For more than a century, the mining town of Lead in South Dakota’s Black Hills attracted gold-loving workers. Today, a landmark experiment under construction at the former mine is attracting scientists in search of even more intriguing riches: answers to the deepest mysteries of the universe.
Construction of the Deep Underground Neutrino (Dune) experiment at the former Homestake mine is scheduled to begin on Monday. Engineers will begin assembling four giant detectors inside caverns carved into rock a kilometer underground.
Once turned on, the detectors spark and flash silently as ghostly particles called neutrinos pass through them. Some will arrive from the sun and distant supernovas, others as an intense beam sent through 800 miles of rock from a government laboratory near Chicago, Illinois.
Observing neutrinos could reveal entirely new scientific discoveries and shed light on cosmic spectacles, such as the death of stars and the birth of black holes. Scientists particularly hope to solve one of nature’s most enduring mysteries: why everything around us is made of matter and not its “evil twin,” antimatter. In other words, why are we, and why is anything, here.
“It’s a hugely exciting time to be working on this,” said Dr Kate Shaw, an experimental particle physicist on Dune from the University of Sussex. “Neutrinos don’t yet make sense, and they could open the door to new physics.”
Neutrinos are the most abundant particles of matter in the universe, outnumbered by photons, the massless particles of light that illuminate the universe. They are produced in natural nuclear reactions, such as those that power the sun, during radioactive decay and in particle accelerators.
Even by physicists’ standards, neutrinos are weird. Chargeless particles barely interact with other matter: about a trillion pass unnoticed into your body every second. There are three varieties of neutrinos, all with tiny but different masses. Oddly, they change from one variety to another, a process called oscillation, as they move. “It’s very strange behavior,” Shaw said. “It’s like I threw an apple at you and it turned into a banana.”
Lead has a history with these particular particles. In the 1960s, physicist Ray Davis followed miners down the shaft and built a detector from a 100,000-gallon tank filled with dry cleaning fluid. Protected so deep underground, the detector became the first to record neutrinos from the sun as they struck chlorine atoms in the fluid and transformed them into argon.
The mine closed in 2001 and was transformed, through visionary thinking, into a dedicated underground laboratory, the Sanford Underground Research Facility (Surf). It is already home to the Lux-Zeplin (LZ) experiment, which last month reported the first potential detection of dark matter.
“We’ve gone from mining the Earth to helping scientists explore the universe,” said Lead Town Administrator Robin Lucero, whose family has lived locally for generations. “We are incredibly proud and lucky that Dune is happening here, as well as Surf, which is running other experiments like LZ. Having world-class science brings new opportunities, new people and new possibilities for our local businesses and especially our youth.”
Unlike Davis’ device, the Dune experiment is enormous. Made from more than 4,000 tonnes of steel, the detectors will rise five stories and contain a total of 70,000 tonnes of liquid argon which will need to be cooled to -200°C. Assembling the detectors is expected to take nearly three years. Fill them with liquid argon, another year.
“This is a heavy engineering operation” and a partnership with the local skilled workforce, said Professor David Newbold, of the UK Science and Technology Facilities Council and a spokesperson for Dune. “It’s like building a ship underground.” The UK is the largest international partner in the US-led experiment and manufactures the core components of the detector, the critical computing to reconstruct events in the detectors and the graphite target needed to generate neutrinos at Femilab, a particle physics facility in Illinois.
Once operational, Dune will study an intense beam of neutrinos sent from Fermilab through 800 miles of Earth’s crust and mantle. Most neutrinos will pass through, but every once in a while one will hit an argon atom, creating a flicker of light and a pulse of electrical charge. Their analysis will reveal intimate details about the mysterious particles.
A big question concerns the mass of different neutrinos. Which is the lightest and which is the heaviest? The answer could reveal new fundamental forces of nature. And to try to answer the matter versus antimatter question, Dune will look for subtle differences between neutrinos and their antimatter twins, antineutrinos.
Beyond particle beams sent from Fermilab, Dune will also study neutrinos arriving from space, carrying with them new information about stellar explosions and the formation of black holes.
Earlier this month, the Nobel Prize in Physics honored Belgian researcher Francis Halzen, who used a cubic kilometer of Antarctica to detect high-energy neutrinos from deep space. But detection is far from the end of the story. “This is truly going to be a golden age,” Newbold said. “There’s a lot more to come.”
Gn bussni
