Historic Underground Dark-Matter Hunt Finds No WIMPs — But Reveals Clear Solar Neutrino Signal

A major dark-matter search using the LUX-ZEPLIN (LZ) detector, positioned about a mile underground at the Sanford Underground Research Facility in South Dakota, has tightened limits on low-mass WIMPs while producing the clearest signal yet of boron-8 solar neutrinos in liquid xenon.

The collaboration analysed its largest dataset to date from a 417-day run conducted between March 2023 and April 2025. After sensitivity upgrades to the detector, which uses roughly 10 tons of liquid xenon in a cylindrical active volume, researchers looked for the brief flashes of light and freed electrons that result when rare particles collide with xenon atoms.

Neutrinos Detected With High Confidence

On the neutrino front, LZ reports a 4.5-sigma indication that interactions from boron-8 solar neutrinos are being observed in the xenon target. While particle-physics discoveries typically require a 5-sigma significance to be declared definitive, 4.5 sigma represents a substantial improvement over sub-3-sigma hints from other detectors last year and strengthens confidence that experiments can identify and account for this background in future dark-matter searches.

No Low-Mass WIMP Signal Found

For dark matter, the collaboration specifically targeted low-mass variants of weakly interacting massive particles (WIMPs). If present, a WIMP striking a xenon nucleus would produce a characteristic coherent nuclear recoil signature that the detector is optimized to detect. The LZ team did not observe that signature in this run, allowing them to place stronger constraints on the possible properties of low-mass WIMPs and to rule out regions of parameter space previously less certain.

"One thing I've learned is, don't ever assume that nature does things in the way that you think it should, exactly," said Rick Gaitskell, head of the particle astrophysics group at Brown University and a lead member of the LZ collaboration. "There are plenty of elegant solutions that you would say, 'That's so beautiful. It has to be true.' And we tested them … and it turned out, nature ignored it."

The results were presented at the Sanford facility and have been submitted to Physical Review Letters; a preprint is available on arXiv. The team emphasises that null results are scientifically valuable because they narrow the range of viable theories and help future experiments avoid false positives.

What's Next

LZ plans a longer, record-setting 1,000-day data run starting in 2028. Extended operation increases the chance of catching extremely rare events — more solar neutrinos, a potential WIMP interaction, or unexpected physics beyond the Standard Model. Longer datasets and continued detector improvements will further refine constraints on dark matter and sharpen the identification of neutrino backgrounds.