1. Introduction to QED Quantum Electrodynamics Part IV

2. Applications of QED Through the use of atom smashers, over 400 particles have been discovered. This multitude of particles has created a need to explain their number and the nature of their interactions. QED deals specifically with electrons and photons, but its form and function can be applied to other particle interactions.

3. QCD A great number of these newly-discovered particles are simply combinations of quarks. The quantum theory of the interactions of quarks via the strong force is called Quantum Chromodynamics (QCD). 3 make a baryon and 2 make a meson

4. Elementary Particles

5. Baryons

6. Gluons Quarks interact via the gluon. The gluon functions in many ways like a photon. The probability of a coupling occurring is the constant “g” (similar in function to “j” for electrons) Diagrams of interactions will look very similar to that of the electron and photon.

7. Elementary Particles

8. Quark-Gluon Coupling

9. Color Quarks and gluons have a property called “color”. Quarks can change color by coupling with a gluon. Colors are red, green, and blue.

10. Change of Color

11. Gluon Coupling

12. Rules of Color All particles created by quarks must be colorless. Baryons have one of each color and mesons have a quark-anti-quark pair. Impossible to have a single quark.

13. Change of Flavor A down quark can change into an up quark. This is done by emitting a W particle, which then decays into an electron-anti-neutrino pair. This process is called beta decay.

14. Beta Decay

15. Elementary Particles

16. Neutral Currents There is a particle Z 0 that is a neutral W boson. Z 0 has no charge. Couplings with Z 0 result in no change in a particle’s charge. (Neutral Currents)

17. Z 0 Couplings

18. W-Anti-W Coupling

19. Electro-Weak Force The observed coupling constant is almost identical as that of the photon. The three W’s and the photon would then appear to be somehow interconnected. Electrodynamics and the weak force were successfully combined by Stephen Weinberg and Abdus Salam

20. “Redundant” Particles As nuclei have been bombarded by protons of higher and higher energy, new particles have appeared. These particles seem to mimic lower-energy versions and differ only by their higher mass. E.g. The Muon is identical to an electron, except it’s about 200 times heavier.

21. Muon Interactions

22. Beta Decay with a Muon

23. More Elementary Particles

24. Even More Elementary Particles

25. Diagrams: Feynman, Richard P. QED: The Strange Theory of Light and Matter. Princeton University Press. Princeton, NJ, 1988.

26. Questions?