Neutrinos at the Main Injector, or NuMI, is a project at Fermilab which creates an intense beam of neutrinos aimed towards the Soudan Mine for use by several particle physics experiments. As of June 2010, the MINOS and MINERνA experiments use the NuMI beam. The proposed NOνA experiment will also use it.
The first step in the production of the NuMI beam is to direct a beam of protons from Fermilab's Main Injector onto a carbon target. Interactions of the proton beam in the target produce mesons, primarily pions and kaons, which are focused toward the beam axis by two magnetic horns. The mesons then decay into muons and neutrinos during their flight through a long decay tunnel. A hadron absorber downstream of the decay tunnel removes the remaining protons and mesons from the beam. The muons are absorbed by the subsequent earth shield, while the neutrinos continue through it to MINERνA and the MINOS near detector on site at Fermilab, then through the Earth to the MINOS far detector cavern in the Soudan Mine 735 km away, then onwards into space.
Because of the close relationship between NuMI and the MINOS experiment, MINOS is sometimes conflated with NuMI. For instance, the MINOS webpage is at www-numi.fnal.gov instead of www-minos.fnal.gov.
^ NuMI Technical Design Handbook, retrieved 5 October 2007.