I have already known the cross sections can be presented like this.
σ（e+e- -> hadrons）∝ Σ eq^2 & σ(e+e- -> μ+μ- ) ∝ e^2,
where eq is the charge of a certain quark(u, d, s, c or b)
But I don't know the relationship between Nc and eq.
(This is my first time to post a thread. I don't know how to...