Nuclear-target effects in J/psi production in 125-GeV/c antiproton and. pi. /sup -/ interactions

The production of the J/psi resonance in 125-GeV/c p-bar and ..pi../sup -/ interactions with Be, Cu, and W targets has been measured. The cross section per nucleon for J/psi production is suppressed in W interactions relative to the lighter targets, especially at large values of Feynman x, which is opposite to the expectation from the various explanations of the European Muon Collaboration effect. Models incorporating modifications of the gluon structure functions in heavy targets show qualitative agreement with the data.