Neutrinos—fundamental particles most often produced in the fiery hearts of stars—are both famously elusive and tremendously abundant. While neutrinos endlessly bombard every inch of the Earth’s surface at nearly the speed of light, they seldom interact with any matter. This ability to sail unhindered and unnoticed through almost anything earned neutrinos the nickname “ghost” particles. But despite their imperceptibility, neutrinos could be the key to understanding how our universe evolved just after the Big Bang and why the world is made of matter.
The Deep Underground Neutrino Experiment (DUNE), a new globally organized endeavor with large international partnerships, grows out of a former neutrino research collaboration known as the Long Baseline Neutrino Experiment (LBNE). The DUNE collaboration, now global, continues to grow, and with 750 scientists, is the largest neutrino experiment collaboration in the world. Based on recommendations from a recent high-energy physics advisory panel, the process of forming a new fully internationalized collaboration to construct the experiment and the Long-Baseline Neutrino Facility (LBNF) in which it will be situated is well underway.
This experiment will build on Fermi National Accelerator Laboratory’s existing accelerator complex to supply its neutrinos. Fermilab’s Main Injector Ring will smash energetic protons into a fixed target to produce short-lived particles called pions and kaons. These particles are aimed into a several-hundred-foot-long tunnel, where they decay, transforming into an intense collimated beam of neutrinos.
From Fermilab’s location just outside Chicago, IL, the intense neutrino beam will travel 800 miles (1300 kilometers) through the Earth before striking its target at the Sanford Underground Research Facility located in Lead, South Dakota. This distance, not much more than a blink for speedy neutrinos, gives the particles time to exhibit one of their strangest and most exciting quirks: quantum mechanical flavor transformations.
Neutrinos oscillate between three distinct flavors: muon, tau, and electron. One of Brookhaven Lab’s Nobel Prizes, for detection of neutrinos from the Sun, revealed the first hint that neutrinos must oscillate. Understanding details of these oscillations remains one of the most intriguing puzzles in fundamental physics.
Most of the neutrinos sent from Fermilab will begin as the muon type, and DUNE will measure these particles as they cross state lines, transforming and passing through the far detector in South Dakota. This vast, multi-kiloton, technological marvel will be filled with super-cold liquid argon and will be built in stages in collaboration with international partners. As the neutrinos interact with the argon atoms, they create charged particles that traverse the liquid argon detector. The charged particles ionize argon atoms that release electrons. These newly minted electrons are then swept by an electric field and collected by wires. Using advanced electronics and software, scientists can reconstruct and analyze a complete 3-dimensional picture of each neutrino interaction to precisely measure the phenomena of neutrino oscillations.