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In particle physics, a lepton is an elementary particle of half-integer spin (spin 1 / 2 ) that does not undergo strong interactions. [1] Two main classes of leptons exist: charged leptons (also known as the electron-like leptons or muons), including the electron, muon, and tauon, and neutral leptons, better known as neutrinos.
There are six leptons in total; the three charged leptons are called "electron-like leptons", while the neutral leptons are called "neutrinos". Neutrinos are known to oscillate, so that neutrinos of definite flavor do not have definite mass: Instead, they exist in a superposition of mass eigenstates.
Half of the fermions are leptons, three of which have an electric charge of −1 e, called the electron (e −), the muon (μ −), and the tau (τ −); the other three leptons are neutrinos (ν e, ν μ, ν τ), which are the only elementary fermions with neither electric nor color charge. The remaining six particles are quarks (discussed below).
All leptons carry a lepton number L = 1. In addition, leptons carry weak isospin, T 3, which is − 1 / 2 for the three charged leptons (i.e. electron, muon and tau) and + 1 / 2 for the three associated neutrinos. Each doublet of a charged lepton and a neutrino consisting of opposite T 3 are said to constitute one generation of ...
There are three generations according to the Standard Model of particle physics. Each generation contains two types of leptons and two types of quarks . The two leptons may be classified into one with electric charge −1 (electron-like) and neutral (neutrino); the two quarks may be classified into one with charge − 1 ⁄ 3 (down-type) and ...
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Thus, there are three generations of quarks and leptons. [37] As first-generation particles do not decay, they comprise all of ordinary ( baryonic ) matter. Specifically, all atoms consist of electrons orbiting around the atomic nucleus , ultimately constituted of up and down quarks.
There are six quarks (up, down, strange, charm, bottom and top), and six leptons (electron, electron neutrino, muon, muon neutrino, tauon and tauon neutrino), along with the corresponding antiparticle of each of these. Mathematically, there are many varieties of fermions, with the three most common types being: Weyl fermions (massless),