Interior of the MiniBooNE tank. The MiniBooNE experiment investigates the question of neutrino mass by looking for oscillations of muon neutrinos into electron neutrinos. It uses a large tank filled with 800 tons of mineral oil to look for particles produced when a neutrino hits the nucleus of an atom. The signature of such an interaction is a cone of light that hits some of the 1,520 light-sensitive devices mounted inside the tank. The first beam-induced neutrino events were observed in September of 2002, and the experiment is currently taking data. The primary goal of MiniBooNE is to investigate a signal reported by the LSND experiment conducted at Los Alamos National Laboratory. If the MiniBooNE experiment confirms the LSND measurement, the current model for understanding the universe will have to be changed to take into account a fourth type of neutrino, in addition to the three currently observed.