FLAVOR STRUCTURE OF THE NUCLEON AS REVEALED AT HERMES

摘要

The flavor structure of the nucleon as revealed in parton distributions (PDF's) is central to understanding the partonic structure of the nucleon. Recent data on unpolarized PDF's and their implications for the flavor- dependent quark helicity distributions are discussed. Results are presented for spin asymmetries in inclusive and semi-inclusive cross sections for production of pions, and kaons measured by the HERMES experiment at DESY in deep-inelastic scattering of polarized positrons on proton and deuterium targets. A full 5 component extraction of polarized quark distributions for u, d, u, d, and (s + s) is reported. Resulting valence quark distributions conform to results of earlier experiments. There is no evidence for a significant polarization of the light sea. In contrast to the conclusions inferred from studies of polarized inclusive scattering, a leading order analysis of the HERMES data suggests a zero or slightly positive polarization of the strange sea. There is no evidence for a measurable flavor asymmetry in the helicity distributions for the light sea.