NuMI Horn.The Main Injector Neutrino Oscillation Search, or MINOS experiment is located half a mile underground in the historic Soudan iron mine in northeastern Minnesota. It probes the secrets of subatomic particles called neutrinos. The neutrinos are produced at a particle accelerator at Fermi National Accelerator Laboratory near Chicago. Beginning in February, 2005, neutrinos in the NuMI (for "Neutrinos at the Main Injector") beam began traveling 450 miles straight through the earth, from Fermilab to Soudan-no tunnel needed. When operating at highest intensity, the NuMI beam line transports a package of 20,000 billion protons every two seconds to a graphite target. The target converts the protons into bursts of particles with exotic names such as kaons and pions. Like a beam of light emerging from a flashlight, the particles form a wide cone when leaving the target. A set of two special lenses, called horns (photo), is the key instrument to focus the beam and send it in the right direction. The beam particles decay and produce muon neutrinos, which travel in the same direction.