Flavor Decomposition of the Sea-Quark Helicity Distributions in the Nucleon from Semiinclusive Deep Inelastic Scattering

Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.

Figure 1

Virtual photoabsorption asymmetries $A_1^h$ for semiinclusive DIS on the deuterium target as a function of Bjorken $x$, for identified charged pions (compared to all charged hadrons from SMC [10] in the $x$ range of the present experiment), and for identified charged kaons. The error bars are statistical, and the bands at the bottom represent the systematic uncertainties. Two data points for ${\mathrm{K}}^{-}$ at large $x$ are off-scale with large error bars.

Figure 2

Quark helicity distributions at $⟨Q^2⟩=2.5{\mathrm{G}\mathrm{e}\mathrm{V}}^2$, as a function of Bjorken $x$, compared to two LO QCD fits to previously published inclusive data shown as dashed [28] (“standard scenario”) and dot-dashed [29] (“scenario 1”) curves. The error bars are statistical and the bands at the bottom represent the systematic uncertainties, where the light area is the contribution due to the uncertainties of the fragmentation model, and the dark area is the contribution due to those of the asymmetries.

Figure 3

The light quark sea flavor asymmetry $x·(\Delta \overline{u}-\Delta \overline{d})$ in the helicity distributions, at $⟨Q^2⟩=2.5{\mathrm{G}\mathrm{e}\mathrm{V}}^2$, compared to a theoretical prediction [30] (dashed curve with theoretical uncertainty band). The experimental error bars and bands have the same meaning as in Fig. 2.