Experimental test of the Drell-Yan model in p+W. --> mu. /sup +/+. mu. /sup -/+X

We report a high-statistics study of the reaction p+W..--> mu../sup +/+..mu../sup -/+X with use of an intense 400-GeV/c proton beam, a magnetized-iron beam dump, and a wide-acceptance detector. Using data near x/sub F/ = 0, we have extracted the nucleon sea-quark distribution and find it to be a factor 1.6 +- 0.3 larger than that obtained by inelastic charged-current neutrino scattering. We then compare the Drell-Yan prediction with our data including the previously unexplored region of large x/sub F/ and find excellent agreement for a wide range of ..mu..-pair invariant mass.