Leptonen

Leptonen, typically referred to in English as leptons, are a family of elementary fermions in the Standard Model of particle physics. They do not participate in the strong interaction and are spin-1/2 particles. Leptons occur in three generations, each consisting of a charged lepton and a corresponding neutrino: the electron and electron neutrino, the muon and muon neutrino, and the tau and tau neutrino. The charged leptons carry electric charge, while the neutrinos are electrically neutral and interact only via the weak force and gravity. The charged leptons have well-measured masses (approximately 0.511 MeV for the electron, 105.7 MeV for the muon, and 1776.86 MeV for the tau), whereas neutrinos have very small masses that are constrained by oscillation experiments and cosmological observations.

Leptons interact through the electroweak sector of the Standard Model. Charged leptons couple to photons and Z bosons and participate in charged-current interactions mediated by the W bosons. Neutrinos interact only via the weak force (and gravity) and thus propagate with minimal electromagnetic interaction. Lepton flavors are described by three quantum numbers, L_e, L_mu, and L_tau, and neutrino oscillations reveal that neutrino flavors mix as they propagate, so a neutrino produced as one flavor can be detected as another. The total lepton number is a conserved quantity in the Standard Model, though neutrino oscillations demonstrate non-conservation of individual flavors.

Leptonen are central to experimental and theoretical particle physics. They are produced in a wide range of processes, from particle decays to cosmic-ray interactions, and are used to test fundamental symmetries, universality of couplings, and mechanisms for neutrino masses and beyond-Standard-Model phenomena.