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# What is Q C D ? - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about 'What is Q C D ?' - gittel

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Presentation Transcript
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

• 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

• 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

• 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

•  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

• New B-factory experiments, such as BaBar at SLAC and Belle at KEK, will reduce the experimental errors, shrinking the areas of each region

• Even tighter constraints will result from better theoretical calculations from LatticeQCD

• If the regions don’t overlap, there must be new physics!