Imaging water Cherenkov detector

(This series of documentations on the Super-Kamiokande detector is based on the Y.Koshio's PHD thesis (Apr. 1998) which is on the publication page. Exceptionally, the colorful documentation on the outer detector is in charge of the USA group.)

Super-Kamiokande is an imaging water Cherenkov detector. It detects Cherenkov light generated by charged particles scattered by neutrinos in water. In a medium with an index of refraction of n the light velocity is c/n. When a charged particle traverses the medium with velocity larger than the light velocity, so called Cherenkov light is emitted. The minimum energy of the particle with this velocity (called ``Cherenkov threshold energy'') is,

Cherenkov threshold energies of various particles.

Cherenkov light is emitted in a cone of half angle from the direction of the particle track:

where , and is for in water. For example, the typical 20MeV electron simulation event is shown in an exploded view of the cylindrical water tank in Fig 1.

The spectrum of the Cherenkov light as a function of the wavelength is

where (fine structure constant) and x is the length of the electron trajectory. A charged particle emits about 390 photons per 1cm of path length in the water in the wavelength region, 300nm 700nm, where the photo multiplier tubes are sensitive.

Fugure 1:

Typical expected event to be observed in Super-Kamiokande.

This is a 20MeV electron simulation. The generated vertex and direction are (-800,0,0)cm and (-1,0,0), respectively.

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revised on 1999/09/27