The picture above is an example of an identified tau neutrino interaction. The interaction vertex, which is originally predicted by the spectrometer data, is identified by the union of the red track (tau particle) and two gray tracks (unknown particles). At that point a tau neurtino interacted with a nucleon in a steel layer, producting its lepton partner. The tau is identified by locating the characteristic "kink" (where the red track abruptly changes color and direction) and observing electron showering (the production of electron-positron pairs) in the emulsion sheets and scintillating fibers. This particular event occurred in the second module, so the majority of the event products were recorded in the emulsion portion of the detector. The track color change is superficial; it is used to show that at that point the tau decayed to a charged particle, green indicating an electron. This is a typical long tau decay because it decays to one charged particle, the electron, which is easily read in the emulsion sheets and scintillator data, and the decay vertex occurs several sheets downstream from the neutrino interaction vertex.
Last updated: 6/29/01 comment