A close-up of the interior of the MiniBooNE tank, before it was filled with ultraclean mineral oil. Image credit: Fermilab.
MiniBooNE (mini booster neutrino experiment), a new experiment at Fermilab, has just begun its search for neutrino oscillations. After five years of construction, the first beam entered the detector in Summer 2002. This beam starts off as highly energetic protons which slam into a target made of beryllium. The collision produces particles called pions and kaons, which then decay into a variety of other particles, including muon neutrinos. The beam travels down 50 meters of pipe, through 5 meters of steel and 500 meters of earth. Only the neutrinos survive this journey. They can then interact with the ultra-clean mineral oil in MiniBooNE's large underground spherical tank. Over 1200 photon detectors look for evidence in these interactions that a muon neutrino oscillated into an electron neutrino.
This experiment differs from most neutrino oscillation experiments, because the neutrinos are produced in the controlled environment of the laboratory, instead of in the sun or the upper atmosphere. If evidence for oscillations from an earlier laboratory experiment is confirmed, this will point to a dramatic departure from the currently accepted Standard Model of elementary particles.