The Lux-Zeplin (LZ) experiment has pushed the hunt for dark matter to new limits.
It is testing one of the leading ideas about dark matter: that it might be made of particles known as WIMPs (weakly interacting massive particles).
Newly published results show that LZ has convincingly detected extremely rare interactions from neutrinos streaming from the Sun’s core, demonstrating just how sensitive the experiment has become.
The hunt for dark matter
Dark matter is thought to make up around 85% of all matter in the Universe, yet it has never been directly detected.
Its gravity shapes galaxies and holds them together, yet because it doesn’t emit or absorb light, scientists must rely on highly sensitive detectors to spot even the faintest signs of it.
Searching for WIMPs
LZ is an international experiment involving researchers from universities across the UK.
Managed by the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), it sits a mile underground at the Sanford Underground Research Facility in South Dakota.
Its goal is to find evidence of dark matter particles called WIMPs, long considered a leading explanation for dark matter.
The detector uses 10 tonnes of ultra-pure liquid xenon to spot tiny flashes of light created when a particle hits a xenon atom. Such an event is so rare it requires the experiment to be shielded from cosmic rays and built from ultra-clean materials to minimise interference.
A major UK role
Funded by the Science and Technology Facilities Council (STFC), the UK plays a central role in LZ through teams at:
- 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
- Rutherford Appleton Laboratory
LZ brings together around 250 researchers from 38 institutions worldwide, with UK researchers contributing major roles in operations and data analysis, as well as key hardware, including:
- the titanium cryostat
- calibration systems
- sensors
- material screening
New limits set
LZ analysed 417 days of data collected between March 2023 and April 2025 but found no sign of WIMPs within the mass range it tested.
This is the first time LZ has searched for WIMPS, the leading candidate for dark matter, only three to nine times heavier than a proton.
The results narrow down what dark matter could be and set some of the strongest limits yet on how these particles might interact with ordinary matter.
A new window into the Sun
Although designed to search for dark matter, LZ is sensitive enough to detect extremely rare signals from neutrinos, tiny particles that constantly stream from the Sun.
In an exciting milestone, the experiment has detected neutrinos produced by boron-8, a short-lived form of boron created deep inside the Sun during nuclear fusion.
When boron-8 decays, it releases high-energy neutrinos that can travel through matter unhindered.
Exceptional performance
By catching these subtle signals, LZ has demonstrated that it is sensitive enough to find dark matter if it lies within the range the experiment is exploring.
It can also measure the flux of boron-8 neutrinos, spot neutrino bursts from supernovae, and study rare particle interactions beyond the Standard Model.
By 2028, LZ will have collected more than twice its current amount of data, boosting its ability to search for heavier dark matter particles and explore new, unexpected behaviour.
The start of a journey
Professor Henrique Araújo, from Imperial College London and the STFC Particle Physics Department, leads the UK team on LZ. He said:
Unfortunately, we cannot calibrate our experiments with a ‘dark matter beam’ that we can switch on and off in the laboratory. But here we have an equally elusive interaction, from solar neutrinos instead of dark matter particles, that produces a very similar, tiny signature in our experiment.
This result confirms that we can trust how LZ is searching for light dark matter particles that should also scatter coherently from xenon nuclei: these neutrinos are interacting in much the same way.
This is the start of a journey where, one day, we will have detected enough boron-8 neutrinos to say something about the Sun itself or about the nature of neutrinos.
Looking ahead
Researchers from LZ, with significant UK contribution, are already designing the next step: the XLZD Rare Event Observatory.
This is an even larger liquid-xenon detector that will combine technology from LZ with other existing dark matter detectors.
The XLZD-UK team is exploring the possibility of hosting XLZD at a major new underground facility at the Boulby mine.
Just the beginning
Professor Pawel Majewski, Dark Matter group leader at STFC’s Particle Physics department and LZ co-investigator, said:
From developing the critical components and technologies behind LUX-ZEPLIN to essential testing at the Boulby Underground Laboratory, researchers from UK universities and STFC’s national laboratories have been central to designing and delivering the experiment’s most vital elements.
Together, their work highlights the UK’s leadership in dark-matter detection technologies.
These results mark a major milestone in the search for dark matter and in scaling up the technologies behind the XLZD double-phase liquid xenon detector, first pioneered by the ZEPLIN programme at the Boulby Underground Laboratory.
This is an incredibly exciting time for particle astrophysics, and it is still only the beginning of what lies ahead.
Read the full press release at the Berkeley Lab website.