates nearly one mile below ground at the Sanford Underground Research Facility (SURF) in South Dakota.
Funded in the UK by the Science and Technology Facilities Council (STFC) for both construction and operations, ten UK teams play a central role in LZ:
• University of Bristol
• The University of Edinburgh
• Imperial College London
• King’s College London
• University of Liverpool
• University of Oxford
• Royal Holloway, University of London
• The University of Sheffield
• University College London
• STFC Rutherford Appleton Laboratory
