MiniBooNE
Between 2002 and 2005, neutrinos reaching the MiniBooNE detector collided with the carbon nuclei of almost a million litres of ultrapure mineral oil. These collisions produced small amounts of light, which were picked up by 1280 photomultiplier tubes (the red objects shown above) lining the tank. By interpreting the signature of the light, physicists at MiniBooNE could tell whether any of the muon neutrinos produced by Fermilab's proton beam 500 m away had oscillated into electron neutrinos on their journey. (Image courtesy: Fermilab Visual Media Services)