Feynman Diagrams

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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.

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Electron Electron Interaction
e-
e-
? a photon (uncharged)
e-
e-
3
b- decay
1
0
n
1
e
p

n

0
1
-1
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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.

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b- decay
n
p
e-
W-
n
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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

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b- decay (identical representation)
n
p
W-
e-
n
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Quark representation
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Quark representation
Proton
Neutron
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b- decay Quark representation
n
e-
W-
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b decay
n
n
e
W
p
12
Electron capture
n
n
e-
W
p
13
Neutrino neutron collisions
e-
p
W
n
n
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Antineutrino proton collisions
e
n
W
n
p
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Electron - proton collisions
n
n
W-
e-
p
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Feynman Diagrams

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