The neutrino is the oddball of particle physics. It has no charge and rarely interacts with other particles, but it comes in three flavors—electron, muon and tau—and madly oscillates from one flavor to the next as it travels along. For the past five years, researchers at the Fermi National Accelerator Laboratory in Batavia, Ill., have been firing beams of muon neutrinos at the MiniBooNE detector, a huge spherical tank filled with 800 tons of mineral oil, to see how many of the particles changed in flight to electron neutrinos. The first results, announced in April, mostly vindicated the Standard Model—the conventional theory of particle physics—but an unexplained anomaly in the data leaves open a more exotic possibility. Some scientists speculate that the cause of the anomaly is a new kind of neutrino that can take shortcuts through the extra dimensions predicted by string theory.