We investigate a hitherto neglected sector of perturbative QCD which is normally hidden in conventional hadron analyses but has observable consequences in nuclei. There is a modification to structure functions arising from the fusion of quarks, antiquarks, and gluons and we derive recombination factors, analogues of familiar splitting functions, and compute the effects of parton fusion on the nuclear structure functions. This mechanism causes the structure functions to extend beyond $x=1\mathrm{}$; as $x\to 0$ we have a source of shadowing within the framework of QCD. We find that the loss of momentum when nucleons bind is shared almost equally between $q\overline{q}$ and gluons. We predict that the nuclear modification of the gluon distribution is a significant suppression as $x\to 0$ and enhancement for $x\simeq 0.2$. We point out how hadronic $\psi$ production may be used to disentangle this shadowing mechanism from other nuclear effects.

• Received 20 March 1989

DOI:https://doi.org/10.1103/PhysRevD.40.2820