https://phys.org/news/2018-06-nova-strong-evidence-antineutrino-oscillation.html

NOvA uses two large particle detectors—a smaller one at Fermilab in Illinois and a much larger one 500 miles away in northern Minnesota—to study a beam of particles generated by Fermilab's accelerator complex and sent through Earth, with no tunnel required.

The new result is drawn from NOvA's first run with antineutrinos, the antimatter counterpart to neutrinos. NOvA began studying antineutrinos in February 2017. Fermilab's accelerators create a beam of muon neutrinos (or muon antineutrinos), and NOvA's far detector is specifically designed to see those particles changing into electron neutrinos (or electron antineutrinos) on their journey.