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Lepton

From Tilcayo Cats, the lean encyclopaedia by Tilcayo Knowledge Systems

In physics, a lepton is a particle that does not feel the strong nuclear force. This sets leptons apart from hadrons, which do feel it.[1] Together with quarks, leptons are one of the two basic types of particle that make up matter. Each type has six particles, which are related in pairs called "generations".[2] The electron, the positron, muons and neutrinos are all leptons. The name means "low mass".[3]

The six leptons

The six leptons come in three generations: the electron and the electron neutrino; the muon and the muon neutrino; and the tau and the tau neutrino.[4] The electron, muon and tau all have an electric charge and a sizeable mass. The neutrinos are electrically neutral and have very little mass.[5] The lightest and most stable particles make up the first generation, while the heavier and less stable particles belong to the second and third generations. All stable matter in the universe is made from particles of the first generation; heavier particles quickly decay to the next most stable level.[6]

Forces

Leptons do not feel the strong force, but they do feel the weak nuclear force.[7][1] The charged leptons are also affected by the electromagnetic force, which acts on all charged particles.[8]

Antileptons

Every particle has an antimatter partner, although some particles, like the photon, are their own antiparticles.[9] Antimatter has the opposite charge to ordinary matter. For example, the positron is positive while the electron is negative.[10]

Lepton family number

The discovery of the electron's neutrino showed that a new quantity, called the electron family number, is conserved in some particle reactions.[11] However, experiments have found that lepton family number is not always conserved, because of neutrino "oscillations", in which a neutrino changes from one family type to another.[12]

Open questions

The Standard Model does not explain why there are three generations of quarks and leptons, or why they have such different masses.[13]

See also

References

  1. ↑ 1.0 1.1 "33.4 Particles, Patterns, and Conservation Laws". College Physics 2e. OpenStax. Retrieved 20 October 2026. Hadrons are particles that feel the strong nuclear force, whereas leptons are particles that do not.
  2. ↑ "The Standard Model". CERN. Retrieved 20 October 2026. These particles occur in two basic types called quarks and leptons. Each group consists of six particles, which are related in pairs, or "generations".
  3. ↑ "33.4 Particles, Patterns, and Conservation Laws". College Physics 2e. OpenStax. Retrieved 20 October 2026. The electron, positron, muons, and neutrinos are examples of leptons, the name meaning low mass.
  4. ↑ "The Standard Model". CERN. Retrieved 20 October 2026. The six leptons are similarly arranged in three generations – the "electron" and the "electron neutrino", the "muon" and the "muon neutrino", and the "tau" and the "tau neutrino".
  5. ↑ "The Standard Model". CERN. Retrieved 20 October 2026. The electron, the muon and the tau all have an electric charge and a sizeable mass, whereas the neutrinos are electrically neutral and have very little mass.
  6. ↑ "The Standard Model". CERN. Retrieved 20 October 2026. The lightest and most stable particles make up the first generation, whereas the heavier and less stable particles belong to the second and third generations. All stable matter in the universe is made from particles that belong to the first generation; any heavier particles quickly decay to the next most stable level.
  7. ↑ "33.4 Particles, Patterns, and Conservation Laws". College Physics 2e. OpenStax. Retrieved 20 October 2026. Leptons feel the weak nuclear force.
  8. ↑ "33.4 Particles, Patterns, and Conservation Laws". College Physics 2e. OpenStax. Retrieved 20 October 2026. All charged particles are affected by the electromagnetic force, as are neutral particles that have an internal distribution of charge
  9. ↑ "33.4 Particles, Patterns, and Conservation Laws". College Physics 2e. OpenStax. Retrieved 20 October 2026. Every particle in nature has an antimatter counterpart, although some particles, like the photon, are their own antiparticles.
  10. ↑ "33.4 Particles, Patterns, and Conservation Laws". College Physics 2e. OpenStax. Retrieved 20 October 2026. Antimatter has charge opposite to that of matter (for example, the positron is positive while the electron is negative)
  11. ↑ "33.4 Particles, Patterns, and Conservation Laws". College Physics 2e. OpenStax. Retrieved 20 October 2026. the existence of the electron's neutrino implied that a new quantum number, called the electron family number
  12. ↑ "33.4 Particles, Patterns, and Conservation Laws". College Physics 2e. OpenStax. Retrieved 20 October 2026. particle experiments have found that lepton family number is not universally conserved, due to neutrino "oscillations," or transformations of neutrinos from one family type to another.
  13. ↑ "The Standard Model". CERN. Retrieved 20 October 2026. "Why are there three generations of quarks and leptons with such a different mass scale?"
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