The project known as DUNE, the Deep Underground Neutrino Experiment, will span 800 underground miles from Fermilab outside of Chicago to the Sanford Underground Research Facility, housed deep underground in an abandoned South Dakota mine. DUNE's quarry is the elusive neutrino, a member of the Standard Model of Physics that constantly changes forms, features a bafflingly tiny mass, and, thanks to its electrical neutrality, just barely interacts with the observed universe (through the weak force). You could be standing in a waterfall of neutrinos and not know it.
In a sense, you are standing in a waterfall of neutrinos. It's been estimated that 65 billion solar neutrinos (neutrinos originating within the Sun) pass through every Sun-facing square centimeter of Earth per second. Unlike sunlight, however, which delivers photons that interact with the materials in your body to create heat and light, neutrinos have nothing to do with light and heat, which is the stuff of the electromagnetic force. The neutrinos mostly just pass on through, completely oblivious.
This makes neutrinos very hard to observe and very hard to understand. In fact, it's fundamentally impossible to directly observe a neutrino (observation relies on electromagnetic interactions), so physicists are forced to go to extreme lengths in the hopes of indirectly observing one of the particles.
The theory is that rare neutrino interactions do occur, but only via the weak force, which is mediated via elementary particles known as W and Z bosons. Should one of these bosons be exchanged between a neutrino and an electron, the result should be the release of characteristic radiation called Cherenkov radiation. Using super-sensitive photodetectors, this signal should be observable, albeit with difficulty.
The weakness or rareness of the neutrino interaction makes it necessary to build neutrino detectors that are very large and, just as crucially, very isolated from atmospheric radiation and potentially interfering cosmic rays. This is why neutrino experiments occur underground; the Sanford facility is nearly two miles deep. When completed, DUNE will feature a detector centered around a multi-kiloton bath/lake of liquid argon. The argon will register incoming neutrinos created 800 miles away at Fermilab, which will send the particles in a dense beam packing neutrinos by the trillion. At one point, this beam will be traveling 19 miles below the surface.
The project is really two detectors. The first is at Fermilab itself, where the neutrinos are produced, and the second is in the South Dakota mine. There's a good reason for this setup, having to do with neutrinos' odd capability for oscillation, or spontaneously changing into a different sort ("flavor") of neutrino, a process that also results in small changes in mass, though the exact masses of neutrinos is itself an open question and one of the chief goals of neutrino research.
The DUNE project hopes to gain insight into this by observing how those 800 miles of underground Earth being traversed by the beam impacts the oscillations of different neutrino flavors.
DUNE is projected to be operational by 2022, and it currently boasts the involvement of 148 different institutions from 23 countries. Somewhat amazingly, it's even managed to secure the blessing (and funding) of the United States' government.
"This will be the flagship experiment for particle physics hosted in the US," Jim Siegrist, associate director of high-energy physics for the US Department of Energy's Office of Science, told Symmetry. "It's an exciting time for neutrino science and particle physics generally."