Quantum ChromoDynamics (Nobel Prize 2004) Chris McLauchlin

Transcription

1 Quantum ChromoDynamics (Nobel Prize 2004) Chris McLauchlin

2 Outline The Four Fundamental Forces The Strong Force History of the Strong Force What These People Did Experimental Support 1

3 Fundamental Forces Gravity Weak Electromagnetic Strong 2

4 Fundamental Coupling α g α W 10-6 α α S 1 3

5 Development of QCD Proton? Neutron Proton? Proton Neutron? Neutron 4

6 Quantum Field Theory Time Space 5

7 Electron Exchange Neutron and Proton 6

8 Electron Exchange Neutron and Neutron 7

9 Electron Exchange? Proton and Proton???????????????? 8

10 Hideki Yukawa Massive Exchange Particle Yukawa Potential Nobel Prize: 1949 E t 9

11 Mesons Mu-Meson Pion Anderson and Neddermeyer 1937 Street and Stevenson Bubble Chambers- Cosmic Rays Powel 1947 Bubble chamber at high altitude 10

12 Murray Gell-Mann Developed the Eightfold Way in 1961 Geometric ordering of baryons and mesons Organization by strangeness and charge

13 Gell-Man and Zweig 1964 Quarks Comprise Hadrons Flavors Pauli s Exclusion Principle p uud n udd p uud n udd 12

14 So What Bonds the Quarks? u u d 13

15 Quantum ChromoDynamics Strong Force = Colour Force u u d 14

16 Quantum ChromoDynamics Strong Force = Colour Force u u d 15

17 Quantum ChromoDynamics Strong Force = Colour Force u u d 16

18 Fundamental Forces 17

19 Nuclear Force 18

20 The Nobel Prize Dr s David J. Gross, H. David Politzer and Frank Wilczek Asymptotic Freedom 19

21 Asymptotic Freedom Opposite of QED Coupling Increases with distance Quark Confinement 20

22 Asymptotic Freedom Shown by the β-function (g) g C T(R) O(g5 ) This is why these guys got a Nobel Prize 21

23 Asymptotic Freedom Shown by the β-function (g) g n f 3 22

24 QED Screening

25 QED Screening 24

26 QCD Anti-Screening 25

27 QCD Anti-Screening 26

28 QCD Anti-Screening 2 V 27

29 QCD Anti-Screening 2 V e kmr V g 2 r V g 2 r 28 e kmr g2 g2 r r 1 1 r r Yukawa Potential e kmr 2 V g 2 k 2 m 2 (r) r e kmr g 2 k 2 m 2 (r) r

30 Quark Confinement u u d 29

31 Quark Confinement u u d 30

32 Quark Confinement u u u ū d 31

33 Experimental Evidence Bjorken Scaling Deep Inelastic Scattering Structure Functions Supports Constituent Quark Model 32

34 Coupling Relation 33

35 Standard Model 34

36 Summary Quarks Flavor Color Charge Hadrons Pions Asymptotic Freedom Quark Confinement Scaling Limits to three constituents 35

37 Thank you Any Questions? 36

38 Quarks Flavor Charge (e) Spin (hbar) Mass (GeV/c 2 ) up 2/3 1/2 2.4x10-3 down -1/3 1/2 4.8x10-3 charmed 2/3 1/ strange -1/3 1/2 104x10-3 top 2/3 1/ bottom -1/3 1/

39 Experimental Evidence Hadron Production, Muon-pair Production, e - e + Production ADONE accelerator Consistent with factor of 2 implied by three colours As opposed to 2/3 without colours Coupling Strength Coupling Constant α Should decrease with an increase in Energy of bombardment 12 (E) (33 2n)ln E

40 Bubble Chambers Mixture of Ne-H Superheating Ionization by particles Can find q/m 3-D tracks of Particles 39

41 Scaling The cross-section of a lepton scattering off of nucleon to depend on a dimensionless quantity Implies multiple components of nucleon q2 2p This is governed by a particle s β-function Must be negative to imply scaling Theories using this refer to it as Asymptotic Freedom 40

42 What is Alpha? (E) 12 (33 2n)ln E 2 2 Quarks are Surrounded by a Gluon Cloud Penetration of the cloud lowers Coupling 41

43 The β Function (g) g 42

44 QED vs. QCD Positive β-function Negative β-function Decays with Distance Increases with Distance Shielding by other Fermions No Shielding * 43

45 Strong Theory Development Hideki Yukawa (1935) 1935 Mediated by a particle like E&M, but with mass E t 2 Richard Feynman QED Yang-Mills (1954) Three field particles: B +, B -, B 0 QED principles applied to Strong Force Non-Abelian Gauge Theory Not Renormalizable/ zeroth order said massless particles 44

46 Strong Theory Development Gell-Mann (1959) Quarks! Make up Protons and Neutrons (three per each) Needed another degree of freedom Colour introduced Nambu (1960) Discovered Spontaneous Gauge Symmetry Breaking Gauge Theories can have Short Distances 45

47 Strong Theory Development Bjorken (1968) Asymptotic Freedom Scaling Cross Section of particles related to charge and momentum Governed by the β-function t Hooft discovered this, but never said anything 46

48 Strong Theory Development t Hooft (1971) Proved Non-Abelian Gauge Theories to be renormalizable! Weak Interaction fixed And mixed with Electromagnetic Also got the negative, but didn t know it was right and forgot about it New People Found it again and got Nobel Prize 47

49 Renormalization Any Technique to deal with Infinities in calculated quantities Such as the electron 48

50 Non-Abelian Gauge Theory Non-Commutative a * b b * a vs a * b b * a 49

51 Strong Force Short Range Very Strong Decreases at close distances 50 [[

52 Quantum Number Conservation Baryon Number Lepton Number 51

53 Bosons and Fermions Fermion: ½ integer spins Proton, Neutron, Electron Matter Particles Boson: Integer spins Force Carrying Particles 52

54 Pictures [[1] [[2]] [[3]] [[4]] [[5]] 53

55 References Baggot, J. (2011) The Quantum Story. Oxford: Oxford University Press. Griffiths, D. (2008) Introduction to Elementary Particles. WILEY-VCH Verlag GmbH & Co. Povh, B. Rith, K., Scholz, C., & Zetsche, F. (1999). Particles and Nuclei (3 rd ) ed.). Heidelberg:Springer-Verlag Berlin Heidelberg. Chapter 9 for this unknown textbook on Particle Physics on Proton Structure Wikipedia (Various) 54

56 Wikipedia