Hadronic R ratio
= Hadronic R ratio
{title2=$R(s)=\sigma_h(s)/[4\pi\alpha^2/(3s)]$}
The <hadronic R ratio> normalizes the photon-channel hadronic <relativistic cross-section> to the leading massless muon-pair value. The free active-quark result is $R=N_c\sum_fQ_f^2$. It depends on flavor charges as well as the number of active flavors; it is not simply $N_cN_f$.