What is q c d
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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

What is qcd

  • 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!