Quark-antiquark annihilation and small-pTinclusive spectra

Assuming that only a part of the valence quarks contributes to the fusion process and that the amount of charmed quarks in the sea of the hadrons is $\frac{1}{5}$ and that of the strange quarks ½ that of the usual quarks, the fusion model provides a quantitative and consistent description of the inclusive vector-meson spectra in $\gamma$, $\pi$, $K$, and $p$ initiated processes. For pseudoscalar-meson production, the model gives only a fair approximation to the data in proton-induced reactions.