Coordinate Space Distributions of Antiquark Flavor Asymmetries in the Proton ∗ )

We examine the space-time properties of the distributions of (d̄− ū) and d̄/ū in the proton. The difference of the antiquark distributions shows the expected peak at the approximate pion Compton wavelength and is supportive of the thesis that the meson cloud of the nucleon is at the origin of the asymmetry of (d̄ − ū), with the pion cloud playing a dominant role. The partonic distribution functions of the proton, particularly the flavor dependence of the antiquark distributions, remain of considerable interest. Experimentally, the NMC measurement of the integral of (d̄− ū) [1], and the more recent measurements of the ratio d̄/ū by means of the Drell-Yan process [2, 3] provide evidence for the excess of d̄ over ū in the proton. Similar results for (d̄ − ū) were obtained by HERMES [4]. One of the simplest (physically ”anschaulich”) explanations for the excess is based on the meson cloud model and the Sullivan process. This model can explain the momentum fraction (Bjorken x-dependence) of the (d̄ − ū) distribution (for reviews, see [5]). Pions play the leading role in this context, while the detailed description of the ratio d̄/ū may also require correlated qq̄ pairs of heavier mass[3, 6, 7]. In this Letter we do not wish to dwell on the differences between theoretical models and experiment, but examine the spacetime properties of the flavor distribution asymmetries in order to see whether they offer any clues as to their origin. In order to obtain the distribution functions in coordinate space, we follow Piller et al. [8] and Vänttinen et al. [9]. We work with light-cone variables and introduce the dimensionless coordinate spacetime variable z = y · P , where P is the momentum of the nucleon. The light cone distance is y ≡ t + y3 = 2z/M , with M the nucleon mass. The dimensionless space work supported in part by BMBF, by the Alexander von Humboldt Foundation and by the US Dept. of Energy