For this landmark discovery the scientists who found it could well be awarded a Nobel Prize in a few years time. It is one thing to think that there are tau neutrinos out there. But to really look for the rare incidence of a tau neutrino hitting an atomic nucleus and transforming into a tau lepton is a hard experiment to do. In 1997, Fermilab's Tevatron accelerator produced an intense neutrino beam which passed through the Donut experiment. In the target, one out of one million, million tau neutrinos interacted with an iron nucleus and produced a tau lepton, which left its one mm tell-tale signature.
Physicists say that the evidence for the tau neutrino is slight but convincing.
They needed three years to identify it by detecting a tau lepton particle and its decay, the key to exposing the tau neutrino's secret existence. The main signature of a tau lepton is a track with a kink, indicating the decay of the tau lepton shortly after its creation. The experiment recorded over six million potential interactions. Of these, four events provided evidence for the tau neutrino. With the tau's detection, matter's construction set is complete.