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Particle Physics: Exploring the World of Subatomic Particles

This article provides an overview of particle physics, including topics such as particle accelerators, quantum electrodynamics, the Yukawa particle, conservation laws, and types of particles. It also discusses experiments conducted in particle accelerators and the discovery of various particles. The text is in English.

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Particle Physics: Exploring the World of Subatomic Particles

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  1. Particle Physics • "three quarks for Muster Mark" • -James Joyce • (Finnegan’s Wake) • Contents: • Particle Accelerators • Quantum Electrodynamics and Feynman diagrams • The Yukawa Particle • Particles and Antiparticles • Conservation Laws • Types of Particles • Strange Things and Quark Theory

  2. Particle Accelerators Experiments +150,000 V Vacuum Proton Source Beam Steering (RevereWare) Basic concept - Vq = 1/2mv2 Provide energy for nuclear reactions Create particles from energy TOC

  3. Particle Accelerators SLAC - electron accelerator Potential switches 50 GeV - mass? TOC

  4. Particle Accelerators Cyclotrons - In a magnetic field to curve path Potential switches Mass dilates as v->c Synchrotrons - Fermilab(1.0 km), CERN (8.5 km) TOC

  5. 8.5 km in diameter

  6. Quantum Electrodynamics Coulomb’s law - Force fields Richard Feynman - EM forces are mediated by photons: Richard Feynman 1918-1988 Feynman Diagram Virtual photons: Et>h/2 (Exist for so short a time - never detected) TOC

  7. The Yukawa Particle • Photons mediate the EM force • Yukawa proposes a particle to mediate strong nuclear force Hideki Yukawa 1907-1981 He names it the meson - (between electron and proton) Et= E(d/c) =h/2 E = hc/2d = 130 MeV TOC

  8. The Yukawa Particle • Muon discovered in cosmic radiation • m = 106 MeV - doesn’t interact • The pi meson (pion) is discovered in 1947 in cosmic rays (3 charge states): • + - 139.6 MeV/c2 • o - 135.0 MeV/c2 • - - 139.6 MeV/c2 • p + p --> p + p + o • p + p --> p + n + + • (conservation of charge) Hideki Yukawa 1907-1981 TOC

  9. The Four Forces of Nature Type Strong Nuclear Electromagnetic Weak Nuclear Gravitational Relative Strength 1 10-2 10-6 10-38 Field Particle Gluons (mesons) Photon W+ and Zo Graviton? TOC

  10. Particles and Antiparticles Name Particle Antiparticle Electron e- e+ Proton p p Pion +- • Some particles have no antiparticle • + and - are electron charges • When particle meets antiparticle - annihilation (rest mass + Ek turns to energy or other particles) TOC

  11. Selected list (there are hundreds of hadrons) • Self as antiparticle • + and - are electron charges….

  12. Conservation Laws - Baryon Number Conservation of charge Conservation of mass/energy Conservation of nucleon.... In general, baryon number is conserved: TOC

  13. Conservation Laws - Baryon Number This reaction can never happen: p + n -> p + p + p In general, baryon number is conserved: (Antiparticles have B = -1) Baryon numbers: 1 + 1  1 + 1+ -1 TOC

  14. Conservation Laws - Baryon Number Heavy baryons decay to lighter ones Proton is lightest - must be stable TOC

  15. Whiteboards: Conservation of Baryon Number 1 | 2 | 3 | 4 TOC

  16. What is the total Baryon number of p + n + n + + 1 + 1 + -1 + -1 = 0 W 0

  17. What is the total Baryon number of + + + + o + + -1 + -1 + 1 + 0 = -1 W -1

  18. Can this reaction occur? p + p ---> - + + 1 +-1 = 1 + -1 W yes

  19. Can this reaction occur? p + n ---> o + + 1 +-1  -1 + -1 W no

  20. Can this reaction occur? o + n ---> o + + B: 1 +-1 = 1 + -1 C: 0 + 0 != 0 + 1 W no

  21. Conservation Laws - Lepton Number • Lepton number is conserved too • Le - Electron/electron neutrino • L - Muon/muon neutrino • L - Tau/Tau neutrino • Remember - anti particles have negative lepton numbers • Neutrinos are believed to have mass TOC

  22. Conservation Laws - Lepton Number 6027Co 6028Ni + - + e 137N 136C + + + e Le L L Electron e- +1 0 0 Neutrino (e) e +1 0 0 Muon - 0 +1 0 Neutrino ()  0 +1 0 Tau - 0 0 +1 Neutrino ()  0 0 +1 Beta Decay: Emission of an electron neutrino allowed Le to be conserved: TOC

  23. Whiteboards: Conservation of Lepton Number 1 | 2 | 3 | 4 | 5 TOC

  24. Does this decay occur? - ---> e- + e Charge is conserved Le: 0 = 1 + -1 L:1  0 + 0 L is not conserved Le L L Electron e- +1 0 0 Neutrino (e) e +1 0 0 Muon - 0 +1 0 Neutrino ()  0 +1 0 Tau - 0 0 +1 Neutrino ()  0 0 +1 W dog biscuit

  25. Does this decay occur? - ---> e- + e +  Charge is conserved Le: 0 = 1 + -1 + 0 L:1 = 0 + 0 + 1 Yes it occurs Le L L Electron e- +1 0 0 Neutrino (e) e +1 0 0 Muon - 0 +1 0 Neutrino ()  0 +1 0 Tau - 0 0 +1 Neutrino ()  0 0 +1 W yo mama

  26. Does this decay occur? - ---> e + e +  Charge is Not conserved Le: 0 = 1 + -1 + 0 L:1 = 0 + 0 + 1 Does not occur Le L L Electron e- +1 0 0 Neutrino (e) e +1 0 0 Muon - 0 +1 0 Neutrino ()  0 +1 0 Tau - 0 0 +1 Neutrino ()  0 0 +1 W the red

  27. What is the missing decay product? - ---> - +  + ??? Q: -1 = -1 + 0 + ? EL#: 0 = 0 + 0 + ? ML#:0 = 1 + -1 + ? TL#: 1 = 0 + 0 + ? Le L L Electron e- +1 0 0 Neutrino (e) e +1 0 0 Muon - 0 +1 0 Neutrino ()  0 +1 0 Tau - 0 0 +1 Neutrino ()  0 0 +1 W 

  28. What is the missing decay product? + ---> ?? +  + e Q: +1 = ? + 0 + 0 EL#: 0 = ? + 0 + 1 ML#:-1 = ? + -1 + 0 TL#: 0 = ? + 0 + 0 Le L L Electron e- +1 0 0 Neutrino (e) e +1 0 0 Muon - 0 +1 0 Neutrino ()  0 +1 0 Tau - 0 0 +1 Neutrino ()  0 0 +1 W e+

  29. What is the missing decay product? + ---> + + ?? +  Q: +1 = +1 + ? + 0 EL#: 0 = 0 + ? + 0 ML#:0 = -1 + ? + 0 TL#: -1 = 0 + ? + -1 Le L L Electron e- +1 0 0 Neutrino (e) e +1 0 0 Muon - 0 +1 0 Neutrino ()  0 +1 0 Tau - 0 0 +1 Neutrino ()  0 0 +1 W 

  30. What is the missing particle? ?? ---> e- + e +  Q: ? = -1 + 0 + 0 EL#: ? = +1 + -1 + 0 ML#:? = 0 + 0 + +1 TL#: ? = 0 + 0 + 0 Le L L Electron e- +1 0 0 Neutrino (e) e +1 0 0 Muon - 0 +1 0 Neutrino ()  0 +1 0 Tau - 0 0 +1 Neutrino ()  0 0 +1 - W

  31. Types of Particles • Gauge Bosons - carry the electro-weak force • Leptons - interact via weak and EM (charged) force • Hadrons - interact via strong nuclear force • Mesons - B = 0 • Baryons - B = 1, (-1)… TOC

  32. Quark Theory • 1960s - Only 4 Leptons, but Hundreds of Hadrons • Leptons seemed elementary/small (<10-18 m) • Not all Hadrons could be elementary • Murray Gell-Mann suggests that Hadrons are made from quarks. • "three quarks for Muster Mark" • -James Joyce • (Finnegan’s Wake) TOC

  33. Quark Theory Murray Gell-Mann suggests that Hadrons are made from quarks. TOC

  34. Quark Theory Proton: +1 charge, B = 1 Neutron: 0 charge, B = 1 Pion+: +1 charge, B = 0 Pion-: -1 charge, B = 0 Kaon-: -1 charge, B = 0 Try making other Hadrons yourself TOC

  35. Truly Fundamental particles Generally accepted fundamental particles Three generations Top quark = 200 GeV/c2 TOC

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