LEAD, SD (AP) – At an ancient gold mine a mile underground, inside a titanium tank filled with a rare liquefied gas, scientists have begun searching for what has not yet been found : dark matter.
Scientists are pretty sure that invisible things make up most of the mass of the universe and say we wouldn’t be here without it, but they don’t know what it is. The race to solve this huge mystery has taken a team to the depths of Lead, South Dakota.
The question for scientists is basic, says Kevin Lesko, a physicist at Lawrence Berkeley National Laboratory. “What is this great place where I live? Right now, 95% is a mystery.”
The idea is that a mile of earth and rock, a giant tank, a second tank, and the purest titanium in the world will block almost every cosmic ray and particle that surrounds, and traverses, us all every day. But particles of dark matter, scientists think, can avoid all these obstacles. They expect one to fly into the liquid xenon tank in the inner tank and crash into a xenon core like two balls in a pool game, revealing its existence in a flash of light seen by a device called “the projection chamber of time “.
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 has not found … anything. At least no dark matter.
Okay, they say. It looks like the team is working to filter out most of the background radiation they were hoping to block. “To look for this rare type of interaction, the number one job is to first get rid of all the ordinary sources of radiation, which would overwhelm the experiment,” said Carter Hall, a physicist at the University of Maryland.
And if all their calculations and theories are correct, they think they’ll only see a couple of fleeting signs of dark matter a year. The team of 250 scientists estimates that they will get 20 times more data over the next two years.
When the experiment is over, the chance of finding dark matter with this device is “probably less than 50%, but more than 10%,” said Hugh Lippincott, a physicist and spokesman for the experiment at a news conference Thursday.
While that’s not a sure thing, “it takes a bit of enthusiasm,” Lawrence Berkeley’s Lesko said. “You don’t get into the physics of rare searches without any hope of finding anything.”
Two thick thickets from the Depression era run an elevator that takes scientists to what is called the LUX-ZEPLIN experiment at the Sanford underground research facility. A 10-minute descent ends in a tunnel with fresh-lined walls lined with netting. But the old, wet mine soon leads to a high-tech lab where dirt and pollution are the enemy. The helmets are exchanged for cleaner ones and a double layer of blue boots over the safety boots with steel toes.
At the heart of the experiment is the giant tank called Cryostat, chief engineer Jeff Cherwinka said on a December 2019 tour before the device was shut down 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.
The xenon is special, explained the physics coordinator of the experiment, Aaron Manalaysay, because it allows researchers to see if a collision is with one of its electrons or with its nucleus. If something gets to the core, it’s more likely to be dark matter that everyone is looking for, he said.
These scientists tried a similar, smaller experiment here years ago. After climbing gaps, they thought they had to go much bigger. Another large-scale experiment is underway in Italy led by a rival team, but so far no results have been announced.
Scientists are trying to understand why the universe is not what it seems.
Part of the mystery is dark matter, which has most of the mass of the cosmos. Astronomers know it’s there because when they measure stars and other regular matter in galaxies, they discover that there is not enough gravity to hold these clusters together. If nothing else, the galaxies would be “flying fast,” Manalaysay said.
“It is essentially impossible to understand our observation of history, of the evolutionary cosmos without dark matter,” Manalaysay said.
Lippincott, a physicist at the University of California, Santa Barbara, said “we wouldn’t be here without dark matter.”
Thus, while there is little doubt that dark matter exists, there are many doubts about what it is. The main theory is that it involves things called WIMP: mass particles that interact weakly.
If this is the case, LUX-ZEPLIN could detect them. We want to find “where the flakes can be hidden,” Lippincott said.
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Follow Seth Borenstein on Twitter at @borenbears.
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The Associated Press Department of Health and Science is supported by the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.
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