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A huge underground search for mysterious dark matter begins

In an old gold mine a kilometer underground, inside a titanium tank filled with a rare liquefied gas, scientists began the search for what until now had not been found: dark matter . Scientists are pretty sure the invisible stuff makes up most of the mass in the universe and say we wouldn’t be here without it – but they don’t know what it is. The race to solve this massive mystery has taken a team deep beneath Lead, South Dakota.

The question for scientists is fundamental, says Kevin Lesko, a physicist at Lawrence Berkeley National Laboratory. “What is this wonderful place where I live? Right now, 95% of it is a mystery. “The idea is that a mile of dirt and rock, a giant tank, a second tank, and the purest titanium in the world will block almost all cosmic rays and particles that wander – and through – all of us every But dark matter particles, scientists think, can avoid all of these obstacles. They hope one will fly into the vat of liquid xenon in the inner tank and hit a xenon nucleus like two balls in a game of pool. , revealing its existence in a flash of light seen by a device called ‘the time projection chamber.’Scientists announced on 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 has found…nothing. At least no dark matter. It’s OK, they say. The equipment appears to be working to filter out most of the background radiation they hoped to block. “To search for this very rare type of interaction, task number one is to first get rid of all ordinary sources of radiation, which would overwhelm the experiment,” said

And if all their calculations and theories are correct, they think they will only see a few fleeting signs of dark matter per year. The team of 250 scientists estimates they will get 20 times more data over the next two years. At the end of the experiment, the chances of finding dark matter with this device are “probably less than 50% but greater than 10%”, said Hugh Lippincott, physicist and spokesman for the experiment during a press conference on Thursday. While it’s far from a sure thing, “you need a little bit of enthusiasm,” Lawrence Berkeley’s Lesko said.

“You don’t go into rare research physics with no hope of finding something.” Two huge Depression-era winches operate an elevator that takes scientists to what is called the LUX-ZEPLIN experiment in the underground Sanford Research Facility. A 10-minute descent ends in a tunnel with cool-to-the-touch walls lined with netting. But the moldy old mine soon leads to a high-tech laboratory where dirt and contamination are the enemy. Helmets are swapped for new, cleaner ones, and a double layer of baby blue booties go over steel-toed safety boots. The heart of the experiment is the giant tank called a cryostat, lead engineer Jeff Cherwinka said during a December 2019 tour before the device was closed and filled.

He described it as “like a thermos” made of “perhaps the purest titanium in the world” designed to keep liquid xenon cold and background radiation to a minimum. Xenon is special, explained the experiment’s physics coordinator Aaron Manalaysay, because it allows researchers to see whether a collision is occurring with one of its electrons or with its nucleus. If something hits the nucleus, 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 arriving empty they thought they had to go a lot bigger. Another large-scale experiment is underway in Italy run by a rival team, but no results have been announced so far. Scientists are trying to figure out why the universe is not what it seems. Part of the mystery is dark matter, which has by far most of the mass in the cosmos. Astronomers know it’s there because when they measure stars and other regular matter in galaxies, they find that there isn’t enough gravity to hold these clumps together.

If there was nothing else out there, the galaxies would “rapidly separate,” Manalaysay said. “It’s essentially impossible to understand our observation of history, of the evolutionary cosmos without dark matter,” Manalaysay said. Lippincott, a physicist from the University of California at Santa Barbara, said: “We wouldn’t be here without dark matter. The main theory is that it involves things called WIMPs – Weakly Interacting Massive Particles. If so, LUX-ZEPLIN may be able to detect them. We want to find “where the wimps may be hiding,” Lippincott said.