The study, led by a University of Bristol astro-particle physicist and also announced today by Berkeley Lab in the US, has potentially detected the very first hint of a dark matter interaction in what appears as the most compelling indication of this mysterious invisible substance to date.
Dark Matter was first proposed nearly a century ago and scientist have spent many decades trying to detect a signal using a range of technologies.
Study lead author Dr Sam Eriksen, Senior Research Associate at the University of Bristol, said: "Scientists have been trying to better understand dark matter, which makes up the vast majority of matter in the universe, for nearly a century.
"What we have observed in this analysis could be the first step in understanding dark matter as a particle. Following a huge amount of scientific effort, this is incredibly exciting."
Dark matter accounts for around 85% of the mass in the universe but it has never been directly detected – until possibly now. The new analysis was presented earlier today by Dr Eriksen in a scientific talk at the 2026 TeV Particle Astrophysics conference in Japan. It is now available as a pre-print for wider scrutiny by the scientific community and has been submitted to a journal for publication.
The study recorded a single particle interaction, which researchers have struggled to explain with known background signals from normal matter. Although this isolated result doesn't yet meet the statistical threshold for an official discovery, it's an intriguing step forward.
The progress was possible thanks to an international collaboration of 250 scientists and engineers from 39 institutions spanning six countries, including nine universities in the UK. For two years they have been rigorously scrutinising data from one of the world's most sensitive dark matter detectors, called LUX-ZEPLIN (LZ), managed by the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), which operates nearly a mile underground at the Sanford Underground Research Facility (SURF) in the US state of South Dakota.
The study, using data collected from LZ, found one particle interaction which could potentially have been caused by a Weakly Interacting Massive Particle (WIMP), a candidate for dark matter.
Professor Rick Gaitskell, from Brown University and spokesperson for LZ, 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."
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 experiment, which is ongoing, used 10 tonnes of ultrapure liquid xenon to search for dark matter and is optimised to look for WIMPs. The LZ collaboration studies experimental data in batches and 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 has been designed and constructed to be particularly sensitive to such signals while also minimising false positives. Statistically, there's around a 1 in 200 chance this is a false positive result.
"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," Dr Eriksen explained.
"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 SURF, substantially improving their search statistics.
The Bristol LZ group, led by Professor Henning Flaecher and funded by the UK Research and Innovation (UKRI) Science and Technology Facilities Council (STFC), started developing this type of dark matter search within LZ eight years ago and published intermediate results in Physical Review D and Physical Review Letters on a smaller data sample in 2024. Two PhD students, Nathan Pannifer and Vedanshu Mahajan, have also been supporting the highly complex analysis.
Prof Flaecher, Professor of Physics at the University of Bristol, said: "We have been working on this kind of dark matter search in Bristol for a long time, and it seems this sustained effort is paying off.
"A huge amount of work has been done by the entire team with countless hours being spent to further our understanding of possible background processes, but to date none provide a convincing explanation.
"It's an incredibly exciting time, the kind of event every astro-particle physicist dreams of, and we can't wait to analyse more data to see if additional candidate events appear."
Bristol is also contributing to the design of XLZD, an acronym combining the names of three leading xenon dark matter research projects: XENON, LUX-ZEPLIN (LZ), and DARWIN. The global scientific collaboration aims to design and build the world's ultimate next-generation dark matter detector.
The project, currently supported by a UKRI Infrastructure Fund, is exploring the possibility of hosting the experiment at STFC's Boulby Underground Laboratory in North Yorkshire, in the UK.
