Is it farther or further?
lepton lep·ton (lěp'tŏn')
Any of a family of elementary particles that participate in the weak interaction, including the electron and its associated neutrino.
Any of a family of elementary particles that interact through the weak force and do not participate in the strong force. Leptons include electrons, muons, tau particles, and their respective neutrinos, the electron neutrino, the muon neutrino, and the tau neutrino. The antiparticles of these six particles are also leptons. Compare hadron. See Note at elementary particle. See Table at subatomic particle.