Testing QCD

QCD is used to predict that the ratio of up to down quarks → 5 as x → 1 and the rigor of the proof and the underlying assumptions are discussed. Measuring $\text{σ}{}^{\mathrm{<mtext>v</mtext><mtext>?</mtext>}}\text{P}\text{σ}{}^{\mathrm{v}}\text{P}\text{as}\text{x → 1}$ gives the best experimental test of this prediction.