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The Standard Model of Particle Physics

The Standard Model of Particle Physics. EM. STRONG. WEAK. P. p. p. p. p. The Electric Force. In the old days, we believed that “force” was transmitted more or less instantaneously by a “field of force”. . Lines of force.

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The Standard Model of Particle Physics

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  1. The Standard Model of Particle Physics EM STRONG WEAK

  2. P p p p p 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).

  3. The New Concept of Force In the 1960’s, 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 thephoton (g)

  4. The Photon (g) • The photon is the “mediator” of the electromagnetic interaction • The photon can only interact with objects which have electric charge

  5. As we go through these slides,note that all particles involved(other than the photon)carry electrical charge!

  6. e+ e+ e+ e- e- e+ e- e+ e+ e+ e- e- g g e- e- e+ e- Electromagnetic Interaction (I) e+ + e- e+ + e-(Annihilation)

  7. e+ e+ e- e- e+ e- e+ e- g Electromagnetic Interaction (I) e+ + e- e+ + e-(Annihilation) e+ e+ e+ e+ g e- e- e- e-

  8. e+ e+ e+ e+ e- e- e- e+ e+ e- e- e- e+ e- Electromagnetic Interaction (II) e+ + e- e+ + e-(Compton Scattering)

  9. e+ e- Electromagnetic Interaction (II) e+ + e- e+ + e-(Compton Scattering) e+ e+ e+ e+ e+ e- e- e- e- e- e-

  10. e+ e+ e+ e+ e- e- g g g g g e- e- Electron-Pair Production g e+ + e-(or “g Conversion”)

  11. e+ e- g g g Electron-Pair Production g e+ + e-(or “g Conversion”) e+ e+ e+ g g e- e- e-

  12. q e+ e+ e- e- e+ e- q q q q q g g q q e+ e- 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!

  13. e+ e+ e- e- e+ e- q q q q q Quark Pair Production e+ + e- q + q e+ q q q g e- * Note: Two completely different particles in the “final state”

  14. e+ q q q q q e- e+ e+ e+ e- e- g g e- e- q q Quark Antiquark Annihilation q + q  e+ + e- * Note: Reverse process to quark pair production!

  15. q q q q q e- e+ e- q q Quark Antiquark Annihilation q + q  e+ + e- e+ e+ e+ g e- e- e- * Note: Reverse process to quark pair production!

  16. 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.

  17. Electron-PositronAnnihilation e+ e- g e- e+ e+ e+ ComptonScattering g e- e- Feynman Diagrams (Electron Scattering) Position time

  18. e- Photon Conversion g e+ g Photon Emission e- e- Photon Conversion and Emission

  19. Quark AntiquarkAnnihilation q e+ g e- More Feynman Diagrams Quark PairProduction q e+ • “q” can be any quark,as long as there isenough energy to create2 of ‘em! g e-

  20. Quark AntiquarkAnnihilation q e+ g e- Hmmm, I’ve 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)!

  21. u d u u d u Where do we get quark and anti quarks from? Hmmm… Introducing, thePROTON… And, antiquarks?… Introducing, thehumble antiparticleof the proton, theANTIPROTON…

  22. u u u d d d u u u u u u d d d u u u 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 !

  23. Quark PairProduction q e+ g e- OK, next question ! 1. You said I could create any quark antiquark pair, as long as there is enough energy to create them. I don’t get it !

  24. q e+ g e- 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

  25. The Photon is the mediator of the EM Interaction.- This means that EM interactions occur via photons. • The photon is massless and has no electrical charge. • Photon can convert into pairs of oppositely-charged, like-type leptons or quarks.g  e+e-, m+m -, t+t—g  uu, dd, ss, cc, bb, tt • Feynman diagrams are a pictorial method for expressing atype of interaction. Summary of EM Interactions

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