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What is QCD - PowerPoint PPT Presentation


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What is Q C D ?. Q uantum C hromo D ynamics is the theory of the strong force the strong force describes the binding of quarks by gluons to make particles such as neutrons and protons

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what is q c d
What is QCD?
  • Quantum ChromoDynamics is the theory of the strong force
    • the strong force describes the binding of quarks by gluons to make particles such as neutrons and protons
  • The strong force is one of the four fundamental forces in the Standard Model of Physics– the others are:
    • Gravity
    • Electromagnetism
    • The Weak force
  • The 2004 Physics Nobel prize was awarded to David J. Gross, H. David Politzer, and Frank Wilczekfor their work leading to QCD
what is lattice q c d
What is Lattice QCD?
  • LatticeQCD is the numerical simulation of QCD
    • The QCD action, which expresses the strong interaction between quarks mediated by gluons:where the Dirac operator (“dslash”) is given by
    • LatticeQCD uses discretized space and time
    • A very simple discretized form of the Dirac operator iswhere a is the lattice spacing
slide4
A quark, (x), depends upon (x + a) and the local gluon fields U
    • (x)is complex 3x1 vector, and the Uare complex 3x3 matrices. Interactions are computed via matrix algebra
    • On a supercomputer, the space-time lattice is distributed across all of the nodes
why do lattice q c d
Why do Lattice QCD?
  • Many QCD problems can only be simulated numerically, using Lattice QCD
  • To test the Standard Model, physicists take experimental data and compare to the theoretical predictions of QCD
    • Differences may indicate new physics, for example, explaining why the universe is dominated by matter and has so little anti-matter
testing the standard model
Testing the Standard Model
  •  and  are two parameters of the Standard Model
  • Theory and experiments constrain the possible values of  and 
  • The regions of different colors correspond to different constraints
  • The allowed values of  and  from the Standard Model would lie in the intersection of all of the colored regions
  • This figure shows the current constraints
testing the standard model1
Testing the Standard Model
  • New B-factory experiments, such as BaBar at SLAC and Belle at KEK, will reduce the experimental errors, shrinking the areas of each region
testing the standard model2
Testing the Standard Model
  • Even tighter constraints will result from better theoretical calculations from LatticeQCD
  • If the regions don’t overlap, there must be new physics!
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