Recently, revolutionary discoveries have shown that while the Standard Model represents a good approximation of nature at the energies of existing accelerators, it is incomplete. A striking development in neutrino physics, thanks to a remarkably broad suite of experiments, is the discovery that the three kinds, or "flavors", of neutrinos have tiny masses and can oscillate (morph from one kind to another), contrary to the Standard Model.
These properties imply that neutrinos play critical roles across many fields of physics and make neutrinos uniquely suitable as probes. Neutrinos have shown us details of the solar core, provided clues to the mechanism of supernova explosions, and most likely play an important role in the early universe. They may even be responsible for the observed preponderance of matter over antimatter.
Physicists have learned much over the past decade about building and operating large neutrino detectors and intense neutrino beams. The unique capabilities and accelerator infrastructure at Fermilab together with a potential Far Detector site 1300 km away (a distance optimal for oscillation studies at the planned energies) at the Sanford Underground Research Facility in Lead, South Dakota, present an extraordinary opportunity to develop a world-leading program of long-baseline neutrino science. The proposed Long-Baseline Neutrino Experiment aims to develop this research complex to measure the parameters that characterize three-flavor neutrino oscillations, study a phenomenon known as CP-violation, which may help explain the matter-antimatter imbalance, and determine the relative neutrino masses.