A new hunt for dark matter has begun in an old gold mine, nearly 1 mile underground

Deep in an old gold mine, in a vat of molten xenon, a new hunt has begun for dark matter — the mysterious thing that makes up about 85% of all matter in the universe.

No one knows what dark matter actually is. Scientists know it exists because they can measure how its gravity affects distant galaxies, but they have never detected it directly. That’s the goal of a new experiment buried deep beneath Lead, South Dakota: to capture dark matter as it interacts with other particles.

This experiment is called LUX-ZEPLIN, or LZ for short. This is a 10-ton vat of pure liquid xenon, equipped with a detector to capture the very faint energy flashes that will come from dark matter particles colliding with xenon atoms. The researchers announced Thursday that it was online and ready to search for new particles.

“Dark matter remains one of the greatest mysteries of particle physics today,” said Hugh Lippincott, spokesman for the LZ team of 250 scientists, in a live announcement.

An array of photomultiplier tubes was prepared to assemble the LZ detector.

Matthew Kapust/Sanford Underground Research Facility

After eight years of preparation, the LZ detector worked as expected during the 63-day trial, according to the researchers, who published a report on the first data set on Thursday. Now they are preparing to run experiments for up to 1,000 days, starting in late summer or early fall. They could have initial results around 2023, but observations could continue for up to five years.

This isn’t the first vat of liquid xenon to search for dark matter, but it’s the largest and most sensitive. His new data have ruled out mass ranges for dark matter particles, and have sufficient sensitivity to search in lower mass ranges.

If they do discover a new particle, it could lead to a new, more precise physics beyond the Standard Model that has defined our understanding of the universe since the 1970s. Detection of dark matter will revolutionize our most basic understanding of the universe.

“Everyone is trying to find some physical evidence outside the standard model. And perhaps the strongest evidence we have of that is dark matter,” Aaron Manalaysay, the project’s physics coordinator, told Insider, adding, “But we really didn’t. know what it is.”

To see dark matter, you have to set a very quiet stage

Aaron Manalaysay explains how underground detectors will interact with dark matter at the Sanford Underground Research Facility in Lead, South Dakota, on December 8, 2019.

Stephen Groves/AP Photo

Dark matter could come from Weakly Interacting Massive Particles (WIMPs) — theoretical particles that would interact with gravity and sometimes, very rarely, collide with visible matter particles. That’s the main theory, but no one has detected WIMP before. That’s the main thing the LZ project is looking for.

You could shoot a WIMP through 10 million light-years of lead and only get one collision, says Lippincott.

Luckily, if anything, a lot of WIMPs have to pass us by all the time. In 10 tons of xenon atoms, there must be regular collisions. The experimenter just needed to be quiet enough so that the faint, fast-disappearing WIMP signal wasn’t lost to background noise.

“Our job is to get to some chunks of matter, which are very clean and very quiet from a particle perspective, and where we can instrument and detect when there are particle interactions,” Manalaysay said.

That’s why the researchers built the LZ detector at the Sanford Underground Research Facility, an old gold mine nearly a mile underground. Location protects it from background noise. For further quietness, xenon is housed in two titanium tanks.

LZ’s central detector in a clean room at the Sanford Underground Research Facility after assembly, before starting its journey underground.

Matthew Kapust/Sanford Underground Research Facility

LZ’s search for dark matter is a process of elimination. Most of its sensors are designed to identify signals that match known particle interactions — something that is definitely not dark matter.

“That’s really the name of the game here in the dark matter search field, having a large detector and having very low background signal levels,” Manalaysay said.

Global search for invisible matter

Look into the LZ Outer Detector, used to veto radioactivity that can mimic dark matter signals.

Matthew Kapust/Sanford Underground Research Facility

Because it has the largest liquid xenon tank, and because of its quiet location, LZ is the most sensitive dark matter detector on Earth. This is not the only one, but will be the most sensitive to potential WIMPs.

In China, a 4-ton xenon experiment called PandaX published its first results in December.

A similar experiment in Italy, called XENON1T, announced in 2020 that it had detected a very high number of collisions in its latest experiment. Neither of them looks like dark matter, but they could point to new, different particles. Data from the LZ detector test should highlight the possibility of that collision, Manalaysay said.

XENON1T, the LZ team, and a large group of dark matter scientists in Europe, called DARWIN, have formed a large consortium of hundreds of scientists. Eventually, they plan to build a giant dark matter experiment together — “one more xenon experiment to set things right,” Lippincott said — although there’s currently no schedule for that project.

#hunt #dark #matter #begun #gold #mile #underground