The Pion Cloud and the Puzzle of the Proton Sea

The light-quark flavor dependence of the proton sea has been of great interest for many years because of its close connection with non-perturbative effects.  A natural explanation is that the sea arises from the pion cloud of the proton, which leads to an excess of dbar over ubar quarks.  However, a theoretical explanation of the momentum dependence of the ratio of dbar to ubar measured by E866 remains a challenge. We make precise predictions, based on the pion cloud idea, for the anticipated final results of the SeaQuest experiment. This is achieved by applying light cone perturbation theory and experimental constraints to a chiral Lagrangian so that the relevant Fock-space components of the nucleon wave function are computed with reasonable accuracy. We compare our results to existing experimental information from E866, and make predictions, including uncertainties, for future experimental measurements. Future experimental results will either confirm or rule out the idea that the pion cloud provides the flavor dependence of the proton's sea quark distributions, and have profound implications for understanding the nucleon-nucleon force.