An investigation of the u-bar d-bar asymmetry in the proton sea through an updated Pion Cloud Model

Recent experimental investigations have found an asymmetry in the distributions of anti-up and anti-down quarks within the proton; a result which cannot be well explained through simple perturbative gluon splitting. Instead, this result is better explained by fluctuations of the proton into pion-baryon pairs. We use a Light Front formulation of the Meson Cloud Model to describe this proton-pion cloud system as an expansion of the proton into pion-baryon states. We construct splitting functions with coupling constraints and cutoffs constrained by experimental data, and model the parton momentum distributions (pdfs) of the pion and baryons in two ways. We begin by using distributions based on experimental data and evolving them to the relevant Q² using the DGLAP equations. We also develop a statistical model of the meson-baryon pdfs and compare the experimentally derived pdfs with the statistical. We then compare our full proton momentum distributions to experimental data collected by the E866 and more recent E906 experiments, focusing specifically on the anti-down/anti-up quark ratio.