A record-breaking investigation using a particle detector located a mile underground in South Dakota may have revealed new clues about dark mattera mysterious substance that is believed to make up most of the matter in the universe.
Using the largest data set of its kind, an experiment called LUX-ZEPLIN (LZ) has constrained the potential properties of one of the leading dark matter candidates with unprecedented sensitivity. The study found no evidence of the mystery substance, but will help future research avoid false detections and better hone in on this little-understood part of the universe.
Wimps vs. Neutrinos
The team had two goals for the new study: to understand the properties of the low-mass material. “flavor” of suspected dark matter particles so-called weakly interacting massive particles (WIMPs), and see if the detector can see solar neutrinos—nearly massless subatomic particles produced by nuclear reactions inside the Sun. The team suspected that the detection signatures of these particles might be similar to those predicted by some dark matter models, but to know for sure, they needed to detect solar neutrinos.
Before the experiment, which lasted 417 days from March 2023 to April 2025, the detector's sensitivity was increased to look for rare interactions with fundamental particles. The scene of action was a cylindrical chamber filled with liquid xenon. Researchers could observe WIMPs, or neutrinos, colliding with xenon, each producing bursts of photons along with positively charged electrons.
The experiment advanced science on both WIMP and neutrino issues. As 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 research avoid false detections of dark matter.
To be considered valid, physical discoveries typically must reach a level of confidence called “5 sigma.” The new work achieved 4.5 sigma, a significant improvement over the sub-3 sigma results obtained at two detectors last year. And this was especially remarkable given that detection of boron-8 occurs at the detector only about once a month, even when monitoring 10 tons of xenon, Gaitskell said.
However, on the question of dark matter, the researchers found nothing definitive for the low-mass types of WIMPs they were looking for. According to the team, scientists would know about it if they saw it; if you're a weakling hits the heart of a xenon molecule, the collision energy creates a characteristic signature, just as the models predict.
“If you take a core, dark matter can come in and actually scatter out of the entire core at the same time and cause it to bounce,” Gaitskell explained. “This is known as coherent scattering. It has a special signature in xenon. That’s why we are looking for precisely those coherent nuclear recoils.”
The team did not detect this signature in their experiment.
Doubling your mileage
Another, longer period will begin in 2028, when the detector is expected to collect results for a record 1,000 days. Longer runs give researchers a better chance of catching rare events.
The detector will be looking not only for more solar neutrinos or WIMP interactions, but also for other physical phenomena that may be outside the scope. Standard model Particle physicists are said to describe much of our environment.
Gaitskell emphasized that the role of science is to keep moving forward even when “negative” results arise.
“One thing I've learned is to never assume that nature is doing things the way you think they are,” said Gaitskell, who has been studying dark matter for more than four decades.
“There are many elegant [solutions] What do you say: “This is so beautiful.” This must be true. And we tested them… and it turned out that nature ignored this and did not want to go down this particular path.”
