• Dark matter is the mysterious substance that makes up most matter in our universe.
• LUX-ZEPLIN (LZ) is a world-leading dark matter detector and specialises in searching for WIMPs, or weakly interacting massive particles.
• One particle interaction found in this study is difficult to explain with known background processes and could potentially have been caused by a WIMP.

For the better part of a century, people have been trying to understand dark matter. This invisible substance makes up roughly 85 percent of the mass in the universe but has never been directly detected. Determining exactly what it is remains one of the biggest questions about our world.

A new analysis from the LUX-ZEPLIN (LZ) experiment has recorded a single particle interaction that researchers have great difficulty explaining with known background signals from normal matter. The result does not yet meet the statistical threshold required to claim a discovery, but is the most compelling hint of dark matter reported by the experiment to date.

The results were presented in a scientific talk at the 2026 TeV Particle Astrophysics conference in Japan on Tuesday. The paper will be released on the online repository arXiv and submitted to the journal Physical Review Letters.

Dr Theresa Fruth, from the University of Sydney’s School of Physics, is one of only two Australian-based researchers in the 250-member international collaboration. She was instrumental in commissioning the LZ detector in South Dakota and continues to play a role in the international collaboration.

Dr Fruth said: “Our previous results have already shown that we understand our detector remarkably well and that it is very sensitive. Now seeing this event is intriguing. It is an outlier that has survived many checks over the past months. There is always the possibility of a very rare background mechanism that we’ll learn about with more data, but we of course also wonder whether this might be the first glimpse of a dark matter signal.”

Dr Fruth has worked on LZ for more than a decade, including at the University of Oxford and University College London, and continues to play an active role in operations and data analysis.

Joining her is fellow Australian collaborator Dr Robert James from the University of Melbourne, who has previously led LZ’s statistical analysis working group.

Dr James said: “A statistical result of 2.6 sigma is below the threshold for when we’d claim we have sufficient ‘evidence’ of a new signal. What it does tell us is that our dataset is approaching statistically significant incompatibility with the backgrounds we understand in our detector, driven by this single event.

“Of course, it’s very difficult to say anything with a single event – that’s why it’s vital that we continue to collect and analyse further data. This will involve focusing our efforts on understanding our detector even better to make sure that we haven’t overlooked any extremely rare background processes that could explain this event. Only then can we start to understand whether we’re seeing the first hints of a dark matter signal. It’s an exciting time!"

LZ is an international collaboration of 250 scientists and engineers from 39 institutions. The detector is managed by the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and operates about 1.5 kilometres below ground at the Sanford Underground Research Facility (SURF) in South Dakota. The experiment uses 10 tonnes of ultrapure liquid xenon to search for dark matter and is optimised to look for WIMPs, or weakly interacting massive particles.

Professor Rick Gaitskell from Brown University in the US, and a 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.”

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 Dr Sam Eriksen, a senior research associate at the University of Bristol in the UK 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 percent 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.

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.

Research

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.

Declaration

LZ is supported by the US Department of Energy, Office of Science, Office of High Energy and Nuclear Physics, and the National Energy Research Scientific Computing Center, a DOE Office of Science user facility. LZ is also supported by the Science & Technology Facilities Council of the United Kingdom; the Portuguese Foundation for Science and Technology; the Swiss National Science Foundation; the Australian Research Council Centre of Excellence for Dark Matter Particle Physics; and the Institute for Basic Science, Korea. Thirty-nine institutions of higher education and advanced research provided support to LZ. The LZ collaboration acknowledges the assistance of the Sanford Underground Research Facility.

This article was based on the original media release from the LZ Experiment, which you can read at this link.