Photomultiplier tube) surrounding ultrapure water (the Super-Kamiokande, Kamioka mine underground 1000m, Gifu Prefecture). When neutrinos collides with a water molecule of the ultrapure water, an electron runs out with high speed and passes through the dielectric substance (water, in this case), accompanying local electromagnetic field. Electrons in water molecules are moved by the field of the electron passing through; the molecules are polarized. After the field disturbance has passed, the electrons attempt to return to equilibrium again and photons are emitted. When the field disturbance propagates beyond the speed of light in the media, the photons will interfere constructively and the radiation is observed to spread in a conical shape (Cerenkov radiation, Figure). As long as it is generated by a scattered electron by an neutrinos, the direction of movement and speed of the electron can be known from the observation result of the Cherenkov light, and from these data one can calculate incident direction of the neutrinos and other properties. (See Wikipedia in Japanese)
Neutrinos, electrons and photons play Rondo that can be seen via light, and I think that such idea makes the world of elementary particles familiar for town as well as gown. Electrons repelled by collision of neutrinos is wearing a localized electromagnetic field (light), whereby photon (energy) is released from the atoms in the media owing to the excitation (polarization). When the electron velocity exceeds the phase velocity of the light in the media, the photons produced one after another interfere with each other, as the shock wave of sound, a cone-shaped propagating light with a vertex at the traveling electron and the axis along its moving d is observed. In the photonic crystal, unusual Cerenkov radiation such that propagates towards the rear (see Wikipedia). In contrast to the polarization of the atom in dielectric materials, collective vibration of free electrons: plasmon in the metal creates a variety of anomalous phenomena in the interaction of light and matter, it is possible to enter into the world of nano by employing light. Such a mew world is waiting for us.