Special Physics Seminar

Measuring Neutrino Oscillations with the T2K Experiment

Alex Himmel

Duke University

Neutrinos oscillate among flavors as they travel because a neutrino of a particular flavor is a also a superposition of multiple neutrinos with slightly different masses. The interferometric nature of oscillations allows this mixing the be measured, but it requires powerful neutrino sources and massive detectors. T2K is a long-baseline neutrino oscillation experiment with a muon neutrino beam produced at the J-PARC facility, a near detector complex located 280 m from the target, and using the Super-Kamiokande water Cherenkov detector, located 295 km away, as a far detector. The beam is directed 2.5° away from the far detector, producing a narrow-band energy spectrum precisely tuned to measure neutrino oscillations at the “atmospheric” L/E. In this beam, we have made the first definitive observation (> 7σ) of the appearance of a new neutrino flavor through oscillations. With this electron neutrino appearance sample we measure the mixing angle θ₁₃, and using the muon neutrino disappearance sample we measure the atmospheric mass splitting and mixing angle, θ₂₃. By combining both of these samples with the precise measurements of θ₁₃ made by reactor experiments, we make the first exclusion of a region of δCP at the 90% confidence level.