Pion Content of the Nucleon as seen in the NA51 Drell-Yan experiment
  In a recent CERN Drell-Yan experiment the NA51 group found a strong asymmetry of $\bar u$ and $\bar d$ densities in the proton at $x\simeq0.18$. We interpret this result as a decisive confirmation of the pion-induced sea in the nucleon. 
H. Holtmann, N.N. Nikolaev, J. Speth and A. Szczurek