A new experiment has begun searching for dark matter in an old gold mine in South Dakota.
LUX-ZEPLIN is a 10-ton vat of liquid xenon that is now the most powerful dark matter detector on Earth.
The detection of a dark matter particle would solve a fundamental mystery of our universe.
Deep in an old gold mine, in a vat of liquid xenon, a new search has begun for dark matter, the mysterious stuff that makes up about 85% of all the matter in the universe.
No one knows what exactly dark matter is. Scientists know it exists because they can measure how its gravity affects distant galaxies, but they’ve never detected it directly. That’s the goal of a new experiment buried deep in Lead, South Dakota: to catch dark matter in the act of interacting with other particles.
The experiment is called LUX-ZEPLIN, or LZ for short. It’s a 10-ton vat of pure liquid xenon, equipped with detectors to pick up the incredibly faint flash of energy that would come from a dark matter particle colliding with a xenon atom. The researchers announced Thursday that it is online and ready to search for new particles.
“Dark matter remains one of the biggest mysteries in particle physics today,” said Hugh Lippincott, spokesman for the 250-scientist LZ team, in the live-streamed announcement.
After eight years of preparation, the LZ detector performed as expected during a 63-day test, according to the researchers, who published a report on that first data set on Thursday. They are now preparing to run the experiment for up to 1,000 days, starting in late summer or early fall. They could have early results sometime in 2023, but observation could continue for up to five years.
This isn’t the first liquid xenon vat to search for dark matter, but it’s the largest and most sensitive. Their new data has ruled out one mass range for dark matter particles, and it has enough sensitivity to search even lower mass ranges.
If they discover a new particle, it could lead to new and more precise physics beyond the standard model that has defined our understanding of the universe since the 1970s. The detection of dark matter would revolutionize our most fundamental understanding of the universe.
“Everyone is trying to find some evidence for physics beyond the standard model. And probably the strongest evidence we have for that is dark matter,” Aaron Manalaysay, the project’s physics coordinator, told Insider, adding, “But We really don’t.” know what it is.”
To detect dark matter, you have to set a very quiet stage.
The dark matter could come from Weakly Interacting Massive Particles (WIMPs), a theoretical particle that would interact with gravity and occasionally, very rarely, collide with particles of visible matter. That’s a leading theory, but no one has detected a WIMP before. That is the main thing that the LZ project is looking for.
You could fire a WIMP through 10 million light-years of lead and only get one collision, Lippincott said.
Fortunately, if they exist, a lot of WIMPs should be passing us by all the time. In 10 tons of xenon atoms, there should be regular collisions. The experiment just needs to be quiet enough so that the weak and fleeting signal from the WIMPs is not lost in the background noise.
“Our job is to get a piece of matter, which is very clean and very quiet from a particle perspective, and where we can instrument and detect when there was a particle interaction,” Manalaysay said.
That’s why the researchers built the LZ detector at the Sanford Underground Research Facility, a former gold mine nearly a mile underground. The location protects you from background noise. For added peace of mind, the xenon is nested inside two titanium tanks.
The LZ search for dark matter is a process of elimination. Most of its sensors are designed to identify signals that match a known particle interaction, something that is definitely not dark matter.
“That’s really the name of the game here in the dark matter search field, is to have a large detector and to have a very low rate of background signals,” Manalaysay said.
A global search for invisible matter
Because it has the largest liquid xenon tank to date and because of its quiet location, LZ is the most sensitive dark matter detector on Earth. It is not the only one, but it will be the most sensitive to possible WIMPs.
In China, a 4-tonne xenon experiment called PandaX published its first results in December.
A similar experiment in Italy, called XENON1T, announced in 2020 that it had detected an unexpectedly high number of collisions in its last run. None of them look like dark matter, but they could point to a different new particle. Data from the LZ detector test should shed some light on what those collisions might be, Manalaysay said.
XENON1T, the LZ team, and a large group of dark matter scientists in Europe, called DARWIN, have formed a huge consortium of hundreds of scientists. Eventually, they plan to build a giant dark matter experiment together, “one more xenon experiment to rule them all,” Lippincott said, though there is currently no timeline for that project.
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