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In a former gold mine a mile underground, inside a titanium tank filled with a rare liquefied gas, scientists began searching for what had been elusive: dark matter. Scientists are pretty sure that invisible stuff makes up most of the matter in the universe, and they say we wouldn’t be here without it—but they don’t know what it is. The race to solve this huge mystery has brought one team into the depths under the leadership, South Dakota.
The question for scientists is fundamental, says Kevin Lesko, a physicist at Lawrence Berkeley National Laboratory. “What is this great place where I live? Right now, 95% of it is a mystery.” The idea is that miles of dirt and rock, a giant tank, a second tank, and the purest titanium in the world will block almost all of the cosmic rays and particles that move around—and through—us all every day . But dark matter particles, scientists think, can avoid all these obstacles. They hope that one will fly into a vat of liquid xenon in the inner tank and smash into a xenon core like two balls in a pool game, revealing its existence in a flash of light seen by a device called a “time projection chamber”. Scientists announced Thursday that the five-year, $60 million search finally began two months ago after a delay caused by the COVID-19 pandemic.
So far, the device hasn’t found… anything. At least no dark matter. It’s okay, they say. The device appears to be working to filter out most of the background radiation they were hoping to block. “To look for this very rare type of interaction, the number one task is to first get rid of all the common sources of radiation that would overwhelm the experiment,” he said.
And if all their calculations and theories are correct, they believe they will only see a few fleeting signs of dark matter in a year. The team of 250 scientists estimate they will collect 20 times more data over the next few years. By the time the experiment ends, the chance of finding dark matter with the device is “probably less than 50%, but more than 10%,” Hugh Lippincott, a physicist and spokesman for the experiment, said at a news conference Thursday. While it’s far from certain, “you need a little enthusiasm,” Lesko told Lawrence Berkeley.
“You don’t go into the physics of a rare find without hoping to find something.” Two massive Depression-era hoists operate the elevator that brings scientists to the LUX-ZEPLIN experiment at the Sanford Underground Research Facility. The 10-minute descent ends in a tunnel with pleasant-to-the-touch walls lined with mesh. But the old, musty mine soon leads to a hi-tech laboratory where dirt and contamination are the enemy. Helmets are replaced with new, cleaner ones, and a double layer of baby booties goes over steel-toed safety shoes. The heart of the experiment is a giant tank called a cryostat, lead engineer Jeff Cherwinka said on a tour in December 2019 before the device was built. closed and filled.
He described it as “like a thermos” made of “perhaps the purest titanium in the world”, designed to keep liquid xenon cool and keep background radiation to a minimum. Xenon is special, explained experimental physics coordinator Aaron Manalaysay, because it allows researchers to determine whether it collided with one of its electrons or its nucleus. If something hits the core, it’s more likely to be the dark matter everyone is looking for, he said. These scientists tried a similar smaller experiment here years ago.
After coming up empty, they figured they had to go much bigger. Another large-scale experiment is underway in Italy led by a rival team, but no results have yet been reported. Scientists are trying to understand why the universe is not what it seems. One part of the mystery is dark matter, which has by far the majority of matter in the universe. Astronomers know it’s there because, when they measure stars and other regular matter in galaxies, they find that there isn’t nearly enough gravity to hold these clumps together.
If nothing else were there, the galaxies would “fly apart quickly,” Manalaysay said. “It is essentially impossible to understand our observational history, the evolutionary cosmos, without dark matter,” Manalaysay said. Lippincott, a physicist at the University of California, Santa Barbara, said: “Without dark matter, we wouldn’t be here.” So while there is no doubt that dark matter exists, there is much doubt about what it is. The leading theory is that it involves things called WIMPs – Weakly Interacting Massive Particles. If so, LUX-ZEPLIN could detect them. We want to find out “where the weak can hide,” Lippincott said.
