Physicists on what is regarded as the planet’s most sensitive dark matter detector have picked up a signal they cannot yet explain, raising the possibility of a genuine breakthrough in one of physics’ longest-running mysteries — with University of Sheffield researchers among those who worked on the analysis.
The result comes from the LUX-ZEPLIN (LZ) experiment, a detector buried almost a mile underground at the Sanford Underground Research Facility in South Dakota. Scientists there have picked up an interaction that could, potentially, be a Weakly Interacting Massive Particle, or WIMP — one of the strongest candidates for what dark matter actually is. Dark matter makes up roughly 85 per cent of all matter in the universe, yet despite nearly a century of searching, nobody has ever detected it directly.
The single event doesn’t clear the statistical bar needed to call it a confirmed discovery, but researchers say it’s the most compelling hint LZ has turned up so far, and cannot easily be explained away using known background sources.
An intriguing result
Professor Dan Tovey, who leads the University of Sheffield’s contribution to the LZ team, 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 LZ detector relies on 10 tonnes of liquid xenon and is specifically built to hunt for WIMPs, watching for tiny flashes of light given off when energy is deposited inside it. To rule out false positives, the whole setup is shielded by roughly a mile of rock blocking cosmic radiation, plus a surrounding water tank and outer detectors that screen out background neutrons, backed by computational tools designed to weed out anything that merely mimics a genuine dark matter signal.
Findings were shared at the 2026 TeV Particle Astrophysics conference in Japan, with a paper due to be posted on arXiv and submitted to Physical Review Letters.
Sharing with the scientific community
Rick Gaitskell, a professor at Brown University and spokesperson for the LZ collaboration, said: “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. 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 finding emerged from 220 days of data gathered between March 2023 and April 2024. Researchers had already combed through this dataset once, looking for the simplest WIMP interactions; this latest pass widened the net to cover interactions that might deposit more energy in the detector — a category LZ is especially well-suited to spot without triggering false alarms.
Sam Eriksen, a senior research associate at the University of Bristol and the study’s lead author, said: “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. 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 event genuinely was caused by dark matter, the particle behind it would likely weigh at least 200 GeV/c² — more than 200 times the mass of a proton — and point to a more complex interaction between WIMPs and ordinary matter than the simplest models predict. The result currently sits at 2.6 sigma, well short of the 5-sigma threshold physics requires to call something a confirmed discovery, but still equating to roughly a 0.5% chance the signal is explained by known background noise. More data collected at the facility should reveal whether the signal strengthens or fades.
Twisting brains
Aaron Manalaysay, a physicist at Berkeley Lab and 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.”
Sheffield joined the LZ collaboration as one of its founding members, with early work led by Emeritus Professor Vitaly Kudryavtsev, and the university’s team has played a significant role in the detector’s design, construction and operation — particularly in modelling the background processes central to this latest result. LZ itself brings together 250 scientists and engineers from 39 institutions worldwide, managed by the US Department of Energy’s Lawrence Berkeley National Laboratory.
In the UK, the project is funded by the Science and Technology Facilities Council, with ten UK institutions involved: Bristol, Edinburgh, Imperial College London, King’s College London, Liverpool, Oxford, Royal Holloway, Sheffield, University College London, and the STFC Rutherford Appleton Laboratory.
