Slow proton production in semi-inclusive deep inelastic scattering and   the pion cloud in the nucleon
  The semi-inclusive cross section for producing slow protons in charged current deep inelastic (anti-) neutrino scattering on protons and neutrons is calculated as a function of the Bjorken $x$ and the proton momentum. The standard hadronization models based upon the colour neutralization mechanism appear to underestimate the rate of slow proton production on hydrogen. The presence of the virtual mesons (pions) in the nucleon leads to an additional mechanism for proton production, referred to as spectator process. It is found that at low proton momenta both mechanisms compete, whereas the spectator mechanism dominates at very small momenta, while the color neutralization mechanism dominates at momenta larger than 1-2 \, GeV$/c$. The results of the calculations are compared with the CERN bubble chamber (BEBC) data. The spectator model predicts a sharp increase of the semi-inclusive cross section at small $x$ due to the sea quarks in virtual mesons. 
A. Szczurek, G.D. Bosveld and A.E.L. Dieperink