Although technically not a member of the class, this particle has historically been referred to as a meson, because its mass lies between that of the electron and the proton.
Although technically not a member of the class, this particle has historically been referred to as a meson, because its mass lies between that of the electron and the proton. It is closer to the former, however, in that it has its own type of neutrino. After the neutron, it has the longest lifetime of any unstable particle, thus allowing it to penetrate the Earth's atmosphere via cosmic rays, a fact that led to their 1936 discovery by Carl Anderson. For ten points, name this elementary particle, a lepton about 207 times as massive as the electron.
Although technically not a member of the class, this particle has historically been referred to as a meson, because its mass lies between that of the electron and the proton.
{muon}