Production of c and b quarks at the Z pole

In the standard model the coupling of the Z to each flavour depends only on the weak isospin of the qq pair. The widths in the Born approximation are from (8.6.9) 

These theoretical results are in quite nice agreement with the data. For instance, from the detection of the lepton produced in semi-leptonic 

Semi-leptonic branching ratios have also been measured yielding 

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