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Feynman Diagrams

Feynman Diagrams. Richard Feynman invented the concept of virtual photons as part of his theory of quantum electrodynamics. The maths is complicated – but, fortunately, Feynman depicted the theory using diagrams to represent the interactions. Electron – Electron Interaction. e-. e-.

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Feynman Diagrams

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  1. Feynman Diagrams • Richard Feynman invented the concept of virtual photons as part of his theory of quantum electrodynamics. • The maths is complicated – but, fortunately, Feynman depicted the theory using diagrams to represent the interactions.

  2. Electron – Electron Interaction e- e-  a photon (uncharged) e- e-

  3. b- decay 1 0 n 1 e p + n + 0 1 -1

  4. The Neutrino • An uncharged particle. • Assumed to have zero mass • Emitted in radioactive beta decay • The “weak” nuclear force is responsible • The antineutrino is the antiparticle of the neutrino = n it has opposite “spin” to a neutrino.

  5. b- decay n p e- W- n

  6. The Weak nuclear force • Responsible for Beta decay – as well as interactions involving electrons or neutrinos with protons or neutrons. • Carried by exchange particles known as W-bosons. • There are two types: the W+ and the W- which can also represented in Feynman diagrams like this …

  7. b- decay (identical representation) n p W- e- n

  8. Quark representation

  9. Quark representation Proton = Neutron =

  10. b-decay –Quark representation n e- W-

  11. b+ decay n n e+ W+ p

  12. Electron capture n n e- W+ p

  13. Neutrino – neutron collisions e- p W+ n n

  14. Antineutrino – proton collisions e+ n W+ n p

  15. Electron - proton collisions n n W- e- p

  16. Feynman Diagrams • Note – questions on the weak interaction will be limited to changes in which a proton changes to a neutron or vice versa.

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