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Introduction to particle physics - Alevel
- The document discusses the elementary constituents of matter and the forces that control their behavior at the most basic level. It provides a history of models of matter, from ancient Greeks' ideas of earth, air, fire and water to the modern understanding of protons, neutrons and electrons. - By the 1930s, scientists understood matter is made up of three elementary particles: protons, neutrons and electrons. Later discoveries found these are composed of even smaller particles called quarks, held together by fundamental forces.
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Introduction to particle physics - Alevel
- 2. What are the Elementary Constituentsof Matter? What are the forces that control their behaviour at the most basic level?
- 3. History of Constituentsof Matter AD
- 5. •In Nuclear Reactionsmomentum 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. 0 0 0 1 1 1 1 0 epn •Largevariations 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. Wolfgang Pauli __
- 7. 0 0 0 1 1 1 1 0 epn 1.008665u 1.007825 u 0.0005486 u 27 10660.1 1 u = 1 J = 19 106.1 __ kg eV
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- 9. It has beenfound by experiment that the emitted beta particle has less energy than 0.272 MeV Neutrino accounts for the ‘missing’ energy 2 mcE 2831 )100.3)(1083724.4( 14 10353516.4 271755 10602.1 10353516.4 19 14 J J eV 272.0 MeV
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- 12. •First artificial splittingof nucleus •First transmutation using artificially accelerated particles •First experimental verification of E = mc2 Irish Nobel Prize E.T.S. Walton 1951 Cockroft and Walton Ernest WaltonJohn Cockcroft
- 14. EnergyHeHeLiH 4 2 4 2 7 3 1 1 Proton+ Lithium Two alpha particles + Energy 1 MeV 17.3 MeV Experimental verification of E = mc2
- 16. • Ancient Greeks: Earth,Air, Fire, Water • By 1900, nearly 100 elements • By 1936, back to three particles: proton, neutron, electron
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- 21. The Four FundamentalForces
- 22. 20 Instituteof Physics PeterKalmus Particles and the Universe Forces Gravity falling objects planet orbits stars galaxies inverse square law graviton inverse square law photon short range W ± , Z0 Electro- magnetic atoms molecules optics electronics telecom. Weak beta decay solar fusion Strong nuclei particles short range gluon
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- 25. 11 Instituteof Physics PeterKalmus Particles and the Universe Neutrinos Antiparticles 1950s, 1960s > 200 new “elementary” (?) particles Feel weak force “predicted” later discovered 100,000,000,000,000 per second pass through each person from the Sun Equal and opposite properties “predicted” later discovered Annihilate with normal particles Now used in PET scans Many new particles created in high energy collisions Convert energy to mass. Einstein E = mc2
- 26. mx 10 101 mx15 101 mx 15 107.0 mx 18 107.0 Thomson (1897): Discovers electron
- 27. 0 0 0 1 60 28 60 27 eNiCo Q = -1e almost all trapped in atoms Q= 0 all freely moving through universe _
- 30. Just as theequation 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.
- 31. 1928 Dirac predictedexistence of antimatter 1932 antielectrons (positrons) found in conversion of energy into matter 1995 antihydrogen consisting of antiprotons and positrons produced at CERN ee In principle an antiworld can be built from antimatter Produced only in accelerators and in cosmic rays
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- 38. 12 Today’s building blocks Leptons (donot feel strong force) electron e- -1 e-neutrino e 0 Quarks (feel strong force) up u +2/3 down d -1/3 proton = u u d +2/3 +2/3 -1/3 = +1 neutron = u d d +2/3 -1/3 -1/3 = 0 4 particles very simple multiply by 3 (generations) multiply by 2 (antiparticles) First generation 1 3 1 3 2 3 2 0 3 1 3 1 3 2 3 2 3 1
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