In a former gold mine a mile underground, inside a titanium tank filled with a rare, liquefied gas, scientists began searching for what had hitherto been undiscovered: dark matter.
Scientists are pretty sure that the invisible stuff makes up the bulk of the universe’s mass and say we would not be here without it – but they do not know what it is. The race to solve this enormous mystery has brought one team to the depths under Lead, South Dakota.
The question for scientists is basic, says Kevin Lesko, a physicist at Lawrence Berkeley National Laboratory: “What is this amazing place I live in? Right now, 95% of it 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 all the cosmic rays and particles that zip around us – and through – every day. But dark matter particles, scientists think, can avoid all those obstacles. They hope that in the barrel liquid xenon will fly into the inner tank and strike a xenon core like two balls in a swimming pool, revealing its existence in a flash light seen by a device called “the time projection room.”
Scientists announced on Thursday that the $ 60 million five-year search finally began two months ago following a delay caused by the COVID-19 pandemic. So far, the device has not found anything. At least no dark matter.
That’s right, they say. The equipment seems to be working to filter out most of the background radiation they were hoping to block.
“Looking for this very rare type of interaction is job number one to first get rid of all the usual sources of radiation that would overwhelm the experiment,” said Carter Hall, a physicist at the University of Maryland.
And if all their calculations and theories are correct, they reckon 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 few years.
By the time the experiment is complete, the chance of finding dark matter with this device is “probably less than 50% but more than 10%,” Hugh Lippincott, a physicist and spokesman for the experiment, told a news conference on Thursday. said.
Although it’s far from a certain thing, “you need a little enthusiasm,” Lawrence Berkeley’s Lesko said. “You do not go into rare search physics without any hope of finding anything.”
Two major Depression-era elevators run an elevator that brings scientists to what is called the LUX-ZEPLIN experiment at the Sanford Underground Research Facility. a 10-minute descent ends in a tunnel with cool-to-the-touch walls lined with net. But the old, musty mine soon leads to a high-tech laboratory where dirt and pollution are the enemy. Helmets are exchanged for new, cleaner and a double layer baby blue boots are about safety boots with steel toe.
The heart of the experiment is the giant tank called the cryostat, chief engineer Jeff Cherwinka said in 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 the liquid xenon cold and minimize background radiation.
Xenon is special, explains Aaron Manalaysay, experimental physics coordinator, because it enables researchers to see if a collision is with one of its electrons or with its nucleus. If something hits the core, it’s more likely the dark matter everyone’s looking for, he said.
These scientists tried a similar, smaller experiment here years ago. After coming up empty handed, they thought they should go much bigger. Another large-scale experiment is underway in Italy run by a competitive team, but no results have been announced so far.
The 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 most of the mass in the cosmos. Astronomers know it is there, because when they measure the stars and other regular matter in galaxies, they find that there is not nearly enough gravity to hold these clusters together. If nothing else was out there, galaxies would have “flown apart quickly,” Manalaysay said.
“It is essentially impossible to understand our observation of history, of the evolutionary cosmos without dark matter,” Manalaysay said.
Lippincott, a University of California, Santa Barbara physicist, said “we would not be here without dark matter.”
So while there is little doubt that dark matter exists, there is much doubt as to what it is. The leading theory is that it involves things called WIMPs – massive particles that have poor interaction.
If this is the case, LUX-ZEPLIN can detect them. And scientists want to find out “where the WIMPs can hide,” Lippincott said.