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Particle Physics what do we know?

Particle Physics what do we know?. Ulrich Heintz Boston University. Particle Physics. What associations does the word particle physics bring to your mind?. Particle Physics. What are the fundamental building blocks of the universe? What are the interactions between them?

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Particle Physics what do we know?

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  1. Particle Physicswhat do we know? Ulrich Heintz Boston University Ulrich Heintz - Quarknet 2002

  2. Particle Physics • What associations does the word particle physics bring to your mind? Ulrich Heintz - Quarknet 2002

  3. Particle Physics • What are the fundamental building blocks of the universe? • What are the interactions between them? • How can we explain the universe? • its history • its present form • its future • Is there a theory of everything? Ulrich Heintz - Quarknet 2002

  4. Particle Physics it’s fun and fascinating Ulrich Heintz - Quarknet 2002

  5. What is a particle? • a small piece of matter... • characterized by • charge • mass • lifetime • spin • particles can scatter off each other like billiard balls • unlike billiard balls, most particles are unstable and decay • particles can be produced by colliding other particles Ulrich Heintz - Quarknet 2002

  6. What was the world made of in 1932? • electrons (1897) • orbit atomic nucleus • proton (1911) • nucleus of lightest atom • neutron (1932) • neutral constituent of the nucleus • photon (1905) • quantum of the electromagnetic field Ulrich Heintz - Quarknet 2002

  7. and... • 1927 Dirac’s relativistic quantum mechanics • 1931 the positive electron (positron) • antiparticles: for every particle there exists an antiparticle with same mass, lifetime, spin, but opposite charge • 1930 Pauli’s neutrino • energy conservation in beta decay requires the existence of a light, neutral particle • n  p+ + e- +  • observed in 1956 • 1936-1947 the muon and the pions (+,0,-) • Rabi: “who ordered that?” Ulrich Heintz - Quarknet 2002

  8. The ascent of accelerators • previous discoveries used • cosmic rays • “natural accelerators” (radioactivity) • after WWII • accelerators Ulrich Heintz - Quarknet 2002

  9. The particle “Zoo” • 1947: strange particles • K0+-, K+++- • p+- • ,  • long lifetime  ¼ 10-10 s • more particles... • p, •  • short lifetime  ¼ 10-24 s Ulrich Heintz - Quarknet 2002

  10. The quark model • 1964 Gell-Mann, Zweig • there are three quarks and their antiparticles • each quark can carry one of three colors • red bluegreen • antiquarks carry anticolor • anti-redanti-blueanti-green Ulrich Heintz - Quarknet 2002

  11. The quark model • only colorless (“white”) combinations of quarks and antiquarks can form particles • qqq • qq • no others observed Ulrich Heintz - Quarknet 2002

  12. mesons qq + - 0 ++ uud ddd udd uuu p n us ds K+ K0 0  + - uus dds uds du uu,dd,ss ud - + 0   dss uss - 0 sd su K0 - K- sss The 8-fold way baryonsqqq Ulrich Heintz - Quarknet 2002

  13. Quark confinement • What holds quarks/antiquarks together? • strong force • acts between all “colored” objects • short range • independent of distance Ulrich Heintz - Quarknet 2002

  14. So what is the world made of? The Standard Model spin = ½ (fermions) quarks leptons Ulrich Heintz - Quarknet 2002

  15. Are these fundamental? • As far as we know.... • we can measure structure as small as 10-18 m • Accelerators are like huge microscopes • To measure smaller distances • go to higher energies Ulrich Heintz - Quarknet 2002

  16. e e Feynman diagram    How do particles interact? • particles attract or repel each other by exchanging “messenger” particles (field quanta) Ulrich Heintz - Quarknet 2002

  17. What holds the world together? spin = 1 (bosons) Ulrich Heintz - Quarknet 2002

  18. The Higgs boson • the standard model requires the existence of one more particle • Higgs boson • uncharged • unknown mass (>115 GeV) • spin = 0 • required to be able to describe massive fermions and bosons Ulrich Heintz - Quarknet 2002

  19. electromagnetism electroweak force GUTs Is this the theory of everything? • NO • Standard Model doesn’t work at all energies • Standard Model does not include gravity • we haven’t found the Higgs yet... • unification stringtheory... Ulrich Heintz - Quarknet 2002

  20. Accelerators • 1983: CERN pp collider • E = 540 GeV  W§ (80 GeV), Z0 (91 GeV) • 1995: Fermilab Tevatron pp collider • E=1.8 TeV  top quark (175 GeV) • ¼ 2008: CERN LHC pp collider • E=14 TeV  discover Higgs? • ????: Linear e+e- Collider • E=1-2 TeV  study Higgs in detail Ulrich Heintz - Quarknet 2002

  21. What might we find? • Super Symmetry • fermions  bosons • we have already found half the particles.... Ulrich Heintz - Quarknet 2002

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