Experimental Results and Perspectives of Polarized Lepton-Nucleon Scattering

Abstract

The spin structure of the nucleon and its spin puzzle is introduced in this paper, followed by a summary of the recent results on polarized lepton nucleon scattering. The spin structure functions of the proton and neutron have been measured and their first moments have been determined. The recent experiments confirm that the Ellis-Jaffe sum rule is violated, whereas the Bjorken sum rule is valid within the precision of the measurement. Results are reported about the flavor decomposition of the quark polarization, a first, direct measurement of a positive gluon polarization, the observation of a double-spin asymmetry in diffractive p° production, the polarization of A hyperons, the observation of transverse single-spin asymmetries and the measurement of the Gerasimov-Drell-Hearn sum rule. Prospects of future fixed target and collider facilities are discussed.