Neutrinos interact only weakly with other matter and had been thought to be massless. However, if their mass is non-zero, they could change flavors as they propagate. Recent results from observations of atmospheric, solar, and reactor neutrinos indicate that they do change flavor and these observations have provided measurements of two of the three possible mixings. The MINOS experiment is now making precise measurements of the νμ↔ντ oscillations seen in atmospheric neutrinos, and extends our reach towards the so far unseen angle θ13 by looking for νe appearance from the νμ beam. 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. This combination also allows investigation of the oscillation properties of anti-neutrinos, as the NuMI beam can focus opposite-charged pions to produce the anti-neutrinos, and the MINOS detectors are magnetized, allowing event-by-event discrimination of the resulting muon charge-sign.
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This work was supported by the U.S. Department of Energy, the U.K. Science and Technologies Facilities Council, the U.S. National Science Foundation, and the State and University of Minnesota. This researcher is supported by NSF RUI grant #0970111.