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Elementary Particle Physics

David Milstead milstead@physto.se A4:1021 tel: 5537 8663/0768727608. Elementary Particle Physics. Format. 19 lecture sessions 2 räkneövningnar Homepage http://www.physto.se/~milstead/fk7003/course.html Course book Particle Physics (Martin and Shaw,3 rd edition, Wiley)

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Elementary Particle Physics

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  1. David Milstead milstead@physto.se A4:1021 tel: 5537 8663/0768727608 Elementary Particle Physics FK7003

  2. FK7003 Format • 19 lecture sessions • 2 räkneövningnar • Homepage http://www.physto.se/~milstead/fk7003/course.html • Course book • Particle Physics (Martin and Shaw,3rd edition, Wiley) • Earlier editions can be used – handouts to be provided where appropriate. • Supplementary books which may be useful but which are not essential • Introduction to Elementary Particles (Griffiths, Wiley) • Subatomic Physics (Henley and Garcia, World Scientific) • Particles and Nuclei (Povh, Rith, Scholz and Zetsche, Springer) • Quarks and Leptons (Halzen and Martin, Wiley) • Assessment • 2 x inlämningsuppgifter • tenta

  3. FK7003 Lecture outline

  4. FK7003           particle physics research   Particle physics is frontier research of fundamental importance.   

  5. FK7003 The aim of this course • Survey the elementary constituents in nature • Identification and classification of the fundamental particles • Theory of the forces which govern them over short distances • Experimental techniques • Accelerator • Particle detectors

  6. FK7003 Lecture 1 Basic concepts Particles and antiparticles Klein-Gordon and Dirac equations Feynman diagrams Electromagnetic force Weak force

  7. FK7003 Going beyond the Schrödinger equation small Classical mechanics Quantum mechanics (Schrödingers equation) fast Quantum field theory (Dirac, Klein-Gordon equations, QED, weak, QCD) Relativistic mechanics

  8. FK7003 Implications of introducing special relativity

  9. FK7003 Negative energy states x t x t

  10. FK7003 What does a particle moving backwards in time look like ? The equation of motion of charge q moving backwards in time in a magnetic field is the same as the equation of motion of a particle with charge -q moving backwards in time.

  11. FK7003 Antiparticles Special relativity permits negative energy solutions and quantum mechanics demands we find a use for them. (1) The wave function of a particle with negative energy moving forwards in time is the same as the wave function of a particle with positive energy moving backwards in time. Ok, the negative energy solutions must be used but we can convert them to positive energy states if we reverse the direction of time when considering their interactions. (2) A particle with charge q moving backwards in time looks like a particle with charge –q moving forwards in time. General argument that a particle with negative energy and charge q behaves like a particle with positive energy and charge -q. We expect, for a given particle, to see the ”same particle” but with opposite charge: antiparticles. Antiparticles can be considered to be particles moving backwards in time - Feynman and Stueckelberg. Hole theory (not covered) provides an alternative, though more old fashioned way of thinking about antiparticles.

  12. FK7003 Electron and the positron 1897 e- discovered by J.J. Thompson 1932 Anderson measured the track of a cosmic ray particle in a magnetic field. Same mass as an electron but positive charge The positron (e+) - anti-particle of the electron Nobel prize 1936 Every particle has an antiparticle. Some particles, eg photon, are their own antiparticles. Special rules for writing particles and antiparticles, eg antiproton p, given in next lecture.

  13. FK7003 Klein-Gordon equation

  14. FK7003 The Dirac Equation

  15. FK7003 Implications of the Dirac Equation

  16. FK7003 How particles interact – exchange forces Electromagnetic force Particles carrying charge interact via the exchange of photons (g) mass=0, spin=1 (boson) + - - - photon + - - - - - - + Attraction Repulsion

  17. FK7003 Electromagnetic processes

  18. FK7003 Feynman diagrams

  19. FK7003 (1) Electromagnetic processes vertex s t

  20. FK7003 (1) Basic electromagnetic diagrams vertex s t ((g) and (h) become clear soon)

  21. s t (2) Is energy conservation violated ? virtual particle (g) real particle Dt FK7003

  22. FK7003 (3) Using Feynman diagrams a a a a Negative energy solutions –antiparticles. QM insists we use them!

  23. FK7003 (3) Using Feynman diagrams a a a + 5 other contributions

  24. FK7003 Question

  25. (3) Using Feynman diagrams e- e- e- e- + e- e- e- e- + e- e- e- e- + …. FK7003

  26. FK7003 Question

  27. Understanding forces FK7003

  28. FK7003 The weak force e- e- e- W- ne e+ (b-decay) (neutrinos – next lecture)

  29. The fundamental forces Different exchange particles mediate the forces: electromagnetic weak strong No quantum field theory yet for gravity FK7003

  30. FK7003 Summary • Antiparticles and spin states are predicted when when relativity and quantum mechanics meet up! • Antiparticles correspond to negative energy states moving backwards in time. • Feynman diagram formalism developed and used for (very basic) rate estimation • Generic approach for all forces • Weak force is weak because of the mass of the exchanged particles.

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