An exam in Subnuclear Physics January 9, 2009Posted by dorigo in physics.
Tags: coupling constants, exams, GIM mechanism, QCD, subnuclear physics, top quark, University, W boson, Z boson
Here are the questions asked at an exam in Subnuclear Physics this morning:
- Draw the strong and electromagnetic coupling constants as a function of , 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 , given the values at (QED) and (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.