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Introduction to Particle Physics

Introduction to Particle Physics. Particle Physicists. What are the Elementary Constituents of Matter?. Aim to answer. What are the forces that control their behaviour at the most basic level?. History of Constituents of Matter. AD. Conservation of energy and momentum

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Introduction to Particle Physics

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  1. Introduction to Particle Physics

  2. Particle Physicists What are the Elementary Constituents of Matter? Aim to answer What are the forces that control their behaviour at the most basic level?

  3. History of Constituents of Matter AD

  4. Conservation of energy and momentum in nuclear reactions

  5. Conservation Laws • In Nuclear Reactions momentum and mass-energy is conserved – for a closed system the total momentum and energy of the particles present after the reaction is equal to the total momentum and energy of the particles before the reaction • In the case where an alpha particle is released from an unstable nucleus the momentum of the alpha particle and the new nucleus is the same as the momentum of the original unstable nucleus

  6. Neutrino must be present to account for conservation of energy and momentum __ Wolfgang Pauli • Large variations in the emission velocities of the  particle seemed to indicate that both energy and momentum were not conserved. • This led to the proposal by Wolfgang Pauli of another particle, the neutrino, being emitted in  decay to carry away the missing mass and momentum. • The neutrino (little neutral one) was discovered in 1956.

  7. Calculate the energy released in the reaction __ 1.008665 u 1.007825 u 0.0005486 u kg 1 u = 1 J = eV

  8. Calculation Mass difference u kg kg

  9. Calculation J J eV MeV It has been found by experiment that the emitted beta particle has less energy than 0.272 MeV Neutrino accounts for the ‘missing’ energy

  10. Acceleration of protons

  11. The Cockcroft and Walton Apparatus + +

  12. Cockroft and Walton • First artificial splitting of nucleus • First transmutation using artificially accelerated particles • First experimental verification ofE = mc2 • Irish Nobel Prize • E.T.S. Walton 1951 John Cockcroft Ernest Walton

  13. Converting mass into other forms of energy

  14. The Cockcroft and Walton Equation Experimental verification ofE = mc2 1 MeV 17.3 MeV Proton + Lithium Two alpha particles + Energy

  15. Converting other forms of energy into mass

  16. History of search for basic building blocks of nature • Ancient Greeks: • Earth, Air, Fire, Water • By 1900, nearly 100 elements • By 1936, back to three particles: proton, neutron, electron

  17. CERN LEP APPLET http://www.hep.ucl.ac.uk/masterclass/Acc_sim2/simulator.html

  18. Proton-Proton Collisions inside the LHC at CERN

  19. Fundamental forces

  20. The Four Fundamental Forces

  21. Families of particles

  22. Mass of particles comes from energy of the reaction Particle zoo The larger the energy the greater the variety of particles

  23. Particle Zoo

  24. Thomson (1897): Discovers electron

  25. Leptons Indivisible point objects Not subject to the strong force produced in radioactive decay _ Q = -1e almost all trapped in atoms Q= 0 all freely moving through universe

  26. Baryons Mesons Subject to all forces Subject to all forces mass between electron and proton e.g. protons, neutrons and heavier particles Composed of three quarks Composed of quark-antiquark pair

  27. Antimatter

  28. Just as the equation x2=4 can have two possible solutions (x=2 OR x=-2), so Dirac's equation could have two solutions, one for an electron with positive energy, and one for an electron with negative energy. Dirac interpreted this to mean that for every particle that exists there is a corresponding antiparticle, exactly matching the particle but with opposite charge. For the electron, for instance, there should be an "antielectron" called the positron identical in every way but with a positive electric charge.

  29. History of Antimatter 1928 Dirac predicted existence of antimatter 1932 antielectrons (positrons) found in conversion of energy into matter 1995 antihydrogen consisting of antiprotons and positrons produced at CERN In principle an antiworld can be built from antimatter Produced only in accelerators and in cosmic rays

  30. Pair Production

  31. Annihilation

  32. Quark model

  33. Quarks Fundamental building block of baryons and mesons

  34. Naming of Quark James Joyce Three Quarks for Muster Mark Murray Gell-Mann

  35. The six quarks

  36. Quark Applet This applet helps identify the nature and charge of a particle given a combination of quarks http://lectureonline.cl.msu.edu/~mmp/applist/q/q.htm

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