The CHORUS Experiment

WA95 - Neutrino Oscillation experiment at CERN

The aim of the experiment is to search for neutrino oscillations in the between muon neutrinos-tau neutrinos by detecting the occurence of the reaction tao neutrino+nucleon giving tau(-) + anything in a background of muon neutrino induced charged and neu tral events. The tau(-) is identified by its charge and the decay kink in its muonic and hadronic one-prong decay modes accompanied with transverse momentum imbalance. A sensitivity of sin^2 (2*theta) < 4 E-4 at the 90% confidence level can be achieved wi th an exposure of 2.4 E19 protons on the target of the wide band neutrino beam of the SPS. For this exposure the prompt tau neutrino induced background and other background events occur at such a level to produce less than one event.

The experimental setup consists of a target region, an aircore magnet, a high precision calorimeter and a moun spectometer. Nuclear emulsion stacks form the 800 kg mass of the fiducial target volume; decays of short lived particles such as the tau are vis ualized with high efficiency in these stacks. Tracks are located into emulsion with high precision scintillating fiber trackers read out with optoelectronic image intensifiers coupled to CCD cameras.

The hexagonal aircore magnet is pulsed to permit the use of thin aluminium windings and it provides the measurement of the charge-sign of low energy hadrons and muons. The high precision calorimeter, which is based on spaghetti technology, tags the tao(-) decay by its transverse momentum imbalance. The spectometer identifies muons and measures their momentum and charge.

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