The 2004 Nobel Prize in Physics

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The 2004 Nobel Prize in Physics

• Craig Tyler, Physics Engineering

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the physics prize

• Usually for experiments, rather than theory
• Often shared, rather than individual

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meet the new laureates

• For the discovery of asymptotic freedom in the
  theory of the strong interaction (1973, when
  Politzer and Wilczek were grad students).

David J. Gross, UCSB H. David Politzer, Caltech
Frank Wilczek, MIT (Theyll share equally a
prize of 1.35 million)
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the particle physics world

• Gravity
• Weak nuclear force
• Electromagnetic force
• Strong nuclear force

• Quarks (which live inside atomic nuclei)
• Leptons (electrons and neutrinos)
• Force carriers (gravitons, weakons, photons, and
  gluons)

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quarks

• Protons contain uud
• Neutrons contain udd
• But there are 6 flavors
• In 3 generations
• Each of which can have 3 colors, according to
  QCD, quantum chromodynamics
• (Weve made these in accelerator experiments)
• Quarks interact mainly by the strong nuclear
  force, by the exchange of gluons

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the discovery

• The new laureates discovered the nature of the
  strong force, asymptotic freedom, which taught
  us all this
• QCD and colors, like red or anti-green.
• Stable quark arrangements are white.
• Stable quark arrangements are confined.
• Gluons, which have colors too, and therefore
  interact with each other.

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asymptotic freedom

• The strong force is unlike the others if gluons
  interact with each other, then at close range,
  when there are lots of gluons zipping around,
  theyll get tied up with each other and forget
  the quarks so the quark force dies!
• Thus, the strength of the strong force is weak at
  close range, and strong at long range!
• Freedom at close range inside atomic nuclei, the
  quarks bounce around freely (contrast electrons
  in atoms)

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some evidence

• 2-jet events

• Collision making quarks
• White confined states needing additional quarks
• Quark-Gluon Plasma, not seen in this universe (as
  far as we know) since the big bang beginning!

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more evidence

• and 3-jet events
• Not to mention strange stars

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what we still dont know

• Why are there 3 generations? 3 colors? 6 flavors?
  Why not some other number?
• Wheres all the anti-matter? You never see it
  around.
• Where do different masses (of quarks, say) come
  from?
• Is there supersymmetry? String theory? Extra
  dimensions? Dark matter? A GUT? A TOE?
• So there are plenty of Nobel Prizes left for
  you, if you want to major in physics.