Tau (particle) Tau (particle) The tau (τ), also called the tau lepton, tau particle, or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of. Together with the electron, the muon, and the three neutrinos, it is a lepton. Like all elementary particles with half-integer spin, the tau has a corresponding antiparticle of opposite charge but equal mass and spin, which in the tau's case is the antitau (also called the "positive tau"). Tau particles are denoted by and the antitau by . Tau leptons have a lifetime of and a mass of (compared to
Charge radius This asymmetric distribution of charge within the particle gives rise to a small negative squared charge radius for the particle as a whole. But, this is only the simplest of a variety of theoretical models, some of which are more elaborate, that are used to explain this property of a neutron. For deuterons and higher nuclei, it is conventional to distinguish between the scattering charge radius, "r" (obtained from scattering data), and the bound-state charge radius, "R", which includes the Darwin–Foldy term to account for the behaviour of the anomalous magnetic moment in an electromagnetic field and which is appropriate