= Tree-level W branching fractions
{title2=$\Gamma_{\mathrm{tot}}=9\Gamma_\ell$}
With three massless <lepton> families, two accessible up-type <quarks>, three colors, and no <Quantum chromodynamics> radiative correction, a <W boson> has total <decay width> $9\Gamma_\ell$. With an identity <CKM matrix>, each leptonic channel has <branching fraction> $1/9$ and each of the two allowed quark-flavour channels has $1/3$. With mixing, each accessible quark channel is weighted by $|V_{ij}|^2$, while row <unitarity> preserves the total at this order if all down-type channels are accessible.
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