Researchers working on the LUX-ZEPLIN (LZ) experiment, with key contributions from Theresa Fruth of the University of Sydney, have reported a new set of results that further narrow the possible properties of dark matter while also demonstrating the detector’s ability to observe neutrinos produced in the sun. The findings mark an important technical milestone for rare-event detection experiments operating at the limits of sensitivity.
Aalbers, J., Abe, K., Adrover, M., Ahmed Maouloud, S., Akerib, D. S., al Musalhi, A. K., Alder, F., Althueser, L., Amaral, D. W. P., Amarasinghe, C. S., Ames, A., Andrieu, B., Angelides, N., Angelino, E., Antunovic, B., Aprile, E., Araújo, H. M., Armstrong, J. E., Arthurs, M., … Zuber, K. (2025). The XLZD Design Book: towards the next-generation liquid xenon observatory for dark matter and neutrino physics. The European Physical Journal C, 85(10), 1192. https://doi.org/10.1140/epjc/s10052-025-14810-w
Dark matter is thought to account for roughly a quarter of the universe’s total mass-energy content, yet its particle nature remains unknown. One leading class of candidates is weakly interacting massive particles, or WIMPs, which are expected to interact so rarely with ordinary matter that detecting them requires extremely large, well-shielded detectors and long observation times. LZ was designed specifically for this purpose and is currently the most sensitive experiment of its kind.
Theresa Fruth of the University of Sydney stated,
“It’s extraordinary that our detector is now sensitive enough to catch neutrinos from the sun. We’re opening a new window into solar and neutrino physics while simultaneously continuing the hunt for dark matter.”
The detector is located deep underground at the Sanford Underground Research Facility in South Dakota and uses around ten tonnes of ultrapure liquid xenon as its target material. By placing the experiment beneath a kilometer of rock, researchers significantly reduce background signals from cosmic rays and other sources that could obscure the faint interactions they are looking for. Photomultiplier arrays positioned above and below the xenon volume record tiny flashes of light and charge signals produced when a particle interacts with a xenon nucleus.
In the newly reported analysis, the collaboration examined data collected over 417 live days between March 2023 and April 2025. This represents the largest dataset ever analyzed by a dark matter detector. No clear signal consistent with WIMPs was observed, but the absence of a detection is itself informative. The results place the strongest constraints to date on WIMPs with masses between roughly three and nine times that of a proton, extending the experiment’s sensitivity to lower masses than previously achieved.
While the primary goal remains dark matter detection, the improved sensitivity of LZ has also brought the experiment into a new regime. The detector is now capable of observing neutrinos produced by nuclear fusion reactions in the core of the sun, specifically boron-8 solar neutrinos. These particles interact with xenon nuclei through a process known as coherent elastic neutrino-nucleus scattering, in which the neutrino transfers momentum to the entire nucleus rather than to individual protons or neutrons.
Detecting this interaction is technically challenging, as it produces signals that are very similar to those expected from low-mass dark matter particles. Achieving this required extensive calibration and careful modeling of instrumental backgrounds. The observation confirms that LZ has reached a sensitivity level where neutrinos become a measurable signal rather than a negligible background.
This regime is often referred to as the “neutrino fog,” a point at which neutrino interactions begin to limit how far experiments can push searches for lighter dark matter candidates. For heavier dark matter particles, neutrinos remain a minor concern, and LZ’s discovery potential in that mass range is largely unaffected. At the same time, entering this regime opens opportunities for precision measurements in neutrino and solar physics using detectors originally built for dark matter searches.
Australian researchers have played a notable role in the collaboration. Alongside Dr. Fruth, Robert James of the University of Melbourne led key aspects of the statistical analysis used to extract the new limits and identify the neutrino signal. Both are members of the ARC Centre of Excellence for Dark Matter Particle Physics, which contributes to LZ as part of a broader international effort involving around 250 scientists.
Looking ahead, the collaboration continues to collect data and refine its analysis techniques, with operations planned through at least 2028. In parallel, members of the team are already involved in the design of a next-generation detector known as XLZD, which aims to combine technologies developed in LZ and similar experiments to further expand sensitivity to rare interactions.
Although dark matter has not yet been directly detected, each new result reduces the space in which it can hide and tests the performance of increasingly sophisticated detection systems. At the same time, the ability of LZ to observe solar neutrinos demonstrates how advances driven by one scientific question can enable progress in others. For engineers and physicists working on large-scale instrumentation, the experiment offers a case study in how precision design, background control, and long-term operation can push measurements into previously inaccessible territory.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
