Past exam of the particle and nuclear physics course of the University of Cambridge / 2014 / Paper 1 / 1 / c

Away from thresholds and narrow resonances, photon-mediated annihilation gives one colour copy proportional to $Q_q^2$ relative to the muon cross-section. The accessible flavours are $u,d,s,c$, each with three colours, soBottom production is closed. QCD radiative corrections raise the leading parton-model result by a relative term beginning at ${\alpha }_s/\pi$; the requested estimate does not require a supplied value of ${\alpha }_s$.