The Standard Model of Particle Physics

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The Standard Model of Particle Physics
EM
STRONG
WEAK
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The Electric Force
In the old days, we believed that force was
transmitted more orless instantaneously by a
field of force.
Lines of force
The proton to the right is repelled by the
electric field created bythe one on the left
(electrical repulsion).
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The New Concept of Force
In the 1960s, a new theory of interactions was
developed.At the heart of it is the concept
that
Richard Feynman, 1918-19881965 Nobel Prize in
Physics
Forces are the result of the exchange of force
carriers between the two particles involved in
the interaction.
The force carrier of the electromagnetic force is
the photon (g)
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The Photon (g)
Property Value
Mass 0
Charge 0

• The photon is the mediator of the
  electromagnetic interaction
• The photon can only interact with objects which
  have electric charge

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As we go through these slides,note that all
particles involved(other than the photon)carry
electrical charge!
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Electromagnetic Interaction (I)
e e- ? e e-(Annihilation)
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Electromagnetic Interaction (I)
e e- ? e e-(Annihilation)
e
e
e
e
g
e-
e-
e-
e-
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Electromagnetic Interaction (II)
e e- ? e e-(Compton
Scattering)
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Electromagnetic Interaction (II)
e e- ? e e-(Compton
Scattering)
e
e
e
e
e
e-
e-
e-
e-
e-
e-
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Electron-Pair Production
g ? e e-(or g Conversion)
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Electron-Pair Production
g ? e e-(or g Conversion)
e
e
e
g
g
e-
e-
e-
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Quark Pair Production
e e- ? q q
Note Two completely different particles in the
final state. Sincequarks have electric charge,
this can in fact happen!
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Quark Pair Production
e e- ? q q
e
q
q
q
g
e-
Note Two completely different particles in the
final state
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Quark Antiquark Annihilation
q q ? e e-
Note Reverse process to quark pair production!
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Quark Antiquark Annihilation
q q ? e e-
e
e
e
g
e-
e-
e-
Note Reverse process to quark pair production!
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Feynman Diagrams

• A great simplification which allows us to
  represent these physical processes are
  facilitated by Feynman Diagrams.
• It turns out, they can also be used to calculate
  the probability for the process to occur
  (Beyond the scope of this module though).
• We will use them more in a qualitative sense to
  visualize various processes.

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Feynman Diagrams (Electron Scattering)
Position
time
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Photon Conversion and Emission
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More Feynman Diagrams
Quark PairProduction
q
e

• q can be any quark,as long as there isenough
  energy to create2 of em!

g
e-
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Hmmm, Ive got a few question,Mister!
1. Where did you get the quarks and antiquarks in
the first place ? (Not at Wal-Mart, I can
assure you)!
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Where do we get quark and anti quarks from?
Hmmm
Introducing, thePROTON
And, antiquarks?
Introducing, thehumble antiparticleof the
proton, theANTIPROTON
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Proton-Antiproton Collisions
BOOM !
At high energies, the collisions actually occur
between the quarks in the protons and the
antiquarks in the antiproton! That is,
quark-antiquark collisions !
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OK, next question !
1. You said I could create any quark antiquark
pair, as long as there is enough energy to
create them. I dont get it !
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How much energy do I need to create
quark-antiquark pairs?
I will answer this by example
Suppose I collide an e- with E(e-)5 GeV and a
positron with E (e)5 GeV.
What is the total amount of energy available?A)
5 GeV B) 10 GeV C) 25 GeV
D) 0 GeV
5. If all this energy were to go into the mass of
a quark an antiquark, what is the maximum mass
quark you can create ? A) 10 GeV/c2
B) 5 GeV /c2 C) 2.5 GeV /c2 D) 0
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Summary of EM Interactions