Leptons are fundamental particles that do not feel the strong force. There are six:• the electron (e-), the muon (μ-) and the tau (τ-), each with charge –1e
• the electron neutrino (νe), muon neutrino (νμ) and tau neutrino (ντ), each with zero chargeThe electron is stable. The muon (106 MeV/c2, about 207 times the mass of the electron) and the tau (1777 MeV/c2) are heavier versions of the electron; they are unstable and decay into lighter particles.Neutrinos have a tiny mass and interact only through the weak force (and gravity), so they hardly ever interact with matter. Trillions pass through your body every second.Each lepton has a lepton number L = +1; each antilepton (e+, μ+, τ+ and the antineutrinos) has L = –1; all other particles have L = 0. Total lepton number is conserved in every interaction.Worked example: check lepton number in β- decay, n → p + e- + νe.
before: L = 0
after: L = 0 + 1 + (–1) = 0
Lepton number stays zero, which is why an antineutrino, not a neutrino, is emitted with the electron.
• the electron neutrino (νe), muon neutrino (νμ) and tau neutrino (ντ), each with zero chargeThe electron is stable. The muon (106 MeV/c2, about 207 times the mass of the electron) and the tau (1777 MeV/c2) are heavier versions of the electron; they are unstable and decay into lighter particles.Neutrinos have a tiny mass and interact only through the weak force (and gravity), so they hardly ever interact with matter. Trillions pass through your body every second.Each lepton has a lepton number L = +1; each antilepton (e+, μ+, τ+ and the antineutrinos) has L = –1; all other particles have L = 0. Total lepton number is conserved in every interaction.Worked example: check lepton number in β- decay, n → p + e- + νe.
before: L = 0
after: L = 0 + 1 + (–1) = 0
Lepton number stays zero, which is why an antineutrino, not a neutrino, is emitted with the electron.