A Lightsaber to Illustrate Neutrino Oszillations

Neutrinos are elementary particles, which appear in three leptonic flavours: electron-, muon-, and tau neutrinos. With matter they interact only via weak interaction and gravity. Characteristic for a neutrino with a certain flavour is its quantum mechanical composition of three different, but very small masses with different velocities, which in propagation interfere and change the flavour periodically with path length. In an experiment the flavour appears and disappears with a varying distance from the source. For two flavours this is just the property of a polarized light beam in a birefringent medium where the polarization (the “flavour”) changes periodically with distance while its propagating main polarization components with different refractive indices (the “masses”) and phase velocities change their relative phase. In order to demonstrate this light effect, we constructed a lightsaber from a linear birefringent Plexiglas rod and a polarized laser pointer. The instrument shows periodically light bands due to Rayleigh scattering of the glas. Our light analogy has only two “flavours”, but it uses real quantum particles and the naked human eye as a detector.