This equation represents the ration of the mass of a neutron to the mass of tau.

The tau (τ), or tau lepton (sometimes called the tau particle or tauon) is an elementary particle similar to the electron, with negative electric charge and a spin of 1⁄2.

Notes

This constant is specified with a standard uncertainty (standard deviation) of: 0.000 048

The electron, the muon, the three forms of neutrinos, and the tau lepton are classified as a leptons. Like all elementary particles, 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 `τ^−` and the antitau by `τ^+`.

Like all elementary particles, 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 `τ^−` and the antitau by `τ^+`.

The electron, the muon, the three forms of neutrinos, and the tau lepton are classified as a leptons. Like all elementary particles, 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 `τ^−` and the antitau by `τ^+`.