Quark Structure Functions of Mesons and the Drell-Yan Process

For massive-lepton pair production in meson-induced reactions, we use quantum chromodynamics perturbation theory to predict that the decay angular distribution in the pair rest frame will change from predominantly 1+cos²θ to sin²θ as the longitudinal-momentum fraction of the pair xF→+1. The two angular distributions are associated respectively with (1-x)² and Q^-2(1-x)⁰ components of the valence-quark structure function of the meson.