tau

A tau is a type (i.e., flavor) of lepton that has an electric charge of -1, like an electron, but far more mass (more than 3000 times more, as well as 17 times more than a muon, and on the order of twice the mass of a nucleon) and is unstable, decaying with a lifetime that is less than a picosecond. Tau particles result from high-energy particle interactions, and decay into a tau neutrino plus one or more pions. Such interactions happen naturally, e.g., the interactions of neutrinos passing through Earth as well as within its atmosphere. Air showers include such interactions.