dbar/ubar Asymmetry and the Origin of the Nucleon Sea

The Drell-Yan cross section ratios, sigma(p + d)/sigma(p + p), measured in Fermilab E866, have led to the first determination of (d) over bar(x)/<(mu)over bar>(x), (d) over bar-(x) - <(mu)over bar>(x), and the integral of (d) over bar(x) - (u) over bar(x) for the proton over the range 0.02 less than or equal to x less than or equal to 0.345. The E866 results are compared with predictions based on parton distribution functions and various theoretical models. The relationship between the E866 results and the NMC measurement of the Gottfried integral is discussed. The agreement between the E866 results and models employing virtual mesons indicates that these non-perturbative processes play an important role in the origin of the (d) over bar, (u) over bar asymmetry in the nucleon sea. [S0556-2821(98)02821-5].