Evidence for Quark-Hadron Duality in the Proton Spin Asymmetry $A_1$

Abstract

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry $A_1$. Longitudinally polarised positrons were scattered off a longitudinally polarised hydrogen target for values of $Q^2$ between 1.2 and 12 GeV${}^2$ and values of $W^2$ between 1 and 4 GeV${}^2$. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable $x$. This finding implies that the description of $A_1$ in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of $Q^2$ above 1.6 GeV${}^2$.

5 pages, 1 eps figure, table added, new references added, in print in Phys. Rev. Lett