The existence of neutrino oscillation is inferred from the occurrence
of charged-current (CC) interactions of 
-neutrinos in the detector:
The detection of the tau lepton in the final state identifies
this reaction.
The 
is detected through its decay modes
into muons, hadrons and electrons:
The identification is carried out by making use of its characteristic
decay topology, by the charge measurement of its decay products, by its distinct decay kinematics
and by the missing energy carried away by the neutrino(s) in the decay process.
In about 85% of the cases the decays into a single charged particle
and in most of the remaining cases into three charged particles.