Historic search for ‘huge missing piece’ of the universe turns up negative — but reveals new secrets of particle physics
A record-breaking investigation, using a particle detector located a kilometer underground in South Dakota, could have revealed new information about dark matterthe mysterious substance believed to constitute most of the matter in the universe.
Using the largest data set of its kind, the experiment – called LUX-ZEPLIN (LZ) – constrained the potential properties of one of the leading dark matter candidates with unprecedented sensitivity. The research uncovered no evidence of the mysterious substance, but will help future studies avoid false detections and better focus on this poorly understood part of the universe.
WIMPs versus neutrinos
The team had two goals for the new study: to elucidate the properties of a low-mass material “flavor” of the proposed dark matter particles called weakly interacting massive particles (WIMP), and to see if the detector could detect solar neutrinos – nearly massless subatomic particles produced by nuclear reactions inside the sun. The team suspected that the detection signature of these particles might be similar to that predicted by some dark matter models, but they needed to spot solar neutrinos to be sure.
Before the experiment, which lasted 417 days between March 2023 and April 2025, the sensitivity of the detector was improved to search for rare interactions with fundamental particles. A cylindrical chamber filled with liquid xenon was the scene of the action. Researchers could monitor either WIMPs or neutrinos colliding with the xenon, either of which produce flashes of photons, as well as positively charged electrons.
The experiment advanced science for both WIMP and neutrino questions. For neutrinos, researchers have increased their confidence that a type of solar neutrino, known as boron-8, actually interacts with xenon. This knowledge will help future studies avoid false detections of dark matter.
Discoveries in physics generally must reach a level of confidence called “5 sigma” to be considered valid. The new work achieved 4.5 sigma, a considerable improvement over the sub-3 sigma results reported in two detectors last year. And that’s especially notable given that boron-8 detections only occur about once a month in the detector, even when monitoring 10 tons of xenon, Gaitskell said.
When it comes to the dark matter question, however, the researchers found nothing definitive about the types of low-mass WIMPs they were looking for. Scientists would have known if they had seen it, the team said; if a wimp hits the core of a xenon molecule, the energy from the collision creates a distinctive signature, as models predict.
“If you take a core, it’s possible that dark matter could simultaneously enter and disperse from the entire core and push it back,” Gaitskell explained. “It’s called coherent scattering. It has a particular signature in xenon. So it’s these coherent nuclear recoils that we’re looking for.”
The team did not detect this signature in their experiment.
Double the race
Another, longer operation will begin in 2028, when the detector is expected to collect results for a record 1,000 days. Longer scans give researchers a better chance of detecting rare events.
The detector will not only look for more solar neutrino interactions or WIMPs, but also other physical phenomena that may fall out of scope. Standard model of particle physics intended to describe most of the environment around us.
Gaitskell emphasized that the role of science is to keep moving forward even when “negative” results arise.
“One thing I’ve learned is that you should never assume that nature does things exactly the way you think,” said Gaitskell, who has studied dark matter for more than four decades.
“There are many elegant [solutions] that you would say: “It’s so beautiful. This must be true. And we tested them…and it turned out that nature ignored it and didn’t want to go down that particular path. »
