1. 1 Quark and Lepton Kihyeon Cho March 22, 2011 HEP

2. Contents Introduction Fermion-Boson History  Particle and Antiparticle  입자물리학과 노벨상 Quark and Lepton Interactions Conservation Natural Units 2

3. Quark and Lepton 3

10. 10

11. Quark Model S=0 S=-1 (Triplet) S=0 S=1 (Anti- Triplet) Perkins 5.1

12. Quark Model Perkins 5.1

13. 13 Perkins 5.1 Spin 1/2 Spin 3/2

14. Quark Model When Gell-Mann proposed the quark model, was not yet observed. Perkins 5.2

15. Quark Model We can guess its mass by observing the mass gap between two adjacent strangeness. Perkins 5.2

16. Baryon Decuplet Baryon Decuplet (J=3/2) Expect 10 states. Prediction of the   ( mass =1672 MeV/c 2, S=-3) Use bubble chamber to find the event. 1969 Nobel Prize to Gell-Mann! “Observation of a hyperon with strangeness minus 3” PRL V12, 1964. Perkins 5.2

17. Quark Model There were a couple of problems in accepting Gell-Mann’s quark model. First, other combinations of quarks such as two quarks were not observed and there is no evidence for the existence of quark. Second, problem of Pauli’s exclusion principle. Perkins 5.2

18. Quark Model The postulate 1.Quarks carry three different “color charges”. 2.Only color-neutral objects can be observed in nature. Suppose three colors are r, y, and g. means anticolor.

19. Quark Model All other combinations would fail to cancel the color charges each other The problem of Pauli’s exclusion principle is also naturally solved

20. Quark Model So, why can only color-neutral objects be observed in nature? Maybe the answer will be provided by QCD(quantum chromodynamics) Nowadays, people have established the standard model of elementary particle physics assuming the six quarks and the six leptons

21. 21 Summary of Quark Model

22. Summary of Lepton

23. 23 Ref. 최성렬교수 (2008) Summary

24. 24 Summary

25. 25 References Class P720.02 by Richard Kass (2003) B.G Cheon’s Summer School (2002) S.H Yang’s Colloquium (2001) Class by Jungil Lee (2004) PDG home page (http://pdg.lbl.gov)

26. Thank you.