LZ sets new limits on the direct search for dark matter and observes rare solar neutrino interactions
"LZ’s largest dataset to date: 417 days of stable operation, from March 2023 to April 2025."
The latest results from the international LUX-ZEPLIN (LZ) experiment, released as a preprint (arXiv:2512.08065; lz.lbl.gov) and submitted to Physical Review Letters, are based on the largest dataset ever collected by a dark matter detector: 417 days of stable, live operation, recorded between March 2023 and April 2025.
This is LZ’s first analysis exploring weakly interacting massive particles (WIMPs) - a leading dark matter candidate - with masses below 9 GeV/c² (gigaelectronvolts/c²). Two previous results focused on higher masses, between 9 GeV/c² and 10 TeV/c² (teraelectronvolts/c²), where the detector sensitivity is highest and where LZ has already set the world’s strongest limits.
Dark matter search: low-mass analysis strengthens limits above 5 GeV/c²
No evidence for WIMPs was found in this new low-mass analysis. Nevertheless, LZ remains the most sensitive experiment searching for WIMPs with masses above 5 GeV/c², setting the strongest constraints in this mass range.
“The existence and nature of dark matter is a fundamental question for our understanding of the Universe, and LZ is the largest and most sensitive experiment designed to detect it,” says Isabel Lopes, researcher at the LIP and professor at the University of Coimbra, who leads the LIP group within LZ.
“We have not yet observed it directly, but with this result we have learned more about its properties, in particular about how likely it is to interact with ordinary matter.”
Solar neutrinos: evidence for coherent elastic scattering in xenon nuclei (4.5 sigma)
Thanks to its exceptional sensitivity, the LZ detector is also capable of detecting neutrinos produced in the Sun. These particles generate well-known signals in LZ through interactions with atomic electrons. The new analysis shows that LZ can also observe a different interaction channel: coherent elastic neutrino–nucleus scattering (CEvNS).
In this process, a neutrino interacts with an entire atomic nucleus, transferring only a minute amount of energy. CEvNS was first observed in 2017 using the intense neutrino flux from nuclear reactors. LZ is the first experiment to observe this process using solar neutrinos, with a statistical significance of 4.5 sigma - above the conventional 3-sigma threshold for evidence.
The PandaX-4T and XENONnT experiments reported hints of this process last year, but with significances below 3 sigma. LZ’s result therefore represents the first evidence of CEvNS associated with extraterrestrial neutrinos.
Photomultiplier tubes inside the LZ detector, capable of capturing faint flashes of UV light potentially produced by dark matter interactions in the liquid xenon target.
A return to the “Davis Cavern”, where the story of solar neutrinos began
This is not the first time solar neutrinos have been detected in the laboratory hosting LZ. In the 1960s and 1970s, Raymond Davis Jr. and John Bahcall carried out the first measurements of the solar neutrino flux using a 380 m³ detector in the same cavern, now known as the “Davis Cavern”. This pioneering work earned Ray Davis the Nobel Prize in Physics in 2002.
“With this new LZ result, the solar neutrino flux is once again being measured in the underground caverns at SURF, following Ray Davis’s original experiment,” comments Paulo Braz, researcher at LIP and deputy physics coordinator of the LZ collaboration.
“What is new here is not the direct detection of solar neutrinos, but the interaction mechanism: coherent scattering off xenon nuclei, where we expect to observe only between 3 and 7 photons and 4 to 14 electrons per interaction - a striking demonstration of LZ’s outstanding sensitivity.”
Next steps: towards 1,000 days of data by 2028
With these new results, LZ continues to lead the field in the direct search for dark matter while also probing neutrino properties. Aiming to reach 1,000 days of data-taking and to double its total exposure, the collaboration will continue operating until 2028. Alongside increasingly sophisticated analysis techniques, researchers expect to achieve unprecedented sensitivities to extremely rare interactions, explore even lower WIMP masses, search for additional exotic processes, and potentially open the door to phenomena never observed before.
View from inside LZ’s water shield, showing the acrylic tanks of the outer veto system surrounding the main detector.
About the LZ experiment and LIP’s participation
Multiple observations across the Universe indicate that dark matter is a fundamental component of the cosmos: it is about five times more abundant than ordinary matter and plays a key role in holding galaxies - including the Milky Way - together. Despite this, its direct detection remains extremely challenging, as dark matter particles neither emit nor interact with light.
The LUX-ZEPLIN (LZ) experiment is an international collaboration involving around 250 scientists and engineers from 37 institutions in the United States, the United Kingdom, Portugal, Switzerland, Australia and South Korea. The detector uses 10 tonnes of ultra-pure liquid xenon, cooled to −98 °C, to search for signals from WIMPs, one of the most plausible dark matter candidates. An interaction in the xenon produces scintillation light (ultraviolet photons) and ionisation electrons, which are detected by 494 light sensors inside the detector.
To maximise sensitivity to extremely rare interactions, the detector was built using materials with exceptionally low radioactivity and installed 1.5 km underground at the Sanford Underground Research Facility (SURF) in South Dakota, USA, greatly reducing background from cosmic rays.
LIP participates in the LZ collaboration through its group based at the University of Coimbra, involving five researchers and two PhD students. LIP’s contributions include studies of the optical properties of detector materials, development of data analysis software, detector monitoring and control, characterisation of environmental radiation signals, and searches for rare xenon decays.
Image credit: Matthew Kapust / Sanford Underground Research Facility