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An exam in Subnuclear Physics January 9, 2009

Posted by dorigo in physics.
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Here are the questions asked at an exam in Subnuclear Physics this morning:

  • Draw the strong and electromagnetic coupling constants as a function of Q^2, explain their functional dependence using feynman graphs of the corrections to the photon and gluon propagators, write their formula, and compute the value of the constants at Q^2=M_Z^2, given the values at Q^2=1 MeV^2 (QED) and Q^2=1 GeV^2 (QCD).
  • The GIM mechanism: explain the need for a fourth quark using box diagrams of kaon decays to muon pairs. How does the charm contribution depend on its mass ? What conclusion could be drawn by that dependence in the case of B mixing measurements in the eighties ?
  • Discuss a measurement of the top quark mass. For a dileptonic decay of top quark pairs, discuss the final state and its production rate.
  • Discuss decay modes of W bosons and their branching fraction values. Discuss decay modes of Z bosons and their branching fraction values.

The student answered well all questions and he got 30/30 points.