Deep-inelastic lepton-nucleus scattering has shown that the momentum distribution of quarks in a nucleon is modified by the nuclear environment. Several different explanations have been proposed. These can be distinguished by proton-nucleus scattering experiments which measure the production of lepton pairs in certain kinematic regions.

• Received 18 June 1984

DOI:https://doi.org/10.1103/PhysRevLett.53.2532