Dynamics of light antiquarks in the proton

We present a comprehensive analysis of the recent data from the E866 experiment at Fermilab on Drell-Yan production in $\mathrm{pD}$ and $\mathrm{pp}$ collisions, which indicates a non-trivial $x$ dependence for the asymmetry between $ū$ and $\overline{d}$ quark distributions in the proton. The relatively fast decrease of the asymmetry at large $x$ suggests the important role played by the chiral structure of the nucleon, in particular the $\pi N$ and πΔ components of the nucleon wave function. At small $x$ the data require an additional non-chiral component, which may be attributed to the Pauli exclusion principle, as first suggested by Field and Feynman.