Feynman Diagrams

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
Quark representation
8
Quark representation
Proton
Neutron
9
b- decay Quark representation
n
e-
W-
10
b decay
n
n
e
W
p
11
Electron capture
n
n
e-
W
p
12
Neutrino neutron collisions
e-
p
W
n
n
13
Antineutrino proton collisions
e
n
W
n
p
14
Electron - proton collisions
n
n
W-
e-
p
15
Feynman Diagrams

• Note questions on the weak interaction will be
  limited to changes in which a proton changes to a
  neutron or vice versa.
• Learn the proton is the only stable baryon
  (made of 3 quarks) into which other baryons
  eventually will decay