Neutrino Physics

Oscillation of a muon neutrino while propagating in space using a simplified 2 neutrino model. It starts as a definite weak state (i.e. muon) associated with a certain quantum superposition of two mass eigenstates. As it evolves in time, the phase difference between two mass eigenstates causes the superposition to oscillate, periodically comes back to the same muon state. Image credit: "Celebrating Neutrinos", Los Alamos Science, 25 (1997).


Left: the Super-Kamiokande (SK) detector with > 11,000 PMTs of 20-inch diameter. Three engineers in the picture gives a sense of the scale. Middle: a clear ring pattern, projected on a cylindrical surface of the SK detector, produced by Cherenkov radiation of a muon from a muon neutrino interaction. The ring is formed around the direction of a muon. Right: a fuzzier ring pattern produced by an electron from an electron neutrino interaction. An electron has 200 times lighter mass than a muon, and its direction is more a affected by local scatterings.

Images of a neutrino interaction recorded by the MicroBooNE Liquid Argon Time Projection Chamber (LArTPC) detector. Left: an electron neutrino interaction with multiple hadronic particles in the product including charged pions and protons. Right: a muon neutrino interaction that produced a muon, a charged pion, and two gamma rays from a decay of neutral pion. In order to infer the neutrino energy and flavor, accurate identification of individual particle type and its energy is fundamental in data analysis.