Rosenfeld chose the name as the common name for electrons and (then hypothesized) neutrinos. Additionally, the muon, initially classified as a meson, was reclassified as a lepton in the 1950s. The masses of those particles are small compared to nucleons—the mass of an electron (): Particle listings— and the mass of a muon (with a value of ): Particle listings— are fractions of the mass of the "heavy" proton (), and the mass of a neutrino is nearly zero.: Particle listings— However, the mass of the tau (discovered in the mid-1970s) (): Particle listings— is nearly twice that of the proton and times that of the electron.
Rosenfeld chose the name as the common name for electrons and (then hypothesized) neutrinos. Additionally the muon, initially classified as a meson, was reclassified as a lepton in the 1950s The masses of those particles are small compared to nucleons—the mass of an electron (): Particle listings— and the mass of a muon (with a value of ): Particle listings— are fractions of the mass of the "heavy" proton (), and the mass of a neutrino is nearly zero.: Particle listings— However, the mass of the tau (discovered in the mid-1970s) (): Particle listings— is nearly twice that of the proton and times that of the electron.