Charge-parity (CP) violation—evidence that the laws of physics are different for particles and antiparticles—is often invoked as a “must” to explain why we observe more matter than antimatter in the universe. But the CP violation observed in interactions involving quarks is insufficient to explain this asymmetry. As a result, many theorists are looking toward leptons—and, specifically, neutrinos—for additional sources of CP violation. Researchers running the Tokai to Kamioka (T2K) experiment—a particle physics experiment at the Japan Proton Accelerator Research Complex (J-PARC)—have now made an important contribution toward the search for CP violation in neutrinos. Writing in Physical Review Letters, the T2K collaboration reports the strongest evidence to date for the appearance of electron neutrinos from a pure muon neutrino beam . Their measurement allows them to determine a fundamental parameter of the standard model of particle physics, called θ13, which can in turn be used to make an early estimate of CP violation in neutrinos. Although this estimate has a large uncertainty, it will serve as a guide to future, more definitive neutrino experiments that are directly sensitive to CP violation.