Neutrino optics

Neutrinos are produced by the in-flight decay of π and K mesons. Neutrinos are uncharged and cannot be focused directly. However, the transverse momentum of the neutrino due to the decay is typically much smaller than the transverse momentum spread of the parent meson. The focusing of the meson beam will then significantly enhance the neutrino flux at a distant detector. Neutrino beams can effectively be focused in the same manner as other charged particle beams, by means of quadrupoles and bending magnets. The bending magnets also can serve to define the momentum of the neutrino beams. Alternatively, neutrino beams can be focused by the use of magnetic horns. Both systems are described here. Proposed experiments with neutrinos to detect neutrino oscillations place the detector hundreds of kilometers away from the source. The flux of neutrinos through the detector then becomes very small. The calculation of the flux by conventional Monte Carlo or numerical integration techniques becomes prohibitively difficult. A alternate mathematical technique can be used to give results which are reliable to about 10%. (orig.)