Dark matter is the invisible stuff that accounts for roughly 85% of the mass within the universe, and for many years, physicists have been making an attempt to determine what it is manufactured from. Now an experimental facility situated almost a mile under floor in South Dakota has recorded a single interplay between subatomic particles that does not match what’s anticipated from regular matter.
Has a dark-matter particle been detected ultimately? It is too early to say, however the anomaly is certainly attracting consideration from dark-matter detectives.
The detection was made on the Sanford Underground Research Facility, or SURF, a transformed gold mine that now homes the world’s most delicate detector for darkish matter. Since 2021, the LUX-ZEPLIN Dark Matter Experiment has been recording flashes of sunshine in a shielded tank that is crammed with 10 tons of ultra-pure liquid xenon. These flashes happen when weakly interacting large particles, or WIMPs, collide with xenon atoms. The outcomes are analyzed by a world workforce of 250 scientists and engineers from 39 establishments. The U.S. Division of Power’s Lawrence Berkeley Nationwide Laboratory manages the experiment.
Researchers lately reviewed 220 days’ price of knowledge collected by the detector between March 2023 and April 2024. An earlier evaluation looked for faint alerts from the best sorts of WIMP interactions, however the follow-up evaluation widened the search parameters to search for extra energetic interactions. One occasion exhibited a spectrum of nuclear recoil vitality that was tough to clarify within the context of recognized background alerts involving regular matter.
“We’re very intrigued to see this occasion within the knowledge, within the area the place we anticipate darkish matter to point out up and the competing backgrounds are very low,” Rick Gaitskell, a professor at Brown College and the spokesperson for LUX-ZEPLIN, said in a news release. “With just one occasion, we don’t need to get forward of ourselves. We’re not claiming to have seen darkish matter. However now we have seen one thing fascinating that we need to share with the scientific group for his or her enter.”
A report on the research was offered this week in a scientific talk at the 2026 TeV Particle Astrophysics conference in Japan. The report will probably be submitted to Physical Review Letters for peer-reviewed publication.
The analysis workforce’s evaluation decided that the particle behind the anomalous occasion would have greater than 200 instances the mass of a proton — if it was really a bit of darkish matter. However it’s too early to make that assumption. The importance stage for the detection was 2.6 sigma, which is properly under the 5-sigma customary for claiming a discovery. For now, the statistics recommend there is a roughly 0.5% likelihood that the occasion may very well be defined by recognized background interactions.
The LUX-ZEPLIN detector, or LZ for brief, makes use of a cylindrical chamber stuffed with liquid xenon to seek for darkish matter. It’s surrounded by further layers to detect or block background particles (left). When a weakly interacting large particle collides with a xenon atom (proper), it emits a flash of sunshine and electrons. The sunshine is detected on the high and backside of the liquid xenon chamber. An electrical area drifts the electrons to the highest of the chamber, the place they generate a second flash of sunshine. (Picture: Greg Stewart/SLAC Nationwide Accelerator Laboratory)
Daniel Akerib, a physicist at SLAC Nationwide Accelerator Laboratory and a member of the LUX-ZEPLIN science workforce, stated it’ll take multiple anomalous occasion to resolve the decades-old mysteries surrounding darkish matter.
“You’ll need to see the consequence confirmed, study its coupling to matter by seeing it in one other isotope — probably liquid argon,” he stated by way of e-mail. “You’ll additionally need to produce it (and its cousins) within the laboratory. Seeing one thing go ‘bump’ is kind of completely different from having the ability to decide its cosmological abundance.”
The dark-matter thriller dates again to the Nineteen Thirties, when Swiss astronomer Fritz Zwicky famous that the full mass of the galaxies within the Coma Cluster needed to be tons of of instances higher than what may very well be accounted for by seen starlight. Within the Nineteen Seventies, American astronomer Vera Rubin discovered that the “lacking mass” drawback prolonged to a variety of galaxies. Astrophysicists ultimately got here to the conclusion that the lacking mass consisted of invisible matter. However what was it, precisely?
WIMPs are at present the prime suspects within the dark-matter thriller. For a time, physicists additionally proposed that darkish objects manufactured from unusual matter — reminiscent of rogue planets, burned-out stars, brown dwarfs and primordial black holes — would possibly make up the lacking mass. Astronomical surveys ultimately decided that there weren’t sufficient of these large compact halo objects, or MACHOs, to clarify the abundance of darkish matter. Different suspects within the cosmic lineup embrace strongly interacting large particles, or SIMPs, and a theoretical class of sunshine subatomic particles often called axions.
LUX-ZEPLIN is not the one experiment searching for indicators of darkish matter. The XENON Dark Matter Project at Italy’s Gran Sasso Nationwide Laboratory and the China Jinping Underground Laboratory are additionally in on the hunt.
Right this moment, scientists say solely about 5% of the universe’s mass-energy content material consists of unusual matter, with 27% consisting of darkish matter. The opposite 68% seems to encompass darkish vitality, the power that is thought to drive the accelerating growth of the universe. NASA’s Nancy Grace Roman Space Telescope, which was launched earlier this week, is predicted to shed further gentle on the character of darkish vitality in addition to darkish matter.