Feynman Diagrams Richard Feynman invented the concept of

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 theory using diagrams to represent the interactions.

Electron – Electron Interaction e- e- a photon (uncharged) e- e-

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

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.

b- decay n p e. Wn

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 Wwhich can also represented in Feynman diagrams like this …

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

Quark representation

Quark representation Proton = Neutron =

b- decay – Quark representation n e. W-

b+ decay n n W+ p e+

Electron capture n n p W+ e-

Neutrino – neutron collisions e- p n W+ n

Antineutrino – proton collisions e+ n p W+ n

Electron - proton collisions n n p W - e-

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