Past exam of the sub-atomic physics course of the University of Oxford / 2016 / 4 / b

Using the measured single-flavor leptonic partial decay width as one unit,This agrees with three leptonic channels plus six color-distinguishable quark channels in the leading massless approximation. The six quark units are two accessible up-type flavors times three color charges, with the sums of squared CKM matrix elements over down-type partners approximately unity. They are not nine generations or nine new flavors. Small mass and Quantum chromodynamics radiative corrections prevent the ratio from being an exactly integer channel count.