A record-breaking study using particle detectors a mile underground in South Dakota may have revealed new insights into dark matter, the mysterious substance believed to make up most of the matter in the universe.
The experiment, called LUX-ZEPLIN (LZ), used the largest dataset of its kind to constrain the potential properties of one of the leading candidates for dark matter with unprecedented sensitivity. Although the study did not reveal any evidence of this mysterious material, future research could help avoid false positives and zero in on this poorly understood part of the universe.
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WIMP vs. neutrinos
The team had two goals for their new study. One is to characterize the proposed low-mass “flavor” of dark matter particles, called Weakly Interacting Massive Particles (WIMPs), and the other is to see if the detector can observe solar neutrinos, the nearly massless elementary particles produced by nuclear reactions inside the Sun. The researchers suspected that the detection properties of these particles might be similar to those predicted by certain models of dark matter, but they needed to detect solar neutrinos to know for sure.
Before the experiment, which took 417 days from March 2023 to April 2025, the detector’s sensitivity was upgraded to look for rare interactions with fundamental particles. A cylindrical room filled with liquid xenon was the scene of the action. Researchers can monitor WIMPs or neutrinos colliding with xenon, both of which produce flashes of photons along with positively charged electrons.
This experiment advanced the science on both WIMP and neutrino questions. As for neutrinos, researchers have become more confident that a type of solar neutrino known as boron-8 is indeed interacting with xenon. This knowledge will help avoid false positives of dark matter in future studies.
For discoveries in physics to be considered valid, they typically need to reach a confidence level called “5 sigma.” The new study achieved 4.5 sigma. This is a significant improvement over the sub-3 sigma results reported with the two detectors last year. And that’s especially noteworthy considering that even when monitoring 10 tons of xenon, a detection of boron-8 only occurs in the detector about once a month, Gaitskell said.
But when it came to the dark matter question, the researchers couldn’t find anything conclusive about the low-mass type of WIMP they were looking for. Scientists would have known it when they saw it, the researchers said. When a WIMP hits the center of a xenon molecule, the energy of the collision creates a unique signature, just as the model predicts.
“When you take a nucleus, dark matter can enter and at the same time be thrown off the whole nucleus and cause it to recoil,” Gaitskell explained. “This is known as coherent scattering. There’s a special feature in xenon. So what we’re looking for is coherent nuclear recoil.”
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The research team did not detect any traces of this in their experiments.
double the run
An even longer experiment will begin in 2028, when the detector is expected to collect a record-breaking 1,000 days of results. The longer the run time, the more likely researchers are to capture rare phenomena.
The detector will track not only more solar neutrinos and WIMP interactions, but also other physics that may deviate from the standard model of particle physics, which is said to describe most of our surrounding environment.
Gaitskell stressed that science’s role is to keep moving forward even if there are “negative” results.
“One of the things I’ve learned is to never assume that nature will do things the way you think they will,” said Gaitskell, who has studied dark matter for more than 40 years.
“There are a lot of elegant things.” [solutions] You’ll say, “It’s so beautiful.” It has to be true. ‘And we tested them…and it turned out that nature ignored it, nature didn’t want to go down that particular route. ”
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