Abstract

Neutrinos interact only weakly with other matter and had been thought to be massless. However, if their mass is at all non-zero, then they could change flavors as they propagate. Recent results from observations of atmospheric, solar, and reactor neutrinos indicate that they do change flavor and have provided measurements of two of the three possible mixings. The MINOS experiment is now making precise measurements of the $\nu_\mu\leftrightarrow\nu_\tau$ oscillations seen in atmospheric neutrinos. It does so by using the intense, well-understood NuMI neutrino beam created at Fermilab and observing it 735~km away at the Soudan Mine in Northeast Minnesota. NOvA is an off-axis long-baseline neutrino experiment, looking for $\nu_e$ appearance in an upgraded NuMI beam of $\nu_\mu$ to search for $\theta_{13}$ acting in subdominant $\nu_\mu\rightarrow\nu_e$ transitions. As an appearance experiment, NOvA might also be sensitive to CP-violating $\delta$ and the neutrino mass hierarchy. To maximize sensitivity to the resulting $\sim$GeV electromagnetic showers, the 14~kton Far Detector is "totally active", comprised of liquid scintillator contained in 15.7~m long extruded PVC cells, with the scintillation light piped out in wavelength shifting fibers then digitized by avalanche photodiodes. Civil construction at the far detector site is underway, and the smaller near detector is being assembled at Fermilab.