Resonance-Parton Duality and the Transverse Response of Nucleons

Abstract

QCD-based scaling arguments predict the predominance of longitudinal over transverse electroproduction of pions by terms $\propto Q^2$. However, data from JLAB, Cornell and DESY, covering a wide kinematical range $1 < Q^2 < 11\, {\rm GeV}^2$ and $2\, {\rm GeV} < W < 4\, {\rm GeV}$, do not show this expected behavior. At the same time standard descriptions of pion-electroproduction on nucleons have given a very good description of the longitudinal components of the cross sections. However, these very same models have failed grossly in describing the transverse component. We discuss here a common solution to these two problems by considering the contributions of high-lying ($W > 2$ GeV) nucleon resonances to pion production. The coupling strengths and form factors are obtained through hadron-parton duality. We show that an excellent description of data in a wide range of electron energies and four-momentum transfers can be obtained in such a model.