About 10 years ago, an experiment at Los Alamos National Laboratory threw another unexpected wrinkle into the mix: the possibility of a fourth kind of neutrino, a "sterile" neutrino that would only interact through gravity. MiniBooNE was conceived to test the results of that earlier Liquid Scintillator Neutrino Detector (LSND) experiment.
Back in 2004, MiniBooNe scientists presented results that seemed to contradict the LSND findings, but this time around, there are some striking similarities. Specifically, the experiment detected more oscillations than would be possible if, indeed, there were only three neutrino flavors. "These results imply that there are either new particles or forces we had not previously imagined," Byron Roe, one of the paper's co-authors, told PhysOrg.com. "The simplest explanation involves adding new neutrino-like particles, or sterile neutrinos."
What made the difference between these two runs? Well, the initial MiniBooNe experimental run used a muon neutrino beam, whereas the original LSND experiment used a muon antineutrino beam; this latest MiniBooNe experiment also used an antineutrino beam.