Scientists detect potential signs of elusive dark matter in cosmic ray study—what is it?

KUALA LUMPUR, 6 OCTOBER 2026 —

If a recent hint of dark matter is real, it would rewrite physics.

On September 1, scientists with the LUX-ZEPLIN, or LZ, collaboration announced they’d seen a signal in their detector that could have been caused by a single particle of dark matter — though it could still be just a blip caused by known physics processes. In the weeks since the detection, dozens of papers have been posted on arXiv.org purporting to explain what LZ saw.

Much interest has focused on a theorized type of particle called a higgsino. If the idea is correct, it would be big. “If we discover it, it would be the first discovery of supersymmetry,” says theoretical physicist Harikrishnan Ramani of the University of Delaware in Newark. Supersymmetry proposes that for each known particle, there exists a heavier counterpart called a superpartner .

It’s an idea that could solve multiple physics puzzles at once, so it has attracted a devoted following of physicists. One of these hypothetical superpartners, such as the higgsino, could be dark matter. The higgsino is the superpartner of the Higgs boson — a particle discovered in 2012 that explains the origin of mass .

“If you asked people in the year 2000, ‘What’s your favorite dark matter candidate?’ probably a lot of people would already have said the higgsino then,” says theoretical physicist Tracy Slatyer of MIT. In recent years, supersymmetry’s popularity has waned , as particle colliders failed to find evidence for it. But as an explanation for LZ’s dark matter hint, a higgsino seems plausible — at least at first glance.

“It comes pretty close to working,” Slatyer says. The LZ detector, located at the Sanford Underground Research Facility in Lead, S.D., consists of a large tank of liquid xenon. The detector searches for dark matter speeding through the xenon, crashing into it and sending a xenon atomic nucleus zinging away. That’s expected to be a rare event, since dark matter interacts very weakly with normal matter.

In the event LZ found, the nucleus recoiled with particularly high energy. Most types of dark matter would produce low-energy recoils in addition to high-energy ones. But LZ didn’t see any low-energy recoils. If dark matter were a higgsino, that could explain the absence of low-energy events. The higgsino differs from typical dark matter candidates in that it would have two different masses.

A collision would happen only if there’s enough energy to bump the higgsino from the lighter to the heavier mass state. That means lower-energy nuclear recoils wouldn’t happen. Within a day of LZ’s announcement, several papers on the arXiv put forth the higgsino possibility. “I got pretty excited,” says theoretical physicist Katherine Freese of the University of Texas at Austin, a coauthor of one such paper , which was submitted September 1.

“First paper I ever wrote in 24 hours.” But further investigation made the higgsino explanation seem less plausible. For example, if higgsinos exist, they would interact in the sun and get trapped there due to its gravitational pull. There, according to the concepts of supersymmetry, they would annihilate one another and produce high-energy particles called neutrinos.

Those neutrinos should have been observed by a neutrino detector located at the South Pole, called IceCube, Ramani and a colleague reported September 2 at arXiv.org. But no such neutrinos have been seen. And there’s another potential issue. Slatyer and colleagues noticed a plot in an appendix to LZ’s paper that looks at even higher energies.

If LZ saw one higgsino at the energy they reported, they’d expect to see even more at these higher energies , the team reported September 3. But LZ didn’t report anything that looked like dark matter at those energies. The LZ detector wasn’t calibrated for those energies, says LZ spokesperson Rick Gaitskell, a physicist at Brown University in Providence, R.I.

“We didn’t make any formal claims about detection or even nondetection in that event region,” Gaitskell wrote in a text message. But, if the data are taken seriously, that makes LZ’s event even more difficult to explain with a higgsino. Considering all these factors makes the higgsino idea a bit of a stretch. But there’s still a little wiggle room.

One possibility is that the higgsino’s mass differs from what theoretical physicists expect it to be, about 1,000 times a proton’s mass. That large mass is chosen to allow higgsinos to explain the amount of dark matter seen in the universe today. So changing it complicates the picture, but could make it align better with what LZ saw. Additional wiggle room comes from the possible speeds of the dark matter particles in the Milky Way.

The particles might reach higher velocities than typically assumed, and that could make the data easier to explain. For a faster higgsino to have shown up in LZ, it would require a larger difference in the two masses of the particle. The resulting bigger energy difference means higgsinos have fewer opportunities to produce neutrinos in the sun, explaining why neutrino experiments haven’t seen those particles.

By playing around with those factors, it’s still possible to make the higgsino explanation work, Freese says. Higgsinos with around 2,000 times a proton’s mass could do the trick , Freese and a coauthor report in an October 2 arXiv paper. “Big picture: We love [the] higgsino, and what we’re doing now is putting in the details that we think are important,” she says.

But, if it’s not the higgsino, “maybe it’s some other particle with the same basic features,” says theoretical physicist Dan Hooper of the University of Wisconsin–Madison. Such particles wouldn’t be subject to the constraints supersymmetry imposes.